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Heathkit Oscilloscope Model OL-1
August 1954 to August 1956
Initial Price: $29.50
Ad in Radio Electronics, September-1954
Excerpt from the assembly manual:
INTRODUCTION
The cathode ray oscilloscope is without a doubt the most versatile electronic instrument available today. Basically, it is an indicating device which can display in usable form, the actual voltage variations in an electrical quantity as compared to time. This however, is merely its basic function and it would be impossible at this time to enumerate all of its qualifications. It is the type of instrument for which the operator can continue to find new applications even after many years of use.
Some of the many desirable features are as follows:
1. It displays instantly information that otherwise would require hours of experimentation.
2. Wave forms can easily be photographed and retained for future reference.
3. It usually has a negligible effect on the characteristics of a circuit under test.
4. It has an extremely wide range of sensitivity.
5. It is rugged, dependable and not easily damaged by overload or surges.
~
The Heathkit model OL-1 Oscilloscope, when properly constructed will provide years of satisfactory service. We therefore urge yo to take all the time that is necessary to do a good job. Do not hurry the work and you will be rewarded with a greater sense of confidence both in the equipment and your own workmanship.
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I find the above paragraph very well put. It encourages the owner to take their time and put a little pride into their work so they will reap the benefits of a job well done. You seldom, if ever, see or hear anything like this these days anywhere including the classroom.
Somewhat interesting, about two months before Heathkit released their O-10 five inch oscilloscope, they released the little three inch CRT scope. It isn't worth much today but back then, a scope with up to 200kHz range was perfect for many hobbyists. The specs say +/- 3db for both vertical and horizontal response. However it's safe to say it's really a 100kHz AC only coupled scope.
October 18, 2019
Tonight mark's a new project start. I obtained two OL-1's from a fellow Heathkit aficionado for about the cost of shipping. One is a parts donor though both are rough. The restore-to-operation (RTO) candidate is cosmetically in better shape and cleaner inside. There is a fine white dust all over everything. I knew this could be cadmium or aluminium dust. I'll err on the side of caution and assume it's cadmium. The cadmium was used as a coating to protect their steel chassis but I don't know if they used it on aluminium chassis or not.
Below are pictures of the RTO candidate.
I will be disassembling this with gloves and a mask or respirator. I'm thinking I'll remove the transformer, CRT and vacuum tubes/valves before I spray it down with Simple Green and rinse it off. This stuff is nasty.
That's it for now. 73!
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So with nitrile gloves on and a dust mask I began to disassemble the scope. The first item to be removed was the CRT. Carefully working the socket off the rear of the tube and pushed aside, the rear mount was loosened. The rear mount rubber was still pliant so with some rubber treatment should last quite a while. The felt that surrounds the display end of the CRT is dirty but intact. A little brushing and vacuum will bring it back to a more acceptable look.
The CRT cleaned up with a microfiber cloth to get the majority of the dusty dirt off revealed it to be a DuMont 3GP1. It is a JAN build but if the date code was stamped on the base cap, it's gone now. I was only just able to make out JAN on the cap after careful cotton swab cleaning.
Sorry for the blurry photo's. Been having trouble with the pain in my fingers the last couple of days so holding the phone steady is a bit difficult. Hopefully you can see the JAN and the very faded 3GP1. It is duplicated on the other end of the tube as shown below.
I was able to find something that might be a part number and build date of the glass stem.
It's possible the S7112D is the part number of the stem assembly and 1N44 may mean 1 November, 1944. However it could be argued it's not November since there are three months that start with J, two months starting with A, and two with M. I'm inclined to believe the year is 1944. Heathkit was well-known for buying up large amounts of military surplus to populate their kits and having JAN parts in the kit only added to its reliability and durability.
Wrapping up the CRT into a cloth wrap I put it in a box for safe keeping and went on the remove the valves. None of the valves look to have equalized as noted by the Getter color. The tubes installed are:
12AU7 x4 all dated 5-43 - GE Electron Tube - 5th day or 5th week of 1943?
12AX7 x1 date code 55-43 - CBS brand - Definitely the 55th day of 1943.
1V2 x1 date code 5-35 - RCS brand - Though the seven-pin miniature tube wasn't mass marketed until 1938 there were early versions like this with only one or two elements inside until they improved the element manufacture to include more elements.
6X4 date code 5-48 - GE Electron Tube
Two of the 12AU7's are for the Vertical control between the probe and vertical plates. The other two are used in the horizontal circuit where one is for the probe and the other for the time base of the sweep. The 12AX7 used to interface the external horizontal sync. The 6X4 is a full wave rectifier tube and the 1V2 is a high voltage diode used in the fly-back circuit.
This is an AC coupled scope and I'm hoping I can find a schematic for the RCA WO-33A he used to see if it also is an AC coupled scope. More research cometh.
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And I'm back. I did some of the research and according to the schematic, the RCA unit is also AC coupled as there are also DC blocking capacitors on the inputs. So I guess I have my answer.
Now back to the disassembly. I cleaned all the wires of the ash/tar/nicotine the best I could. It looks much better now. From there I used DeoxIT D5 on all of the control pots and the one rotary in preparation. It'll dry long before I get this back together but I can test them now for consistency.
Next I cleaned up the gunk from the tubes. These needed rubbing alcohol and cotton swabs. I very carefully cleaned the top, then the bare glass between the printings, and finally dry-wiped the printed part to clean it up a little. This worked pretty well. I only lost part of one production date on one of the 12AU7's. I think I had the swap too saturated and it ran around the glass over it before I caught it. The tubes cleaned up well and are ready for a pin bath in DeoxIT later.
The two main filter capacitors were removed. Those are .1uF 1200V pieces. One looks like it shorted after overheating. One looks like it tried to vent as the wax plug on one end was pushed out most of the way. The other one vented via a hole it made in the end and dribbled molten wax down to the bottom of the chassis. I haven't opened up the other OL-1 yet to see how it fared. I'm guessing it's worse inside as the outside is quite bad.
So making some more progress. I don't think I'll build a jig for the CRT testing. I want to pull the circuit board out, scan it, clean it, scan it again and reinstall it. However, I found the manual and it has a foil pattern in it. I can scan that and hopefully import it into Eagle PC software or KiCad. I'm not too savvy on CAD so maybe this is good opportunity to learn them better.
That's it for now.
73!
