[Amps] Why does power output increase?

[Victor Rosenthal]

Thanks, Paul.

I'm going to look into possible line voltage drops. I can think of some 
areas of concern that I can improve.

Thanks for the signal report! I'm running about 1300-1400w into a dipole 
at 35m.

73,
Victor, 4X6GP
Rehovot, Israel
CWops #5
Formerly K2VCO
https://www.qsl.net/k2vco/

On 05/06/2022 15:56, Paul Christensen wrote:
 >> "I still wonder if the filament voltage should be measured while 
transmitting or on standby..."
 > Vic,
 >
 > This may be unrelated to your amp issue, but I nearly ruined a FU728F 
tetrode tube because of filament voltage starvation.  That tube uses a 
9.0 VAC filament.  The amp is an OM Power 2000A+.  The installation 
section of the manual recommends setting the transformer tap to match 
the AC lines voltage - in my case that's 250VAC.
 >
 > Unlike your problem, output power would drop to 50-70% of the initial 
keyed power.  Filament voltage dropped to under 8V when trying to make 
1500W.  That's a big problem with indirectly-heated cathodes.  Changing 
to the 240V transformer tap fixed the problem.  Filament voltage at full 
power is 9.0V and 9.4V during key-up.  The moral of that story is to 
ignore the installation instruction and choose the tap setting that 
results in 9.0V filament voltage at 1500W.
 >
 > So, to answer your question, I believe filament voltage should 
normally be set at full output power.  OTOH, if there's AC line sag due 
to a long cable run, or a long undersized power cord, then that should 
be corrected in order to minimize the filament voltage differential 
between key up and key down at full output power.  Otherwise, it's 
possible to end up with dangerously high key-up filament voltage when 
filament voltage is set for full output power.
 >
 > By the way, your 20m sigs have been very loud into N FL for the last 
two weeks -- sometimes the strongest DX on the band.
 >
 > Paul, W9AC
 >