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
...
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