From: msv@unlinfo.unl.edu (mark vanroojen)
Subject: hk citation II
Date: 24 Dec 1992 20:44:58 GMT

The HK citation II is not an amp that is readily modifiable into a 
class A design.  (I'm actually just going by what I know of it's 
output rating.)  The B+ on the output tubes is high enough that the 
plates would be way over their dissipation ratings if run class A.  
(If run in that fashion, it would be no wonder if a tube, KT88 or 
otherwise exploded as someone suggested to you.)  Furthermore, the 
Power transformer is not capable of putting out the kind of current 
necessary to run the amp class A.

The citation II is a favorite with modifiers because of it's highly 
regarded transformers.  Many suggested circuit suggestions are 
floating around.  Try to snag one of those.  MFA used to build it's 
amps using the citation transformers.

As for the difference between 6550s and KT88s, I suspect that the 
origin of the tube is more important than the name on it.  Old stock 
British and American tubes tend to be better than what is made now a 
days, though the situation is improving.

Hope this helps!

MvR