[Milsurplus] 125 VAC Line? Make Your BA's Happy, Cheap.

[Bruce Gentry]

There are many rigs both surplus and otherwise that were designed for 
110 volts. I have a surplus morale receiver built by Crosley that I 
restored, and the power transformer was shorted and obviously 
overheated. Once I found a scrap receiver with a good transformer, I 
finished the restoration and was surprised and concerned about how hot 
the power transformer got in a short time. I noticed the rating being 
for 110 volts, and reducing the power to that level with a Variac 
completely eliminated the heating problem.  I didn't want to use the 
Variac all the time, so I took a 50 VA control transformer with two 120 
volt primaries and two 12 volt secondaries, mounted it under the 
chassis, and connected it as an autotransformer. The morale receiver 
transformer has dual primaries to allow 220 volt operation, the control 
transformer with it's dual windings allowed each primary on the power 
transformer to be supplied seperately and allow the radio to be operated 
on 240 volts if needed. The autotransformer connection gives 108 volts 
out to each power transformer primary for 120 volts in, and the power 
transformer only gets warm. I think a lot of rigs with 115 volt ratings 
could be marginally overheated by 120 volts, and may be  why I see so 
many National NC-183 and HRO 50/60 receivers with fried or substitute 
power transformers.

   Bruce Gentry, KA2IVY



On 1/14/16 12:00 PM, David Stinson wrote:
> Got 125 VAC + on you shack's AC power buss?
> Ronnie, W5SUM and I worked this problem.
>
> There must be a zillion old, broken Uninterruptable
> Power Supply (UPS) units laying around.  These typically
> have an AC cord going in and AC sockets going out plus circuit 
> breaker, etc.   In 99% of the cases, the
> transformers in these units are still good and are perfect
> for building a "line bucker."
>
> We found a couple of dead 12 Amp APC units.
> The transformers had a 120 V primary,
> a lo-current 15 V and a Hi-current 15 V windings.
> The lo-current winding is not used, unless you want
> to light a pilot light or something.
>
> Pulled the "hot" leads from the dead circuit board
> and directly powered the transformer through
> the circuit breaker.  Wired the Hi-current 15 V
> winding in the "bucking" configuration with one side to the junction 
> of the incoming "hot" and the other side going to the "outgoing Hot" 
> sockets on
> the back.  Left all neutrals connected together
> as normal.
> If the voltage is boosted instead of bucked,
> swap the 15V secondary wires.
> Mine drops my line voltage from 125 V to 110 V
> and my boatanchors are happy.
> 12 A service will run a lot of stuff and broken UPSs are cheap, so you 
> can add more.
>
> Important Tip:  A transformer "line bucker" acts as
> an "autotransformer."  To measure the output voltage
> accurately, you must connect a load- even a small one.
> The load current sets-up the magnetic field the autotransformer needs 
> to work.
>
> 73 Dave AB5S
>
>
>
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