[AMRadio] GK500 OTA almost


Rob Atkinson ranchorobbo at gmail.com
Fri Jan 6 12:46:19 EST 2017


On Fri, Jan 6, 2017 at 6:06 AM, Jim Candela <jcandela at prodigy.net> wrote:
> Collin,
>
>    I am glad you made progress. Is it really fixed though? \


agree with some of Jim's comments but if it looks like a duck, quacks
like a duck, walks like a duck, it's a duck.  IOW, the rig's problems
are reportedly gone.  In my book that means it got fixed.
Don't get too anal looking for probs that don't exist, however, it's a
good idea to check for neutralization by dipping the plate and seeing
if the grid current peaks at the same time.

A common misunderstanding regarding plate parasitic suppressors is
that they stop oscillation.  Actually they create an environment where
they are simply not possible at all.


> Think of this
> like a regenerative receiver that was breaking into oscillation. What you
> did could have been similar to turning the regen knob CCW till it wasn't
> oscillating. But is there enough regeneration left that might make the GK
> 500 final unstable under various tuning conditions and then under
> modulation?
>
>    What I and others said still might need to be considered. Look at plate
> dip, screen peak, and maximum RF output. If they do not ALL occur at the
> same point, then the PA stage might take off under certain conditions, kind
> of like a dog seeing the tip of his tail, and deciding to go for it, round
> and round.
>
>    Others have mentioned neutralization. This would be ideal, but WRL and
> Leo made a trade off to NOT do that. Doing so now might be a bigger project
> than what you want to take on.

that occurred to me also.  You might be into modifying the grid input
to get the capacitor back to the grid out of phase.  But I don't know
anything about the GK tetrode rig so I'm out of my area.

73

Rob
K5UJ


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