Alan Ibbetson wrote:
>I recently got a Drake L-4B amplifier. I've been using (abusing) it a
>couple of weeks on CW on the high voltage SSB position. Pretty much
>everybody seems to do this. After all, it's only running 2500 volts on
>the anodes and they just glow a dull red when I'm keying.
>
>Yesterday, in the middle of a QSO, the short circuit protection resistor
>(R12) in the power supply gave an impressive firework display and
>expired.
>
>
>
That happened to me last year - caused by a bad tube. I sent the tubes
to Rich Measures for his hipot service ;-) One of the tubes had a
filament-grid BD potential of around 2000V (it should be 6000V or
higher). I replaced the tube and no more problems.
>Second question: the manual is very explicit that only an IRC type BWH
>resistor should be fitted. Can someone help with a translation of what
>this specification means, so I can buy an equivalent here in the UK?
>
>
Hunt for the type Mr. Measures mentioned earlier: "10W surge protection
type of approximately 10 to 15 ohms"- you are looking for the
equivalent of a high voltage fuse. BWH was probably the best option
available at the time (I can't say, my L4 was built before I was born).
I'm not sure where you can find the type of resistor he recommended -
but if you find a source, let me know because I would like to buy a few.
73 Jason N1SU
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