Hi all,

I just begun restoring the SP-210-LX (guessed model from the bands,
there's no model name in the back plate). One of the previous owners had
the "brilliant" idea to include the power supply transformers into the
main chassis and removed the last AF (push-pull) amplifier stage tubes,
T-7 and T-8 to make some room.
Is there any hope to find these two transformers? Maybe someone has a
part unit?
Is there any data available about T-7 and T-8 so I can try to make
replacements?
Thanks in advance and season greetings!

Frank IZ8DWF (mycall at amsat dot org)

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.

73, Colin K7FM

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 6V6 and 6F6 is pretty much interchangeable, so the standard output
transformer should work. 500 ohms is not a common output today, although
the pp 6V6 to line output may get you in the ball park. It should use a
standard interstage transformer.

A push-pull old Hallicrafters transformer would work, since they had a 500
ohm output, too. SX-28, SX-62 and SX-42 all would have the right
transformer if you can find one being parted out.

73, Colin K7FM

"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

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.

frank wrote:
Hi all,

I just begun restoring the SP-210-LX (guessed model from the bands,
there's no model name in the back plate). One of the previous owners had
the "brilliant" idea to include the power supply transformers into the
main chassis and removed the last AF (push-pull) amplifier stage tubes,
T-7 and T-8 to make some room.
Is there any hope to find these two transformers? Maybe someone has a
part unit?
Is there any data available about T-7 and T-8 so I can try to make
replacements?
Thanks in advance and season greetings!

Frank IZ8DWF (mycall at amsat dot org)
Here is the manual for the SP2xx aka BC779
http://63.227.91.114/Common/Manuals/Desc_Manuals.php/

"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

"Kenneth Scharf" wrote in message
...
frank wrote:
Hi all,

I just begun restoring the SP-210-LX (guessed model from
the bands, there's no model name in the back plate). One
of the previous owners had the "brilliant" idea to
include the power supply transformers into the main
chassis and removed the last AF (push-pull) amplifier
stage tubes, T-7 and T-8 to make some room. Is there any
hope to find these two transformers? Maybe someone has a
part unit?
Is there any data available about T-7 and T-8 so I can
try to make replacements?
Thanks in advance and season greetings!

Frank IZ8DWF (mycall at amsat dot org)
Here is the manual for the SP2xx aka BC779
http://63.227.91.114/Common/Manuals/Desc_Manuals.php/

Note that there were three versions of the SP-200/210
with different frequency ranges. The standard version
covered from 535 Khz to 20mhz, the second version covered
from 1250 khz to 40 mhz and a third version, which carries
the military designation BC-779 covered from 2500 Khz to 20
mhz plus 100 khz to 400 khz in two bands. These were
intended mainly for aeronautical work where the low bands
were used for navigation aids and for control tower
communication.
The circuit of the standard version and low frequency
version is quite similar but the high frequency version uses
shunt fed RF amplifiers rather than series fed in order to
get higher Q and better image rejection. On the broadcast
band of receivers having it there is a resistor across the
RF tanks to _lower_ the Q and increase the bandwidth in
order to obtain high-fidelity reception.
The headphone connection to the transformer in the
later series receivers is loosely coupled so that plugging
in headphones will not affect the level of the regular 500
ohm output. This is in order to allow local monitoring of a
receiver connected to a phone line or recorder other use
without disturbing the level.
Some Super-Pros were evidently modified to allow
crystal control of the receiving frequency. I have seen
pictures of these but have never seen a circuit for it.
These receivers would have been used in fixed frequency
operation. They had two knobs over the main tuning dial,
presumably one for choice of crystal and the other for fine
adjustment.



--
Richard Knoppow
Los Angeles
WB6KBL

Kenneth Scharf wrote:
Here is the manual for the SP2xx aka BC779
http://63.227.91.114/Common/Manuals/Desc_Manuals.php/

Kenneth,
thanks for the link and informations about the transformers. It appears
I have to find someone who can make them or find some old original
replacements.
By the way, the model I have is the one with 100-200 Kc and 200-400 Kc
bands.
best regards
Frank IZ8DWF