|[AMRadio] GK500 OTA almost|
jcandela at prodigy.net
Fri Jan 6 07:06:34 EST 2017
I am glad you made progress. Is it really fixed though? 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.
The neon bulb trick is handy here. Anytime it goes from orange to violet you have VHF/UHF energy present.
On Friday, January 6, 2017 4:53 AM, Rob Atkinson <ranchorobbo at gmail.com> wrote:
Glad you got it working Colin & hope to hear you on the air with it.
Hope the audio is smooth sailing also.
On 1/5/17, Collin <n4tua at aol.com> wrote:
> Great Day, we got it. I believe the GK500B is behaving now. It was parasitic
> oscillations and Rob hit it right on. I should have tried that first. Took
> two 240 ohm two watt carbon resistors from the junk box. Didn't have any 200
> ohm. Paralleled them and wound 4 turns of wire around and replaced that
> copper strap with my new lash up. Now she tunes very smooth and predictable
> with NO arc/flash and no wild uncontrollable plate current. There may well
> be other GK500s out there that would benefit from this simple and cheap
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