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City: Irvington, NY
Check and make sure you have plate voltage on the 6K7 magnetic tuning (AFC) amplifier tube. With no IF signal on its plate no AFC signal will be developed.
Check the voltage across each side of the AFC defeat switch to ground. As you tune through a station the DC voltage should swing from positive to negative or vice versa. If no voltage is seen there is a problem in the AFC amp or discriminator transformer.
Read the description of the Philco AFC circuit starting on page 93 of Rider's book. Although based on the 37-116 circuit it is practically identical to the 38-690. He goes into a lot of detail on how the AFC voltage is developed and applied to the 6N7G control tube to tune the oscillator frequency.
https://worldradiohistory.com/BOOKSHELF-...-Rider.pdf
Messages In This Thread
RE: 38-690 Code 125 - by Mondial - 01-02-2022, 07:59 PM
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Recent Posts
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Restoration of the Canadian General Electric A-87
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| Thanks for your help Michael. In fact, this video is only an intermediate result. Later I had to apply another tinting l...RadioSvit — 09:01 AM |
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Restoration of the Canadian General Electric A-87
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| Great job on the cabinet.
PS. In the US notation, "kenotron" refers to specific type of tubes; we call re...morzh — 08:24 AM |
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Part numbers to model cross
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This document has at least some tables of models and parts used.
Example: Choke 32-7572, used in 604 radio.
Search f...morzh — 08:19 AM |
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Restoration of the Canadian General Electric A-87
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| I also checked all the radio tubes on my Hickok 530 tube tester. The 5Z3 kenotron turned out to be faulty, all the other...RadioSvit — 08:02 AM |
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Restoration of the Canadian General Electric A-87
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Well... While the varnish is drying up, I started repairing the chassis...
Of course I started by replacing the pa...RadioSvit — 07:12 AM |
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Philco Model 38-7: what caps & resistors do fail typically?
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| Hello Martin,
Welcome aboard our little community what great Model 38-7
Sincerely Richardradiorich — 12:30 AM |
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Philco Model 38-7: what caps & resistors do fail typically?
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| Welcome to the Phorum Martin.
I count about 9 paper caps, the 3 electrolytic caps and 2-Y2 safety caps to replace th...RodB — 09:44 PM |
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Part numbers to model cross
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| Jim,
We have this index put together by Dale Cook but I don't think that is quite what you are looking for.
The Parts...klondike98 — 09:37 PM |
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Philco Model 38-7: what caps & resistors do fail typically?
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| Yep the dim bulb test is OK but I'd definitely replace all those electrolytics before I did it. Since those #47 conden...klondike98 — 09:18 PM |
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Philco 42-345 Restoration/Repair
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| The resistor is a 2.2 Meg, it was the last one I hadn't replaced. The broadcast is coming in after replacing it.osanders0311 — 09:09 PM |
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