[Amps] Why does power output increase?

[Victor Rosenthal 4X6GP]

The line voltage was 235, about what it usually is. The amp is wired for 
240v (my model also has a 220v tap). When I removed the resistor that I 
had added, the filament voltage was 5.1 volts in standby. I suppose I 
could have changed to the 220v tap and left the resistor in, but I don't 
want to tempt fate.


73,
Victor, 4X6GP
Rehovot, Israel
CWops #5
Formerly K2VCO
https://www.qsl.net/k2vco/
On 05/06/2022 14:05, gudguyham at aol.com wrote:
> If you rx filament voltage is around 5.25 that’s ideal.
> 
> 
> Sent from the all new AOL app for iOS 
> <https://apps.apple.com/us/app/aol-news-email-weather-video/id646100661>
> 
> On Sunday, June 5, 2022, 6:56 AM, Victor Rosenthal 4X6GP 
> <k2vco.vic at gmail.com> wrote:
> 
>     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
>     voltage.
> 
>     I have noticed the phenomenon with two wattmeters, an Alpha 4510 and an
>     Elecraft W2.
> 
>     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).
> 
> 
>     73,
>     Victor, 4X6GP
>     Rehovot, Israel
>     CWops #5
>     Formerly K2VCO
>     https://www.qsl.net/k2vco/ <https://www.qsl.net/k2vco/>
>     On 04/06/2022 18:35, jim.thom jim.thom at telus.net
>     <mailto:jim.thom at telus.net> wrote:
>      > Date: Sat, 4 Jun 2022 13:26:32 +0000 (UTC)
>      > From: "gudguyham at aol.com <mailto:gudguyham at aol.com>"
>     <gudguyham at aol.com <mailto:gudguyham at aol.com>>
>      > To: Shane Youhouse <kd6vxi at gmail.com <mailto:kd6vxi at gmail.com>>, 
>     Victor Rosenthal 4X6GP
>      >          <k2vco.vic at gmail.com <mailto:k2vco.vic at gmail.com>>
>      > Cc: Amps reflector <amps at contesting.com <mailto:amps at contesting.com>>
>      > 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
>      > increase.
>      >
>      > ##  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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