Another way to test I've used, was to disconnect the +B lead, power on
the
amp and then measure the Grid-Filament isolation.
In those three times tubes were blown, was any other event registered?
(explosion, no explosion at all, transmitting, during standby?).
Best regards
Guillermo - LU8EYW.
W5CUL escribió:
> 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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