[AMPS] L-4B

[w8jitom@postoffice.worldnet.att.net]

> To:            amps@contesting.com
> Date:          Mon, 8 Sep 97 12:43:48 +0000

>         Don't see much commentary on the L-4B, but mine just cratered. Was
> in standby when a crack and long fizzle sound came out of the RF section.
> The grid resistor opened up, and the meter needle pinned to the left
> (minimum) direction. 

Most likely a tube arced internally Jim, although it's tough to say 
for sure.

What grid resistor opened up?

> Since the tubes were biased off at the time, parasitics don't seem likely,

Even if the tubes were biased on, a parasitic doesn't seem likely. 
Systems are either unstable, or they are not. Even a parasitic won't 
make an otherwise good tube arc.

> and I ohmed the tubes and see no shorts.

The arc will sometimes "getter" the tube, or remove the debris 
causing the arc, IF that is what happened.

But an ohm meter will often never detect a shorted or gassy tube, 
since it can be voltage breakdown related.

>         I had a diode stack go out on this unit once, but never had a RF
> section pronlem in the 12 years I've had this amp.

Where is the blown resistor located?

 
73, Tom W8JI

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