[Amps] FAA AM-6154 trouble

[RICHARD GEORGE]

You may have blown the zener diodes for the screen supply
  ----- Original Message ----- 
  From: Larry<mailto:n1miw at cox.net> 
  To: amps at contesting.com<mailto:amps at contesting.com> 
  Sent: Tuesday, February 19, 2008 7:37 PM
  Subject: [Amps] FAA AM-6154 trouble


       Well, now I've done it. I purchased a "box lot" of various 4X150 &
  4X250 tubes, and after acquiring an anode adapter (which fit the tubes
  perfectly), I decided to test them to see how they would perform. The first
  4X150 tested fine with ~300 watts out on 2 meters, but the next one didn't
  have any output. I put the third one in, turned the amp on, and when the HV
  turned on, I heard several light POPs, and the ammeter pegged itself each
  time it popped (and dimmed the lights in the shack quite a bit!), so I shut
  the amplifier off immediately. Next I smelled something funny (well, not
  really funny, but sad) coming from the amplifier. I put the original known
  working tube back in the amp, and with 10 watts drive, I cannot get any more
  than 50-60 watts out. HV is still around 2300V, and max current is only
  ~175ma - it used to be 250-275ma. Idle current is ~60ma. If I crank up the
  idle, my RF out will increase. SWR seems to be fine. What could I have blown
  up? Any ideas on where to check? I took the RF deck out & didn't see
  anything burnt. It sounded like the arcing came from the power supply
  section, but didn't take the cover off to look yet. It may be obvious when I
  do, but it's too late now to pull the amp out of the rack. Any help from the
  experts here will be greatly appreciated (I'll buy the first couple of
  rounds for the local Elmer!) 73's...    Larry N1MIW


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