"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

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.


--
--
Richard Knoppow
Los Angeles, CA, USA

"Henry Kolesnik" wrote in
message ...
Rich
45s don't need DC for the filament...
They have been working fine on AC for years!
Hank
Well, an ancient RCA tube handbook does list the 45 as
being for AC operated sets. It needs a center tapped
filiment transformer for cathode return although it could be
done with a center tapped resistor across the filiment. The
45 (AKA RCA UV-245) was an old and obsolete design when the
Super Pro was designed. Why do you think this tube is
superior to trioded connected 6F6's?


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--
Richard Knoppow
Los Angeles
WB6KBL

Richard
I don't know if the 45 triode is superior to a triode connected 6F6, I
was just wondering out loud at the keyboard. I know that audio
aficinianodos like 45s in class A but this is PP, B. It was a thought
that shouldn'thave made it to the keyboard, hi hi..
I took the beast to the hamfest but only found lookers and knob
twisters. Now I have the back breaking chore of bringing back to the
bench and checking the audio PP xfmr.
Hank
"Richard Knoppow" wrote in message
...

"Henry Kolesnik" wrote in message
...
Rich
45s don't need DC for the filament...
They have been working fine on AC for years!
Hank
Well, an ancient RCA tube handbook does list the 45 as being for AC
operated sets. It needs a center tapped filiment transformer for
cathode return although it could be done with a center tapped resistor
across the filiment. The 45 (AKA RCA UV-245) was an old and obsolete
design when the Super Pro was designed. Why do you think this tube is
superior to trioded connected 6F6's?


--

--
Richard Knoppow
Los Angeles
WB6KBL