[78-L] RCA dealers' phono?

[DAVID BURNHAM]

From: "Robert M. Bratcher Jr."

Well the 5Y3-GT was the rectifier. I don't know what they used the 6J5 for 
(anybody know?) & either the 6K6-GT's or the 6SQ7's were the final amplifier 
tubes in push pull I'm fairly sure. What the other pair of tubes (either 6K6-GT 
or 6SQ7) were for I have no idea without looking at the schematic for this amp. 
If anybody knows more about this amp & how it works please let us know......

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The 6K6s were definitely the push-pull output tubes.  These were common tubes in 
Victor machines in the late 30s and 40s, yeilding an out put of 5 watts 
undistorted and 9 watts maximum.  Later they were replaced by 6V6s which were 
beam power tubes whose characteristics were similar enough that they could 
replace the 6K6s directly with no other modifications.  The 6J5 was a triode, 
medium gain, probably used to raise the cartridge output signal to a level 
suitable for the tone control circuit.  The 6SQ7 is an interesting tube, it 
contained two diodes and a triode.  The diodes were used for AM radio detection, 
but this unit doesn't appear to have a radio in it, so I suspect they're just 
using the triode sections for driving the 6K6s.

db