H. M. 'Puck' Motley W4PM wrote:
>
> I mistakenly deleted the message from the fellow about the Centurion
> problem so I'm sending this to the list.
>
> I appears that the bias cutoff circuit has failed and is not cutting off
> the amp in the standby mode. The components for this circuit reside on
> the 81537 Filament-AC board and consist of:
> D1 1N5344 8.2 V Zener
> Q1 2N3055
> Q2 MPSU01
> a 30 V MOV
> That's what in my Centurion which is serial no 40A10072 (April 1992).
> Most likely the Zener and/or the MPSU01 transistor have failed.
>
> The purpose of the circuit is to apply a slight bias to the tube to cut
> if off in the standby mode. If the tubes are not cut off they will draw
> 100 ma or more or current. At 100 ma and 2500 volts, that's 250 watts
> being dissapated with nothing going on! That will warm up the cabinet
> quite nicely!
>
> 73,
> Puck, W4PM
>
> --
Puck,
I had a problem with my bias cutoff board when I first get my Centurion.
Since you bought yours in '92, they have had several revisions to that
board and put in some beefier components (Rev C sticks in my mind). If
that is indeed his problem, I would call Ten Tec for the latest
component types/values before I got an exact replacement for the
existing part(s).
Also, the way he is describing the problem, it may be more than the
cutoff circuit. When my board failed, I read some plate current, but the
tubes certainly weren't glowing!!!
GL
73/Carter/K8VT
--
FAQ on WWW: http://www.contesting.com/tentecfaq.htm
Submissions: tentec@contesting.com
Administrative requests: tentec-REQUEST@contesting.com
Problems: owner-tentec@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|