Evan,
You may be right on the cold solder joint on one of the feed-thrus.
I remember it was a tricky soldering job on that stiff enameled wire
from the RFC, even with a 140 watt weller gun. Crimp solder lugs
probably would have been a good idea in hindsight. It seems unlikely
that solder would melt out of the pins on two tubes at around the
same time, but most anything is possible. Sure hope it wasn't
sequential failures as you mentioned
I'm clearing the bench of a couple of "works in progress" to make
room for the amp. I'll take a look tonight and report back on what I
find
Many thanks
Rick
On Oct 25, 2009, at 10:23 AM, k9...@aol.com wrote:
Rick,
That is a strange one. If you have the panel lights that does show
at least some energy is coming out of the filament circuit. You
might look for cold solder joints on the feedthrough caps. I
suspect a visual inspection might reveal something on the underside
that is obvious. I've never seen two filaments open
simultaneously. I have seen "sequential" failures of 3-500 tubes
where one has a failed filament and then the user attempts to load
up the remaining tube to full input, not knowing the one tube has
failed. So look for circuit elements that are common to both
tubes. Please keep us posted so we all can learn from this.
73,
Evan
-----Original Message-----
From: Richard Radke <rar...@excite.com>
To: drakelist <drakelist@zerobeat.net>
Sent: Sun, Oct 25, 2009 10:55 am
Subject: [Drakelist] L4B Question
All,
I was working the CQ WW DX Friday night (C line and L4B) on 40,
picking up a couple "new ones", cndx here were just so,so. All was
well, shut down. Resumed Saturday morning,
20 sounded in great shape. Tuned up the twins on the new band,
kicked in the L4B, and nothing. Amp turns on, no smoke, meters
light, but tubes are dead. HV present (1900 and 2600 volts).
I installed Mike's upgrade kit 2 years ago, with new bleeders, in-
rush protection, and additional cooling. I replaced the feed-thru
caps last year because of a gird current issue. It's been working
well, putting out about 1300 watts into a dummy load.
My question is. What are the chances of both tubes going at the
same time? In looking at the schematic, the panel lights are on the
same side of the filament xfmr as the tubes. Assuming if the panel
lights light, I've got voltage out of the xfmr. One or both of the
feed-thru caps or filament choke? Those are pretty robust
components, rated at 20 amps (if I remember right) and very hard to
find and get out. I can probably build the choke if needed.
Any thoughts on what to be looking for before I dive in?
Rick
W9WS
_______________________________________________
Drakelist mailing list
Drakelist@zerobeat.net
http://mailman.zerobeat.net/mailman/listinfo/drakelist
_______________________________________________
Drakelist mailing list
Drakelist@zerobeat.net
http://mailman.zerobeat.net/mailman/listinfo/drakelist
