OK guys,
Tonight I opened the amp and replaced the tube (a Federal project in and
of itself!). Put everything back together. No pops, snaps or blue
glows. Except now, no output power either! And input SWR to the amp is
horrible. The only plate current is the tube zero signal idle current.
It's like the RF is not getting to the tube.
So I pull it apart again and removed the bottom cover and check all my
input circuitry. I thought perhaps a blocking cap on the input failed
when all heck broke loose last night with the bad tube. According to my
MFJ-259, everything looks great. I check out the bias switching
circuitry and that is OK too. All is fine. So I put back together.
Same problem. I put in a different tube. Still no output power and only
the zero signal idle current.
Note these tubes were both good and worked in the amp 3 months ago.
So what gives? I am beginning to think that perhaps it is a blocking cap
problem. It might not show up due to the low power level of the signal
from the MFJ-259. But with 100 Watts from my rig, the characteristics of
the caps must change. That's the only thing I can think of! And that's
the only thing that would keep RF from getting to the tube.
I was also thinking that perhaps the output cap on my input pi-network
went bad. But the problem occurs on all bands and it also occurs if I
by-pass the input pi-nets. The only common components are the coax and
the bypass caps. So I figure it must be them.
Anyone else got any ideas??
73,
Jon
KE9NA
-------------------------------------
Jon Ogden
KE9NA
http://www.qsl.net/ke9na <--- CHECK IT OUT! It's been updated!!!!!
"A life lived in fear is a life half lived."
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|