[BC] FM10K

[Cowboy]

On Sunday 10 November 2013 05:12:16 pm Tom Taggart wrote:

> What I have now is IPA trouble. No drive to final, the transmitter will come up, but with a boatload of PA current, and no output (have Bird in line).  Only small amount of IPA cathode current.  Outboard exciter drives 4cx300A IPA which drives the final.  Thought the IPA might have gone--been in the transmitter since July 2012.  However, same symptoms with new IPA tube, Eimac, bought 2 years ago when they were being discontinued.

 Sorry to say, but it sounds like you've lost the IPA tube.
 ( the stage anyway )

 How does the IPA grid current compare to "normal" ?
 What's the screen voltage ?
 Could have lost screen supply to the IPA, which would produce
 normal grid, normal plate voltage, low plate/cathode current, and
 about 10% output from that stage.

 If the IPA shows "normal" grid current, then look hard at the screen.
 If you can confirm screen voltage at the tube, then you ought to swap 
 the tube with a known good ( has worked recently, or is currently working
 in something else ) tube to confirm, OR put your suspect tubes
 into something else, and actually confirm the tube will make power.

 Without more data ( grid and screen current/voltage ) can't say.

-- 
Cowboy