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Philco 37-62 head scratcher - Printable Version

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Philco 37-62 head scratcher - Guest - 02-13-2009

Hi Everyone...my first restoration project here. Its fun working on the set until you change everything that is supposed to be changed and its still doesnt work, its still fun, but it leaves me scratching my head more. right now the unit hums when the volume it turned up, but no stations. Ive touched the grid of each tube and it buzzes on the 2nd detector/1st audio 6Q7G tube and none of the others. This I assume would indicate that audio section is good. (buzz in fact can be quite loud) I've replaced 3 tubes (det/osc, if, and rect) all bakelite and tubualar caps. I have inspected 1st and 2nd IF coils...wires are fine but none broken and contacts are good.
I can only think of one thing suspect at this point and would like to hear some feedback before prodeeding further. det/osc and IF screen grid voltage reads 125 volts... diagram indicates it shoud be around 85 volts. Resistor on the screen grid ((part 11) should be 25 K ohms, color code and markings indicate that is is a 15K ohm resistor. (meter reads about 18K) Interestingly there is a change note with the schematic that states that the resisitor should be changed to a 32 K ohm to eliminate oscillation. Why would there be a resistor of that value there beats me... or am I sniffing too much solder? could this value resistor and high screen voltage cause the hum and no receive?

I feel like im easter egging here but hope this makes sense, feedback appreciated. Thanks in advance

Re: Philco 37-62 head scratcher - exray - 02-13-2009

Check and see if the oscillator section is working. Get a second radio and place beside the Philco. Set its dial to some random frequency like 1200 and then tune Phil around 700-800. You should hear the oscillator strong in the second radio. To be exact you should find the osc signal with Phil tuned about 450-460 below radio number two.

No carrier heard, or if its way off from that ~460 kc difference, or if its fine, will be a big clue for further guesses.

Re: Philco 37-62 head scratcher - Guest - 02-13-2009

thanks exray...oscillator is loud and clear on 2nd radio right where it should be..Very cool! IF stage screen grid resistor is still my suspect. Thanks!!

Re: Philco 37-62 head scratcher - exray - 02-13-2009

Hmmm. That screen resistor issue is easy enough to solve but I don't think thats the problem. I'd skip over it for the moment.

How about connecting the antenna directly to the grid of the converter/1st detector tube? Or just put a finger there. Do you hear signals? That would narrow it down to ant coil or bandswitch problems which are very common.

Re: Philco 37-62 head scratcher - Guest - 02-14-2009

no change...as mentioned no buzz or signal past 2nd detector. thx!!!

Re: Philco 37-62 head scratcher - Texasrocker - 02-14-2009

check for good-clean solder connections at the I.F. cans wiring connections under chassis.A cold-solder connection there could also be suspect altho rare cases have been found. If you have a spare known-good antenna coil, try "jump-wiring" it into the circuit also. I agree with exray. You may also try jumpering the BCB terminals on the bandswitch.Make sure your antenna connections are correct and your test antenna is long enough. My wife says my antenna isnt long enough, so I dont know just how long test antennas are supposed to be anyways!(hee hee) Just tryin to help.

Re: Philco 37-62 head scratcher - exray - 02-14-2009

Do you have a signal generator? You could try force feeding a 450-460kc IF signal via the input to see if the IF stage is working.

Re: Philco 37-62 head scratcher - Guest - 02-15-2009

its alive!..I poked around it with a signal generator. i was able to hear signal coming thru the grids of the detector/oscillator tube, putting problem between antenna and detector. I found plates of the variable condenser were shorted to ground and upon further inspection found the wire from the frame of the variable condenser chafing against the hole in as it went thru the chassis. now works great thanks exray and tex for your help!

Re: Philco 37-62 head scratcher - exray - 02-15-2009

Congrats, dontcha just love it when you bring an old radio back to life!

Re: Philco 37-62 head scratcher - Guest - 02-15-2009

You bet exray, but kinda weird listening to ESPN on a depression era radio! but its very cool..take care.