If you rx filament voltage is around 5.25 that’s ideal.
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On Sunday, June 5, 2022, 6:56 AM, Victor Rosenthal 4X6GP <email@example.com>
This morning, for some reason, the phenomenon did not occur. I was
getting close to 1400 watts the whole time. I always operate CW in the
SSB position -- the warning in the manual against this is (I think) only
relevant if the original slow t/r relay is in use, which hot-switches
with semi-QSK. My amp has a reed/vacuum relay QSK circuit.
Because I do not use SSB, I have adjusted the idle current lower than
normal. It is 140ma for two tubes. This requires a bit more drive but
produces more output without generating clicks. It didn't change more
than 5 ma (a slight drop) during my test. The Zener that is in there is
a 50-watt one.
I agree that it is unlikely to have anything to do with the filament
I have noticed the phenomenon with two wattmeters, an Alpha 4510 and an
I've heard about using diodes instead of zeners, but the curve of
current vs. forward drop of the diodes is sharper than that of zeners.
The temperature characteristic also compares unfavorably. So I've stuck
with zeners. I put in a 50 watt one because that is the one I had with
the appropriate voltage.
I still wonder if the filament voltage should be measured while
transmitting or on standby, given that even during a transmission the
plate current is only drawn at a maximum of 50% of the time, and the amp
is probably in standby with zero plate current most of the time (my
biasing circuit cuts off the tubes in standby).
On 04/06/2022 18:35, jim.thom firstname.lastname@example.org wrote:
> Date: Sat, 4 Jun 2022 13:26:32 +0000 (UTC)
> From: "email@example.com" <firstname.lastname@example.org>
> To: Shane Youhouse <email@example.com>, Victor Rosenthal 4X6GP
> Cc: Amps reflector <firstname.lastname@example.org>
> Subject: Re: [Amps] Why does power output increase?
> ## what is the idle current ??? Try it on SSB (hi voltage)...and also on
> CW (low voltage). IE: put xcvr on SSB, mic gain on zero, key the PTT.
> ## IF the resistor in the fil primary heated up, it's resistance would
> INcrease, not decrease. Tube emission would decrease. PO would drop, not
> ## Your bias vdc may be screwed up..and changing with a load applied.
> Even this doesn't make sense. Typ, when zeners fail, I believe they typ
> fail shorted....which would result in sky high idle current. Which would
> make it easier to drive the amp.
> ## But in this case, it's as though the zener V starts off normal, then
> decreases, and I find that hard to believe. Something else is amiss, and
> it maybe one or both tubes has gone wonky.
> ## do u have a dead on wattmeter to test with....or a scope ?
> ## The zener has to handle cathode current....which is the sum of the plate
> and grid current. I'd replace the zener with a string of 1N5408's. I
> have had no luck with zener's.
> Jim VE7RF
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