18Watt.com

I have a prebuilt 18 watt
It has a hum
Could the black wire to pin 9 across the base of the valves be causing it?
Never seen heater wired this way
See attachment

No, that's actually even less likely to cause hum than the common method. I do that in my amps now too. I think it was recommended by Valve Wizard (Merlin).

It's probably okay, but I usually wrap the heater wires tighter than what I see there. Insignificant wraps could contribute to hum, but I don't think it's that bad.

I have mixed feelings about the quality of work I see there, but overall it looks like fairly well researched amateur work.

Chances are that lead dress is causing the hum, and you need to (very carefully) do some chopsticking.

Thanks,
Josh

I wired mine like that too. Merlin recommends that method.

crgfrench wrote: ↑

Tue 07/09/19 12:37 pm

I wired mine like that too. Merlin recommends that method.

Yeah, I thought it was him. I'm reading his book now, pretty good stuff.

BTW- you may not want your heaters so close to the socket. It could be fine, but it also could contribute to noise issues being that close to the other pins. It's also a PIA soldering the neighboring pins with the heaters that close.

I would re-route that orange wire connecting to pin 3. It looks like it once looped over the black wire, but has now been pushed down.