[ARC5] Reviving squealing "command" receivers (re-capping)

[Kenneth G. Gordon]

On 6 Mar 2011 at 7:41, David Stinson wrote:

> It's worth the effort to be sure which caps are bad, rather than
> just "shotgunning" them.

I am trying to do that "even as we speak" with an R-25/ARC-5 which had 
been badly hacked before I got it.

Surprisingly, the triple 0.22 mfd job, which is ALWAYS bad, is good in all 
three sections, and all sections passed a repeated leakage test at 450 
VDC. I have cleaned that one up and set it aside for use in a restoration.

However, so far, of the two triple 0.05 mfd jobs I have tested, all showed 
considerable leakage in the capacitance test, yet low leakage with the 
voltage test, passing very well at 350 VDC, yet showing considerable 
leakage of beeswax. I am not completely certain how to interpret those. I 
put them aside as being bad. I may attempt to restuff them.

>  The 5 mFd B+ filter is always "bad"
> and gives trouble over about 40-50 volts B+.

That one in this particular receiver showed well over 5 MFD capacitance 
(more like 9 MFD), and absolutely no leakage at all up to 450 VDC. I think 
mine is OK. Furthermore there is no leakage of beeswax from it either. I 
have reinstalled it.

> Same thing with the 15 mFd cathode bypass.

THAT one showed zero capacitance and zero ohms. I have replaced it with 
a modern cap.

> A surprising amount of the other caps will be good,
> especially if you run reduced B+.    

So far, I have found all of the triple 0.05 mfd caps I have so far tested to be 
bad or very seriously "questionable". All have leaked beeswax.

For this particular receiver, due to its severe "hacking", I am not going to 
attempt to restuff caps or to restore it. 

Who ever got to this thing first had already removed the large choke at the 
rear, the audio transformer (I have some spares stored away somewhere), 
had hacked various wires loose leaving them unconnected, had hacked a 
hole in the side near the front panel for what appears to be a slide-switch,  
and had rewired the filaments VERY weirdly with crappy too-small teflon 
coated wire so that some tubes had no filament voltage at all. 
Workmanship was just plain awful.

I have almost finished rewiring the filaments back to stock. 

Yet the power connector (at the rear), dynamotor connector and front 
connector and "adapter", and all the original tubes were all still there.

It is like he started to modify it, but never finished it.

Except for the hole, the outer case is in unusually good condition.

Unfortunately, with that big hole in the side and other damage done, it is not 
worth attempting to restore to me.

However, I do want to use it in my very small stable of usable receivers to 
monitor the high end of the BC band, 160 meters and 2.5 Mhz WWV.

Very fortunately, he did NOT remove the BFO transformer or its 
connections.

I could also, perhaps, use this receiver as a "Q-5er" for the BC-348 I hope 
to aquire some day.

A BC-348 with an R-25/ARC-5 "Q-5er" was my very first, really decent, 
receiver back in 1957. One of my Elmers sold it at a very cheap price to my 
Mother for a surprise birthday present for me. I've never forgotten their 
kindnesses.

Ken W7EKB