Rick -
No problem, better a dupe than not to the list! :-)
"Fire in the hole" is almost always a 'missing antenna' problem.
Mismatched PA tubes can cause neutralization problems, sometimes with
oscillation and fireworks. You don't say what MFJ tuner you have, but
is it actually rated for 250W? MFJs also have a habit of things melting
and/or coming apart over time. Don't forget that the coax also has a
connector on each end!
The relay coil is usually wrapped in a 'varnished cambric' tape,
red-brown fabric soaked in varnish, that is heat resistant. Does the
relay pull in ok? It is connected directly to the +250V bus, so a short
on the 'wrong' end of the coil could account for some fireworks.
Keep us posted!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com>
Richard Palmer wrote:
I have tried tuning her up only to find a disconnected coax ( 2 rigs
no switch ). But when it's connected... it goes into a 300w dummy
load. I do have to tune the antenna on air though. I noticed on your
great CD, while looking for a titanium cap, that the relay there is
wrapped in what looks like asbestos. I'm not certain mine is there...
should it be???
All three PA tube are Sylvania. I run Times LMR400 UF... it's new but
my old MFJ might be causing me problems. I bought it used over ten
years ago. It seems to be ok with 100w but maybe the Drake stresses it
out. That is on my have to replace next list. I'm not even going to
try it with the drake again.
Thanks everyone for the great ideas. When this get this sussed out
you'll be the first to know.
Rick Palmer
Sorry for the dupe Garry
On Fri, Aug 20, 2010 at 10:34 PM, Garey Barrell <[email protected]
<mailto:[email protected]>> wrote:
Richard -
The fact that it didn't tune indicates that perhaps the antenna
was either not connected (relay?) or wrong band? or bad coax, or
... Possibly arcing in the relay contacts or coil.
What is the BIAS current? It should be 100 mA, if it's now 65 mA
or so you may have lost a final tube.
Really not much to flame in the PA cage. You could get corona on
variable cap plates, again due to mismatch, but that is typically
an ozone smell. A parasitic could have fried one of the parasitic
suppressors on the PA plate caps. Are all three PA tubes from the
same manufacturer?
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com <http://www.k4oah.com>>
Richard Palmer wrote:
My TR-4 did not want to tune... it caught on fire that looked
like it was at the PA section probably around the relay. All I
could really do was grab switches and plugs faster than
anything I've done in the last twenty years.
The smoke was not the conventional electric smell. It was very
acid and burning. I sorta took in a nose full doing the above
and felt high, in a bad way. I just got around to looking at
it and can not find any burnt or distorted part. There is
absolutely no sign of soot or heat anywhere. Seeing this I
tried to tune her up again. I was getting a very solid 4.5 for
the plate current. Now it's only 3. Is it possible (likely)
that I "smoked" one of my PA tubes?
Thanks in advance,
Richard Palmer
KB8NXO
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