Q about change in hum volume when biasing Hiwatt 100

[dlp]

I had to add a voltage doubler to my 100 watt Hiwatt with el34s and discovered that while the 60hz hum diminishes as the left and right side bias voltages gets closer, it seems the amp is the quietest when there is a couple mv offset between the left and right sides. Should I ignore that or go with the silence? Thanks

[martin manning]

I guess you have installed separate bias controls for each side, and when you say a couple of mV, you mean a couple of mA difference in the static current flow? I say make it quiet. By doing so you are compensating for small side-to-side mismatches in the tubes and output transformer.

[pdf64]

Yes, aim for minimum hum / most linear output wave.
Bear in mind that cathode current = plate current + screen grid current, so the cathode current discrepancy (?) you're seeing maybe be due to the screen grids.
Or the current sensing resistor value.

[dlp]

Thanks a lot guys I appreciate it.

[Stevem]

If you will use the amp driving it to the point of output stage clipping then I would choose your final bias setting by playing the amp that way.
The most noiseless setting will cancel odd order upper harmonics generated by the output stage and a slightly off set setting will allow them to pass and be heard.
The noiseless setting will make more power by a tad, but the matching for some folks makes the amp sound too sterial although it will have the best sustane so in the end and as always with amps it boils down to a trade off.
Spend time and listen close and you will feel and hear the differences!

Also note that the Hightwatt bussed grounding scheme is not the most noiseless to begin with!

[Stevem]

You could likely rework the stock grounding layout so that you could keep the bias set closer, but I would also confirm that the heaters are wired pin 2 to 2 and 7 to 7 first .