[ARC5] Powering an ARC-5 Receiver After Long Storage

[Kenneth G. Gordon]

On 21 May 2014 at 12:06, D. Platt wrote:

> In my current project involving 5 SCR-274-N and ARC-5 receivers, I elected
> to re-cap these bad boys 100%. 

For those I intend to USE, I do the same.

>  Yes, some of the caps were arguably OK for further use. 

Yes, but in my experience, very few survive the application of 250 VDC for 
very long.

>  This is also the case, generally, with the ceramic top types such as with
> later ARC gear. 

Yes. Those seem to be excellent caps. I have yet to find a bad one of those, 
although I have a very limited number to use as a test sample.

>  But, all said and done, in each and every case I found that they worked
> better and that B+ current was seen to reduce, measurably. 

Yes. I have experienced the same thing. In addition, the receivers are always 
"quieter". Furthermore, best MDS levels are reached with the new caps. 
Commonly, 1 microvolt...sometimes a bit less.

>  The new type caps are much smaller, of course, and I was able to mount at
> least 50% of them exactly where they were used rather than hung on the
> chassis wall. 

The caps I have been using are so much smaller that I am able to mount all 
of them where they are used. However, I always install screws, held in place 
with lock-washers and nuts, to the empty mounting holes.

> The balance were mounted via teflon terminals installed in original mtg
> holes.  I understand that re-stuffing these cans is popular with some and I
> applaud the effort, as always. 

Well, for "museum quality" receivers, I would consider doing that, but NONE 
of mine are even, at first glance, usable, let alone "museum quality". 

I thoroughly enjoy restoring these receivers to both operating and good 
cosmetic condition.

>  I, personally, look for proper operation and outward appearance, only. 

Same here.

> For information, B+ currents at a nominal 210vdc is from about 40ma to 55ma.
>  I also find that I can run these receivers with no ill effects at B+
> voltages as low as about 120v, and maybe even a bit less. 

I have determined that the BEST voltage to operate these receivers is 170 
VDC to 180 VDC. Lower voltages can result in very incorrect screen 
voltages. The ratio of screen-to-plate voltages really should be maintained. 
Since the screen-voltage dividers are fixed, this results in that ratio being 
upset. At the above mentioned voltage, nothing needs to be adjusted to keep 
the receivers operating at their peak performance level.

Yet heat-production and stress on components is significantly reduced.

> Finally, I've had the most success with receivers built with plastic
> insulation wiring, vice the older cotton stuff.  That's probably a blinding
> glimpse of the obvious, however..... 

I have only one or two receivers here with that plastic insulated wire. All of 
mine that I have worked on have the older cotton-covered wire. A SHARP 
and properly-set wire stripper makes working with that wire easy.

I have yet to test resistors, though, which is a fault on my part. The info from 
Bill was the prod I needed to investigate this aspect of our favorite receivers 
more closely.

Ken W7EKB