[ARC5] Receiver AC Power Supplies

[Bill Cromwell]

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
> ______________________________________________________________