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Electromuse A-46

 

Electromuse was a musical instrument retailer of the post-WWII era. Like Oahu, Bronson, and Noble, they sold steel guitars, microphone and amplifiers. It is thought that Valco or National built the amplifiers. This one is a 1947 example, and I think it was called the A46. I think this was the most deluxe of the Electromuses. Others were SE amps, with single inputs, or no tone controls. There is a schematic floating around for an SE model, but I couldn't find one for the A46, so I drew this up.

Controls

The volume controls are typical of forties era amps as they are placed between the input and the first stage. The tone control might look to be in the wrong place, but since this is para-phase inverter, that tone control effects both signals in the push-pull circuit.

The Brillance control is an NFB control. I had to increase the R8 30K resistor because at max volume, it squealed until the Brillance knob was turned down. I bumped the resistor to make the total resistance to be what it was right before it squealed.

Other Notes

It is interesting that 600K ohm resistors are used throughout. For load resistors in the 6SL7 and 6SN7 gain stages, this must lend itself to the very unique sound of this amp.

Also, the two channel mix resistors R15 and R16 are before the coupling capacitor.

Speaker

I haven't seen a A46 with an original speaker, but it seems that most of the A46's I've seen (maybe 2 or 3?) have 12" speakers. This one came with a non-original 12". I recently did some tests on the output transformer and determined the original speaker load was 2ohm. This makes sense for two 4ohm speakers in parallel (the transformer tests out at 7.4KCT:2ohm). So, did these also come with 2ohm 12" speakers? Or two 4ohm oval speakers?

Tubes

My schematic indicates 6V6's, but mine has metal 6F6's dated 1947. The 6F6 has the same pinout as the 6V6, but produces less overall power.

 
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