[Amps] LK500ZB (2 x 3-500Z), most likely cause of zap/arc?

[Carl]

Glad you found it. The LK-500's arent prone to parasitics unless the 
resistors radically changed value. My ZC has been through countless hours of 
contesting and DXing since 1986 and still has original tubes and 
suppressors. No voodoo nonsense required.  Some of those Teflon disc caps 
just cant handle RF current well and I replaced mine with a pair of ceramic 
doorknobs around 87-88.

Dust around HV is always a problem. The 3-500 is prone to gas and should get 
some bright red workouts on a regular basis. Having some glass (and a few 
external anode) tubes unused for many months or years is not conducive to 
long life.

Carl
KM1H




>> Thanks all for the good advice, on- and off-list.
>>
>> Closer inspection shows a new-looking crack along the edge of
>> the HV bypass cap at the bottom of the plate choke. Also,
>> that area is very well coated with accumulated dust. I will
>> kick myself for not cleaning it up at the outset.
>>
>
> And thanks again. The cracked bypass cap was a red herring but I replaced 
> it
> anyway. It was arcing across the plate blocking caps where there was a
> distinct carbonized trace situated just where it was hard to see until I
> bent them around to get a closer look. The suggestion Carl made to look 
> for
> marks left by the arcing was key...I couldn't find a mark anywhere else. 
> Amp
> works fine now after replacing the caps. No idea what may have caused the
> first arc. Dust buildup, parasitic, ???
>
> I may have lost the grid current meter on the last bang. It's not reading 
> in
> either Vp or Ig position. It's pretty well protected and hopefully I'll 
> find
> it's just a bad connection, but...we'll see.
>
> 73, Carl WS7L
>
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