[AMPS] parasitics

[km1h@juno.com]

On Tue, 21 Apr 1998 14:47:54 -0400 "Kenneth D. Grimm"
<grimm@lynchburg.net> writes:
>Usually a lurker, I can't help but jump in here with an "amen" to your
>comments about arcs vs. parasitics.  The big "bangs" in my experience
>had to do with blocking caps letting go, HV connectors breaking down,
>etc.  My first and really most frustrating effort at amp building was 
>4
>811As.  I had managed to collect 16 of the bottles and thought I had a
>lifetime supply.  I foolishly watched while the plates turned white 
>hot
>and melted in a matter of a few seconds with no noise and no drive. 
>What was this demon that was destroying my tubes?  After sacrificing 
>all
>16 on the alter of the demon parasitic, I gave up on 811s and moved on
>to 813s.  No problems there with parasitics, but there were a few 
>bangs
>before I got the right components in place.  I'm not saying that
>parasitic activity can't be accomponied by sound and fury, just that 
>in
>my experience it was a silent killer.

Well Ken, I just had that experience yesterday. Put a new set of Svetlana
572B's in a otherwise fine SB-200 and watched them light up and go white.

Must be a bad case of internal gas since after the fact the tubes had a
fine coat of gettering material. Put in a new set of Chinese and the amp
is running a stable 800W.

73  Carl  KM1H 

>
>Ken K4XL
>
>km1h@juno.com wrote:
><a bunch of stuff snipped> 
>> Even an out of control parasitic will not cause a bang initially. 
>The
>> tube will run away, the plate current will soar and the tube may 
>fail but
>> this takes several seconds from start to finish and is usually a 
>silent
>> process in the vacuum of the tube. The bang in this case is usually 
>a PS
>> path failure.
>> 
>> 73  Carl   KM1H
>
>-- 
>Ken K4XL
>grimm@lynchburg.net
>Boatanchor Manual Archive - ftp://198.28.36.115/pub
>
>

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