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RE: Phono hum in Scott 222c

Posted by Triode_Kingdom (A) on August 30, 2014 at 16:43:58

In Reply to: Phono hum in Scott 222c posted by mr9iron on August 29, 2014 at 23:56:14:

Well, my first mistake was downloading a schematic from the HH Scott site. There's a glaring mistake in the negative power supply (see below). No wonder it hums!!

That aside, this amplifier powers the phono and tone stage filaments with DC from the bias supply. The supply would have to be really dirty for the problem to become so obvious at the output. A serious defect in that supply would also affect bias on the output stages, but that woldn't be a phono-only issue. That leaves the B+ caps C202 and C201 (phono/tone B+ filtering) as possible culprits. Are those the caps you replaced? Also, I know you said it sounds like 120 Hz, but are all the tube shields in place?

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