-----Original Message-----
From: measures <2@vc.net>
To: Tom Rauch <W8JI@contesting.com>; AMPS <amps@contesting.com>
To: <amps@contesting.com>
Date: 04 August 2000 06:14
Subject: Re: [AMPS] SB1000 parasite question for Tom and Rich+
>
>>
>>> Rich it seems to me that one way to reduce vhf gain would be not to use
>>> tubes ( very expensive ones) that have max. ratings to 500 mhz on
>>> frequencies of 30 mhz or below. if it will amplify at 200 mhz it should
>>> also oscillate.....yes?? HANK
Hank,
An important factor (maybe the most important factor) in whether a g-g amp
is stable is whether the grid is at rf ground. Once it is not, feedback
increases and instability becomes more likely. Inductance in the grid
circuit controls how well the grid is grounded. A VHF tube has much lower
internal inductance than a glass tube, so it is capable of being more
stable. That's not the same as a guarantee of stability. If the tube has
gain at 200MHz, the designer must ensure that the circuit loads the tube up
to that frequency so as to avoid oscillation. I would expect that to be an
easier task than trying to tame something that wants to go off below 100MHz.
Steve
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