Model 16 high frequency hum. - Printable Version

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+--- Thread: Model 16 high frequency hum. (/showthread.php?tid=24071)

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Model 16 high frequency hum. - Mikeym53 - 01-31-2023

I finished restoring this nice model 16 Tombstone. It has a tone coming through the audio much higher than power supply hum. I would describe it more like an audible note or tone. All Bakelite blocks recapped, New filter caps. There were a few dog bone resistors out of range so I replaced them. The radio plays fine otherwise. Shadow meter works good. Alignment went well. Any ideas would be appreciated. Thanks, Mike.

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RE: Model 16 high frequency hum. - Mikeym53 - 02-01-2023

Fixed it. I started grounding the grids of the 42 output tubes, no change. Then the 42 second audio, no change. Then the grid cap of the 77 first audio no tone noise. I replaced the 77 first audio, problem fixed. No noise, radio plays and sounds great. Thanks to all that looked at this thread. Mike

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RE: Model 16 high frequency hum. - morzh - 02-01-2023

It is also possible the 77's grid cap wire was outside of the shield and not inside, and while replacing the tube you put it back inside.

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