[Chuck Schwark]

If you disconnected the Shadow Meter, you need to sub in a 1.5K, 1watt resistor in place of the coil, otherwise the front end tubes, RF Amp and DET-OSC, get no B+.

[Steve Chambers]

Scott:

If you've removed the shadow meter coil from the circuit you'll have no plate voltage on the Det-Osc. tube or the RF tube (unless you've substituted a resistor).

Steve Chambers

[Robbie Roberts]

I already put it back in place... Still no radio sounds...
Scott

[Chuck Schwark]

Now you need to start checking voltages on your tubes according to the diagram in Fig. 1 of the service bulletin. Note that these voltages are taken with an older 1000 ohms-per-volt VOM at 115 volts AC mains. With a newer VOM or a DVM (and also higher mains voltage) they will be appreciably higher.

That's why I have 1000 ohms-per-volt VOMs on my bench to make sure I match the original mfrs specs with sets that specify how the voltage readings were taken at the factory.

[Robbie Roberts]

The multimeter on my tube tester is 1000 ohms per volt AC/20,000 ohms per volt DC. How much of a real difference does this make?

Scott

[Chuck Schwark]

In high impedance circuits - a lot. Just be aware of it. Using a 20K meter will be ok - all DC readings will be proportionally higher that's all, since the meter does not load down the circuits under test like a 1K-P-V meter does. You're looking for ball-park readings and looking for way--off or missing readings.

[Robbie Roberts]

Thanks Chuck!- I'm actually getting so frustrated with my lack of knowledge at this point, that I am now reading through my father's "RCA Radio and Television Electronics Course for home study" from the 1950's! Looks to be about 20 lesson books, and 20 matching service practices books.(and I have actually discovered I have most of, if not all, the experimenter pieces which came with it! Even the soldering iron is there! ) I haven't gotten to the books on meter use yet- although I do know the rough basics, of course... ;) I didn't know about the "ohms per volt" issue until very recently, and still fuzzy about it... However, at least we know I can ballpark with the equipment I have for this issue.

I did check votages the other day, and they were within reason, but it was not an "organized" check. I will recheck them, and post the results here. I do have few quick questions regarding the 37-650 in particular: On figure 1, it shows the 2nd DET.- AVC. 6J5G, but gives no voltage for term. "P", although there is an arrow. I am assuming this is "Plate" voltage, and should be 250V as the others? Also, there are no voltages to check on the grids? And are there voltages for the 5Y4G to check? Lastly, it appears I check the one electrolytic cap first across the two terminals for 330V, then from pos. to ground for 315V?

I have tested the tubes, and all are in fine shape, hold well under emissions testing. I remember the radio had been working ok, except for the volume issue, but then just blinked out- and hasn't made radio sounds since... Driving me nuts.

I am now an expert at tearing down and reassembling an RF subchassis, so it isn't all bad...

Thanks!
Scott

[Robbie Roberts]

Ok- My voltage check results are as follows- they follow the format of >tube location, type: (result-) pin: should be/is, next result...

For All Tubes: H: 6.3VAC/6VAC

Det. Osc. 6A8G: Osc Plate 150V/135V; P:250V/265V; S:100V/100V

I.F. Amp. 6K7G: P:250V/270V; S:100V/100V

2nd Det.-AVC. 6J5G: P: ?/0 No "P" voltage specified, none showing when tested. According to the specs in my RCA tube guide, it should be between 90V and 250V. The overages on the other tubes add up to about 90-100V, and I will be rechecking my connections for this tube.

1st Audio 6K5G: P: 170V/210V

Output 6F6G(1)(from below, on right): P:250V/265V S:240V/255V

Output 6F6G(2)(from below, on left): P:250V/260V; S:265V/280V

R.F. 6K7G: P:250V/255V; S:100V/100V

Electrolytic #57 connected to both sides: 330V/300V; + and Ground: 315V/280V


Let me know how this sounds...

A side question, should I be getting a voltage at the yellow/green tracer wire out of the power transformer? I am not currently, but was wondering if I should be. There is none listed on the voltages chart in the service bulletin. I am trying to figure where the power for the 2nd DET. AVC tube comes from, as it appears absent, as indicated above.

Thanks!
Scott

[Steve Chambers]

A side question, should I be getting a voltage at the yellow/green tracer wire out of the power transformer? I am not currently, but was wondering if I should be. There is none listed on the voltages chart in the service bulletin. I am trying to figure where the power for the 2nd DET. AVC tube comes from, as it appears absent, as indicated above.

The yellow/green tracer wire is the B-. It's the most negative point in the radio. You can measure a negative voltage between it and the chassis. The 2nd detecter gets it's "power" from the radio signal itself. It is a diode (actually connected as a double diode) and conducts on the positve swings of the signal only enabling detection.

Steve Chambers

[Robbie Roberts]

So what is my next step in unravelling this mystery? Are my numbers in the ballpark?