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I debated on replacing the old green plastic encapsulated or molded paper capacitors from Micamold with Orange Dips or tubular poly types. I went with the tubular Poly type since the leads are long enough and have the correct axial look for the design. Orange Dips will work just fine but ruins the aesthetics of the unit. I'm not into restoration to factory new condition. I'm more of a resurrectionist. Sometimes the character of the radio or test gear is lost when cleaned up pristine like. Sure it looks nice but loses the passing of time it has been through thus losing much of the impact of that recognition of what we call, "old".
So I need to test the resistors out and put together a list of those that are out of spec. I've already found a couple. I will replace them with Metal Film types. I did a comparison between DigiKey, Mouser and Just Radios. If were to replace all the capacitors and resistors the cost would be around $120 from DigiKey or Mouser. Just Radios would be a little more expensive due to the cost of the capacitors. Odd ain't it.
I don't prefer KEMET resistors and those are what Just Radios sells. If you like them, keep using them. Their capacitors are good but I do prefer Illinois Capacitor or Vishay/Sprague for most of my work when I can get them in all the values needed. Vishay/Dale resistors are my go-to brand for precision values. Cornell Dublier Capacitors owns Illinois Capacitor now but they don't seem to have change anything IC was doing, which is good. Why ruin a good thing? They probably bought them to have an economical line of product here in the USA.
Electrolytic capacitors are, from preferred to less preferred:
Illinois Capacitor, Cornell Dublier (CDE), Nichicon, Rubycon, Panasonic.
There's nothing wrong with Nichicon or Rubycon. The counterfeits are Nishicon and Rubicon or other name variations. The good ones are Japanese brands regardless if they are made in Japan or elsewhere, including China. The counterfeits are Chinese engineered knock-offs and are found in the Bad Caps forums. It seems when they stole the formula they only got 90% of it. One or two ingredients were deliberately missing from all documents to prevent corporate espionage. So back in the late 1990's when the stolen papers for the good capacitors were manufactured, millions of them would soon fail. So many in fact there's still a huge stock that hasn't been depleted since 2000 or is allowed to continue to manufacture bad capacitors by the government's turning a blind eye. We know what they want and it doesn't include the rest of the world.
I look at it this way. If a reputable company designs something then sends it over to China to have manufactured, it's still the originating design and of good quality. It's when the designs are stolen and crappy engineering ensues just to make a buck, that makes for a cheap, no good product, or cheap Chinese make. They can make good products for others but to engineer their own leaves much to be desired. Look at Alibaba.com and Aliexpress and try to tell me any of that stuff isn't the cheap copies. If you thought greed is bad in America, you haven't taken notice of China's intentions.
I'll close this entry off by stepping off my soap box now.
73!
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I did, however measure the resistors and found that only the 2.2 megohm pieces are within tolerances. In fact I was very surprised to find them to be nearly spot-on. None were above their rated value and the lowest was less than 2% down from rated value. Those can be re-used but I will replace them all the same with metal film types with a 1 watt rating.
I’m finding that many new carbon composition resistors have already drifted up as much at 3 to 5% as tested when I get them. KEMET makes many of them and they are inexpensive but I don’t like them. I believe the consistency of their compound leave much to be desired. Allen-Bradley’s are hot molded and are well known for their consistency, predicable behavior and are still available here and there. West Florida Components routinely has them including many of the values in MIL-Spec.
No more to tell this time.
73!
November 18, 2019
It’s been a while (ten days actually) since my last post. So I’ll make it quick.
I achieved my Extra Class certification for my amateur radio license. I know it’s a bit lackluster with the no-code requirements but I can now work on technique and expand my interests at my own pace instead of being force-fed and becoming resentful for the experience.
Now the the OL-1….I mentioned last post the resistors are all but too far gone for acceptable limits. With that I ordered all new metal film resistors in 1W handling characteristics that replace all of the ½ watt originals. The cost is comparable and they will be able to handle the heat better. All 1W and/or 2W originals will be replaced with 2W or 3W as available.
In addition, the two high voltage .1µF 2000VDC power film capacitors from Kemet were also ordered. Here is the datasheet for the product line.
https://www.mouser.com/datasheet/2/212/KEM_F3042_C4C_AXIAL-1104255.pdf
I should have the parts in hand on the 20th so I will have the weekend to work on it and possibly resurrect it to operational use.
Other than that I don’t have anything else to impart. Godbless and…
73!
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I have gotten a little work done on the project. The resistors are all replaced as are the tubular and electrolytic capacitors except for the multisection capacitor. It's going to take a bit to restuff it so I'm thinking I'll go ahead and replace it with separate caps to do the same job. If I had remembered to order them, that is. For now I need to get them on order.
The intensity control with power switch had to be disassembled. The switch action was very stiff and the rotational movement sluggish like I was turning something in semi-molten wax. So after disassembly the grease used over fifty years ago was wax. It was sticky and wasn't coming off easily. Part of the shaft contains a phenolic wafer to support the wiper. This was gummed up bad and took a bit of QD Electronic Cleaner to get it off. Phenolic can absorb stuff and it was a risk even to use the stuff from CRC. I didn't need the lubricant in DeoxIT and so didn't use it. Rubbing alcohol would have worked but again, not sure how the phenolic would have reacted.
After cleaning off all the gunk from the control I turned my attention to the switch portion. It's riveted so I wasn't able to take it apart. I let it soak in the CRC cleaner and worked the switch many times. Junk came out of the holes and the switch worked much better. The contacts sounded much better and made a solid click with a solid tactile feel to it now.
Before reassembling the control I greased up the bushing for the shaft with Labelle 106 grease. I have used this on many control shaft bushings and have found it to work very well. I originally used it on model trains to lube the gear boxes with. The gear boxes never needed reapplication after several hundred hours of run time.
After the control was reassembled I reattached the switch can to it and remounted it to the front panel. From there I installed a new 150K resistor, reattached the wires and went to installing the two large .1uF filter capacitors and a new Vishay-Dale 47K resistor for pin 9 of the 1V2 regulator tube (V7).
It's almost done. All I need now are the four capacitors to replace the "Can" style capacitor with and it'll be ready for testing.
73!
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Carefully prying up the crimped edge of the can away from the phenolic disc the terminals are seated through, I tried to slip the disc off to get to the rubber gasket. It would not move and I felt it would snap if I tried any further. Not an ideal situation, to say the least. This, then led to tonight’s exciting even with vintage technology.
I know what you’re thinking. It was inevitable, so why do it? I don’t own a heat gun, blow torch, or acetylene torch. I do have an oven. ;D
As I I mentioned above, I had gotten the capacitor’s crimp turned out but wasn’t able to slip the phenolic disc base off. So instead I lined a tray with aluminium foil, put it in the oven and turned the oven to 250 degrees F and waited for it to preheat. I figured 250 was a safer way to start the process since I’ve not done this before.
