Hallicrafters S-40B - SOLD

Hallicrafters S-40B

Type: Amateur Radio Receiver
Level: Mid-range Consumer Product
Year: 1950-1955
First year pricing: $99.95US

Description (excerpt from a manual)

Models S-40B and S-40BU are sensitive superheterodyne communications receivers which provide reception of standard broadcast and foreign or domestic shortwave stations over four frequency ranges with continuous tuning from 540 KC to 44 MC.  The receivers employ seven tubes plus rectifier and provide both AM and CW reception.

The four frequency ranges or bands are clearly indicated on the large main tuning dial.  The locations of the amateur bands and foreign stations are indicated on the dial for convenient reference.  Also on the main tuning dial is a special logging scale for use when logging frequencies of special interest.

The electrical BAND SPREAD control provides a vernier or fine tuning adjustment throughout the entire tuning range of the receiver.

Other special features included in the receiver are automatic volume control (AVC) {a type of automatic attenuation}, automatic noise limiter and provision for headphone operation.  The STANDBY/RECEIVE switch permits disabling of the receiver for standby periods {for use with a transmitter when transmitting to prevent overloading the receiver's front end}, at the same time maintaining the tube heaters at operating temperature.

The receiver is housed in an attractive, well ventilated steel cabinet which has a length of 18-1/2 inches, a height of 8-1/2 inches and depth of 11 inches.

The S-40B is designed to operate from a 105-125 volt, 50-60 cycle AC power source.  The S-40BU, a universal model of the S-40B, permits operation from 25-60 cycle AC sources at voltages ranging from 110 to 250 volts.  The power consumption of each model is 75 watts.
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May 15, 2019

Thank you for visiting this project page.  This project may be a while in the making so I hope you get a chance to stop by and check out my other projects located on my Shack Happenings page.

So let's begin....

I bought this receiver in October of 2017 because the price was right and the owner said it was complete.  He said he hadn't used it for a long time but it was working when put away.  Good enough for me. After unboxing the unit I noticed some of the usual wear of a 60+ year old rig.  Overall it didn't have any dents in it, the knobs were all there, the dials looked to be in excellent shape as were the plastic windows.  I'd say it had some work done to it at some point.  It's possible the dials aren't original but it doesn't matter.  I love working things even if it doesn't have hardly any original parts.

After I raised the hood I took note that the 6H6 and the 5Y3GT tubes were missing.  I expected missing tubes which is par for the course.  I wasn't disappointed in the least.  The unit was otherwise whole and missing tubes or bad tubes, it didn't matter.  Now it was time to get a look underneath.

The missing tubes are a 5Y3GT next to the upper left corner of the transformer.
The other missing tube is a 6H6 twin diode metal tube.
I acquired both and during the restoration I will use these in place of the two
solid state diodes soldered under the 5Y4GT octal socket.

 I had it out of the case and immediately noticed most of the rig is original right down to the paper and wax capacitors.  A 'blue' drop capacitor and a couple of Orange Drops had made their way into the unit as did an International 1000µF 450V electrolytic capacitor, a fuse holder and a pair of diodes on the socket for the rectifier tube.  So it had be gone through and modded.  That was unexpected so a bit of a plan was made to get the receiver back to original working condition.  So the mod has to go as do all of the wax capacitors, the electrolytic and several resistors that have seen very high temperatures.  All in all, most of the guts will be replaced.  Tubular style capacitors from Illinois Capacitor are the choice here but I've got a couple of others in mind too in I can't get a particular value.  Getting some of the values used back then are more difficult as new standard values were put in place.  Many '50s technology have pre-war value components.  After the war, there was a lot of surplus that took years to deplete before the new 'post-war' standard values were used.

Mostly original!

This mod was supposed to eliminate the need for expensive rectifier tubes.
Unfortunately whoever did the mod didn't take into account the original
tube's voltage drop.  In the case of the 5Y3GT, it's about a 20 volt drop.
These diodes only have a .7 volt drop so you can see how the extra voltage
will get to the rest of the receiver circuits and over power them.  In practice
two 10 watt wirewound resistors would be needed in series to simulate the
voltage drop so the rest of the receiver got what it was designed for.

I'm almost convinced these dials are reproductions as is the
sight window.

So the BOM has been made.  I'm building a project cart on Digikey for this so I don't miss anything this time.  Then I can export it and save it locally.  Once that is done I'll order the parts over a couple of paychecks to spread it out.  There's a lot of cleaning I'd like to do too.

That's it for tonight.
73!
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May 17, 2019

Well, after all the excitement of getting to work on this rig, my bubble has burst.  After having gone through the rig more thoroughly I've discovered a number of discrepancies from the schematic.  First off, I'm reasonably sure the "RUN 4" stamp on the chassis isn't different from RUN 3 models as I cannot locate any schematics for RUN 4.  However, I'm going to inquire to the Hallicrafters group at group.io about that as well as the Amateur_Repair group on Yahoo.

So far I found a big, concerning modification that really makes me wonder.  The big 'Can' capacitor is not at all original and is supposed to be a 30-10-10 MFD multi-section capacitor.  What's in there now is an 80-50-20-50.  Even though the second 50mfd is not connected, I shudder to think how many other mods were actually done to this radio.  I'm not comfortable tackling this one right now.  Between the two solid-state rectifiers to try to eliminate the 5Y3GT tube without the proper resistors to simulate the voltage drop of the tube it replaced and the wrong 'can' capacitor, I think this will be more expensive than worth it for now.  I will be on the lookout for the correct can capacitor so it will look right even though I will re-stuff it with modern caps.

So with these unexpected surprises I will put the chassis back in the cover and return it to the 'to-do' shelf.  I will pull my Heathkit SB-301 out and begin work on it instead.  Very disappointed myself for not going thoroughly going through this rig when I bought it.

73
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