The 6146, by the way, is a very tough cookie. I have never burned one up
yet. I've replaced some when they probably didn't really need it, though.
I still have the originals in my 1981 TS-830 that I bought new. It has
withstood RTTY etc., and still go on as well as they ever did.
Phil
"Angel Vilaseca" wrote in message
...
Hi
I was recently given a TS 820 and I noticed it behaved strangely:
-output power was only 50 W CW instead of 100.
-one of the tubes plate (the final stage of the TS820 uses two 6146B
tetrodes) glowed red after a few seconds of xmitting.
- on the 40 meter band, when tuning for max RF out while watching the
built-in dial, you could reach 100 W output and even beyond, then the rig
fuse would blow. (I did this only once, before taking out a screwdriver
and
opening the rig, realizing that something was really wrong!)
I ordered a new set of 6146Bs and while waiting for them to arrive I
checked all components and voltages in the final stage ( not an easy task
when one knows how the 820 PA is built!). All were OK.
Replacing the 6146Bs with the new ones cured the problem.
Now I should be happy, since my rig is working again right? wrong! I would
like to understand what was going on when running with one of the tubes
bad.
-OK, putting 50 watts out seems only logical if one of the tubes is bad,
but
-why was one of the tubes plate glowing red?
-Was it the good or the bad tube? Which one of the two can I keep as a
spare?
-And why dit it glow red? Could it be that the grid could not stop the
electron flow and the power dissipated in the red hot plate was DC power?
Was it that RF from the good tube went into the bad, dissipating into
heat?
A more general question: how do the 6146B tubes fail tipically?
Do they fail quickly or progressively?
Is it because the grid melts?
what about the screen?
what about cathode emission?
what about secondary emission? I read that this was a common problem in
the
4CX250B, another tetrode.
What is the best parameter to monitor to see if the final 6146B tubes
start
getting tired?
Retrospectively I realize that i operated the rig for quite some time with
only one of the final tubes working! *blush* Could this have caused some
damage to the circuit? or spewed out a "dirty" signal?
73 de HB9SLV
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