[AMRadio] GK500 OTA almost


Don Rasmussen don.kd2fo at gmail.com
Thu Jan 5 22:34:03 EST 2017


Further Note.....I just wrote suggesting neutralizing the final of the
GK-500.    IF there is NOT a neutralizing capacitor installed on your rig,
please see the ARRL Handbook (older issues) to see where to place a
neutralizing capacitor on grid driven amplifier projects.....this could
well save the day for an amplifier that is "a little unstable" !

73, Don KD2FO

P.S. - Vacuum tube Heathkit AM Transmitters Just used a Wire sticking up
through the chassis (insulated from chassis - of course) up fully along
side the final tube, which could be bent back and forth for proper coupling
to the tube plate....inside the envelope.      This forms a nice
neutralizing capacitor for many TETRODE FINALS.....which require less
neutralizing capacity than triode finals !

On Thu, Jan 5, 2017 at 10:21 PM, Don Rasmussen <don.kd2fo at gmail.com> wrote:

> I believe you may need to NEUTRALIZE the final.     Any grid driven Class
> C final will need to be neutralized.     Sometimes you can avoid
> re-neutralizing going to new final , but maybe not.
>
> To neutralize you need to REMOVE BOTH PLATE & SCREEN VOLTAGE.....then
> listen with a sensitive device coupled to the GK-500 plate circuit, while
> applying normal grid drive.....up o the 10 or 15 meter band.      There is
> a neutralizing capacitor which should be tuned for MINIMUM RF
> "FEED-THROUGH"​ on your sensitive device (i.e. rcvr s-meter reading)
> coupled to the temporarily disable RF plate circuit.
>
> When the procedure is finished , re-connect both PLATE and SCREEN
> vooltages to the tube for normal operation.
>
> CAUTION.....IF PLATE VOLTAGE IS REMOVED WITHOUT DISCONNECTING SCREEN
> VOLTAGE.....YOU WILL BURN UP THE SCREEN INSTANTLY.
>
> I am the owner of a GK-500A (currently running a 4-400A) and you have my
> opinion.....even if there is some other issue, for best NON-OSCILLATING
> operation of the final.....it SHOULD BE NEUTRALIZED.      A badly out of
> neutralization final will OSCILLATE.....it sounds like this is possibly
> your problem.
>
> 73, Don KD2FO
>


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