[AMPS] 572s and Yeasu FL 2100

Tom Rauch W8JI@contesting.com
Fri, 8 Sep 2000 22:24:17 -0400


> Does anyone have a procedure for neutralizing the FL 2100?  My amp needs
> the tubes replaced and I was thinking of using the Svetlana 572B's.  I
> read that they recommend the mod even if your using the same brand of tube
> that it came with.  I do not want a band aid fix.

Hi Bert,

The Svetlana tubes have a high percentage of tubes with low 
breakdown voltage. Keep that in mind.

The Svetlana tubes also have slightly higher than normal cutoff 
bias. The FL2100 will not cut them off, and they will oscillate when 
the amp is higher bands in some cases and the relay is not closed.

You can add bias voltage and cure that problem, but what I'd do is 
rewire the bias system or add an additional relay in the filament 
center-tap return to open the center tap when the amp is unkeyed.

This relay would ideally be a slow make (15-20mS), fast break 
(break time<10 mS) relay. So you would want to plan accordingly.


73, Tom W8JI
w8ji@contesting.com

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