Richard
The volume decreased with the filament transformer so I need to open it
up and see if someone made some mods. I downloaded the military manual.
It seems to me that someone at Ham went nuts changing model numbers for
very insignificant reasons.
"Richard Knoppow" wrote in message
m...

"Henry Kolesnik" wrote in message
...
Getting old is not recalling the alternatives offered, so I'm a
dummy. I found the filament xfmr first and tried it but it reduced
volume so I assume my radio which is non-military doesn't have 600
ohms like the military manual I have. So I guess mine is commercial,
either a SP-200-SX or more likely a SP-210-SX and I think it has a
3.2 ohm output transformer.
I can't find any info and I wonder if anyone knows for sure on the
commercial models output transformer's impedance.

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Thanks & 73
Hank WD5JFR


All of the Super-Pro models from the SP-100 on had 500 ohm outputs
for the loudspeaker and a loosly coupled 8K winding for headphones.
The 500 ohm output will drive a loudspeaker at much reduced volume. A
12.6V filiment transformer has about the right impedance ratio (100:1)
to drive a 4 to 8 ohm speaker from this tap. These tramsformers have
enough core material to work down to low audio frequencies and
surprizingly good high frequency response. 70V public address
transformers also work very well as Scott Dorsey pointed out. The
original Hammarlund speakers for the Sp-200, 400, 600, had matching
transformers built-in.
The SP-100 has a front panel switch for the loudspeaker but the
later versions do not. You need to mount a switch (maybe in the
loudspeaker cabinet) to cut it off. Use a DPDT switch with a 500 or
600 ohm resistor switched in when the LS is turned off to provide a
load to the audio transformer. It should handle a couple of watts.
The headphone winding is not critical of load impedance and will
work with phones from 50ohms to high impedance.
The military and commercial versions of the SP-200 and 210 were
identical except for the use of hermetically sealed transformers and
chokes and oil filled filter capacitors in the military versions, and
some variations of panel finish.
There is an owner's manual for the SP-210 somewhere on the web,
maybe on BAMA, I have a copy but don't remember where I downloaded it.
Most of the communications receivers built up to perhaps the 1950s
had 500 ohm or 600 ohm outputs. A few even had the output transformer
in the loudspeaker cabinet.
--

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Richard Knoppow
Los Angeles
WB6KBL