Why should anyone, even on a helpful site like this one, read an
essentially anonymous post?
> [Original Message]
> From: me <n1miw@cox.net>
> To: <Amps@contesting.com>
> Date: 11/11/2008 7:19:41 PM
> Subject: [Amps] SB-200/572B issues
>
> Hello group. I'm trying to find the answer to why I'm having so much
> trouble with my amplifier, but not having much luck.
> The SB-200 performs well on 80, 40 and 20. However, on 15, it will not
tune
> properly - I may have a problem with the input circuit. My biggest problem
> is on 10. Yesterday, I tried to tune on 10, but I can get only 50 watts
out
> for 100 in. I had the AG6K parasitic suppressors installed, took them out,
> and re-installed the original Heathkit suppressors which resulted in only
> 200 watts out. A big increase, but not near what the amp should be
> producing. Now, while I could tune for 200W, if I turned the "load" past 6
> on the scale, the amp would begin to peg the forward and reflected power
> needles on my SA-2060 tuner. The tubes I'm using are Taylor brand from RF
> Parts - received in August. I also had a pair of Chinese tubes which had a
> failure (filament went open). Is this "pegging" of the needles an
> oscillation? I can actually get the amp to do this without any RF input.
The
> Taylors failed last night on me while sitting idle - taking out the power
> supply. My first set of Taylors had failed too, but there wasn't any
further
> damage. Are the Chinese making tubes of such poor quality lately? While
> tuning up, if I saw any more than a dull red glow from the tubes I'd stop
&
> let them settle for a couple of minutes. My plate voltage is 2250V. On the
> lower bands, the plate current was 400ma, grid current was 250 - 300ma. On
> 10, the plate current was 400-450ma, but the grid current was only
150-200ma
> with 200 watts out (if I remember correctly). The bias voltage is -133V
> standby, and -1.99V keyed. I even dropped the filament voltage to 6.15V
from
> 6.45V to try to keep everything in check.
>
> When I get the oscillation & watch those needles move, I can "play"
with
> how much they deflect using the "load" knob. If I do this with the amp
> keyed, but no RF input, there's an increase in receiver noise, and the
more
> the needles are deflected, the more noise in the radio. This noise has
also
> taken out an automatic antenna tuner on me that was between the radio and
> amplifier, so whatever it is, it's harmful! Hoping someone here can help.
> ...Larry
>
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