The preheat beeper sounded and I put the capacitor on the foil upside-down (terminals up) to let it warm up for about 15 minutes to start with.
After pulling it from the oven and holding it with an oven mitt, I tried to pull slightly on the terminals. Well, nothing happened so I put it back in the oven for 10 more minutes. The results of this were good, right up until the capacitor slid out of the can. From that point on, the house began to fill with the incredible aroma of “old” consisting of vintage tar, glue, or whatever-is-inside-that-thing. Ah it was heaven. The sound of the exhaust fan wasn’t. At least until the wife and daughter asked if I was cooking something. Daughter’s nose was wrinkled up too. That was the definitive reaction that told me I should have waited until the weekend when everyone could have gotten away.
I put the empty can back in the oven right-side-up and shut the oven off to cool down slowly. Any of the stuff in there might run down the sides toward the open end and land on the foil. Lacquer thinner will get the rest of it out later. My current focus was to get the disc and terminals off as an assembly to reuse. The steel ring the can was crimped over is what held the whole thing to the chassis. I’d need that to do the same even if I didn’t use the can again.
Now technically I don’t need the can. The modern capacitors are in their own cans but the original look is part of what makes the equipment what it was. I don’t debate the reforming of capacitors. Too many examples show it can be done but not with ALL capacitors in any condition. There’s just too much at stake should this capacitor fail and take out the transformer. Sure, a fuse would do justice but the leakage of DC current into a circuit that isn’t supposed to have DC current justifies the modification. This capacitor tested as shorted in one section which prompted testing the transformer. All appears OK.
So with the vintage aroma of time in the air no longer being fueled by the oven, I can’t help but feel a sense of nostalgia working on this project with that familiar odor. As if I’d just walked into a radio service shop as a little kid. I know the feeling couldn’t last forever but the aroma will linger for a while much to the dismay of the other family members.
73!
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Good evening. I apologize for the formatting and missing photos. Another failure of Microsoft Office is that it embeds html coding that is completely superfluous to the content on the web page. So I am having to rebuild this page yet again due to these issues.
On to the main event:
I had pulled out the capacitor from it's can and tonight I unwrapped it to bare the electrodes.
The tar still inside the can will be removed. I might use a heat source again but not the oven when the family is home. I'm considering just letting it soak in lacquer thinner or acetone for now.
The electrodes have been trimmed and the base is ready to be cleaned up. There is a disc of some kind of material that sandwiches the rubber gasket with the other disc. I presume it's phenolic as well. Not sure what I can use that won't break down the phenolic. Maybe nothing and will have to procure blank printed circuit boards to cut out new discs from.
That's it for now.
73!
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I had a little time to do some work today. I was able to disassemble the base and clean up the terminals. The electrodes couldn't be soldered no matter how much RA flux I used. It's a really soft metal. Whatever it was, it could be spot welded since that's how it was attached to the foil wrap layers of the original. Oh well. Maybe one day I'll have a spot welder on the workbench.
So I dug the electrodes out of each of the terminal's crimp holding it in place. This allowed me to solder the new capacitor leads to them directly. It turned out to be an easier job that I thought. The most difficult was getting the tar out of the can. But I digress.
So far, so good. The capacitors tested good after mounting them on the base. Next was to get the can cleaned up. I had some Carquest Contact Cleaner and sprayed it into the can carefully so as not to blow it out all over. Once the can was filled about 2/3rds the way I used a brass brush and worked at it for quite some time before I was starting to see the tar dissolving. This was done outside of course.
All cleaned up and ready for its new occupants.
The steel ring was cleaned of old solder on the one lug that was soldered tot he chassis mounting plate. This plate is removable but I didn't need to undo the bolts holding it to the chassis. I needed the chassis as a holder to rid the terminals of solder to remove the connecting wires. Now it's cleaned up so I can reinstall the assembly once I get the can assembled and crimped again.
73!
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A belated Merry Christmas! I was able to get some more work done on the oscilloscope Christmas afternoon. It wasn't until late I would be able to power it up and discover the power switch was bad. My bad for not testing it after I'd cleaned it, or rather thought I'd cleaned it.
I de-soldered the connections and removed the switch from the front panel. Next I took the switch shell assembly off the intensity control by bending the tabs up again. Next there was the spring wire holding the Bakelite shell to the aluminium shell together. I was rather concerned wire would break rendering the switch unusable and have to fall back to the parts donor OL-1. But they bent nicely and I could separate the switch from the aluminium shell. From there I discovered the rivet holding the switch actuator also ran through the wafer the makes up the switch. I wasn't able to get it off so I had to copious amounts of contact cleaner to break up the old, dried up grease I suspected was insulating the contacts. Once I got the material out as much as possible I then sprayed DeoxIT D5 up under the wafer and more old grease ran out. After letting the mechanism soak overnight in the contact cleaner I shot it once more with DeoxIT and let it sit a while.
The switch was reassembled and tested for operation before being reattached to the intensity control. Passing this I soldered all connections back in place. Now I was able to try a power on test. I brought the voltage up to 80 volts with the load limiter bulbs switch IN for protection.
It failed. Only two 12AU7's, the 6X4 and the CRT heaters lit. One heater in another 12AU7 was lit but not both. I turned the unit upside down and put a meter on the lead points for each tube. All filament voltages were there, in respect to the main voltage set to 80VAC. I checked the valves again and the filaments lit up brightly in the checker except the 1V2. The meter, when the TEST switch was activated, went to nearly 90% but jittered some and began to fall. Each time the TEST switch was pulled to test it, the meter would come up lower and drift down until it stayed in the Yellow band of the meter. I checked the plate voltage again and it was set to 95V and the Type set to 4 as per the reference roll in the window. So down went the power and another evening's mental notes began as I listened to a winter storm on YT.
Tonight I pulled each valve and retested using the TC-2 emission checker. I pulled the 1V2 from the donor OL-1 and it checked out okay. All the other tubes seemed to be okay. Using the DeoxIT again, I sprayed some into a small tuna can, dipped the end of a precision screwdriver into the solution and applied a drop to each valve pin socket on the circuit board. Next was to insert in a round-a-bout rocking motion to work the pins through the socket receptacles to work through the oxidation. I performed the same procedure on the CRT's socket as well. I will be looking for something to do that function without a valve or use a dead valve. I don't wish to make a dead valve from a good one. Here's the end result of my efforts.
