[Johnson] Viking Thunderbolt

[Steve H]

Ok turns out the bias cable connector is NOT keyed, so it can go in 4 
different ways.
For sure it was in the wrong position. So I made sure pin 1 (gnd) is marked 
so its put in
the right way all the time.

Before I did this fix, the VR75 tube was not lighting up at all, its the 75V 
regulator.
Now it lights with the mode switch in TUNE or LINEAR position which I 
believe is correct,
as CW  is full duty cycle.

While I was in there saw my 6BY5 has been removed and an octal socket is 
stuck in there. Opened it up
and its got 2 diodes tacked in.

http://www.mediafire.com/view/cef1j9tst8u48a5/HPIM0835.JPG/file

I do have a large metal square 0.5uF / 600V cap, stuck accross C120 
(assuming its not
defective) which is clearly a mod. Apparently its buffering pin 2 of the 
VR75 /
OA3, possibly part of the new AB1 config?

Almost brave enough now to apply plate voltage, only I was warned tubes that 
have sat a while
ought to be "de-gettered" on the bench first.


--
Steve Hearns
KA2PTE