Wurlitzer 3100 console with 546B amplifier Humming.

[dgrin]

I'm refurbing this for a friend. I initially powered it up on Variac and DBT and got it to play several selections. It had very pronounced hum but was producing sound on both channels and record selector was working. Plan was to replace all electrolytic capacitors and then to move onto cleaning and lubrication of the rest of the mechanism. 

Capacitors are replaced, Cans are re-stuffed, rectifiers are replaced, "dog turd" caps in pre-amp circuit are replaced with film caps. Driver and output transistors are re-greased to the heat sink. Now, hum is reduced but it is still there. Grounding inputs does not cancel the hum. I disconnected preamp from driver and have around 2mv peak out of preamp output.
I tried splitting the circuit by removing volume control plug from preamp and grounding line pre section input. Same thing or close to it. At the same time, driver input is extremely sensitive. I tried it with 3.9uf film capacitor to ground but output was very noisy still. I think the issue is in the grounding of the amplifier to begin with and thinking of converting it to bus ground. Have anyone done that on those amps?

I want to attach schematic but it's larger then forum allows.

[Ron Rich]

Wood be my GUESS, that if it's truly the amp "humming"( check for a lamp ballast !!), something's still not correct internally in the amp. Never experienced any hum problems with WurliTzer SS amps., that had good filter caps. Ron Rich

[dgrin]

Not ballasts for sure. Hum is coming from speakers, even with lights unplugged from the AC socket. Definitely amp issue.
This is not my first SS rebuild but first one that operates on negative voltages (can common positive). All capacitors that cans are stuffed with are low impedance Nichicon and Elna caps. Polarity and cap insulation inside of cans was observed.
I have a small ripple on the chassis and it varies depending on where I probe it with the scope. With power OFF it's nice and flatline. Flip the switch and there's about 1mv ripple on the chassis. Can it be due to connected dummy loads? I don't know if it's safe to run this amp without load. I don't quite understand the purpose of the output transformer, other then just providing additional taps for multiple speaker systems connected, while controlling the impedance overload.

[Ron Rich]

You should be OK running with no in, or, output load -- the transformer's purpose is to do exactly as you said--provide additional output taps. Ron Rich