[Drake] L-7 vs. L7-PS failure

[k8wbl@wb8nut.com]

>Hello Torrey, yeah thats the infamous "glitch" resistor....you might want
to read some of Rich Measures info on it....  http://www.somis.org/  I
think he makes a good case to use something larger like a 10 ohm  7 watt
ceramic wire wound resistor...anyways...good luck...Tim   K8WBL

 Good evening all.
>
> As I was tuning up my L-7 amp this evening there was a very loud bang and
> a visible flash behind the plate voltage meter on the left.  Foolish or
> not I reset the power supply circuit breakers and tried again with low RF
> drive.  Same story again.  I took the top of the L-7 and could see no
> evidence of arcing or burned components.  Final tubes and attached
> resistors look normal.  In short, everything looks normal topside.  I have
> not removed the bottom panels to look.
>
> The L7-PS power supply reveals charring and a burn-through of the R12
> resistor (2 watt 0.82 ohm IRC type BWH).  The charring put a big black
> mark on the adjacent large tubular capacitor, but the capacitor does not
> look damaged and all the large resistors across these capacitors appear
> intact.
>
> The R12 resistor appears to function as a protective fuse in the high
> voltage output line.  Am I thinking correctly?  If so, where could such a
> impressive short circuit have occurred in the linear amplifier without any
> evidence of damage topside?  I may have to send both units out for repair,
> but I certainly would like to avoid it...given all the weight, 3 boxes,
> etc.
>
> Are the R12 resistors hard to find?  Hope not!  Specific recommendations
> for L-7 repair?
>
> Any thoughts or help will be most appreciated.
>
> Thanks,
> Torrey N9AUJ
> cell 515-778-2354
>
>
>
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