[Amps] Alpha 87A Power Supply Question
Jim
jimw7ry at gmail.com
Fri May 7 14:05:42 EDT 2021
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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