[TenTec] Centaur Tubes odd ones in parallel

[Rick - DJ0IP / NJ0IP]

Hi Stuart,

I couldn't find the article you were referring to.
Can you give more details or perhaps better words to search on?

What is really needed here is a means of adjusting the idle current of each
tube individually. I have never come up with a way of doing that with
grounded grid triodes.

With sweep tube amps, I was able to accomplish this by using a diode string
in the bias voltage.  Then each tube was tapped to the appropriate junction
between two diodes, enabling me to set the idle current of each tube almost
exactly the same.  This equates to a static matching of the tubes; not quite
as good as dynamic matching but far better than doing nothing at all.

I see no way to implement this with triodes in grounded grid, short of
giving each it's own filament supply and giving each a combination of Zenor
diode and diode string.  In other words, I can't think of any means to match
unmatched triodes in the Centaur.

73 - Rick, DJ0IP
(Nr. Frankfurt am Main)

-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Stuart
Rohre
Sent: Tuesday, March 31, 2015 11:48 PM
To: tentec at contesting.com
Subject: Re: [TenTec] Centaur Tubes odd ones in parallel

I think QST had a piece on balancing tube emission characteristics.

That would probably let you match them "close enough".  If they were made
pretty close to the drawing for standard tube of that type, likely you could
operate them although of differing brands.

You could also back off on operating the tubes at maximums, and extend their
life even if exactly matched.

Stuart Rohre
K5KVH
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