[Amps] Alpha 87A Power Supply Question

[Jim Thomson]

Date: Fri, 7 May 2021 09:34:25 +1000
From: Adrian <vk4tux at gmail.com>
To: 'Amps group' <amps at 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