[TenTec] Help with blown Titan 425

[Dr. Gerald N. Johnson]

On Fri, 2007-04-06 at 03:49 +0000, Dave Heil wrote:
> Rick, W6RKC wrote:
> 
> > 
> > R1, the series plate resistor however is really weird. The 10 ohm 25 
> > watt resistor now reads almost 8000 ohms. Also, there is a big black 
> > carbon spot on the back of the TUNE capacitor where it arced on the 
> > HV input side of R1.
> 
> Rick, I've had R1 go before.  I replaced it with one with a heavier 
> wattage rating mounted diagonally from one of it's former mounting
> insulators with a heavy copper wire lead directly to the end of the
> plate choke.  I've had no problems since.
> 
> 73,
> 
> Dave K8MN

That 10 ohm resistor hasn't much drop at normal operating, maybe ten
volts peak. Might part of its function besides limiting peak arc current
in a tube be to act as a fuse? I know smaller resistors have been used
that way in transmitters. If so replacing it with a higher power rating
may prevent it acting as a fuse. Even using a metal film in place of
carbon composition or wire wound may negate the fuse function. No
matter, keeping it physically isolated from grounds is necessary because
no resistor insulation is good for PA plate voltage.

-- 
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer