[Amps] What to do about 'Neutral' in HB amp?

[Jim]

Steve...


There are several ways, both of which I have used.

Use a 240 to 120 volt transformer available at Mouser:

https://www.mouser.com/ProductDetail/Hammond-Manufacturing/1182F240?qs=qPaGMJUC%252BSvZvVY5qAgjgQ%3D%3D 
Is just one possibility.


Or if you have a 240/120 volt filament transformer, you can run the 
blower on half of the primary of it if the primary can handle the 
current (which it probably could).

I used the filament transformer out of the Ameritron AL-1500 amplifier 
for my last project. It also has a 12 volt AC secondary as well.

Most ham amplifiers use the filament/plate transformer to do this.... 
Drake, Heathkit, Ameritron, etc etc..

Also, you can buy the PABST aluminum frame squirrl frame blowers in 
240/230 volt varieties.

Most of the Hammond control voltage (low current 12 and 24 volt 
varieties) have 120 and 240 volt primaries now  days.


73, Jim W7RY



Thanks, 73, Jim W7RY

On 12/28/2022 8:22 AM, Steve Bookout wrote:
> Hello all,
>
> I'm building a HB amp for 10 meters and am looking for the best 
> solution to a problem I've wondered about for DECADES.
>
> Other than using a 4 conductor plug/outlet (2-120 volt, one neutral 
> and one ground) how should a person deal with the 120 volt neutral?
>
> This would be a concern for the blower, small 12 volt DC power supply 
> and filament transformer, and maybe something else I'm overlooking as 
> I write this.
>
> I know I am guilty of just taking the neutral side of a 120 volt 
> component to ground, but as I understand it, the ground is never 
> supposed to carry current, with the neutral carrying the current from 
> the 120 volt stuff.  The ground and the neutral are connected together 
> at the breaker box, but are treated as different lines in the 
> equipment.  Back in the day, I suppose taking neutral to ground was 
> done, as several times I've been slightly shocked by an old boat 
> anchor with leaky caps.   Also, GFI circuits would always trip, as 
> they should, when that piece of equipment was turned on.
>
> These are things I've thought of, in no particular order.
>
> Using a 240 > 120 step down transformer and run the 120 volt things 
> off of that.
>
> Neutral to chassis ground and ground, ground, ground everything 
> together, and to the 240 ground coming into the power supply.
>
> Use the common connection point between two 120 volt windings, wired 
> in series, on the input of the HV transformer for 240 use.
>
> Looked at a bunch of schematics and some are kinda lacking in detail.  
> Most either use dedicated 120 volt winding off of the secondary of 
> transformer, or a separate 240 volt input transformer,   I'm sure the 
> ones lacking in detail are not doing for nefarious reasons but to keep 
> from cluttering up a schematic. It's combining block diagrams with 
> detailed schematics.  I'm sure they're doing it right, otherwise, 
> would not get UL approval.
>
> I seem to remember from decades ago, seeing where someone had two 
> resistors between the two input lines of a 240 volt input transformer 
> and was using that point as neutral.  Would love to know  how that 
> worked out.  Short the 240 input with two resistors in series and use 
> the point between the two resistors as 'neutral'.
>
> The transformer I have, and will use, is a Peter Dahl, with no 120 
> volt winding, only terminals marked '0', '240', '230' and '240'. 
> Secondary is NOT center-tapped, so will be using a FW bridge.  No joy 
> there.
>
> I guess I'm leaning toward a 240/120 step down transformer.
>
> It would be much more straightforward if I was building with all new 
> parts from scratch.  Actually, as I think of it, my DC power supply 
> will take either AC voltage inputs, and automatically deal with it.
>
> Love to hear what everyone thinks, and to hear if you've ever done 
> anything just a wee bit 'shady', when dealing with this issue.
>
> 73 de Steve, NR4M
>
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