The gun in the CRT began to glow around 90VAC via the auto-transformer and isolation transformer. I turned the voltage to 115 and it did get a little brighter. However, the intensity seemed a bit lackluster as I turned it up all the way and got what you see in the photos. I turned up the voltage to 124VAC to match what is available at my wall outlets with no improvement so I backed it back down to 115VAC.
I was able to focus the beam to a fine point but left it out of focus for testing. Next were the vertical and horizontal centering controls. That's when I found a new problem to trace. I got very little vertical movement and no horizontal movement. I'll have to check the Pots for linearity. I cleaned them while they were still installed and zipped the knob back and forth many times. These may have gunk in them too so they will be taken apart and cleaned up.
So I've been able to bring this back to life partly. This is exciting and I'm looking forward to further detailed work to correct these currently known issues. I'm sure there will be other items as I progress further. For now, I'm glad it did at least this much.
73!
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A little progress has been made on the OL-1. After discovering rust inside the parts donor transformer, I pulled the shield caps off and cleaned it up. Testing revealed the same readings, within reason, of the other unit. Testing at 10VAC IN also confirmed the voltages through winding ratio calculations. Lastly, a full-power test of the two unloaded transformer's filament windings (one for CRT) and the 360-0-360 VAC secondaries showed higher than rated but expected. I performed the same test on the unit I pulled from the resurrection project and found the readings to be similar. However, and this is completely my fault for not thinking about it, I tested the 870VAC portion and popped something in the IM-13 VTVM. The meter went dead and I kicked myself for a while for not remembering the unloaded potential was much higher than rated. However, I didn't think it could be higher than 1500VAC which is the top rating for the meter. Odd that either the voltage was higher or I had a lower voltage component installed. I'll pull the meter apart and troubleshoot it soon.
For now I've reassembled the donor transformer and will be checking all the wiring and component placement in the rest of the unit. I may remove the circuit board and swap it with the donor's board as it has not been messed with to see if I get the same results with the slanted trace that's supposed to be round. If it does exhibit the same issue then I'll replace the filter capacitors in the restuffed can with another set of e-caps without the can and see what I get.
That's it for tonight.
73
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Today's work session was as fruitful as could have been hoped for. Previously I had a transformer from a donor unit that appeared to be OK. It ohm'd out okay and when tested with a variac and dim-bulb load limiter and isolation transformer, unloaded voltage on all but the 870VAC winding also seemed good. When I checked the voltage of the 870VAC I blew something in my IM-13 VTVM. Shouldn't have since loaded it's supposed to be the aforementioned 870VAC and unloaded shouldn't have exceeded 1000VAC.
Having nothing better to do than to go through the entire wiring of the oscilloscope I pulled the original manual out and run through the assembly. I found one incorrect wiring connection and one broken one. Since the incorrect one had everything to do with the Horizontal control, I figured I had found the problem relating to the un-round dot on the CRT. The broken connection was to one of the horizontal deflection plates giving me no horizontal control.
Now having done those items it was time to put a transformer back in it. I decided to try the donor piece first to see if it did work. It had been subjected to moisture and possible submersion considering the amount of rust inside the transformer's shield caps. Having threaded the wiring through the hole with a new grommet, all the connections were made and soldered. The tubes were installed except the 1V2 and 6X4.
The OL-1 is plugged into an isolation transformer which is plugged into the Autotransformer. A pair of 100 watt incandescent bulbs are wired in parallel to each other in series with a switch to the output. The switch is in the IN position to run all power through the bulbs to limit the amount of current available at the output (isolation transformer in this case).
The oscilloscope power switch was turned on and the intensity turned all the way up as per the testing and calibration instructions.
Next the Autotransformer was turned up half way. The bulbs lit up pretty good and the output was only at 43VAC at the output of the isolation transformer. This wasn't a good sign. I did some voltage tests at each of the secondary winding pairs with my DMM. It seemed the voltage for the 870VAC winding didn't measure up to the ratio previously calculated and I shut it down. The transformer in the OL-1 was warm to the touch and knew there was a short somewhere in it. My guess is the rust had migrated into the layers of the windings causing the problem. So out with the old and in with the original transformer. I say that since I believe the donor unit is actually older than the one I'm resurrecting.
So I took a break, went grocery shopping with my daughter and returned to work with a clearer head now. I got something to eat.
After installing the original transformer I did the same test as before with all but the 6X4 and 1V2 tubes with nothing significantly different except that my DMM showed an OL on the screen when I tried to test the 870VAC winding. Still not sure why it would run above 1kV unloaded unless the load on that winding is such that it needs that much more to make up for a huge drop while loaded down. The 1V2 handles the HV on the CRT in lieu of a fly-back transformer. That's how they did things back then. The HV was on the focus control as well and the manual states to be very careful handling the unit with the cover off since the focus control connection points are easily touched.
So here's the result of today's work.
So I'm very happy with the results. After shutting it down I drained the capacitors to do some tiding up of the wiring. I noticed the donor unit had a couple of modifications done. One was a power indicator via a capacitor and neon indicator dome. The other was a test point socket but was unlabeled. I'll have to make those mods on the schematic to get a better idea what the owner was doing. It's possible it's a test port constant with a fixed frequency reference instead of having to switch the horizontal mode to 60Hz.
The wiring of the donor unit also seemed a bit more tidy. Wire lengths weren't overly long as the instructions would have you make them and most were pressed to the chassis for noise suppression reasons. The solder joints also look better and the components seemed also be of higher quality for the period. If my work unit hadn't come out like it did today, I might have swapped the board out with the donor board just to see what difference it would have made.
With having seem the better wiring workmanship I worked over the wiring in mine a little bit. I also raised the transformer up on flat washers so the wires from the multi-section filter capacitor were routed the same as the donor unit. This shortened the wiring by more than an inch. Most of the rework had at least an inch removed, stripped and reconnected one wire at a time. It made it look better to be sure.
So with this portion complete, I can run through a few tests to see the clarity of wave forms on this. Completing that part I can start working on the signature tracer project plans while I think about the next piece in the SB series of radio equipment to work on.
73!
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Heathkit Oscilloscope Model OL-1
August 1954 to August 1956
Initial Price: $29.50
Ad in Radio Electronics, September-1954
Excerpt from the assembly manual:
INTRODUCTION
The cathode ray oscilloscope is without a doubt the most versatile electronic instrument available today. Basically, it is an indicating device which can display in usable form, the actual voltage variations in an electrical quantity as compared to time. This however, is merely its basic function and it would be impossible at this time to enumerate all of its qualifications. It is the type of instrument for which the operator can continue to find new applications even after many years of use.
