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Re: [Amps] Why does power output increase?

Subject: Re: [Amps] Why does power output increase?
From: Victor Rosenthal 4X6GP <>
Date: Sun, 5 Jun 2022 15:39:11 +0300
List-post: <>
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.

Victor, 4X6GP
Rehovot, Israel
CWops #5
Formerly K2VCO
On 05/06/2022 14:05, wrote:
If you rx filament voltage is around 5.25 that’s ideal.

Sent from the all new AOL app for iOS <>

On Sunday, June 5, 2022, 6:56 AM, Victor Rosenthal 4X6GP <> 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)
    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
    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
    is probably in standby with zero plate current most of the time (my
    biasing circuit cuts off the tubes in standby).

    Victor, 4X6GP
    Rehovot, Israel
    CWops #5
    Formerly K2VCO <>
    On 04/06/2022 18:35, jim.thom
    <> wrote:
     > Date: Sat, 4 Jun 2022 13:26:32 +0000 (UTC)
     > From: " <>"
    < <>>
> To: Shane Youhouse < <>>, Victor Rosenthal 4X6GP
     >          < <>>
     > Cc: Amps reflector < <>>
     > 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
     > INcrease, not decrease.  Tube emission would decrease.  PO would
    drop, not
     > increase.
     > ##  Your bias vdc may be screwed up..and changing with a load
     > 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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