It could be the loading padder cap/s. They may be getting warm and going
open circuit. If that is the case, then no amount of retuning will bring
the power back up.
I make this suggestion because in my experience with several of the old
Yaesu FL-2100 amps, the fixed caps in the input tuning network go open
circuit from heat after some time of operation. In those cases, you can
stick the cap on a C meter and watch it go open and come good by using a
hot air gun and freezer spray.
Good luck.
Alek. VK6APK
On 11/09/2013 9:35 AM, Mike Waters wrote:
Thanks, Vic. Someone else (in a private e-mail) just suggested line
voltage. I do monitor the filament voltage, but I should monitor the 240
VAC and look at the HV meter, too. There is a "too-long" run of #12 from
the breaker panel to the amp, and if that wiring heats up, that might do it.
As for the pi-net caps, that's what I thought at first. I have padder caps
--some with a high negative temp coefficient--- on both C1 and C2 in the
pi-net output. However, re-tuning should compensate for that and bring it
back up to full power out (shouldn't it?), but it never does.
73, Mike
www.w0btu.com
On Tue, Sep 10, 2013 at 8:29 PM, Vic K2VCO<k2vco.vic@gmail.com> wrote:
Does the line voltage droop when you transmit, causing a drop in filament
voltage?
Do you have ceramic capacitors in the tank circuit that heat up and detune
the tank?
On 9/10/2013 6:03 PM, Mike Waters wrote:
`
Anyone have an idea why the power output of my dual parallel 833C 160m amp
often drops 200+ watts after several seconds? Re-tuning does not bring it
back up to the initial output.
Not that a drop from 1500 to 1300 watts is a big deal, but inquiring minds
want to know the reason. :-)
Description:
www.w0btu.com/833C_linear_amplifier.html
More photos:
w0btu.com/files/misc/833C_linear_amplifier/?C=M;O=D
--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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