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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