[ThomDP]

What is their purpose and are they required for operation of the amp?

Thanks
Dennis

[GMuffley]

The tubes appear to be 807s and the connection to the plate is the top connection.  There is no connection for the plate through the socket as most tubes have.

[Roger A. Modjeski]

Those tubes are either 807's or 1625's and the cap is for the plate. It allows the tube to work at higher voltages and reduces input capacitance. If the tube is in the front end of a radio that is usually a grid cap. In either case the cap has to be used as it is the only connection to that element.

The two tubes previously mentioned are electrically equivalent to the good old 6L6 which was the basis for many small transmitter tubes and horizontal output tubes in early TV.

I will soon be releasing some products with caps... so hang on to your hat.

[Alan]

I sure wouldn't leave those amps uncaged if you have kids or pets.

[Roger A. Modjeski]

Yes, I agree the caps should not be so easy to get to. As I did in the SA-4 OTL, the tubes and their caps are inside the amp.