07-04-2024, 08:43 PM
I know this is an old thread, but I had the exact same problem on an 89 code 123 I'm restoring and I found answers and inspiration here. I wanted to add a bit.
First I re-worked the electrolytics and dug out all the Bakelite caps and replaced their guts which is typical for any restoration.
The small outer winding on both the oscillator and the detector coils were open on mine. I rewound them both by hand with 34 AWG wire, first covering the existing coils with one layer of 10mm Kapton tape and using small bits of double-sided Scotch tape placed in four places on top of the Kapton to hold the wire in place as I wound. As mentioned in this thread, there were 12 turns on the T7 detector coil and 27 turns on the T11 oscillator coil. Both wound clockwise as viewed from the bottom. I finished with another two layers of Kapton over the windings.
The coil under the small coil on the T7 detector coil was also open. If anyone needs to replace this, it's 45 turns of 30 AWG.
I was very proud of myself, as I had never attempted this kind of surgery. It turned out to not be that difficult. The only problem was that while I could align the IF section, the radio didn't work. Only motorboating and squeals. I went back and studied this thread and tripped across this nugget from skyscraper-
So I clipped a lead to the top of the primary of the oscillator, which happens to be the plate of the 77 on my set, and it magically came to life and I started receiving stations. Yay!
I can only guess that there was different capacitive coupling between the windings with the old cellulose insulating material. I know what a gimmick is but before this set I never actually saw one that made a difference.
In the end, I added a 5 pF 1 kV capacitor from the T7 primary to ground, which corresponded to the plate and the grounded suppressor grid on the 77 converter tube (Sp on the schematic - Rider Philco 7-78) and now it works as it should.
Thanks, guys!
Joe T.
First I re-worked the electrolytics and dug out all the Bakelite caps and replaced their guts which is typical for any restoration.
The small outer winding on both the oscillator and the detector coils were open on mine. I rewound them both by hand with 34 AWG wire, first covering the existing coils with one layer of 10mm Kapton tape and using small bits of double-sided Scotch tape placed in four places on top of the Kapton to hold the wire in place as I wound. As mentioned in this thread, there were 12 turns on the T7 detector coil and 27 turns on the T11 oscillator coil. Both wound clockwise as viewed from the bottom. I finished with another two layers of Kapton over the windings.
The coil under the small coil on the T7 detector coil was also open. If anyone needs to replace this, it's 45 turns of 30 AWG.
I was very proud of myself, as I had never attempted this kind of surgery. It turned out to not be that difficult. The only problem was that while I could align the IF section, the radio didn't work. Only motorboating and squeals. I went back and studied this thread and tripped across this nugget from skyscraper-
Quote:At the moment, my oscillator circuit requires a jumper lead connected to the top of the primary in order to oscillate. Not connected to anything
So I clipped a lead to the top of the primary of the oscillator, which happens to be the plate of the 77 on my set, and it magically came to life and I started receiving stations. Yay!
I can only guess that there was different capacitive coupling between the windings with the old cellulose insulating material. I know what a gimmick is but before this set I never actually saw one that made a difference.
In the end, I added a 5 pF 1 kV capacitor from the T7 primary to ground, which corresponded to the plate and the grounded suppressor grid on the 77 converter tube (Sp on the schematic - Rider Philco 7-78) and now it works as it should.
Thanks, guys!
Joe T.
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