Some of the many desirable features are as follows:
1. It displays instantly information that otherwise would require hours of experimentation.
2. Wave forms can easily be photographed and retained for future reference.
3. It usually has a negligible effect on the characteristics of a circuit under test.
4. It has an extremely wide range of sensitivity.
5. It is rugged, dependable and not easily damaged by overload or surges.
~
The Heathkit model OL-1 Oscilloscope, when properly constructed will provide years of satisfactory service. We therefore urge yo to take all the time that is necessary to do a good job. Do not hurry the work and you will be rewarded with a greater sense of confidence both in the equipment and your own workmanship.
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I find the above paragraph very well put. It encourages the owner to take their time and put a little pride into their work so they will reap the benefits of a job well done. You seldom, if ever, see or hear anything like this these days anywhere including the classroom.
Somewhat interesting, about two months before Heathkit released their O-10 five inch oscilloscope, they released the little three inch CRT scope. It isn't worth much today but back then, a scope with up to 200kHz range was perfect for many hobbyists. The specs say +/- 3db for both vertical and horizontal response. However it's safe to say it's really a 100kHz AC only coupled scope.
October 18, 2019
Tonight mark's a new project start. I obtained two OL-1's from a fellow Heathkit aficionado for about the cost of shipping. One is a parts donor though both are rough. The restore-to-operation (RTO) candidate is cosmetically in better shape and cleaner inside. There is a fine white dust all over everything. I knew this could be cadmium or aluminium dust. I'll err on the side of caution and assume it's cadmium. The cadmium was used as a coating to protect their steel chassis but I don't know if they used it on aluminium chassis or not.
Below are pictures of the RTO candidate.
I will be disassembling this with gloves and a mask or respirator. I'm thinking I'll remove the transformer, CRT and vacuum tubes/valves before I spray it down with Simple Green and rinse it off. This stuff is nasty.
That's it for now. 73!
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October 20, 2019
Greetings! Got a little more progress on the OL-1's disassembly. Dealing with the potential of the cadmium residue isn't fun but it is just one more aspect of restoration one must be aware of in antique equipment.So with nitrile gloves on and a dust mask I began to disassemble the scope. The first item to be removed was the CRT. Carefully working the socket off the rear of the tube and pushed aside, the rear mount was loosened. The rear mount rubber was still pliant so with some rubber treatment should last quite a while. The felt that surrounds the display end of the CRT is dirty but intact. A little brushing and vacuum will bring it back to a more acceptable look.
The CRT cleaned up with a microfiber cloth to get the majority of the dusty dirt off revealed it to be a DuMont 3GP1. It is a JAN build but if the date code was stamped on the base cap, it's gone now. I was only just able to make out JAN on the cap after careful cotton swab cleaning.
Sorry for the blurry photo's. Been having trouble with the pain in my fingers the last couple of days so holding the phone steady is a bit difficult. Hopefully you can see the JAN and the very faded 3GP1. It is duplicated on the other end of the tube as shown below.
I was able to find something that might be a part number and build date of the glass stem.
It's possible the S7112D is the part number of the stem assembly and 1N44 may mean 1 November, 1944. However it could be argued it's not November since there are three months that start with J, two months starting with A, and two with M. I'm inclined to believe the year is 1944. Heathkit was well-known for buying up large amounts of military surplus to populate their kits and having JAN parts in the kit only added to its reliability and durability.
Wrapping up the CRT into a cloth wrap I put it in a box for safe keeping and went on the remove the valves. None of the valves look to have equalized as noted by the Getter color. The tubes installed are:
12AU7 x4 all dated 5-43 - GE Electron Tube - 5th day or 5th week of 1943?
12AX7 x1 date code 55-43 - CBS brand - Definitely the 55th day of 1943.
1V2 x1 date code 5-35 - RCS brand - Though the seven-pin miniature tube wasn't mass marketed until 1938 there were early versions like this with only one or two elements inside until they improved the element manufacture to include more elements.
6X4 date code 5-48 - GE Electron Tube
Two of the 12AU7's are for the Vertical control between the probe and vertical plates. The other two are used in the horizontal circuit where one is for the probe and the other for the time base of the sweep. The 12AX7 used to interface the external horizontal sync. The 6X4 is a full wave rectifier tube and the 1V2 is a high voltage diode used in the fly-back circuit.
This is an AC coupled scope and I'm hoping I can find a schematic for the RCA WO-33A he used to see if it also is an AC coupled scope. More research cometh.
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And I'm back. I did some of the research and according to the schematic, the RCA unit is also AC coupled as there are also DC blocking capacitors on the inputs. So I guess I have my answer.
Now back to the disassembly. I cleaned all the wires of the ash/tar/nicotine the best I could. It looks much better now. From there I used DeoxIT D5 on all of the control pots and the one rotary in preparation. It'll dry long before I get this back together but I can test them now for consistency.
Next I cleaned up the gunk from the tubes. These needed rubbing alcohol and cotton swabs. I very carefully cleaned the top, then the bare glass between the printings, and finally dry-wiped the printed part to clean it up a little. This worked pretty well. I only lost part of one production date on one of the 12AU7's. I think I had the swap too saturated and it ran around the glass over it before I caught it. The tubes cleaned up well and are ready for a pin bath in DeoxIT later.
The two main filter capacitors were removed. Those are .1uF 1200V pieces. One looks like it shorted after overheating. One looks like it tried to vent as the wax plug on one end was pushed out most of the way. The other one vented via a hole it made in the end and dribbled molten wax down to the bottom of the chassis. I haven't opened up the other OL-1 yet to see how it fared. I'm guessing it's worse inside as the outside is quite bad.
So making some more progress. I don't think I'll build a jig for the CRT testing. I want to pull the circuit board out, scan it, clean it, scan it again and reinstall it. However, I found the manual and it has a foil pattern in it. I can scan that and hopefully import it into Eagle PC software or KiCad. I'm not too savvy on CAD so maybe this is good opportunity to learn them better.
That's it for now.
73!
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November 3, 2019
Good evening! I got a little more done tonight. I replaced all six of the paper capacitors and two 20uF electrolytics. I haven't ordered the two .1uF 1200V capacitors or the ones I need to replace the can type capacitor yet. I can use Polypropylene's for the high voltage ones. I am still debating whether I want to restuff the can with modern equivalents. Electrolytic capacitors in the high voltage I need aren't available any longer so the Poly's will do fine.I debated on replacing the old green plastic encapsulated or molded paper capacitors from Micamold with Orange Dips or tubular poly types. I went with the tubular Poly type since the leads are long enough and have the correct axial look for the design. Orange Dips will work just fine but ruins the aesthetics of the unit. I'm not into restoration to factory new condition. I'm more of a resurrectionist. Sometimes the character of the radio or test gear is lost when cleaned up pristine like. Sure it looks nice but loses the passing of time it has been through thus losing much of the impact of that recognition of what we call, "old".
