[ARC5] Receiver AC Power Supplies

[Rich Post]

I have a nice 25 amp variac for that purpose but I don't use it.  Instead,
I re-purposed a couple of dead UPS.  The older UPS have nice transformers
in them, typically around 16 volts or so center tapped. Either use the
whole winding or the half from the center-tap.  Also re-use the housing,
breaker and outlets. Here is an example (at the bottom of the page).
<http://www.ohio.edu/people/postr/bapix/S-76.htm>

Rich KB8TAD

On Sat, Dec 13, 2014 at 10:25 AM, Bill Cromwell <wrcromwell at gmail.com>
wrote:
>
> Hi Jeep,
>
> I don't have any of those SOLA thingies but I do run a couple of bucking
> transformers with some of my more elderly gear. I has occurred to me now
> that I did not have a bucking transformer in that command receiver power
> supply with the antique B+ transformer. Duh... My bad. The late model, RS,
> 25 volt iron seems to be okay with the late model power line voltage. The
> repacement for the B+ should be okay since it is brand new.
>
> I have acquired a variac but maybe I should get another. The one I have is
> intended for what I perceive as "megger" work and some other bench
> experiments/measurements and NOT for running the old radios. I can at least
> use it to see how much I want to buck the power line for the old gear.
> Maybe I should just buy a big honking 12 volt transformer and buck the
> power line for my entire radio shack. That should keep me closer to 115 to
> 117 volts. Has anybody done that already? Gotchas to watch out for?
>
> 73,
>
> Bill  KU8H
>
>
>
> On 12/13/2014 09:49 AM, DSP3 wrote:
>
>> Corollary to this discussion, I have recently had the occasion to work on
>> three BC-348 receivers I acquired this past summer.  All three
>> (unfortunately, perhaps) were previously modified for a.c. operation.
>> Going over these supplies, I found that virtually all of them suffered p.s.
>> issues, most often the iron was not up to the task.  Heat, noticeably high
>> heat, were present in all three units at the on-set.  I believe that these
>> receivers were modified probably in the 50's, judging by the type and
>> manufacture of the p.s. components used.  Aside from the filter cap issues,
>> voltages were not what was expected.   Using a variac and adjusting the
>> input to about 110v things got better.... a lot better.  Using silicon
>> diodes, vice a tube rectifier, also helped un-load the small, over-taxed
>> power transformers, a bit.  The aforementioned issues were not new ones.  I
>> generally run the "Vintage Bus" here at a nominal 110v, via a Sola
>> regulator unit.  Receivers such as the National NC-183D and others run ever
>> so much cooler and voltages are generally at spec.   A lot of older
>> components are apparently really pushed to the limit(s) by current "normal"
>> line voltages.  Just after the above activity,  I went around a bit with my
>> local provider (First Energy/Potomac Edison) about high line voltage, at
>> about 125.8v.  Turns out, they had mis-applied some line comp capacitors
>> (they actually informed me of same). After removal, things are steady at a
>> comfortable 120v.
>>
>> We think that the older stuff was made better than today, and in some
>> cases it may be.  However, things like better insulating materials and
>> advanced core design have made a big difference. The thing is, though, most
>> of the old stuff _is_ just fine, operated in the environment for which it
>> was designed.
>>
>> Jeep - K3HVG
>> ______________________________________________________________
>>
>
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