"Kenneth Scharf" wrote in message
...
Richard Knoppow wrote:
"frank" wrote in message
...
Hello Colin,
COLIN LAMB wrote:
Hello Frank:
The push-pull output transformers should be fairly
common and easy to
obtain. Antique Electronic Supply, in USA, is a good
source. As I recall,
the output tubes are 6V6s, so that would use a common
transformer as
well as driver transformer.
actually the output tubes and the driver are all 6F6.
Also the output
audio impedance of the SP-200 series is 600 ohms, I
wouldn't mind too
much to have directly an output impedance for driving a
4-8 ohm
speaker, but my first option would be restoring the set
as much as
possible close to the original. I'd be happy to find any
information
about the transformers, like power, turn ratios and so
on.
Best 73 es HNY
Frank IZ8DWF
The 6F6 tubes are connected as triodes and operated
nearly at Class-B, the output transformer is 10,000 plate
to plate. This is a common impedance. The original
transformers have a 500 ohm main output and a loosly
coupled 8,000 ohm winding for the headphones.
--
Richard Knoppow
Los Angeles
WB6KBL
On old tube manual shows that the 6F6 in push pull triode
connection with self bias (730 oh cathode resistor)
delivered 14 watts with 350 volts on the plate and a load
resistance of 10,000 ohms plate to plate. With fixed bias
(-38 volts) it would deliver 18 watts into 6000 ohms plate
to plate. For fixed bias the input transformer ratio
primary to 1/2 secondary was 1.67. For self bias the
ratio was 1.29. The driver tube would also be triode
connected, 250 volts plate, -20 volts bias and a plate
load of 10,000 ohms.
No figures given for operation at 250 volts for the output
stage, but the output impedance would be about the same
and resting plate current would be adjusted to about 45ma.
Power output would probably be about 2/3 the value at 350
volts.
BTW, the types 42 and 6F6 are the same except for the
base, types 42 and 2A5 are the same except for the heater
voltage.
(some SP models might have used the other tubes)
The tube lineup in the SP210 was 6K7x2(rf), 6L7 mix, 6J7
vfo, 6K7 if#1, 6SK7 x2 IF 2-3, 6H6 detector, 6N7 nl, 6SJ7
bfo, 6SK7 avc, 6H6 avc rect, 6C5 af#1, 6F6 driver, 6F6 x2
output, 5Z3 rectifier, 80 rectifier
Must have had two different plate voltages, hence the two
different rectifier tubes. The SP400 power supply used
the second rectifier as a bias rectifier, maybe that's
what was done here? I'm looking at the tube lineup from
the book 'communications receivers' by R.S. Moore.
The 80 tube (5Y3 in later versions of the supply) is
a -50 volt bias supply for the AVC and other circuits. The
SP-600-JX has a similar arrangement but using a 6AL5 as the
bias rectifier.
Earlier versions of the Super-Pro did use glass tubes.
I think there are a couple of early instruction manuals on
line showing this version. The early 1940's version used all
metal tubes except for the rectifiers and post war sets
including the SP-400 used a 5U4 in place of the 5Z3 and 5Y4
in place of the 80. These two are identical except for the
base and envelopes.
--
Richard Knoppow
Los Angeles
WB6KBL