All,
I appreciate everyone's comments and advice. Unlike some lists groups that
I have subscribed to in the past, this group's participants are extremely
knowledgeable and quick to respond in a time of need.
UPDATE: When I arrived home today, based on all of the advice, I pulled the
tube and measured the resistance between the grid and filament. At the
time, it was wide open. Considering that this could be a heat caused issue,
I reseated the tube, powered up the Amp, verified 150ma Ip present, and gave
the tube a slight tap. This produced a fluctuation of the Ip from 150ma
down to almost 0ma returning to 150ma. Leaving the Amp powered up, I
verified the bias circuit was at least producing voltage. After this, I
powered down the amp, waited for the caps to dissipate and the tube to cool
off. Once cooled, I unseated the tube and again measured the resistance
between the grid and filament. This time it measures a dead short between
the two. It looks like I am a certified victim of recent Amperex "common
occurrence" trending.
HELP: Hopefully my last question regarding this amp. Given that this is a
common occurrence for the Amperex 3-500Z tube, I do not plan on replacing it
with another one. So my dilemma now is what flavor of 3-500ZG tube is the
best fit for the AL-80B? I hear it is a toss up between the 3-500ZG-RFP and
the 3-500ZG-TAY. Your input would be greatly appreciated.
Thank you,
Mike
W5CUL
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Scott Manthe
Sent: Saturday, August 26, 2006 12:06 AM
To: amps@contesting.com
Subject: Re: [Amps] AL-80B Trouble
Rich,
Hundreds of empirical observations from all makes of amplifiers must be
wrong. Clearly, the problems must be the mysterious parasitic
oscillation, which obviously is pushing the filament sideways. Thank God
I'm not an expert, so I don't have to debate you on this very tired and
worn-out subject. Please feel free to tell Mike your interpretation of
his problem- we are all waiting with bated breath.
73,
Scott, N9AA
R L Measures wrote:
>
> On Aug 25, 2006, at 9:30 AM, Scott Manthe wrote:
>
>> This seems to be a very common occurrence in later Amperex tubes. The
>> tube is at fault, not the amp
>
> I do not agree, Scott. New Amperex tubes typically have a
> grid-filament potential withstanding ability of > 8kV, and a short is
> not going to occur unless some anomaly pushes the filament sideways,
> causing it to touch the grid.
>
>
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