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.