So I need to test the resistors out and put together a list of those that are out of spec. I've already found a couple. I will replace them with Metal Film types. I did a comparison between DigiKey, Mouser and Just Radios. If were to replace all the capacitors and resistors the cost would be around $120 from DigiKey or Mouser. Just Radios would be a little more expensive due to the cost of the capacitors. Odd ain't it.
I don't prefer KEMET resistors and those are what Just Radios sells. If you like them, keep using them. Their capacitors are good but I do prefer Illinois Capacitor or Vishay/Sprague for most of my work when I can get them in all the values needed. Vishay/Dale resistors are my go-to brand for precision values. Cornell Dublier Capacitors owns Illinois Capacitor now but they don't seem to have change anything IC was doing, which is good. Why ruin a good thing? They probably bought them to have an economical line of product here in the USA.
Electrolytic capacitors are, from preferred to less preferred:
Illinois Capacitor, Cornell Dublier (CDE), Nichicon, Rubycon, Panasonic.
There's nothing wrong with Nichicon or Rubycon. The counterfeits are Nishicon and Rubicon or other name variations. The good ones are Japanese brands regardless if they are made in Japan or elsewhere, including China. The counterfeits are Chinese engineered knock-offs and are found in the Bad Caps forums. It seems when they stole the formula they only got 90% of it. One or two ingredients were deliberately missing from all documents to prevent corporate espionage. So back in the late 1990's when the stolen papers for the good capacitors were manufactured, millions of them would soon fail. So many in fact there's still a huge stock that hasn't been depleted since 2000 or is allowed to continue to manufacture bad capacitors by the government's turning a blind eye. We know what they want and it doesn't include the rest of the world.
I look at it this way. If a reputable company designs something then sends it over to China to have manufactured, it's still the originating design and of good quality. It's when the designs are stolen and crappy engineering ensues just to make a buck, that makes for a cheap, no good product, or cheap Chinese make. They can make good products for others but to engineer their own leaves much to be desired. Look at Alibaba.com and Aliexpress and try to tell me any of that stuff isn't the cheap copies. If you thought greed is bad in America, you haven't taken notice of China's intentions.
I'll close this entry off by stepping off my soap box now.
73!
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November 8, 2019
Well with all that’s happened since the loss of my original Shack Happening’s posts and my upcoming Extra Class exam, I haven’t got much done with the OL-1.I did, however measure the resistors and found that only the 2.2 megohm pieces are within tolerances. In fact I was very surprised to find them to be nearly spot-on. None were above their rated value and the lowest was less than 2% down from rated value. Those can be re-used but I will replace them all the same with metal film types with a 1 watt rating.
I’m finding that many new carbon composition resistors have already drifted up as much at 3 to 5% as tested when I get them. KEMET makes many of them and they are inexpensive but I don’t like them. I believe the consistency of their compound leave much to be desired. Allen-Bradley’s are hot molded and are well known for their consistency, predicable behavior and are still available here and there. West Florida Components routinely has them including many of the values in MIL-Spec.
No more to tell this time.
73!
November 18, 2019
It’s been a while (ten days actually) since my last post. So I’ll make it quick.
I achieved my Extra Class certification for my amateur radio license. I know it’s a bit lackluster with the no-code requirements but I can now work on technique and expand my interests at my own pace instead of being force-fed and becoming resentful for the experience.
Now the the OL-1….I mentioned last post the resistors are all but too far gone for acceptable limits. With that I ordered all new metal film resistors in 1W handling characteristics that replace all of the ½ watt originals. The cost is comparable and they will be able to handle the heat better. All 1W and/or 2W originals will be replaced with 2W or 3W as available.
In addition, the two high voltage .1µF 2000VDC power film capacitors from Kemet were also ordered. Here is the datasheet for the product line.
https://www.mouser.com/datasheet/2/212/KEM_F3042_C4C_AXIAL-1104255.pdf
I should have the parts in hand on the 20th so I will have the weekend to work on it and possibly resurrect it to operational use.
Other than that I don’t have anything else to impart. Godbless and…
73!
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December 11, 2019
I have gotten a little work done on the project. The resistors are all replaced as are the tubular and electrolytic capacitors except for the multisection capacitor. It's going to take a bit to restuff it so I'm thinking I'll go ahead and replace it with separate caps to do the same job. If I had remembered to order them, that is. For now I need to get them on order.
The intensity control with power switch had to be disassembled. The switch action was very stiff and the rotational movement sluggish like I was turning something in semi-molten wax. So after disassembly the grease used over fifty years ago was wax. It was sticky and wasn't coming off easily. Part of the shaft contains a phenolic wafer to support the wiper. This was gummed up bad and took a bit of QD Electronic Cleaner to get it off. Phenolic can absorb stuff and it was a risk even to use the stuff from CRC. I didn't need the lubricant in DeoxIT and so didn't use it. Rubbing alcohol would have worked but again, not sure how the phenolic would have reacted.
After cleaning off all the gunk from the control I turned my attention to the switch portion. It's riveted so I wasn't able to take it apart. I let it soak in the CRC cleaner and worked the switch many times. Junk came out of the holes and the switch worked much better. The contacts sounded much better and made a solid click with a solid tactile feel to it now.
Before reassembling the control I greased up the bushing for the shaft with Labelle 106 grease. I have used this on many control shaft bushings and have found it to work very well. I originally used it on model trains to lube the gear boxes with. The gear boxes never needed reapplication after several hundred hours of run time.
After the control was reassembled I reattached the switch can to it and remounted it to the front panel. From there I installed a new 150K resistor, reattached the wires and went to installing the two large .1uF filter capacitors and a new Vishay-Dale 47K resistor for pin 9 of the 1V2 regulator tube (V7).
It's almost done. All I need now are the four capacitors to replace the "Can" style capacitor with and it'll be ready for testing.
73!
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December 18, 2019
I got out the capacitors I’m going to use to restuff the can capacitor with to verify whether my research and careful selecting of capacitor size paid off. Luckily it did. They will fit with just a hairs width of wiggle room. Now it was time.Carefully prying up the crimped edge of the can away from the phenolic disc the terminals are seated through, I tried to slip the disc off to get to the rubber gasket. It would not move and I felt it would snap if I tried any further. Not an ideal situation, to say the least. This, then led to tonight’s exciting even with vintage technology.
