I don't consider this receiver as being an Amateur receiver, but a SWL receiver. It's pre-war and it never could've worked properly.
It has resistors that are from the old convention, even resistance values, IE 25K, 50K etc. Most of the resistors read within tolerance except the 50K's. All of them read between 84 to 86K, every one. They couldn't have increased in value that drastically. They must've been wrong from the beginning.
I'm going to replace all of them. The color code is green, black and orange with a silver tolerance band and all look pristine.

It'd be interesting to hear the performance diff before-&-after changing out the 50Ks.

It'd be interesting to hear the performance diff before-&-after changing out the 50Ks.
I have another one and I checked the 50K's in there. They are all within 10% of spec.
That receiver seems to work rather well.

I have an S-19R that I reworked a couple of years ago.

In mine, the only resistors that were out of specification were the four 50k ones. They were all 70k and above.

I liked the look of those dogbone resistors so instead of replacing them I calculated the resistor required to pad them back to the proper rating. I used small carbon film resistors soldered to the leads of the dogbones and tucked behind them so they don't show.

It's a nice general purpose receiver.

Jeff

I have an S-19R that I reworked a couple of years ago.

In mine, the only resistors that were out of specification were the four 50k ones. They were all 70k and above.

I liked the look of those dogbone resistors so instead of replacing them I calculated the resistor required to pad them back to the proper rating. I used small carbon film resistors soldered to the leads of the dogbones and tucked behind them so they don't show.

It's a nice general purpose receiver.

Jeff
It is a nice receiver! A lot better than their later SWL receivers.
The S19R was the last one produced before the start of the war.
Riders shows grid cap tubes, where my two examples have a 6SK7 and a 6SQ7 but it still uses a 6K8 osc & mixer tube. It has a 41, 76 and an 80 rectifier.
It adds to the interest. :thmbsp:

Mine has the 6SK7 and 6SQ7 also. It seems that some were equipped with the grid cap versions 6K7 and 6Q7. I've found documentation showing both configurations.

Jeff

Mine has the 6SK7 and 6SQ7 also. It seems that some were equipped with the grid cap versions 6K7 and 6Q7. I've found documentation showing both configurations.

Jeff
I think that was the last of the run.
The schematic is incomplete regarding the BFO circuit. It shows no injection from the detector stage. The receiver has it, a gimmick wrapped around the 2nd IF transformer lead.

"The S19R was the last one produced before the start of the war."


Where does the S20R come in? I have my father's radio, including the original box! Someone once told me the box was probably worth more than the radio.

Where does the S20R come in? I have my father's radio, including the original box! Someone once told me the box was probably worth more than the radio.

According to Communications Receivers 2nd edition by Raymond S. Moore :

S19 1938 5 tubes, S19R 1939 to 1942 6 tubes
S20 1938 to 1939 8 tubes, S20R 1938 to 1945 9 tubes

jr

According to Communications Receivers 2nd edition by Raymond S. Moore :

S19 1938 5 tubes, S19R 1939 to 1942 6 tubes
S20 1938 to 1939 8 tubes, S20R 1938 to 1945 9 tubes

jr
I had a post-war S20R. IDK if I still have it!
It had a label that stated "Zenith Radio Corp Engineering Dept"
I have so many radios, I lose track. :sigh:

It'd be interesting to hear the performance diff before-&-after changing out the 50Ks.
Getting back to working on that receiver, the former owner(s) tried to get the BFO circuit working with the original resistors. Working now!
It's funny, I seldom check the resistor values. I will now!
As a side note, I never "shot-gun" an old radio or TV. I trouble-shoot the set first, then I replace the aging components. :scratch2:

Getting back to working on that receiver, the former owner(s) tried to get the BFO circuit working with the original resistors. Working now!
It's funny, I seldom check the resistor values. I will now!
As a side note, I never "shot-gun" an old radio or TV. I trouble-shoot the set first, then I replace the aging components. :scratch2:

This receiver refuses to stay repaired!
I got the BFO working, when others couldn't. Putting the coil back in place, I pulled the terminal end loose and broke one of the thin wires going to the winding. The wires are like hair and I can't see were it's broken, even under a magnifying glass.
This think must've had a history of problems. When I got it at a swapmeet, the top and bottom covers were missing. The receiver is in unusually nice condition. No rust and the silk screening is perfect. :D

If you're able to find the broke end of the fine wire, the old 'aspirin trick' might be useful in stripping it. Instead of scraping, a little puddle of molten aspirin does the trick. With a soldering iron, just melt an aspirin tablet on a tin can lid or something, and dip the end of the wire in it. Hot acetacylic acid does the stripping. Fumes are gawdawful however, so use plenty of ventilation.

(That other feller with the Coronado open oscillator coil might find this useful.)

If you're able to find the broke end of the fine wire, the old 'aspirin trick' might be useful in stripping it. Instead of scraping, a little puddle of molten aspirin does the trick. With a soldering iron, just melt an aspirin tablet on a tin can lid or something, and dip the end of the wire in it. Hot acetacylic acid does the stripping. Fumes are gawdawful however, so use plenty of ventilation.

(That other feller with the Coronado open oscillator coil might find this useful.)
It's broken off too close to the winding. I got a BFO coil from a scrap receiver.
Regarding the aspirin trick, a Cuban old radio restorer uses aspirin for solder flux. Read about it on the UK radio website.
I guess, we don't know how good we have it here!
One of the UK website members sent him some rosin core solder.

Just curious, but wouldn't it be possible to use a winding from a regular IF xfmr for the BFO?

Just curious, but wouldn't it be possible to use a winding from a regular IF xfmr for the BFO?

The BFO coil from the parts receiver works fine.