Re: [Amps] Drake L-4B PSU burned resistor

[R.Measures <r@somis.org>]

On Nov 1, 2005, at 3:09 PM, Alan Ibbetson wrote:

> In message <ac2be72401684c739d03a4198d0ddd80@somis.org>, R. Measures
> <r@somis.org> writes
> > The first things I would look at is the tubes, testing them for
> > filament-grid breakdown potential.
>
> No hi-pot tester here, but seeing as the valves are somewhat low on
> emission I might invest in a pair of new ones on my trip to CA next
> week.
>
> >   Next, I would measure the R of the VHF suppressor resistors.
>
> They measure OK.

So it's unlikely that you have bent filament helices in either tube.  .
> > This requires a larger resistor - such as a 10W surge protection type
> > of approximately 10 to 15 ohms.
>
> The 10 or 14 watt ones commonly available from the big UK supply houses
> are wire wound vitreous enamel types, with a maximum voltage rating of
> only 500 or 750v.

That rating is case to chassis withstanding potential.  Glitch service 
is a whole nuther ballgame.

> I guess I'll need several of these in series, not so
> much for the power rating as for a breakdown voltage safety margin.
> Messy, but just doable within the rather cramped confines of the L-4B
> PSU.

We buy surge-rated 120J, 15Ω resistors for our retrofit kits.  The sell 
price is $1.77.
> Thanks very much for all the helpful replies I've had, both on and off
> the list, and for the several offers of components. The ham spirit 
> ain't
> dead yet!
>
> --
>
> Cheers,
>
> Alan G3XAQ
> alan@g3xaq.demon.co.uk
>
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org

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