One must increase load and repeak tuning to reduce grid I.
Sent from my iPad
On Jan 15, 2019, at 14:06, Gary Smith <Gary@ka1j.com> wrote:
Here's a new bit that happened last night.
I was on 160 and discovered the grid
became excessive as I was transmitting, I
had to back the loading cap back down to
keep it WNL and the power was dropping
proportionally to the increase of grid
current.
When I stopped transmitting and let the
tubes cool for 30 or so seconds, the power
came back to normal. Transmit again and
shortly after, the grid current rose and
power output fell. SWR always remains
constant.
Before I open the amp up, any suggestions
what I might look at? I'm thinking the
caps have failed and with Tx, there's heat
in the the caps & the values change and
show the issue. Maybe I need to replace
the 160 padding caps? It shows this on no
other band.
73,
Gary
KA1J
> Here's a curiosity I'd be interested in
> getting input on.
>
> The 77SX seems to be easier to tune using
> the "B" setting, rather than the A.
>
> It used to be easier to tune on 160M using
> the A position on the band switch but now
> I find in the "A" position, I have to
> rotate the loading cap maximally to the
> zero position for tuning and it seems to
> dead end out in the A position. I now have
> to use the "B" position to tune it, and it
> now comes close to bottoming out at zero,
> whereas it never used to have any
> requirement to go to the "B" position.
>
> I'm thinking the padding doorknobs for
> 160M have softened over the years.
>
> Idears?
>
> 73,
>
> Gary
> KA1J
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