I know what you’re thinking. It was inevitable, so why do it? I don’t own a heat gun, blow torch, or acetylene torch. I do have an oven. ;D
As I I mentioned above, I had gotten the capacitor’s crimp turned out but wasn’t able to slip the phenolic disc base off. So instead I lined a tray with aluminium foil, put it in the oven and turned the oven to 250 degrees F and waited for it to preheat. I figured 250 was a safer way to start the process since I’ve not done this before.
The preheat beeper sounded and I put the capacitor on the foil upside-down (terminals up) to let it warm up for about 15 minutes to start with.
After pulling it from the oven and holding it with an oven mitt, I tried to pull slightly on the terminals. Well, nothing happened so I put it back in the oven for 10 more minutes. The results of this were good, right up until the capacitor slid out of the can. From that point on, the house began to fill with the incredible aroma of “old” consisting of vintage tar, glue, or whatever-is-inside-that-thing. Ah it was heaven. The sound of the exhaust fan wasn’t. At least until the wife and daughter asked if I was cooking something. Daughter’s nose was wrinkled up too. That was the definitive reaction that told me I should have waited until the weekend when everyone could have gotten away.
I put the empty can back in the oven right-side-up and shut the oven off to cool down slowly. Any of the stuff in there might run down the sides toward the open end and land on the foil. Lacquer thinner will get the rest of it out later. My current focus was to get the disc and terminals off as an assembly to reuse. The steel ring the can was crimped over is what held the whole thing to the chassis. I’d need that to do the same even if I didn’t use the can again.
Now technically I don’t need the can. The modern capacitors are in their own cans but the original look is part of what makes the equipment what it was. I don’t debate the reforming of capacitors. Too many examples show it can be done but not with ALL capacitors in any condition. There’s just too much at stake should this capacitor fail and take out the transformer. Sure, a fuse would do justice but the leakage of DC current into a circuit that isn’t supposed to have DC current justifies the modification. This capacitor tested as shorted in one section which prompted testing the transformer. All appears OK.
So with the vintage aroma of time in the air no longer being fueled by the oven, I can’t help but feel a sense of nostalgia working on this project with that familiar odor. As if I’d just walked into a radio service shop as a little kid. I know the feeling couldn’t last forever but the aroma will linger for a while much to the dismay of the other family members.
73!
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December 20, 2019
Good evening. I apologize for the formatting and missing photos. Another failure of Microsoft Office is that it embeds html coding that is completely superfluous to the content on the web page. So I am having to rebuild this page yet again due to these issues.
On to the main event:
I had pulled out the capacitor from it's can and tonight I unwrapped it to bare the electrodes.
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| Unwrapping |
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| Another metal foil layer |
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| Spot weld electrodes |
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| The tar inside. Imagine a smoker's pair of lungs after several years of smoking. |
The tar still inside the can will be removed. I might use a heat source again but not the oven when the family is home. I'm considering just letting it soak in lacquer thinner or acetone for now.
The electrodes have been trimmed and the base is ready to be cleaned up. There is a disc of some kind of material that sandwiches the rubber gasket with the other disc. I presume it's phenolic as well. Not sure what I can use that won't break down the phenolic. Maybe nothing and will have to procure blank printed circuit boards to cut out new discs from.
That's it for now.
73!
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December 21, 2019
I spent some time restoring the photos on this blog post using the Word document I saved to find the photos that were used.I had a little time to do some work today. I was able to disassemble the base and clean up the terminals. The electrodes couldn't be soldered no matter how much RA flux I used. It's a really soft metal. Whatever it was, it could be spot welded since that's how it was attached to the foil wrap layers of the original. Oh well. Maybe one day I'll have a spot welder on the workbench.
So I dug the electrodes out of each of the terminal's crimp holding it in place. This allowed me to solder the new capacitor leads to them directly. It turned out to be an easier job that I thought. The most difficult was getting the tar out of the can. But I digress.
So far, so good. The capacitors tested good after mounting them on the base. Next was to get the can cleaned up. I had some Carquest Contact Cleaner and sprayed it into the can carefully so as not to blow it out all over. Once the can was filled about 2/3rds the way I used a brass brush and worked at it for quite some time before I was starting to see the tar dissolving. This was done outside of course.
All cleaned up and ready for its new occupants.
The steel ring was cleaned of old solder on the one lug that was soldered tot he chassis mounting plate. This plate is removable but I didn't need to undo the bolts holding it to the chassis. I needed the chassis as a holder to rid the terminals of solder to remove the connecting wires. Now it's cleaned up so I can reinstall the assembly once I get the can assembled and crimped again.
73!
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December 27, 2019
A belated Merry Christmas! I was able to get some more work done on the oscilloscope Christmas afternoon. It wasn't until late I would be able to power it up and discover the power switch was bad. My bad for not testing it after I'd cleaned it, or rather thought I'd cleaned it.
I de-soldered the connections and removed the switch from the front panel. Next I took the switch shell assembly off the intensity control by bending the tabs up again. Next there was the spring wire holding the Bakelite shell to the aluminium shell together. I was rather concerned wire would break rendering the switch unusable and have to fall back to the parts donor OL-1. But they bent nicely and I could separate the switch from the aluminium shell. From there I discovered the rivet holding the switch actuator also ran through the wafer the makes up the switch. I wasn't able to get it off so I had to copious amounts of contact cleaner to break up the old, dried up grease I suspected was insulating the contacts. Once I got the material out as much as possible I then sprayed DeoxIT D5 up under the wafer and more old grease ran out. After letting the mechanism soak overnight in the contact cleaner I shot it once more with DeoxIT and let it sit a while.
The switch was reassembled and tested for operation before being reattached to the intensity control. Passing this I soldered all connections back in place. Now I was able to try a power on test. I brought the voltage up to 80 volts with the load limiter bulbs switch IN for protection.
It failed. Only two 12AU7's, the 6X4 and the CRT heaters lit. One heater in another 12AU7 was lit but not both. I turned the unit upside down and put a meter on the lead points for each tube. All filament voltages were there, in respect to the main voltage set to 80VAC. I checked the valves again and the filaments lit up brightly in the checker except the 1V2. The meter, when the TEST switch was activated, went to nearly 90% but jittered some and began to fall. Each time the TEST switch was pulled to test it, the meter would come up lower and drift down until it stayed in the Yellow band of the meter. I checked the plate voltage again and it was set to 95V and the Type set to 4 as per the reference roll in the window. So down went the power and another evening's mental notes began as I listened to a winter storm on YT.
