EH Scott Radio Enthusiasts
Scott Export Set and "amp"
Although it was built after the war, the Export set is a relatively scarce set. At the end of WW2, Scott was "stuck" with a large number of partially completed SLRM sets. They put a better face on them and the Export was born. They removed the BFO, but otherwise, the Export is an SLRM. The SLRM is an AC/DC (transformerless) set with AM and SW coverage. I have only ever seen 4 or 5 of these sets, however, there is an odd little thing going on. In the pics here, I provided the front and top view of an Export set I have. It came with the small "amp" unit which appears to be partly Scott components but is quite crude. Initially, I thought it was something someone jacked up and pretty much ignored it, in fact, I almost pitched it. But then I found another Export, with an <identical> ugly amp. And then I got wind of a 3rd one. So I pulled out the little amp and drew up a quick diagram.
The amp includes an isolation transformer, which makes a lot of sense for the AC/DC set. The 8ohm speaker output becomes an input to a pair of 6V6s which can drive a 500ohm load. The set was modified with a 4-pin cable to connect to the amp, it includes the on/off switch line and the isolation power. A twin lead wire has speaker terminal connections. The two sets I have with the amp are both modified with the 4-pin wire (identical mods). I do have a theory: Cliff Coon.
Cliff Coon was a <long time> Scott employee, his signature is on many of the schematics (C L Coon). After the great schism in 1945, Cliff left Scott and advertised "Precision Radio Laboratories" in Chicago. I greatly suspect (but can't confirm) that Cliff might have built these units for Export owners. I'm not sure why anyone would want a 500ohm output off the 6V6s, but otherwise, the unit makes sense. I'm interested in any other thoughts or info about this...thanks!!
Kent
David C. Poland
So, with the outboard amp, the radio still have/run the pair of 25L6s?
Jan 19
Kent King
Yes, this unit just connects to the speaker output from the set, driven by the 25L6s.
Jan 19
Russ Webb
I think that I may have just found a purpose for my 510 amp. If I added a octal style plug to the SLR-H I could do away with the little accessory trans (pic upper left). That way I can still use it as a test fixture, it's current job. And there would be plenty of audio out, something that is in short supply in a lot of vintage boat anchors.
Jan 19
Norman S Braithwaite
Those audio transformers appear to be swapped! The SLRM has a 500-ohm output which would match up with the 500-ohm winding of what you show as the output transformer. I'll investigate my Export receiver with amp and original speaker when I have a chance.
Norman
Jan 20
Norman S Braithwaite
Okay, the only thing I am finding that relates to a line impedance is the label on the speaker output terminal strip. It is marked 600-ohm speaker. However, measuring DC resistance across the terminals yields approximately 3-ohms. Hence the actual output transformer impedance is approximately 8-ohms. The original Scott labeled speaker has an 8-ohm voice coil matching the output transformer speaker impedance. Made from spare parts. The 600-ohm label is incorrect.
Norman
Jan 20