[Heath] SB-200 weirdness

[Kenneth G. Gordon]

I am hoping that someone else here, besides me, has had the following 
problem with their SB-200 and can tell me what, if any, solution they came 
up with:

My SB-200 has had this problem since the day I bought it from a friend: idle 
current appears to be 10 mA instead of the correct 50 mA....most of the time.

There will be times when the idle current suddenly appears to be correct (50 
mA), staying that way for, perhaps, a day, then dropping back down to 10 
mA.

During the times when the idle current is correct, input plate current at 
resonance, and power output rise to what I consider to be correct values, 
and grid current drops.

During those times when the idle current is low, I have difficulty keeping grid 
current below 100 mA (I prefer it to be about 50 mA), and both plate current 
and power output are low, plate current being lower than 400 mA at those 
times.

I have examined every component several times, subsituting a good 
component where and when I thought I had a "marginal" one, but nothing 
seems to help.

I have also substituted final amp tubes, and the same thing occurs with all of 
those I have tried.

It seems to me that I am overlooking something, but I have, so far, not 
discovered what that might be.

Is there any help out there for this?

I am about to dismantle the entire thing and rebuild it from scratch in hopes 
that I will somehow find the intermittant part...if there is one.

Ken Gordon W7EKB