The method requires that you know the input and output impedances of the
the tube (I think you are talking about tube amplifiers?)
Then you put non-inductive resistors of the appropriate values in place
temporarily. So, for example, if the plate impedance of an amplifier
when operating properly is 2000 ohms, you put a 2000 ohm resistor from
plate to ground. Then you connect the analyzer to the output of the
amplifier (you might need to bypass a relay) and adjust the amplifier
tuning for lowest SWR. 1:1 means that you have matched the 50 ohm
analyzer to the 2000 ohm plate impedance.
Once matched you can look at the capacity required in the tuning and
loading caps and estimate if the Q is reasonable.
You do something similar for the input circuit. You leave the tubes in
place but of course no power is applied.
On 4/5/2014 12:05 PM, Paul Decker wrote:
Hello amp builders,
I've been attempting to convert some commercial vhf and uhf
amplifiers over to the ham bands. The gear operates in the 150 Mhz
and the 550 Mhz range.
Someone a while back said I could use one of the fancy impedance
analyzers to tune the input and output circuits. I'm wondering if
this really works? Before making any changes, I tested the input and
output circuits, and the best "match" the analyzer could see was a
6:1.
What am I typically supposed to see when using this method? Does
this 6:1 imply resonance? Does the input and output change that much
when voltage is applied to the tube?
thanks in advance,
Paul, kg7hf
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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