Noisy D75A

Part substitutions and replacements, rebuilds, before/after measurements, challenges encountered discussed here.
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John Warren
Posts: 14
Joined: Sat Feb 10, 2018 8:58 pm

Noisy D75A

Post by John Warren » Sun Mar 04, 2018 4:28 pm

Ran into an interesting problem on a NOS D75A, buzzing transformers. I've worked on a few Chinese D75As but the two I've been sent for rework had an annoying transformer hum that was noticeable even from a few feet away.

Two sources of noise, outer coils vibrating on the primary side of the transformer and the mounting material used to damp core vibrations from the chassis. Pulling the transformer, replacing the spongy material with a more compliant material solved the second problem. The first was solved by tightly wrapping the coils with Vycor self-adherent membrane.
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North Reading Engineering
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