[Jukebox-list] Hot Plate (6973)

[Jimmy Day]

Carl -

Yes, I would double-check bias, but I will put money on the fact that the 
problem is that you are using the "substitute 6973" tubes, and there is 
really nothing wrong with your amp.  The "rebranded" tube may be a 6CZ5 
tube, which is widely used as a sub.

I tried some of them once and had the very same thing happen in a Seeburg 
AY.   I looked up the specs for all of the "recommended" types and there is 
NO SATISFACTORY SUBSTITUTE for the original 6973 in the Seeburg amps.

The plate maximum plate voltage specs are higher.  I believe Seeburg runs 
these tubes to their limits whereas RO, Wurlitzer and others may not. 
Seeburg uses fixed bias and a 400v plate supply, perhaps the others are 
using cathode bias.  Using 6CZ5's or other types in this situation is 
dangerous.

A red plate means the tube is being run beyond its design specs and could 
possibly short out and there goes your transformer.  Or house.  You are 
fortunate you saw this!

I have a Q100 which is using the Electro-harmonix 6973 tubes, which are 
physivcally smaller but seem to work OK.  They run cool.

*jimmy

   *******************************

< I looked down and noticed a red glow coming from plate on
one of the "6973" tubes.  Since I recapped the amp recently, I figured
the fault was with the tube.  I moved the tube around including the
other channel and the problem followed the tube.  This "6973" is one of
those National brand tubes that is a relabeled substitute and I have no
idea of what the original tube is.  I know it is a sub since it has the
strap on the bottom to connect the appropriate pins.