[AMRadio] GK500 OTA almost


Collin n4tua at aol.com
Fri Jan 6 13:31:58 EST 2017


I am reluctant to reinvent the wheel so to speak. It is working and making much RF. I will investigate a little better as I go with the scope and the watt meter. 

I am not sure how to add neutralization to this rig. 

The plate current moves up and down smoothly and equally as I rock the tune capacitor back and forth from resonance and the screen current peaks at resonance and and dips on either side. Much unlike it was doing. 

Good Day, Collin

> On Jan 6, 2017, at 12:46 PM, Rob Atkinson <ranchorobbo at gmail.com> wrote:
> 
>> 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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