Scott

[Steve Chambers]

Scott:

Chuck will have the most knowledge here, but I'll try to help if I can. Forgive me if my questions make you repeat yourself, but it might be the best way to proceed.

Was the radio working when you got it? What I like to do is fix any safety and power supply issues (electrolytic caps, check transformer, replace cord, etc.) and then try it out with a dim bulb tester. At this point you can look for unlit tubes or tubes in the wrong sockets, etc. This way I have a starting point. If one just replaces everything first, it seems too easy to make a mistake (or not know if some else messed eveything up) Just one man's opinion as RR would say.

Next if nothing works, or it works poorly, I measure the voltages. If any are wrong I try to figure out why. Bad cap, bad resistor, bad tube, etc. You can inject an audio signal at the top of the volume control. This divides the radio in half. If you can hear the audio, you know the speaker, audio transformers, and the whole audio chain is good. If no sound or it is distorted you have only half the radio to troubleshoot.

Next comes the "radio" part. You can inject RF at various points. I sometimes start with the IF frequency right at the top cap of the IF amp. Whever the signal stops getting through, that's where the bad part is. There's more to go wrong here. Coils can open. The oscillator can refuse to run. I check this with another radio. You can hear the oscillator signal or a harmonic. Band switches are often dirty. Grid caps can come unsoldered. Resistors and caps can be bad. Eventually you can narrow the defective part down.

Once I get the radio going, I'll replace all the caps, except the micas, and any out of tolerance resistors. About half the resistors may be out, maybe fewer.

You mentioned blown fuses. Where were these fuses?

You said at one point the radio would pass an audio signal. Will it still do that?

When the fuses blew was anything burning?

I think the voltages look OK. Chuck or Ron will know for sure.

Have you done any of the other checks I mentioned above?

If you have replaced multiple components all at once, I think you are really going to have to trace the signal chain. One missing part can break it. Start again with audio (assuming nothing is letting out smoke) and let us know if you can pass a signal.

Keep trying. I'm basically self taught. If I can do it (I've done over 50 Philcos now) you can too. Chuck will let us know if I'm on the wrong track.

Steve Chambers

[Chuck Schwark]

Couldn't have said it better . . . .

[Robbie Roberts]

Hi Steve- I don't mind the questions- shows you're interested, and helping Maybe Chuck will see something I missed here. as well... My reply may seem slightly jumbled- A lot went on while I was in there, and I'm trying to recall everything. I broke it into short paragraphs, however :

Ok- The radio was flat dead when purchased. I replaced all the caps(including Micas) with new(10% rule, when original values not available) and all the resistors(10% rule, as well), as many had value changes. (The only resistors I really question are the two wire wrapped power ones: they were replaced with metal oxide ones.) All the bakelite caps were replaced with orange drops in the original bakelite cases.

All the electrolytics have been rebuilt. The fuse mentioned was aded to the circuit by me, and is a 1.5amp. Tubes have all been checked, and rechecked on a Precision 654 tube tester, both for shorts and emissions.(This is the kind of tester where it heats up the tube, and runs it to test.) all at this point are either good, or very good condition.

All the switches have been cleaned. All the RF coils from all three sections have been checked for continuity(all were good). All the wiring, save for the Shadow Meter, has been replaced with new(I did one wire at a time, and all is about the same gauge as original. Only difference, most of the original solid wire now replaced with stranded.) Wire is 20ga. 600vt. cloth covered.

The RF cans have been checked for continuity, and the leads replaced, due to deteriorated wiring.(Most of the wiring in this set was well cooked- if I moved it, the coverings would break instantly.)

I've been working to the original schematic(Provided by Chuck S.- Thanks!) to ensure my wiring was correct.

I have checked the Tone switch assembly, and substituted another Philco Volume switch in place of the original, which doesn't seem to be properly continuitized. This was done after I had it operating, after it stopped working properly.

When first switched on after the initial rebuild, the radio did operate, but with very low volume on most stations, and only on BC and the first SW bands. The volume never got very loud, save for a couple very strong local stations. I was able to hear all sorts of broadcasts on BC. Then, after a couple hours, it just got quiet all over, and hasn't made a decent sound since. If I scrabble about with the RF adj. cond.s, I can get a wee-oooweeee sound while turning the tuning coils. Other than cheap special effects, of no real use to me that way... ;) lol

Oh, and Chuck- I never bothered putting in the cloth covered power cable... After all that discussion with you and Ron, I decided to reuse the original, which is in good shape, but not with a molded plug... I'll save the other for the Model 20 sitting here, waiting to become a topic of discussion...

Thanks for any ideas-
Scott

[Chuck Schwark]

If you replace the mica caps in the RF and OSC stages, they need to be EXACT replacement values - no 10% allowed with frequency determining caps. If you replaced with "close enough", your oscillator may be running way off freq and you'll get nothing.

[Robbie Roberts]

Let me take a look and see what I put in there... I still have the originals... I don't throw nuthin out... lol ;)

Scott