On Wed, 03 Mar 1999 01:04:50 -0500 Ron Rollinson <ronr@nowonder.com>
writes:
>
>Hi folks, I've only been subscribed to the list for a couple of days
>but I
>can tell there is a lot of knowledge floating around here regarding
>amps.
>I don't know if it's related in any way to me subscribing to the list
>but
>the other day, there I was on 20 meters cw when my Dentron 160-10L
>(4-811a's) made a loud bang and popped the breaker in the back of the
>amp.
There are at least 2 different PS xfmrs used in that amp which was
available with either 811A's or 572B's. If you have the 572B xfmr or the
other one with a tapped secondary and run 811A's at 2500V you will have
lots of tube problems.
>When I opened it up I noticed one of the tubes appeared discolored and
>in
>the process of removing it the parasitic resistor in the plate line
>easily
>broke in half. One thing I noticed is that this particular resistor
>must
>have been replaced previously but a carbon resistor wasn't used,
>instead it
>looks like one of those metal film tv type resistors... Anyway, the
>damage
>is done,
Get a set of 4 new suppressors from Ameritron for their 811H amp.
For long term reliability, even on the low HV tap, go to 572B's.
ne tube is shot, and there appears to be a problem with the
>plate
>supply, I'm only getting about 1000 volts and a weird buzzing noise.
Sounds simple.
>I'm
>sure I can troubleshoot the plate supply and get it running again but
>while
>I've got the thing apart I'd really like to do some mods to it (Step
>start
>for one).
A waste of money. The PS and tubes can handle the inrush with no problem.
Since I've seen very little disussed here about 811A amps I
>have
>several questions. Should I consider updating the parasitic
>suppression in
>the plate line (could this be what fried my amp to begin with)?
Could be the other tubes are already pretty weak and the one was doing
most of the work.
Are
>there
>any other things I should consider doing such as grid current
>protection,
>high speed t/r switching, etc?
A HV surge resistor would tend to save tubes during an arcing condx. A
vacuum relay t/r setup would be nice if you use VOX CW but that is not an
amp to sink a lot of money into.
I actually kind of like this amp but
>I've
>been unable to find anything in back issues of QST or on the net as
>far as
>mods or updates.
It was the predecessor to the Clipperton L .
Any advice or info on this amplifier would certainly
>be
>very much appreciated!
GL Carl KM1H
>
>73, Ron NR8O
>
>
>
>--
>FAQ on WWW: http://www.contesting.com/ampfaq.html
>Submissions: amps@contesting.com
>Administrative requests: amps-REQUEST@contesting.com
>Problems: owner-amps@contesting.com
>Search: http://www.contesting.com/km9p/search.htm
>
>
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