Good idea, but I pulled V12, 6SC7, and the hum remains. It is definitely in the output stages
Tom
On Thursday, February 13, 2025 at 08:10:23 PM EST, don Root <drootofallevil@...> wrote:
Tom Good for you
Presumably, the base ¡°In¡± position filters out the hum as expected¡ And the hum comes from upstream, maybe the AF gain? Pot area or a bad contact in the phones switch, or even before that. ??
I just finished pretty much a complete overhaul of a nice condition (physically) SX-28A. Replaced just about every resistor and all caps.
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Radio is working well except for a 120hz hum. When I switch the Bass in, the hum goes away.
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Yes, there is ripple on the plates of the 6V6¡¯s, about 6vrms, but that is there independent of the bass switch position. The output side of the HV filter is clean, no ripple. I paralleled another 47uf 450v cap across the choke input cap and there was no difference.
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I double checked the wiring against the schematic along with component values. Is the schematic correct in this area? I found once schematic error maybe there is another?
