Scott 800 PM vs electromagnetic speakers

[Daniel Kingloff]

I have an 800 chassis that I bought some years ago without a speaker or cabinet.  I'd like to get it working again but have some confusions about the speakers.  I understand that some were PM and some electromagnetic and the ones with PM's have a resistor to add some impedance substitution for the coil in the EM version.  Was there an electrical difference in the 2 versions?  I'm assuming that the PM version utilized a choke in the power supply. If there was a difference in the electronics, how can I tell which version I have.  Thanks in advance!

[Norman S Braithwaite]

There were two versions of the Model 800B, early and late.  The late version had two chokes on the power amplifier and a revised tube layout.  Many of the early version were updated to add the additional choke.  The early version had two tubes adjacent to the 6L6 output tubes whereas the late version had one tube adjacent to the 6L6 tubes.  The revision included moving the voltage regulator tube away from the output tubes.  The field coil on the 800B speaker was also used as a choke in the B+ supply.  The PM speaker version simply had a power resistor mounted on the speaker basket to replace the DC resistance of the field coil.  Going from recollection, the speakers were interchangeable.

Norman

[Daniel Kingloff]

So what is the native output impedance of the output transformers?

[Alex R. Whitaker]

Check the Scott Info Archive on this page.....it might have that information.  Based on my experience with other brands, in that post-war era, it's probably 3.2 ohms to the speaker voice coil.  Input would be typical 6L6 class B impedance, which can be found in any tube manual.