Quite sometime ago, I had to walk away from a 60 that has been stumping me for years. I've restored several other radios since, all with good luck, but this 60 is not cooperating with me. I'm determined to fix it!
I've re-capped the radio, changed out all the necessary resistors and believe the radio is in spec regarding the discreet components. The coil windings all seem to be giving the correct ohm readings, and the tubes all check out. Voltages seem to check out. I've gone through the radio wire/wire against the schematic, and all seems to be proper. When powered up, I get a loud howl through the speaker. That is where I left the radio some time ago.
OK. I'm back on the set, starting at where the antenna connection is made into the radio. What I thought was simply a trimmer cap, has an antenna coil mounted beneath it. (Hadn't noticed it in the past) The schematic does not give a specific value. I'm reading 21 ohms.
Hi and Welcome,
If that trimmer is connected to the ANT post it's not suppose to be there. The antenna connects directly to the bandswtich to the ant coil. There is a 10K swamping resistor across the primary but no caps. If if measures 21 ohm I assume it going from the ANT post to the chassis. What you are measuring is the resistance of the primary of the ANT coil+ the capacitance of the trimmer.
Very common issue for the model 60 is to have an open primary on the antenna and feedback winding on the oscillator coil.]
Just to get us on the same page. I notice that some of the schematics do not show this coil. (See pic). After the antenna post, there is a small coil mounted beneath the trimmer cap, (previous pic), and then onto the band switch. The 10K swamping resistor is there and in-spec. Beyond that, I do get the 11 ohms and the subsequent .7 ohms on the main coil.
Just to get us on the same page. I notice that some of the schematics do not show this coil. (See pic). After the antenna post, there is a small coil mounted beneath the trimmer cap, (previous pic), and then onto the band switch. The 10K swamping resistor is there and in-spec. Beyond that, I do get the 11 ohms and the subsequent .7 ohms on the main coil.
I'm guessing that I am not oscillating. Is there a slick way to test? I bought a scope and will have it here next week. I also just received an old signal generator as well. Been able to get by thus far, with nothing more than a VOM. Trying to improve the bench for tube radio work.
>Amateur here. Me too I'm N3GTE.
Sorry I was looking at the Riders schematic and it doesn't show the wave trap. Philco made a bunch of different versions of the model 60 over it's 3 or so yrs of it's production run. To adjust it inject an signal in to the ant post at the IF frequency and adjust the trimmer for the WEAKEST signal in the speaker.
The oscillator circuit is a little different from the model 80. Now the great chase begins have to find where the electrons start and stop! Things to look for: Must have HV on pin 4 of the 6A7. If not feedback winding is open on the osc coil. If you do have hv on pin 4 you should have a few negative volt on pin 5.
You can still listen for it in another radio but the voltages will help pinpoint the problem.
GL
Terry
ps Whats an oscilloscope?????
(This post was last modified: 10-02-2015, 04:28 PM by Radioroslyn.)
(10-02-2015, 04:11 PM)Radioroslyn Wrote: >Amateur here. Me too I'm N3GTE.
Sorry I was looking at the Riders schematic and it doesn't show the wave trap. Philco made a bunch of different versions of the model 60 over it's 3 or so yrs of it's production run. To adjust it inject an signal in to the ant post at the IF frequency and adjust the trimmer for the WEAKEST signal in the speaker.
The oscillator circuit is a little different from the model 80. Now the great chase begins have to find where the electrons start and stop! Things to look for: Must have HV on pin 4 of the 6A7. If not feedback winding is open on the osc coil. If you do have hv on pin 4 you should have a few negative volt on pin 5.
You can still listen for it in another radio but the voltages will help pinpoint the problem.
I never use one (Oscope) . Just use a good VTVM , tracer, and generator. They have served me well over the last 45yrs or so.
As for your IF you can inject a modulated RF signal into the cap of the 6A7 at 460KC. If you are using an older generator I would check the output frequency with a counter or a receiver that has known good calibration at 460KC.
Terry
(This post was last modified: 10-02-2015, 05:04 PM by Radioroslyn.)
