[AMPS] L-4B grid ckt shorts

[Rich Measures]

>Oh Powerful Reflectees:
>
>        Ok I am now stymied. I replaced the 1-ohm 10w resistor and the
>multimeter that blew. 

Which 1 ohm 10w resistor blew?

>Put new tubes in it, and it came right up working
>fine. Could not determine for sure if one of the 3-500Zs had a fil-to-grid
>short or not.
>
If you see anode/plate current  on standby, you probably have a grid/fil. 
shorted tube. To determine which tube, test one at a time.    

>        But after 20 hours or so, again in standby mode, the same
>fizzle-bang and blown meter. This time also popped one of the 2 240v ckt
>breakers in the ps.
>And again I cannot be sure of the failure mode. 

IMO, 3-500Z filaments gets bent by an unusual event.  

>I think it is odd that this
>has suddenly happened twice, with 2 sets of tubes, 

I have heard about Henry 3K-A amplifiers that grid/fil. shorted four, 
new, Eimac 3-500Zs in the same week.  

>and I wonder if anyone
>has experienced this on their L-4B and might have found the cure.
>
>73 de Jim, KF7E

What kind of parasitic suppressors are you currently using, Jim?  Do you 
have a dipmeter?  Do you have access to a high-pot?
Rich---

R. L. Measures, 805-386-3734, AG6K   


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