I have to ask as I'm not familiar with the AL-1200, but the legal
limit CCS is well within the ratings of the tube, so:
Is the cooling in the AL1200 anemic, if one has to be concerned with the
RTTY operation?
If I read the post correctly there is *no* current showing with the amp
keyed whether there is drive or not, but like Gerald I'm not sure about
the phrasing.
You have high voltage indicated. (Normal?) Even with the grid cooked I'd
expect some plate current.
Bias is normal?
Have you checked the tube pins to make sure they are sill soldered?
Are the switching relays and contacts OK?
Those are my only thoughts at present.
73 and good luck,
Roger (K8RI)
On 10/18/2010 5:45 PM, knormoyle@surfnetusa.com wrote:
>
> Billy, AA4NU and Gerald K5GW both I guess asked the
> same question..
> do I see any plate current due to bias when the amp
> is keyed to transmit (even if no rf in)
>
> I'll check that again tonight. My recollection is no.
> It sounds like I need to check those zeners too? if
> they are involved in the bias?
>
> Yes I was pushing the output power for rtty duty
> cycle. Between 1000 and 1200W. But I kept grid
> currents low. 150mA or so?
> hmm. I'm thinking back now.. I think maybe on 15M the
> grid currents are a little higher. Most operation on
> 40M/20M so less on 15M.
>
> How long? Well, 2nd day of the contest. But actually
> in terms of long run periods, it wasn't during a
> "worst case" sustained run period..
> I think though it being 15M was more stressful.
>
> I was monitoring temps, which didn't seem bad.
>
> The problem with tube replacement seems to be
> availability of the 3CX1200A7 ? (are there no China
> 3CX1200A7 replacements?)
> I was nicer to the AL-80B afterwards. pretty quiet
> fan in comparison :)
>
> -kevin
> ad6z
>
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