Tonight I pulled each valve and retested using the TC-2 emission checker. I pulled the 1V2 from the donor OL-1 and it checked out okay. All the other tubes seemed to be okay. Using the DeoxIT again, I sprayed some into a small tuna can, dipped the end of a precision screwdriver into the solution and applied a drop to each valve pin socket on the circuit board. Next was to insert in a round-a-bout rocking motion to work the pins through the socket receptacles to work through the oxidation. I performed the same procedure on the CRT's socket as well. I will be looking for something to do that function without a valve or use a dead valve. I don't wish to make a dead valve from a good one. Here's the end result of my efforts.
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| It lives! |
The gun in the CRT began to glow around 90VAC via the auto-transformer and isolation transformer. I turned the voltage to 115 and it did get a little brighter. However, the intensity seemed a bit lackluster as I turned it up all the way and got what you see in the photos. I turned up the voltage to 124VAC to match what is available at my wall outlets with no improvement so I backed it back down to 115VAC.
I was able to focus the beam to a fine point but left it out of focus for testing. Next were the vertical and horizontal centering controls. That's when I found a new problem to trace. I got very little vertical movement and no horizontal movement. I'll have to check the Pots for linearity. I cleaned them while they were still installed and zipped the knob back and forth many times. These may have gunk in them too so they will be taken apart and cleaned up.
So I've been able to bring this back to life partly. This is exciting and I'm looking forward to further detailed work to correct these currently known issues. I'm sure there will be other items as I progress further. For now, I'm glad it did at least this much.
73!
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January 10, 2020
A little progress has been made on the OL-1. After discovering rust inside the parts donor transformer, I pulled the shield caps off and cleaned it up. Testing revealed the same readings, within reason, of the other unit. Testing at 10VAC IN also confirmed the voltages through winding ratio calculations. Lastly, a full-power test of the two unloaded transformer's filament windings (one for CRT) and the 360-0-360 VAC secondaries showed higher than rated but expected. I performed the same test on the unit I pulled from the resurrection project and found the readings to be similar. However, and this is completely my fault for not thinking about it, I tested the 870VAC portion and popped something in the IM-13 VTVM. The meter went dead and I kicked myself for a while for not remembering the unloaded potential was much higher than rated. However, I didn't think it could be higher than 1500VAC which is the top rating for the meter. Odd that either the voltage was higher or I had a lower voltage component installed. I'll pull the meter apart and troubleshoot it soon.
For now I've reassembled the donor transformer and will be checking all the wiring and component placement in the rest of the unit. I may remove the circuit board and swap it with the donor's board as it has not been messed with to see if I get the same results with the slanted trace that's supposed to be round. If it does exhibit the same issue then I'll replace the filter capacitors in the restuffed can with another set of e-caps without the can and see what I get.
That's it for tonight.
73
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January 12, 2020
Today's work session was as fruitful as could have been hoped for. Previously I had a transformer from a donor unit that appeared to be OK. It ohm'd out okay and when tested with a variac and dim-bulb load limiter and isolation transformer, unloaded voltage on all but the 870VAC winding also seemed good. When I checked the voltage of the 870VAC I blew something in my IM-13 VTVM. Shouldn't have since loaded it's supposed to be the aforementioned 870VAC and unloaded shouldn't have exceeded 1000VAC.
Having nothing better to do than to go through the entire wiring of the oscilloscope I pulled the original manual out and run through the assembly. I found one incorrect wiring connection and one broken one. Since the incorrect one had everything to do with the Horizontal control, I figured I had found the problem relating to the un-round dot on the CRT. The broken connection was to one of the horizontal deflection plates giving me no horizontal control.
Now having done those items it was time to put a transformer back in it. I decided to try the donor piece first to see if it did work. It had been subjected to moisture and possible submersion considering the amount of rust inside the transformer's shield caps. Having threaded the wiring through the hole with a new grommet, all the connections were made and soldered. The tubes were installed except the 1V2 and 6X4.
The OL-1 is plugged into an isolation transformer which is plugged into the Autotransformer. A pair of 100 watt incandescent bulbs are wired in parallel to each other in series with a switch to the output. The switch is in the IN position to run all power through the bulbs to limit the amount of current available at the output (isolation transformer in this case).
The oscilloscope power switch was turned on and the intensity turned all the way up as per the testing and calibration instructions.
Next the Autotransformer was turned up half way. The bulbs lit up pretty good and the output was only at 43VAC at the output of the isolation transformer. This wasn't a good sign. I did some voltage tests at each of the secondary winding pairs with my DMM. It seemed the voltage for the 870VAC winding didn't measure up to the ratio previously calculated and I shut it down. The transformer in the OL-1 was warm to the touch and knew there was a short somewhere in it. My guess is the rust had migrated into the layers of the windings causing the problem. So out with the old and in with the original transformer. I say that since I believe the donor unit is actually older than the one I'm resurrecting.
So I took a break, went grocery shopping with my daughter and returned to work with a clearer head now. I got something to eat.
After installing the original transformer I did the same test as before with all but the 6X4 and 1V2 tubes with nothing significantly different except that my DMM showed an OL on the screen when I tried to test the 870VAC winding. Still not sure why it would run above 1kV unloaded unless the load on that winding is such that it needs that much more to make up for a huge drop while loaded down. The 1V2 handles the HV on the CRT in lieu of a fly-back transformer. That's how they did things back then. The HV was on the focus control as well and the manual states to be very careful handling the unit with the cover off since the focus control connection points are easily touched.
So here's the result of today's work.
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| A round, albeit out of focus dot. |
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| Let me point it out to you in case you didn't see it. ;-) |
The wiring of the donor unit also seemed a bit more tidy. Wire lengths weren't overly long as the instructions would have you make them and most were pressed to the chassis for noise suppression reasons. The solder joints also look better and the components seemed also be of higher quality for the period. If my work unit hadn't come out like it did today, I might have swapped the board out with the donor board just to see what difference it would have made.
With having seem the better wiring workmanship I worked over the wiring in mine a little bit. I also raised the transformer up on flat washers so the wires from the multi-section filter capacitor were routed the same as the donor unit. This shortened the wiring by more than an inch. Most of the rework had at least an inch removed, stripped and reconnected one wire at a time. It made it look better to be sure.
So with this portion complete, I can run through a few tests to see the clarity of wave forms on this. Completing that part I can start working on the signature tracer project plans while I think about the next piece in the SB series of radio equipment to work on.
73!
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