[Amps] Alpha 87A Power Supply Question

[Jim]

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 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
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