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[Amps] Emtron DX3sp

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Subject: [Amps] Emtron DX3sp
From: Thomas Carlsson <thomascarl@gmail.com>
Date: Tue, 2 Feb 2016 13:17:54 -0200
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Any help or comment would be appreciated.

The 6 x 100 ohm HV protection resistors burned some time ago and have been
replaced by same type as well as a 3A fuse put in series with them, to
change fuse instead of resistors.
During CQWW160 the 3A resistor started to burn, 1st time just changed it
but burned again. Checked the tubes and one had ratteling grids, changed
the tube and tuned the Bias(es) and it worked OK for long time but after
the contest burnt again. Of course, this may be a flash over in one of the
tubes, but how to find out which one?

I have another indication that may affect this. Tuning on 160m is very odd.
At full or almost full drive (indicated by Ig2) Tune and Load capacitors
have very little effect, on 80m and higher, the tuning is normal, so I kind
of suspect that some of the Padding Caps has gone by west 470 or 1500 pF.
The 1500 seems to be 2 x 750pF and on one of them the green paint is
totally gone in a diameter of about 3cm around the terminal screw, this may
have been caused by heating. This may explain the tuning problem and also
may be - the flash-over. The cap may momentarily flash over causing hi-A at
the HV.

Any comment and thoughts are welcome, please.

73,
-- 
Thomas, PY2ZXU/SM0CXU
Member of the PW2D Team
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