[Amps] Matching GU-74Bs

[gdaught6 at stanford.edu]

Carl wrote... 

< snip >

> I modified the HF and 6M NCL-2000's Ive had since 64-65 for individual bias 
> adjust back then. A delta of around 5V is tolerable before IMD starts to 
> suffer from the lower value biased tube being easier to drive. With static 
> matching and a single adjustment a pair within 1V was considered matched.
> 
> Ive deliberately kept far away from Russian tubes so cant say what their QC 
> is like. However if Alpha is making such a fuss over it Id suspect that they 
> vary considerably.

I have a bit of experience with the Russian tubes.  I was surprised by how different 
the bias requirements for the tubes can be.  I have measured variations in grid bias 
voltage of over 20 Volts to produce a given anode current (at constant screen voltage 
and anode voltage) .  

Or as Carl correctly suspects, "...they vary considerably."

However, when the bias was adjusted to give the desired resting anode current, the 
performance was very similar.

73,

George T Daughters, K6GT
CU in the California QSO Party (CQP)
October 2-3, 2010