[AMRadio] GK500 OTA almost


w5jo at brightok.net w5jo at brightok.net
Wed Jan 4 22:41:17 EST 2017


You are and thanks for posting so everyone can see.

WRL documentation is sometimes terrible Collin.  Also there is always the 
possibility that the set has been "modified" by previous owners which can 
make thing more difficult.

I think I speak for everyone here, we are here to help if you want.

Jim
W5JO
Moderator


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


OK, Jim, I think I am posting with reply all. Here goes.

I had a few minutes to work on the GK500B tonight and checked the schematic 
again around the buffer amp plate circuit. One capacitor is not connected as 
it is shown on the schematic. Incidentally, the same capacitor on the 
crystal oscillator is misconnected the same way. Although, I don't think it 
makes any difference because that capacitor blocks DC from going through the 
coil in either position. I have the luxury of having a junker to compare 
with also and it is wire the same way as my keeper, different from what the 
schematic shows.

That is not the only problem I have found with this GK500B documentation. 
There are two resistors with different values that what the parts list 
shows. Both of these check out on my junker example also.

So, I did find what might be a poor ground on the bypass capacitor at the DC 
input to the plate choke. I have cleaned it up and reassembled everything.

Check these,
buffer amp parasitic choke and blocking capacitor
final amp DC input bypass capacitors (2) and plate choke
All look and test good.

Tomorrow evening I will fire it up again and note any changes in results. I 
hate to do to many things and fix the problem and then not know what it 
actually was that caused the problem.

Best 73rds, Collin






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