Scott Sixteen with output balance pot- schematic

[Pete Olin]

Previous servicing on my Sixteen has left two wires floating in what appears to be the output tube bias balance pot.  This pot does not appear on any schematics that I've seen (located on the end of the supply /amp chassis).  Does anyone have a schematic of this section of the output stage with the pot?

[David C. Poland]

As we know, Scott made running changes/improvements on his radios.  I have an example of an early version Sixteen without the pot, and (at tis moment) two later Sixteen amps with the pot. I plan to restore one having the pot in January.  I plan to document such changes on a copy of Aug 1937 diagram. If no one else has a diagram for you, I will happy to send you a copy of my modified diagram when available.  

Meanwhile, here are 3 photos. An early amp without the pot. And two later examples with the pot.  The only additional part in the later amps is the pot.   However, in the 2 examples with the pot, note differences in the resistors going to the pot.  One amp with no pot uses the same value resistor as the one amp having small size resistors connected to the pot. In the other photo, the large resistors are 11,000 ohm and appear original to that amp.   I will not know the resistance of that pot until I begin the restoration.  I have no explanation for the difference in resistors in the 2 later amps. 

You suggest your amp still has the pot  mounted on your amp, and that the required resistors are still present.  My photos show which resistors to reconnect to the pot, and that the center tap of the pot just returns to the middle lug of the same terminal strip.  Hope this helps.

-Dave Poland.

[Pete Olin]

Dave-

Thanks very much for the excellent photos; now I should be able to undo someone's carelessness of years ago.  My version has 10K resistors going to each leg of the pot and the center tap going back to the -20 source.  Now I see that my two floating wires went to the speaker jack; it shouldn't be difficult to find a home for them. Once you get going on your project in January, I would definitely like even a scribble of a schematic just in case I miswire.

Thanks again-  Pete