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need input tuning capacitor info

G

groundwire

Sr. Member
Jul 19, 2014
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hey guys, i have a new texas star dx1600 (sweet sixteen) with hg transistors and i want to replace the fixed value input tuning capacitor with a variable capacitor so i can tune the high input swr as flat as possible. the input swr is to high for my liking when the amp is on, i need to know which one it is. im not an amp guru so i need help with this one. i put a parts layout with numbers so you can see. thank you for all your help...
 

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C2 is a DC blocking capacitor. It is not the input tuning capacitor.
Even looking at the parts layout diagram, I spotted the input and output tuning capacitors.
But it is easier to initially find it on the schematic.

Groundwire, I'll be glad to help you. I'm just trying to get you to look at it and the schematic to figure the path of the incoming RF signal.
(hint) .... The input and output tuning capacitors are in the circuit between the RF signal path and ground.
 
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groundwire said:
hmmm, for the input tuning cap, if it is before the toroid splitter i would guess C3?
for the output i would guess C54,C55,C56 in series caps?
Click to expand...

That would be a correct guess.
One of these will work.

https://www.rfparts.com/463.html

https://www.rfparts.com/capacitors/capacitors-certrimmer/capacitors-46series/464.html

https://www.rfparts.com/s464.html (TAKE THE BRACKET OFF)

I have found that about 140pf silver mica on the 1600 works out most of the time on the input. (USING A DUMMY LOAD)
 
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Ranch55 said:
C2 is a DC blocking capacitor. It is not the input tuning capacitor.
Even looking at the parts layout diagram, I spotted the input and output tuning capacitors.
But it is easier to initially find it on the schematic.

Groundwire, I'll be glad to help you. I'm just trying to get you to look at it and the schematic to figure the path of the incoming RF signal.
(hint) .... The input and output tuning capacitors are in the circuit between the RF signal path and ground.
Click to expand...
I would not suspect a lot of DC on that line from a properly working radio. But you are right. the caps around the torrid splitter is where the impedance changes.
 
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Tallman said:
I would not suspect a lot of DC on that line from a properly working radio. But you are right. the caps around the torrid splitter is where the impedance changes.
Click to expand...

I wouldn't expect much, if any, DC at that point either. You could remove C2 capacitor and install a straight jumper wire, and I would expect the amplifier to operate just fine.
 
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