Rich
45s don't need DC for the filament...
They have been working fine on AC for years!
Hank
"Richard Knoppow" wrote in message
m...

"Henry Kolesnik" wrote in message
...
I haven't tested the impedance yet, need to find a pot, but I noticed
that the two 6F6es are connected as push pull triodes. I wonder why
they didn't use a pair of 45s?
Hank

The 6F6 was a much newer tube at the time and is a metal, octal
base, tube. It has sufficient plate dissipation and works well as a
triode audio amp. The 45 also has 2.5V a filament and is not a heater
type cathode, meaning that it needs a DC filiment source for audio
use.
Triode audio amps have lower source impedance than tetrodes when
used without feedback which is an advantage in driving variable load
impedances like loudspeakers, and generally more pleasant overload
characteristics. The 6F6 was a good choice at the time and could also
be used as a driver.


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Richard Knoppow
Los Angeles, CA, USA