Leave it without the resistor. Don’t mess with it anymore. Tube failures are
more likely G-F shorts.
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On Sunday, June 5, 2022, 8:39 AM, Victor Rosenthal 4X6GP <email@example.com>
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.
On 05/06/2022 14:05, firstname.lastname@example.org 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
> <email@example.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)
> 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
> https://www.qsl.net/k2vco/ <https://www.qsl.net/k2vco/>
> On 04/06/2022 18:35, jim.thom firstname.lastname@example.org
> <mailto:email@example.com> wrote:
> > Date: Sat, 4 Jun 2022 13:26:32 +0000 (UTC)
> > From: "firstname.lastname@example.org <mailto:email@example.com>"
> <firstname.lastname@example.org <mailto:email@example.com>>
> > To: Shane Youhouse <firstname.lastname@example.org <mailto:email@example.com>>,
> Victor Rosenthal 4X6GP
> > <firstname.lastname@example.org <mailto:email@example.com>>
> > Cc: Amps reflector <firstname.lastname@example.org <mailto:email@example.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
> > 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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