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Re: [TowerTalk] Fw: [CQ-Contest] Amplifier repair warning

Subject: Re: [TowerTalk] Fw: [CQ-Contest] Amplifier repair warning
From: K8RI <>
Date: Fri, 13 Apr 2012 21:04:47 -0400
List-post: <">>
On 4/13/2012 2:50 PM, Bob Ad5vj wrote:
> For your viewing and contemplation.
> tnx Bob AD5VJ
> Sent from my Samsung Epic™ 4G
> -------- Original message --------
> Subject: [CQ-Contest] Amplifier repair warning
> Date: Fri Apr 13 10:25:51 CDT 2012
> From: Tom W8JI<>
> To:
> Several times over the past 30 years Hams have been hurt, or killed, poking
> around inside tube-type amps with power on. QST, with total disregard for
> common sense, even published an article suggesting people defeat interlocks
> to make a measurement with a hand-held meter.
> Last week I mentioned something about a certain V31, who killed himself
> poking around inside an amplifier with power on. I gave the V31 a similar
> warning to this weeks or months before he killed himself.
> A story surfaced today about an AL1200 amplifier, which has about 3600 volts
> inside. Apparently someone instructed someone else to measure HV with a
> small handheld meter. As the story goes, the handheld meter blew up.
> I'd like to remind everyone to remind others, when they see or hear
> something like this going on, to say something before it happens, if
> possible.

Although it's a good idea to always keep the covers on it's not always 

> It is NEVER necessary to run an amplifier with the cover off,

Unfortunately that is not true. If you have a modern amp it is often 
necessary to have the covers off to set the bias, screen voltage and EBS 
among other things.
That means to position yourself so you do not reach over any HV 
circuits. If necessary lay a piece of clear plastic over the PS and 
particularly the HV circuits.

I have several amps here that I'd never be able to set any of the above 
with the covers still in place. If a tube has to be replaced you have to 
do the whole thing again.

>   and especially
> HV on, to check things. Anyone advising defeating an interlock, or powering
> up a tube-type amplifier with the cover off and HV exposed, it is a fool.

We used to have to do that with amps running several hundred KW that 
were running well over 10KV
It takes training, it takes care, it takes procedures, and it takes 
working with some one. We were not allowed to work alone on the big stuff.


Roger (K8RI)
> If we don't know anything about electronics or how things work, at least we
> should know what we should never do. We should never remove a cover and
> power up a tube-type amplifier with HV exposed, and it is especially foolish
> to go poking around inside with a meter, no matter how careful you think you
> are.
> 73 Tom
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