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
On 05/06/2022 15:56, Paul Christensen wrote:
>> "I still wonder if the filament voltage should be measured while
transmitting or on standby..."
> 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
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