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Re: [Amps] Alpha 87A Power Supply Question

To: amps@contesting.com
Subject: Re: [Amps] Alpha 87A Power Supply Question
From: Jim <jimw7ry@gmail.com>
Date: Fri, 7 May 2021 13:05:42 -0500
List-post: <mailto:amps@contesting.com>
I put a 240 to 120 transformer (to run the filament transformer and the blower) in my HB 3CX800 amp because the Dahl plate transformer only had a 240 volt primary winding.
The transformer was about $30.00 from Mouser.


Works perfectly!


Thanks
73
Jim W7RY

On 5/7/2021 12:32 PM, Jim Thomson wrote:
Date: Fri, 7 May 2021 09:34:25 +1000
From: Adrian <vk4tux@gmail.com>
To: 'Amps group' <amps@contesting.com>
Subject: Re: [Amps] Alpha 87A Power Supply Question

<It is dangerous, additional to my earlier post connecting neutral to
<chassis and wiring 120v returns to same terminal, if the neutral
<connection opens anywhere from within the amp back to the supply, then
<you have 120v on the amp chassis at turn on, waiting for you to grab.

<Usually, it takes about 30 mA of current to cause respiratory paralysis.
<Currents greater than 75 mA cause ventricular fibrillation (very rapid,
<ineffective heartbeat).


<vk4tux

##  On a related note,  IF a sub panel is used, like in my case, I installed a
100 amp sub panel on the other side of the wall of the basement shack, with 
short runs
through the wall to the 4 x amps, 4 x  xcvrs  etc, etc.    In the case of a sub 
panel, the neutral
and ground can  NOT be bonded together.   Reason is, if a fault occurs, ALL  
the fault current has
to  return to the main 200 amp panel via the  ground  wire...straight through 
to the main  200 amp panel.

##  IF the neutral and ground are bonded  together in a sub panel, the fault 
current  from the equipment in
the shack will  initially return through the ground wire back to the SUB panel, 
then the  fault current  will  split,
with 30-40 %  going back to main 200 amp panel via the grnd wire....and the 
remaining 60-70%   returning via the
neutral wire.   Grnd wire these days is typ smaller gauge than the neutral, 
hence the offset split in current.
Any fault current returning via the neutral is a big no-no.   The ONLY place 
the neutral + grnd is  bonded is in
the main 200 amp panel.

## my drake R4C  and  T4XC  came with 2 prong plugs, no grnd.   Drake installed 
 .01 uf disc caps, between hot and
chassis.......and also between neutral and chassis.   That puts  120 vac  
across the 2 x caps..that are effectively
in series.... via the chassis.  That’s  60 vac  per cap.   You end up with 60 
vac on the chassis.   I got zapped one day, when
disconnecting coax, etc.   I measured  60 vac  between the chassis of the 
drake..and the  cold water tap !   Easy fix, replace
the 2 wire cord, with a 3 wire cord, and use proper   X-Y  AC rated 
caps..instead of  .01 uf  at  1 kv rated  disc caps.

## on my  4 x drake L4B amps,  I replaced the oem fubar  120 vac blower with 
the  230 vac  EBM papst  blower, as used in the  AL-1200,
AL-1500, AL-82  amps.   For some reason, the   230 vac version of that EBM 
blower is almost half the price of  the 120 vac version.
Mouser and digikey sells the  230 vac version for aprx $112.00   The  115 vac 
version is almost  $200.00  from mouser +  DK.   The 115 vac
version used to be $137.00  from  MFJ, but price has now gone up to  $168.00
But this precludes running the amp on low power, on 120 vac..which I have never 
done anyway.   Drake had used the quasi  neutral scheme
to obtain  120 vac for the oem 120 vac blower.   For  115 vac operation,  I 
could use a 115  to  230 vac small xfmr to run the 230 vac  blower.

##  On a lot of commercial henry amps, they used a 240  to  120 vac  small  
xfmr to run the  120 vac  blower.

##  I have never seen the  3 wire,  2 hots + grnd  wired in any home here in  
BC.   Its been  4 wire at least since 1960, or earlier.
I assume the  USA  3 wire  fubar scheme was to save 1 wire...and some money.   
Seems silly, since  copper was dirt cheap way back then.

Jim   VE7RF
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