51-934 code 122 - Printable Version
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RE: 51-934 code 122 - philco4me - 09-16-2025
So I did The testing as you described and I do Get a hum on the if. I also Get static on the 12at7 but still unable to get a station. Checked all joints for any runoff and all seems clean.
RE: 51-934 code 122 - philco4me - 09-16-2025
I will also give the band switch contacts a good cleaning. Thanks for the info. More to come ……
RE: 51-934 code 122 - philco4me - 09-17-2025
Progress. I had A lose cap that I fixed And now the static changes when I move The dial like it’s so close to getting a station on AM with the internal antenna hooked up. I wil Continue to play around and maybe I’ll get lucky. I will Also do the radio test as described in a post.
Thank you all
philco4me - philco4me - 09-17-2025
I did the radio side by side test and both just had static. However I moved The radio to the upstairs and I was Able to get one am station. There is static but I can hear it. Still no fm but looking better.
RE: 51-934 code 122 - David - 09-17-2025
Double check all work around the 12AU6. I have a love hate for 12AT7 tubes testing them in a tester does not always indicate there real condition. Good to have more than one spare. David
RE: 51-934 code 122 - MrFixr55 - 09-18-2025
Hi Philco4Me,
In AM mode with the antenna connected, if you tune across the band, does the nature of the static change? Does it get louder and softer?
Another member had suggested to place another radio nearby and tune through the broadcast band on that radio, to note what stations are available in your workspace. In addition, try to shut off all computers, Alexa devices, your router, fluorescent and LED lights, etc. If you receive AM stations now, the issue is all the EMI that is literally killing AM. I cannot receive AM in my house. If not much change in the tone of static, it is possible that the local oscillator does not work. In superheterodyne radios (of which almost all radios from the 1940s on are) the station frequency tuned is "mixed with a local oscillator frequency. The difference between these frequencies (from the heterodyne effect) is a fixed frequency no matter what station frequency is tuned. The IF (Intermediate Frequency) stage is tuned to this fixed frequency.
To determine if the local oscillator is working, try doing this:
- Again, you need a working radio. Tune the radio to a station around 1000 KHz.
- Have the radio in question close to the "good radio". CAUTION: Do not allow metal parts of the two radios to touch and do not touch both radios at the same time!
- Tune the radio in question through the AM band.
- At a frequency approximately 455KHz below or above the station tuned, you should hear squealing or a lowering of the volume of the station tuned on the good radio. This is due to interference from the local oscillator in the radio under test. If this happens, this confirms that the oscillator is working. If the local oscillator is not working, the radio will not create the "heterodyne" signal (Local Osc frequency - tuned frequency) that the IF stage amplifies.
Hope this helps.
RE: 51-934 code 122 - radiorich - 09-18-2025
Hello Philco4me,
I too have had problems with EMI that is literally killing AM. everything now uses switching powersupplies too .
Check to see if local oscillator is working!!
Sincerely Richard
RE: 51-934 code 122 - Paul Philco322 - 09-18-2025
I live pretty old school, I do have one newer LED fixture that my radios don't like. Usually I can play a radio with no issues. Sometimes I do get static problems. For sets with internal antennas a TERK or other brand antenna can be an amazing help. So if the radio is OK look into an inductive coupled antenna. Paul
RE: 51-934 code 122 - MrFixr55 - 09-18-2025
OOps, started the above post and had to leave before sending. The fact that you received at least one AM station means that you are getting close. Dittos on David's comments on the 12AT7. Emissions tests essentially test the tube as a rectifier. Consider replacing the tube. Also make sure that it is a 12AT7 and not a 12AU7. 12AT7, 12AU7 and 12AX7s al have the same pinouts but only the 12AT7 was designed to operate ate VHF frequencies. The 12AT7 was a somewhat early (but not the earliest) tube for oscillator / mixer or RF amp stages in early post-war TV sets. Consider replacing the 12BA6 and 12AU6s. You can borrow a 12BA6 from any 1960s AA5 set. The 12AU6s are a little harder to find in the average hobbyist workshop unless they have this, a Zenith or RCA tabletop AM FM set of this vintage. However, these tubes are available NOS (New, Old Stock) rather cheap and used rather cheaper.
Consider making voltage measurements, particularly for the plate and cathode.
The other step is rather dangerous, and that is adjusting the trimmer caps (little screws) on the AM Oscillator and RF sections of the tuning cap. Dangerous as adjustment usually calls for a signal generator and VTVM. Again, caution, as you are working on a HOT CHASSIS set. The AM sections have many more plates than the FM sections. Mark or photograph the positions prior to attempting adjustment.
RE: 51-934 code 122 - philco4me - 09-18-2025
Thank you for the replies. That is a 12at7 that tested strong. Most other tubes were replaced. I will try to adjust the rd cans and see what I ising your advise. I will post when I have A result.
Thank you all very much
RE: 51-934 code 122 - philco4me - 10-20-2025
Sorry for this delayed fallow up but I had Made the adjustments and the AM band is working. FM seems to be dead as I get no stations at all but that’s ok. It’s come a long way from a dead short to working. I would Like to thank all who has helped on this project. With out you it would have been in the trash. Much appreciated to all.
FCC
RE: 51-934 code 122 - David - 10-20-2025
Your set also has a 19V8 tube if I say what I think of that tube I will be banned from the site. David
RE: 51-934 code 122 - philco4me - 10-20-2025
That was replaced as the one that came with it was bad