Philco PT-12 Chassis - Videokarma.org TV - Video

knockbill · #1 02-12-2013, 06:48 AM

HI Guys,
I just joined today, first post,,,
I have a 1941 Philco table radio, didn't work when I got it,,,,I recapped, and changed out a lot of teh cracked wire,,, and also tested all teh tubes. I found a schematic, but I really can't read it. Is anyone familiar with this set, that would be willing to help me sort it out? I tested teh voltages, the ones I could decipher, and it doesn't seem to be wired correctly...
I have a little experience, just restored a little 3 tube amp,,, but, the schematic was very clear, easy to follow....
Thanks in advance for any help you can offer,
John

Heres a couple pics,,,,

old_coot88 · #2 02-12-2013, 08:29 AM

What sort of problem(s) does the radio exhibit? Do the tubes light up?
Have you double checked that all the tubes are in the right sockets?

Reece · #3 02-12-2013, 08:39 AM

Hi, John, and welcome.

That's a good radio to start out on, not too complicated. You didn't say what the trouble was but I guess it doesn't work yet? You tested all the tubes and they are good, I believe. Be sure that they all light. One problem with those locktal tubes is that the pins corrode. The way to easily remove those tubes is to tilt them away from the side that has the bump on the metal base. The octal tubes just pull straight out, of course. Clean all the pins with contact cleaner and plug in and out of the sockets several times while wet.

First live test would be, with tubes all lit, touch your plugged-in soldering iron to the center contact of the volume control. Should hear a loud hum from the speaker. If so, the audio section: 7C6 and 50L6 are good. Check back in and off we go.

knockbill · #4 02-12-2013, 09:49 AM

Quote:

Originally Posted by old_coot88

What sort of problem(s) does the radio exhibit? Do the tubes light up?
Have you double checked that all the tubes are in the right sockets?

good morning,,
thanks for teh reply,,, excuse my typing,, left hand is faster then the right sometimes,,,
yes, all teh tubes light up in teh set,,, i tested them sunday, and the 7A8 was bad, my buddy had a new one, so i am using it,,,,
the set doesn't make any sound,, it will somewhat amplify the dirty volume control, as you turn it,, and i can get static as i probe certain pins with the vom...
i did get a copy of the philco schematic, and my son cleaned it up and made a better copy of it,,, however, it still difficult for me to follow,,, also,, i noticed some discrepancies on it,,,firsrt, the schematic shows two 7C6 tubes,, however, the tube location chart on teh radio shows a 7C7 in the socket next to teh tuning cap...i have tried it with both tubes (no difference in performance),,, and decided that teh schematic was a typo, and teh proper tube layout was on teh radio....

now,, someone was into this set before i got it,, there was half of the 20-20 lytic replaced with a 33mf i believe,, and it was just twisted into teh old wiring!!! so, i figured i'd be in for an interesting ride...
looking forward to your input,,,
regards,
john

knockbill · #5 02-12-2013, 10:00 AM

Quote:

Originally Posted by Reece

Hi, John, and welcome.

That's a good radio to start out on, not too complicated. You didn't say what the trouble was but I guess it doesn't work yet? You tested all the tubes and they are good, I believe. Be sure that they all light. One problem with those locktal tubes is that the pins corrode. The way to easily remove those tubes is to tilt them away from the side that has the bump on the metal base. The octal tubes just pull straight out, of course. Clean all the pins with contact cleaner and plug in and out of the sockets several times while wet.

First live test would be, with tubes all lit, touch your plugged-in soldering iron to the center contact of the volume control. Should hear a loud hum from the speaker. If so, the audio section: 7C6 and 50L6 are good. Check back in and off we go.

thanks for teh welcome... hope to learn some radio theory here,,,

well,, first test is completed,, i touched teh center volume lug with a solder gun, loud tone from speaker,, tone changes slightly with gun on or off...
thanks for your help... now for the theory,, does that mean the gun is acting as a sort of signal generator, thus proving teh amp section is working?
regards,
john

dieseljeep · #6 02-12-2013, 10:51 AM

Quote:

Originally Posted by knockbill

thanks for teh welcome... hope to learn some radio theory here,,,

well,, first test is completed,, i touched teh center volume lug with a solder gun, loud tone from speaker,, tone changes slightly with gun on or off...
thanks for your help... now for the theory,, does that me the gun is acting as a sort of signal generator, thus proving teh amp section is working?
regards,
john

Regarding the audio generator, the gun produces a 60hz signal. I always use my finger.
The proceedure I use is, I try the radio first and see how it works, if at all. If the tubes light up, they don't need testing at this time. Evidently someone took a shot at getting it to work, as the 'lytics were crudely replaced.
I never shotgun a circuit until I troubleshoot the set.
Those early Philco schematics were hard to read and they were scanned poorly by the freebee site. A lot of missing imformation.

