[AMPS] Resoldering 3-500Z Filament Pins ??
A. J. (Jim) Movius
ajmovius@gci.net
Sun, 4 Apr 1999 16:52:37 -0800
My dad, W7IWW became a silent key because of the error of not waiting long
enough for the power supply volts to bleed off after turning off the amp
which he had been operating with the cover off. He was putting the cover
back on and the cover in his hands contacted B+ plate choke while his tummy
contacted his mike to complete a circuit through his chest area. Instant
death resulted.
My thought is make your procedure "Murphy Proof" such as by watching the
plate voltage meter after turning off the HV, using a "crowbar",
disconnecting the power source, etc. Take your time- better to be late in
this world than early in the next.
I am glad those telling their experiences are around to tell them.
Best wishes to all,
Jim, KL7EGO
-----Original Message-----
From: Graham Jones <g.jones@bom.gov.au>
To: Jon Ogden <jono@enteract.com>; Dick Green <dick.green@valley.net>;
Michael Tope <W4EF@pacbell.net>; 'AMPS' <amps@contesting.com>
Date: Sunday, April 04, 1999 2:59 PM
Subject: Re: [AMPS] Resoldering 3-500Z Filament Pins ??
>
>Yeah likewise,
>
> About a year ago when I was just getting started on Amp gear, I was doing
>some tube tests. I was going through a routine of powering down, replacing
>the 4 PA tubes, powering up again to test the tubes, then powering down
>again for the next set of tubes etc. After a while, I got out of sync. and
>I was just putting my hand into the PA compartment to remove the anode
>clips when I barely noticed a very faint purple-ish glow through the tube's
>ceramic insulator. Fortunately this registered somewhere in the deep
>recesses of my brain suggesting that perhaps this wasn't a good time to
>proceed! Sure enough the HV was still on. It was only 2KV and not 6KV like
>yours Jon, but I still shudder when I think how close I came. If it hadn't
>been dark enough in the tube compartment to see the faint glow
>.................. ?
>
> The manufacturer's maintenance manual points out that that interlocks were
>not deemed necessary because they had plastered the chassis with adequate
>high voltage warning stickers!!
>
> I now try to keep the habit of always shorting out the anodes before going
>in, regardless of the powered status of the amp, even at the risk of
>possibly damaging something if the HV is on. At least I will stay undamaged
>:-)
>
> I recall that thirty years ago when I worked at Collins Radio here in Oz,
>building 208U-10 10Kw SSB transmitters, it was a sackable offence for the
>test technician to work in the PA compartment without first applying the
>built-in shorting wand to the HV supply.
>
>Cheers,
>
>Graham (VK3BKG)
>
>----------
>> From: Jon Ogden <jono@enteract.com>
>> To: Dick Green <dick.green@valley.net>; Michael Tope <W4EF@pacbell.net>;
>'AMPS' <amps@contesting.com>
>> Subject: Re: [AMPS] Resoldering 3-500Z Filament Pins ??
>> Date: 02 04, 1999 7:51 AM
>>
>>
>> >Semiconductors all over the radio blow before
>> >the fuse does.
>>
>> One of Murphy's Laws of Electronics! The circuit intended to be
>> protected BY the fuse will blow first, thereby protecting the fuse!
>>
>>
>> > And let's not talk about the time I touched one of the plate
>> >caps on an SB-200 because I thought it was loose and forgot that HV was
>on.
>>
>> Ouch! Makes me think of what I almost did. About a year ago I powered
>> up the filaments on my amp as part of some initial smoke tests. I was
>> tempted to touch the anode and make sure the tube was well seated in the
>> socket. I didn't. When I went to turn the filaments off, I noticed my
>> HV meter was not zero. Unbeknowns to me, I had earlier left the HV
>> supply switch turned on so when I turned on the filament switch, the HV
>> was on as well - at 6 KV! I about fainted and I still get queasy till
>> this day thinking of what I almost did.
>>
>> **** But I followed a rule I set for myself and I lived. And that was
>> to NEVER touch the tube when the filaments are on w/o first DOUBLE and
>> TRIPLE checking to make sure that the HV is off. I'm grateful I made
>> that rule!
>>
>> 73,
>>
>> Jon
>> KE9NA
>>
>>
>>
>--------------------------------------------------------------------------
>> Jon Ogden
>>
>> jono@enteract.com
>> www.qsl.net/ke9na
>>
>> "A life lived in fear is a life half lived."
>>
>>
>> --
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>
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>
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