On Dec 5, 2004, at 2:14 PM, Clay Curtiss W7CE wrote:
Thanks for the responses. I didn't think about an internal tube short
as a
possibility.
Hello, Clay -- An internal tube short makes very little sound. A loud
pop is in the atmosphere, not a vacuum
I removed the plate caps from the 3-500's and the HV measures
normal (2100V CW, 3100V SSB). Is it logical to assume that one (or
possibly
both) of the 3-500's has developed an internal problem
If the anode-grid leakage is <10uA @ 8kV, the vacuum is good. If the
grid-filament breakdown potential is >5kV, the tube should not short
when it is hot.
or should I be
looking for other causes as well, such as a bias supply problem. I
don't
have access to a hy-pot tester, but a simple resistance check from
filament
to grid on both tubes doesn't reveal a short.
Tubes with only a few kV of withstanding potential will grid-fil short
when hot, and this problem can not be detected with an ohm-meter.
One thing I didn't mention earlier (because I don't believe it's
relevant)
is that the small filament choke (L20) that connects to the filament
transformer center tap, has overheated in the past.
Since one of the tube
filaments came unsoldered from the pin (a simple soldering job fixed
it), I
figure all of the extra current flowing through the small choke was the
cause of that. Other than some discoloration, it appears ok.
Any and all suggestions are welcome. I don't want to risk my power
supply
by blowing more fuses trying to determine which of the tubes might be
at
fault.
Does the 922 blow fuses with the tubes removed?
73,
Clay W7CE
----- Original Message -----
From: "K7RDX" <k7rdx@earthlink.net>
To: "Clay Curtiss W7CE" <w7ce@curtiss.net>
Sent: Saturday, December 04, 2004 5:42 PM
Subject: Re: [Amps] TL-922A - Loud Pop, Blown Fuses
Hi Clay, pull the tubes and start the amp again. If plate voltage is
normal
and the fuse doesn`t blow again, shut everything down and inspect the
tube
sockets for burnt or damaged rf chokes from the three grid pins to
ground.
If one of the tubes flashed over, some of these chokes will probably
be
destroyed or at least damaged. 3-500z tubes sometimes develop a short
from
grid to filament after a period of use and will flash over on the next
start-up. If you have access to a hypot tester, a shorted tube is
easy to
spot...Hope this helps you find the problem...A flashover might
damage the
bias as well as the high voltage supply. 73,Jim.
----- Original Message -----
From: "Clay Curtiss W7CE" <w7ce@curtiss.net>
To: <amps@contesting.com>
Sent: Saturday, December 04, 2004 12:05 PM
Subject: [Amps] TL-922A - Loud Pop, Blown Fuses
Yesterday morning when I turned on my TL-922A, there was a very loud
pop
followed by blown fuses. I replaced the fuses, changed the setting
to
CW
to
reduce the B+ voltage and tried again. Similar result with several
smaller
pops and then blown fuses. I use a footswitch for T/R control and it
wasn't
depressed nor was I transmitting with the exciter when I powered up.
I
should also mention that I've heard a pop on power up two times
previously,
but neither time caused a blown fuse. I opened it up today for a
visual
inspection and see no signs of arcing or anything unusual.
Before I dig into this thing, has anyone else experienced this
problem?
Any
hints or suggestions to reduce the troubleshooting time will be
appreciated.
Thanks and 73,
Clay W7CE
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|