The PHILCO Phorum
37-650 Issues - Printable Version

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- Robbie Roberts - 02-02-2006

Ok- Micas replaced:

Location Value Repl. Value Type
#8- 40mmfd replaced with .39mmfd silver mica
#19- .003mfd replaced with .0033mfd axial film
#22- 250mmfd replaced with 250mmfd silver mica
#29- 110mmfd replaced with 120mmfd silver mica
#40- .75mmfd replaced with 82mmfd silver mica

These were the closest values I could find to the original ones: #40 struck me as a very odd figure ".75mmfd" and I believed the decimal was a mistake, and replaced it with an 82mmfd, believing I was replacing a 75mmfd, not .75mmfd.

Remember- this radio did operate, albeit at lower than optimum volume, for several hours. Is it possible I killed a few micas in the process, perhaps? Should I swap back in the originals?

Scott

- Chuck Schwark - 02-02-2006

You didn't throw anything out of whack there with those cap replacements. Sounds like you have to start tracing the wiring against the schematic to be sure your re-wiring is correct. Osc coils, bandswitch, etc.

If not even a 470 kHz modulated test signal from your sig gen is getting through to the audio section, you have a problem in the detector and or IF. If you do hear the modulation tone from your gen through the IF, then the fornt end has the problem.

- Robbie Roberts - 02-02-2006

How do I hook up the RF gen? I have no manual for it! I just bought it, and have no clue... LOL Icon_smile

Thanks-
Scott

- Bill Hutchinson - 02-03-2006

Scott,

The simplest means of hooking up the signal generator is put the main lead through a .01 uf capacitor (voltage doesn't matter in this case) onto the antenna input, and the shielded lead to chassis ground.

There are a couple of other places to inject the signal, but this method will work the majority of the time.

I've been following this thread with interest. I'm rootin' for you Scott! Icon_smile

(I'm sure many others are as well)

Bill

- Robbie Roberts - 02-03-2006

Thanks, Bill- Appreciate the support Icon_smile Now- I have a BNC type connector (Marked "RF Output") on the front of my signal generator (Heathkit IG 5242) and a pair of banana jacks marked "EXT MOD". Which one do I connect to? And what settings should I make? (Range, Millivolts FS, Meter- MOD-RF, Function- CW;MCW;EXT)

I'm GUESSING connect to the BNC, Meter on RF Carrier, Function on CW(Continuous Wave?) and Range???

And how do I measure the result- hook up the oscilloscope somewhere?

Sorry for all the "dumb" questions, but I'm still getting this pulled together on the test equipment part Icon_smile
Thanks!
Scott

- Bill Hutchinson - 02-03-2006

You'll want to connect to the RF output as I described earlier. For now, disregard the EXT MOD (this is for external modulation, which for this purpose you won't be needing).

The RF signal level (millivolts) should be set at midrange to start - you can vary it as you need to, but that's a good starting point. I don't have one of these generators, so I'm going to assume CW is for "carrier wave" and MCW is for "modulated carrier wave". Anyone here, feel free to chime in to correct me.

To make sure it works the way you want, use a known good radio and set the frequenct to 1400 Khz with internal modulation (which should have a 1 Khz tone), and tune the radio to that frequency. If all is well, you should get an audible tone through the radio, good and strong. Then try setting for 455 Khz and tune the radio to the far high end of the dial. This is your method of confirming the IF frequency. In practice, when aligning the set, you'd do the IF alignment as the first adjustment.

I don't remember what the IF is for the 37-650 off the top of my head, but it's printed right there on the schematic - obviously, that's the frequency you'd use. For your starting point, set it for that frequency, tune to the high end (tuning cap plates open full), and you should hopefully have tone. If not, we'll talk you through the next step. Icon_smile

Best of luck!

Bill

- Robbie Roberts - 02-04-2006

Just to add to the fun, my RF Generator is on the fritz... Pops its fuse (1/2 amp slo-blow) as soon as you switch it on. So now I am troubleshooting THAT. If this keeps up, I'm gonna switch to fixing cast iron wood stoves. I am in the process of checking diodes, wires for dead shorts, melted items. I have found none of the above as yet, but will go on to caps next.(With the exception of one can electrolytic, pretty much everything is newer type stuff: no paper caps, etc.) I think I am going to start by disconecting the power switch, and one by one reconnecting, until the fuse pops, then trace that part of the system... I have already checked all the diodes I can see, and tested the transformers for shorts.

So, I have not been able to run the RF through the 37-650 yet...

Thanks for the hook-up info-
Scott

- Robbie Roberts - 02-05-2006

And to add fun... I just purchased(by e-bay way) a Heathkit audio signal generator and signal tracer... See where that gets me... lol...

Scott

- 49Stude63 - 02-05-2006

Robbie, I know the feeling I have a mystery radio (4 tubes with a ballast tube) and forever I was trying to track down or figure out how to continue with it. I finally get it completely recapped, ready to put the speaker back on and wire pulled out from the secondary of the audio output coil. Good luck I keep checking back to see if you have it figured out yet, the 650 is a very nice radio so I hope you get it running.