The Souper 38

OR

The second life of a cosmetically impaired Hallicrafters S-38C

Before-Not the actual rcvr- but close



After

Image1.jpg (23655 bytes)

S38S.jpg (101414 bytes)





I was listening to a QSO with several old timers talking about their first receivers being as highly modified 1930/40s commercial AM/SW sets to which they had added BFOs, bandsspread capacitors, vernier dials etc and thought that might be a pretty cool project (Half my fun in this hobby is dreaming of projects, not doing them!).For several months, I looked at hamfests, junk shops and on the net for a late 1930s receiver that was so badly trashed I would not feel guilty about throwing away the cabinet. I refuse to trash a radio that can be restored. The junked up ones I found were either too expensive or just not the right thing. Then, one of the email groups I belong to got involved in the extensive trashing of the Halicrafters S-38. During this discussion there were a number of people who came to the defense of the radio for nostalgic reasons, but admitted that as a ham receiver it left a lot to be desired. Now I will admit that the S-38 was not the top of the line by any measure but I have a soft spot for it.  At the the age of 5, long before I became a ham  a friend of my Dads had one in his study that I used to love to play with.  

All of this came together when I remembered that I had an S-38C chassis in my attic junk box. It met all of my criteria for several projects. It was small, simple, basic, metal tubed and there was no cabinet to harm. It looked like heck but I had bought it only for the knobs to finish the restoration of another one. With a little preliminary playing I determined I could turn the BC band into 160, Band B into 75/80 and Band C into 40.Thus the Souper 38 was born

The S-38 is notorious in part because it is an AC/DC set. Although some people address this issue by installing isolation transformer I decided to completely replace the power supply. I installed a small 150v 50 ma/6.3v 2A VAC transformer, fused it, and installed a 3 wire plug. I had to wire all filaments in parallel to run it off the 6.3 V.  I then rectified the AC with the use of one diode. I replaced the filter caps with new ones using the same general values.  I used the 35Z5 socket to install an OC3 Voltage regulator tube controlling the voltages for the BFO, IF,and Osc.  i I also replaced the AC cord with a 3 wire grounded one.

Every tube in the original design has a 6 volt equivalent with the exact same nomenclature (except for the filament voltage) so swapping them out was an easy task

Since I was building a ham band only radio, there was no need for main tuning and band spread.   I calculated that an  80 pf variable capacitor would give me  the tuning range I wanted on each band. (Plus I had two of those in my junk box.) I removed the exiting osc tuning caps and replaced them with the two new variable caps of 0 to 80 PF ganged together as can be seen in the picture. I found that with a little bit of fixed capacitance across each alignment trimmer (located on the osc coil that runs left to right on the bottom) I was able to set the bands where I wanted

The S-38 BFO is a notoriously simple and cheap affair that never works well. For cost reduction, the BFO is a a regenerative Intermediate Frequency (IF) Using a BFO coil scrounged from another receiver (an S-19), I mounted a 6C5 on the chassis to the left of the tuning caps and installed a real BFO circuit.  coupling it via a gimmick twist on the output of the last IF can. I used a double pole double throw toggle that both turns on the plate supply to the BFO and turn off the AVC.

One of the things missing from the S-38 is an RF gain control. By studying various schematics I decided the easiest way to get there was a pot in the cathode circuit of the IF amplifier. A 5K pot in series with the cathode of V2 was the best balance I could find

Now what is a receiver without an S-meter? I considered an eye tube which would have fit in with the style I was looking for but I had reached the limits of the transformers current capabilities. In addition an eye tube requires more voltage then I was supplying at the end of the transformer limits. I located a nifty little circuit  on the web  developed by Walter Heskes and located on Phil Nelsons site at http://antiqueradio.org/smeter.htm  It reads the current in the cathode circuit of the IF. A 2200 ohm, 1/2 watt resistor is added in series with the meter to lower the current in the circuit and prevent overloading the meter. The 2K potentiometer is used to align the needle with the zero value on the dial scale when you calibrate the meter to a null signal.

This S-meter is a "reverse meter." That is, the needle rests all to the way to the right at zero signal and deflects toward the left as you tune in a station.

My preference is that an S Meter ping to the right when hit with a strong signal. In addition, I had little space for the meter. And finally there were no small meters that read backwards with S meter scales, But not a problem. A meter that is turned up side down now shows low voltage on the right and high on the right. Buying a small meter from one of the email lists solved the second one, space. And finally a little time spent with a photo program on a scan of the meter scale allowed me to set up my own S meter scale. Is it accurate? NO. But I get to watch the meter move up and down in the correct direction with different signals.

With the radio pretty well finished I focused on the front panel. I used the National vernier dial mounted on a nice black crinkle bud cabinet I had had picked up somewhere on my travels. I considered setting the scale so that all of my favorite frequencies (1880, 3885 and 7290) were at 12:00 but the frequency spread would have pinched some ends of the bands out. So I let them fall where they did. With a scan of the National dial and my photo editing program I was able to lay out a nice looking dial. This ain’t no digital readout.

I did expend considerable effort trying to tighten up the selectivity with no success.  I tried incorporating some Kia filters from junked CBs and bought a CBC filter, a 6 pole unit with a built in IF amplifier. All of them pinched the audio much more then I cared for and caused weird behavior in the receiver. So I gave up. I am considering replacing the IF coils with 455KHZ ones from a good communications radio as I suspect these are not the most selective in the world. Finally I may add a Q multiplier as a way of addressing the issue (Hey my first receiver in 1964, a Lafayette KT-320 went that route). I think I may have just enough room to squeeze it into the right hand side of the chassis.

In the final analysis the receiver is stable, has nice tone and in my opinion looks pretty nice. It is also fairly accurate on frequency readout. It does lack some selectivity and on 75 I get some odd images from data up around 6 KHZ. I have just bought a used preselector and hope that will cure the problem.

Before- Again, not the actual victim

After

Souper38_htm_m202aa267.jpg (15403 bytes)

IMG_5252.JPG (231187 bytes)





IMG_5251.JPG (178670 bytes)



Go see the reviatlized Knight T-60, also known as the KPD T-160

Or

Go back to The WA1KPD  Radio & Boatanchor Page

 

Last updated 09/05/08