Mike, the resistor at the bottom end of thos caps is listed as R-10 but the
manual does not list it at all. The one that is in mine is a 2 watt 100 ohm
with wire wound around the outside and the impedence is of course like .1 ohm
...is that what you have there?
Tim
--- On Sat, 3/19/11, Mike Baker <k7dd@cox.net> wrote:
From: Mike Baker <k7dd@cox.net>
Subject: RE: [Amps] Dentron amplifier problems
To: "'Tim Kass'" <k8wbl@yahoo.com>, amps@contesting.com
Date: Saturday, March 19, 2011, 11:59 PM
Hi Tim,
I have one as well.
First, disconnect the high voltage output from the transformer and make sure
the AC output is where it is supposed to be.
The supply uses a voltage doubler so the output from the transformer should
be about 635VAC. IE: 1800V X .707 divided by 2. Or, 636 X 2.814.
The resistor at the bottom of the string of caps to ground has an unknown
value but if it is open then the voltage should be half.
With only 1KV output I am thinking bad caps. They aren’t exactly Hi Spec
parts to begin with so if you replace them use something larger in value.
Say 450MFD @ 450V and 85C operating temp rating. There is usually a guy on
E-Bay that sells them fairly reasonable. He in in China/Taiwan ??
Check the value of the individual resistors that make up the voltmeter
string as well.
IF, the transformer is doing its thing then you at least have the biggest
fear behind you. Everything else is easily replaceable and serviceable.
Sounds like you are headed in the right direction and I have done exactly as
you have done already to mine except I used 6A10 diodes and mine has 4 572B
tubes. If a set of those becomes available for a reasonable price you might
just want to grab them. You could just plug in two 572's and have the same
plate dissipation with half the heater current. It matches up pretty well at
the input but a WD7Y input board is a nice improvement as well.
Once you have it cooking like normal, you might want to get rid of the
crappy, noisy, slow antenna change over relays and go with the mod done by
NE7X, Tom. Check his web site. He used 3 vacuum relays and a sequencer board
made for the job. That is my next upgrade. About $260 for everything new.
Less if you have the relays and just need to change out the 24V coils for
12V coils. $22 each for the coils from MaxGain Systems. The relays are
available NEW from Gigavac for $69 each.
OK good luck and keep us posted on your progress.
Best 73,
Mike K7DD
K7dd@cox.net
Mike Baker K7DD
K7dd@cox.net
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Tim Kass
Sent: Friday, March 18, 2011 1:26 PM
To: amps@contesting.com
Subject: [Amps] Dentron amplifier problems
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@contesting.com>
Subject:
[AMPS] My dentron 160-10L
From:
ronr@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
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