[Amps] Dentron amplifier problems

[Tim Kass]

Hello Group... I took over this project just recently when I purchased this amp from Ron, NR8O ..  here is his original post...amp has apparently been sitting since that time..
 

[AMPS] My dentron 160-10L




from [Ron Rollinson]
[Permanent Link][Original]




To: 
<amps at contesting.com>

Subject: 
[AMPS] My dentron 160-10L

From: 
ronr at nowonder.com (Ron Rollinson)

Date: 
Wed, 03 Mar 1999 01:04:50 -0500




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.
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, one 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.  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).  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)?  Are there
any other things I should consider doing such as grid current protection,
high speed t/r switching, etc?  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.  Any advice or info on this amplifier would certainly be
very much appreciated!

73, Ron NR8O

I have since replaced the bad 811A, which likely shorted out...replaced the RF choke with a larger AL-572 choke and also a new harmonic supression board on top of the 811A's.. close fit..replaced the glitch resistor with a 10 ohm 10 watt variety... replaced the 1 amp diodes with 3 amp 1000 PIV jobies but still only getting 1000 VDC out.. brought up the amp slowly as well with a variac.  There have been some mods to this amp as well.  Someone replaced the meter switch with a 3 position switch and, according to Ron, was a by-pass switch.  I removed the wire on this as to try to make this original to the original schematic and go from there.  Now... at this point I think I have to consider checking and/ replacing the electrolytic caps... could some of them being open cause this low voltage situation or could it possibly be a problem with the primary transformer (heaven forbid) and costly..   Thanks for any input into this project.
 
73, Tim K8WBL