AC-10 Speaker

[Robert Meader]

I just purchased a bunch complete scott's with cabinets.  Included in the mix is a radio which is to me the most valuable piece a Scott AC-10 with power supply/amplifier.  What's missing is the speaker (and a cabinet).  Anyone know what is the resistance of the speaker field?

[Kent King]

I'll check one of mine sometime soon...Kent

[Kent King]

I checked both of my speakers. They read around 2500 ohms on the field. One was slightly higher, but for a working number, I'd use 2.5k

Kent

[David C. Poland]

Take a careful look at the amp diagram for the speaker wiring. Not quite what you would expect.

The power feed to the output tube plates are through a center tapped choke mounted on the amp. 

The speaker holds a separate step down transformer for the voice coil.

Somewhat different than the more modern center tapped output transformer for push-pull output tubes.

At that time, speaker voice coils impedance were highly varied, not standardized at 4, 8 &or 16 ohm like post war hi-fi. Your Scott  AC-10 dates from 1929-30 and evidently, push-pull amps designs were still an evolving technology. I too will eventually decide how to use an early Jensen Concert 11 inch pedestal speaker with my AC-10. The Scott D-90 speaker was a 9 inch pedestal speaker with simple step down transformer with primary wired across the two 45 tube plates and secondary for the voice coil. Not sure if it is as simple as ignoring the primary winding center tap of a more modern universal output transformer for what ever speaker you choose.

[Robert Meader]

I lucked out someone had a Roland d-90 speaker on ebay.  I just got the speaker field wires are cut so I will need to check it to see if has the correct  field coil resistance.  The output transformer it is a simple step down type.