[Bob Andersen]

Thanks for all the info and kind words. Comments like yours keep me motivated

Interesting about the 6L6s. This 37 version uses a pair 6B4Gs. Apparently they need to be fairly well matched to reduce hum.

Here's a quote from this excellent article by Bruce McCalley: http://www.antiqueradios.org/gazette/philco690.htm

Balancing the plate currents of the 6B4G output tubes was done by using a separate filament supply for each tube and by using a dual potentiometer across these windings which served as a variable "center tap" for the windings. This control was adjusted for minimum hum. (Unfortunately, as the tubes heated up they did not do so exactly alike. The hum adjustment had to be made when the tubes were well-heated. When first turned on, though, unless you had a well-matched set of output tubes, there was always some hum for a short period.)

I haven't tested any of the 20 tubes yet - I'm almost afraid to

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