[TenTec] K4VUD & Titan 425

[David J Windisch]

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 at sonic.net>
To: "Discussion of Ten-Tec Equipment" <tentec at 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