[Milsurplus] dynamotor relics

[J. Forster]

While I am personally a fan of dynos ( he sound of a WS19 Mk III dyno
spooling up when you push the transmit button is just too kewl), I do draw
the line at rotary inverters and use a commercial, solid state static
inverter for 400 or 800 Hz stuff. But a good static inverter is HEAVY
(like 200 pounds plus!!)

-John

================


> A bit more about dynamotors, etc:
> The typical ac power supply has an LC filter, which "rings" upon a step
> load change when you hit the key, causing an interesting damped
> oscillation on the leading edge of your signal.  I have not observed
> that with dynamotors, or had no reason to look.  Also voltage drop in
> dynamotors occurs over several seconds as it slows under load, won't be
> noticeable in use, and is small anyway.  I am also partial to regulated
> supplies, but do give dynamotors a chance.
>
> A word about the 800-1 inverter being "over the top."  The noise is
> mostly from magnetostriction at 1600 cycles from the iron, and I
> measured 95 dB at three feet, which is the same as a subway train
> running through the shack. (Headphones won't help much.)  Upon advice
> from a local noise abatement expert, I constructed a box of 3/4 inch
> plywood, with joints glued and screwed, (no gaps!) lined with 2 inch
> thick fiberglass batts.  Also two chimneys two feet long, folded
> underneath, also lined with fiberglass batts, to move air in and out.
> This reduced the noise to about 50 dB, which is the same as normal
> conversation.  Depending on where you stand you may hear nothing, or a
> distant whine.  I find this very satisfactory, and less noisy than some
> ac supplies.  I suspect we would complain more about noise from ac
> supplies, but we don't hear good at 60 or 120 cycles.
>
> Richard, AA1P
>
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