knockbill · #7 02-12-2013, 11:06 AM

Quote:

Originally Posted by dieseljeep

Regarding the audio generator, the gun produces a 60hz signal. I always use my finger.
The proceedure I use is, I try the radio first and see how it works, if at all. If the tubes light up, they don't need testing at this time. Evidently someone took a shot at getting it to work, as the 'lytics were crudely replaced.
I never shotgun a circuit until I troubleshoot the set.
Those early Philco schematics were hard to read and they were scanned poorly by the freebee site. A lot of missing imformation.

thanks for jumping in,, this set will be working by the end of teh day,, at this pace,,, i'll tell you about teh other one i have later!!!!!!

yep,, i am having trouble sorting out teh schematic,,, i spent a lot of time looking up teh tube pin numbers, and put them on teh schem.. at least i can follow a ckt now... another thing they did, is use the tube socket pins, taht aren't used by teh tube, for a tag terminal... saves money i guess, but hard to follow, as teh insulation falls off teh wire when its touched...
i agree with not "shot gunning" anything i work on before i do some trouble shooting,, but i couldn't plug this set in,, needed a cord set, and the wire insulation was crumbling, and that "replaced" lytic,,so as i replaced it, i kept trying it, and changed teh caps while i was at it,,,

dieseljeep · #8 02-12-2013, 11:57 AM

I did a little research on this project and I looked up a little better schematic for a set simular to years. It's found as a model 46-421, at the same site. There's several pages of information. In this model, there's a slight difference in the power supply and possibly a few other differences.
When doing this type of work, I compare both copies, as Philco built the same radios. both pre and post war.

knockbill · #9 02-12-2013, 12:05 PM

Quote:

Originally Posted by dieseljeep

I did a little research on this project and I looked up a little better schematic for a set simular to years. It's found as a model 46-421, at the same site. There's several pages of information. In this model, there's a slight difference in the power supply and possibly a few other differences.
When doing this type of work, I compare both copies, as Philco built the same radios. both pre and post war.

thanks again,,
i will do some searching,,, i also found a rider schematic on this radio,,, however it seems to be a copy of teh philco... i can imagine the tube changes,,,
the other set i need some help with needs two tubes, and they don't seem to have substitutions,,, i started with this one, because teh tubes all work,,,
just a side note, i had teh other set somewhat working,, could pick up quite a few stations but teh audio was poor,, i tested teh tubes and found two bad,,, i put them back in to continue trouble shooting, and the rectifier was shorted, so i have to get some new tubes before i can proceed on that set,,, but,,, i have my hands full here!!!
regards,
john

knockbill · #10 02-12-2013, 04:14 PM

just got back in,,,
reese... ready for test two...

dj....i got the philco schem from my buddy, he copied from his philco archives,,,i'll have to see if he has 46-421

thanks guys,,,
regards,
john

DavGoodlin · #11 02-15-2013, 06:47 AM

If you take each of the tube numbers, make a list of pins for the 7C7, 7A8, 7B7cathode, G1, G2, Plate and then post the dc voltage you read, we can offer some clues.

Based on your initial check of the AF stages, 7C6 and 50L6 are OK
beyond checking voltages, a signal tracer like the EICO 407 can locate RF/IF issues.

knockbill · #12 02-15-2013, 08:07 AM

Thanks for your reply...here are teh readings...
I blew up teh schematic as much as possible, the ??? are letters I couldn't read, so I included teh pin numbers..

7B7 PL 99.3, K .04, G -7.45, G?(pin3) .03
7A8 PL 99.4, K 1.05, G -7.50(pin 6),,, GA(pin3) 99.5,,,, G?(pin4) .6,,,,G?(pin5) 67.5
7C7 PL 99.4, K 1.04, G -35.00 G?(pin3) 99.5

Thanks again for your help, hope to hear back,,,
Regards,
John

dieseljeep · #13 02-15-2013, 08:28 AM

Quote:

Originally Posted by knockbill

just got back in,,,
reese... ready for test two...

dj....i got the philco schem from my buddy, he copied from his philco archives,,,i'll have to see if he has 46-421

thanks guys,,,
regards,
john

You can print it off Nostalgia Air. The 46-421 print is very clear and has a trouble shooting proceedure.

knockbill · #14 02-15-2013, 10:40 AM

Quote:

Originally Posted by dieseljeep

You can print it off Nostalgia Air. The 46-421 print is very clear and has a trouble shooting proceedure.

ok,,, i copied it,, looks pretty clean,, the rectifier and power tube are different,, but i think teh problems are past the audio circuit... funny thing, teh layout and four tubes are like the pt-12, i'm working on now,,, but the case is just like the 1948 set i also have to get into,,,

thanks for your reply,
regards,
john