How did they get away with the plate bypasses so far away from the cold end
of the rf choke, and the cold end of the rf choke so close to the plate
tank? Luck?
Make sure that teflon-tubed wire from the hot end of the plate choke to the
plates is nowhere near the choke windings. Mine arced, melted the ptfe, and
burned the choke windings.
Open up the power supply and make sure the resistors across the caps are all
the same value, 150K for all but one in mine. It was 150 ohms, not 150K.
It survived the cap with which it was paralleled. The resistor was taking
the startup-current surge and repeated I x R spikes finally took out the
cap.
It might be well to parallel the traces to the soft-start resistor with #14
wire. Mine vaporized with an outstanding BANG.
Now that I'm aware of the soft spots, I can buy the next 425 with
confidence, as long as the tubes are good ;o)
73 Dave N3HE
----- Original Message -----
From: "Ron Castro" <ronc@sonic.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Thursday, October 25, 2007 7:49 PM
Subject: Re: [TenTec] K4VUD & Titan 425
I don't know about the rant, but the technical problem seems to be the
voltage rating of the ceramic disk capacitors used to bypass RF on the HV,
which are located on the meter shunt board. IIRC the original caps are
rated at 3 kV, which is fairly close to the working DC voltage. Mine blew
up because they were too close to the chassis, and I could see the burn
marks where the arc happened. I replaced the caps with 6 kV units and
have
had no problem after 6-7 years. Charles mentioned that he will be using
10
kV caps which will give him an extra measure of safety.
SNIP
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