[Milsurplus] R-45/ARR-7 Questions

[Mike Hanz]

On 3/24/2012 10:08 PM, Joe Connor wrote:
> 1. From what I've read, it's a good idea to bypass V-12 (6AB7), the radiation suppression tube. How do I go about bypassing it?

Just stick a .01uF capacitor across pins 4 and 8 of the tube socket, 
Joe.  I used a couple of pins from an old tube socket so it just plugs 
in.  No soldering required.

> 2. Interestingly, most of the bypass caps are .0082 mfd, not .01 mfd. Are these mica caps or paper caps? If they're mica, I'll probably leave them alone.

As you observed, they are not mica.

> 3. The audio output (6V6) and 1st audio (6SQ7) each have a 20 mfd bypass cap. I'll be damned if I can find them. Does anyone know where they are located.

The schematic is in error.  C-49 for the 6V6 is .0082uF, not 20uF.  The 
bathtub capacitor on the side of the chassis is C-82, the cathode cap 
for the 6SQ7, from what I recall, though it might be the one at the 
corner of the BFO box near the center.  One of 'em, anyway.

> 4. I know this is probably a needle in the haystack, but might anyone have a front-panel cover for the scanning mechanism?

They aren't hard to make if you can handle a hacksaw and file, and can 
silver solder.

> 5. Is there anything else that I should watch out for?

The motors on these sets fail rather easily.  I would use the scanning 
capability sparingly.  Other than that, only the usual SX-28 foibles 
apply.  Oh, and I would make sure the B+ is 270v or less.  Less is 
better.  Without the need for the hifi output of the SX-28, it will work 
fine at less than 200vdc and your tubes will thank you for it.

Best 73,
Mike  KC4TOS