[AMRadio] GK500 OTA almost


w5jo at brightok.net w5jo at brightok.net
Tue Jan 3 10:01:42 EST 2017


When things are right with the RF deck a parasitic suppressor is not needed 
on the plate of the final tube.  The design by WRL did not use one.
There is one on the plate of the driver, a 6146.  What is the condition of 
that one?

Is there any evidence of burn marks or arcing of the RF choke feeding the 
plate of the tube.  Is there a doorknob bypass at the bottom of the choke 
and one beside the input for the HV?  If so, what is their condition?
Do you know the condition of the tube itself?  Have you a spare 4-400 or 
even a 4-250 you can try?

What about the RF bypass capacitors, .005?  Any burn marks or cracked discs 
around the socket of the final?

The one I have tunes smoothly from 160 meters all the way up through 10 
meters.  Because of the size of the variable, it is delicate but it works.

Did you start trying to tune with the coarse switch in the #6 position and 
reduce it after the plate dips?  I tune into a cantenna before putting mine 
on the air and, when tuned that switch is in the #2 position.

Jim
W5JO



-----Original Message----- 


Well, I have had many great responses. Thank you all.
First of all some more info. I am testing using a cantenna dummy load with 
only the RF deck and the Power Supply deck lashed together with a  home-brew 
HV power supply made from parts of an old BC-610 PS. Rectifiers are SS and 
all of the rest of the PS is BC-610 parts. I am using a variac to dial down 
the HV to about 1800 vdc. I am monitoring HV as I go.
I am using a crystal and it is on 3883 kcs.
The final tank is stock. There is some problem with the coarse load switch 
but the problem contact finger is not being used.
Parasitic oscillations sound possible.  Now that I think about it there is 
NO parasitic choke. I will have to look at the schematic when I get back 
home to see if it is shown. It did not have one when I got it. My 2 meter 
rig nearby does occasionally pick up hash when key down on GK500.
I hope everyone who replied to my post can see all of the responses here. I 
will send my comments to the reflector so all can see.


Thank you, Collin





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