Stuck on non-receiving Silvertone 4769
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For reference here is the schematic:
https://worldradiohistory.com/hd2/IDX-S ... e-0054.pdf
And the component layout:
https://worldradiohistory.com/hd2/IDX-S ... e-0055.pdf
Set has been recapped, and the audio output section is working strong, but I'm not able to receive anything other than static. Not even a faint hint of a station.
I get a signal on the antenna terminal and on each grid cap.
For voltages I'm getting:
5Y3 : 392
6V6 : P 270 , S 286
6B6 : P 88 , G -4.9
6K7 (IF) : P 287 , S 105 , G -5.5
6L7 : P 286 , S 100 , G -5.5
6J6 : P 71
6K7 (RF) : P 285 , S 100 , G -5
Greg V.
West Bend, WI
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Can you post an audio file of the static you are getting?
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I would apply a 465kc modulated signal to the grid cap of the 6L7 to check the IF and stages further back. If all is working back there go ahead and adjust the IF trimmers. Check pin 5 of the 6J5 w/ a hi Z volt meter. Should see a few volt - if the osc is running. You can also take a listen for it @ 465kc above the dial setting/ incoming frequency. If not normal suspects are in play, dirty switch contacts, bent plate on the tc, open coil, or bad grid leak resistor. If all that checks ok we can go further...
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 06-27-2021, 08:21 AM by Radioroslyn.)
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Try injecting a modulated IF signal to the antenna. If you hear the tone then the 6J5 oscillator is not running. If you don't hear a tone then put the signal at the second IF control grid and work forward. The IF is your friend.
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Terry, you type faster than me!
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Thanks Terry and Rod. I will dig out the signal generator this evening but for now what I've done is tried the OSC test with another radio set at 1000Kc. I didn't get any clear whooshing or OSC whine on the Silvertone at either 465Kc above or below the 1000kc of the test radio. The Silvertone is all but silent on the high end of the dial (1500Kc). As you dial down towards 700Kc the static gets louder. It is at its loudest when you're around 540Kc. I did a voltage check on pin 5 of the 6J5 tube and get zero. Nothing. The plate voltage is also very low on that tube at around 70v (sorry for the typo, it's not a 6J6)
Now when I have the Silvertone set around 540Kc and I turn off the test radio which is set to 1000Kc, I can hear a click coming from the speaker and the static changes tone slightly.
Greg V.
West Bend, WI
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City: Roseville, MN
If you find the oscillator isn't running and it's on all 3 bands then look for general stuff like Terry said. Also dirty tube pins, bad C7 or C8.
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That almost sounds like the IF's have been detuned by a large amount by someone that had the set before you. You need to establish where they are tuned before going any further. Connect your signal generator to the grid of the IF amp tube, and tune the output (modulated) slowly from about 400-600 or so and see where you begin to hear the signal. If it's not at 465, you will need to retune the 2nd IF transformer. Once you have established this, you can go back a stage and connect the generator to the mixer/1st detector tube and see if the signal still gets through. You may have to brute force it to start with. Keep your set tuned to the bottom of the dial while doing this. If the signal is very weak at that point, adjust the 1st IF transformer until you get a strong signal. You should then begin to hear stations, if the oscillator is running.
BTW, you did your oscillator test backward. Use the second radio as the receiver, set it to a dead spot on the top of the dial, and slowly tune the one you are working on between 1000-1200 and see if you hear the carrier on the other radio.
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Success!
Thank you so much Terry, Rod, and Brenda. You were right, Brenda, it had been a few years since I had to do the OSC test with a second radio and did it backwards.
I had previously tested resistors R4 and R5 (50K and 30K respectively). R4 read 52K and R5 read 33K so I left them in. But tonight before trying to inject a signal I decided to replace those two resistors, along with C7 (with a 100 pf) and C8 (with a 27 pf....I didn't have a 25 pf on hand). After replacing those 4 components I turned the set on and checked voltages. I now had the correct plate voltage on the 6J5 and pin 5 read -5.3 instead of nothing. So I slowly began tuning and....the stations came in as they should! I still need to do an alignment but already the set plays strong across the dial. I haven't checked the other bands yet but will do that tomorrow. I feel pretty confident they will receive as well.
Apparently one or both of the two mica's had gone south, thus losing the connection to the OSC coil.
Greg V.
West Bend, WI
Member WARCI.org
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Score another one for the team! Oscillators are so fickle!!
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