Sparton 16A211 Width Problem

[Penthode]

Originally Posted by Steve McVoy

This set uses parallel 6BG6s, probably the only tube available in 1953 when the set was designed. I've tried a bunch of NOS tubes with no luck.

The 6BG6 was a carry over to the tube base octalization process in the mid thirties. It started out as a UY (5 pin) based 807. By about 1951-52, the transition was on to newer and better power tubes. Your Sparton from 1954 is the latest set I can recall using a 6BG6! (I will research this further and would appreciate feedback from everyone on this). Incidently, it is one of my favorite tubes: see my avatar!

Nevertheless, the 6BG6 cathode current appears low and the voltage drive to the grid appears adequate. To get the cathode current up a bit, you may try increasing the screen voltage slightly by reducing the screen feed resistor value. If you increase the screen voltage slightly to raise the cathode current, I would expect you will get the width you require.

The low width may be inherent in the design and it seems with the considerable effort that has expended elsewhere to fix this problem, I would see this solution as a good bet.

Terry