Motorboating/buzzing - Printable Version

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+--- Thread: Motorboating/buzzing (/showthread.php?tid=25589)

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Motorboating/buzzing - rotolactor - 01-31-2025

Working on a 40-130.  Recapped it, got rid of the rubber wires, and it's been working fine.  The tuning capacitor mounts were shot, so I replaced those, and the tuning mechanism works great.  In that process, I desoldered and resoldered three wires on the tuning cap, and removed and replaced two tubes close to the tuning cap.  Turned it on, and I get motorboating with no stations under it.  The frequency increases as you increase the volume.  Where should I begin in troubleshooting this?

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RE: Motorboating/buzzing - morzh - 01-31-2025

Is there any tube that maybe had the grid wire inside the shield and now it is outside?

Guess not...


OK. The tubes are loctals. In those you replace, make sure the pins are cleaned. Loctals reuqire scrubbing every pin with something to remove oxidation.

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RE: Motorboating/buzzing - rotolactor - 01-31-2025

When I said I replaced the tubes, I meant I pulled them out and put them back in, to make room to desolder and remove the tuning cap.

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RE: Motorboating/buzzing - morzh - 01-31-2025

OK.

Still. Retrace what you have done, and (if the tubes are the same) clean the pins.
And make sure the tubes are installed in their places (loctal bases might not keep you from swapping them).

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RE: Motorboating/buzzing - radiorich - 01-31-2025

Hello Rotolactor,
Yes, double check and tripple check plus I would make sure you hooked the grounds back up to the tunning capacitor too.
Sincerely Richard

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