Hi Jeff, etc.,
I lost one of those resistors many years ago. I would say old age. Maybe
some stray current, but I replaced the 33 ohm 1W with 33 ohm 2 Watt
resistors. One of my tubes was not working with the 33 ohm resistor blown.
The other was bright orange, taking all the load. You may have one tube
either cut off or "floating along". I do not remember if I was getting 300
or 500 watts when this happened. By the way, I was on 40 phone and happened
to stand up and look down on the amp, and saw one tube bright orange and one
black.
If you are getting 500+ watts out and an indication of only 200 ma plate
current, I would also look at the plate current resistors, R12 and R14 and
make sure the plate meter is reading close to 500 ma. R12 could be low or
R14 could be high or both.
The grid current at 500 ma plate current should be about 150 ma. Look up
the current data sheets by Svetlana or similar on line. My old ARRL handbook
does not give grid current for grounded grid operation, just 500 ma max for
a pair and 600 watts out for 1100 to 1200 watts input.
Good luck, George K8GG
----- Original Message -----
From: "Jeff Stewart" <stewgoat@indy.net>
To: "amps" <amps@contesting.com>
Sent: Friday, June 13, 2003 9:18 PM
Subject: [Amps] Sb-200 plate current (again)
> I just did a visual and a 33 ohm resister off the grid of one tube
R21 or R22 is cracked in two. The tube on that side has a discoloration on
one side (the gitter appears to be at the bottom) so it may be toast. Now
to figure cause and effect I guess before I replace the resistor.
Suggestions?
>
> Jeff
>
> http://www.qsl.net/ka9dad/
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