[Milsurplus] R-45/ARR-7 Questions

[Al Klase]

Hi Joe,

My approach would be to hit that cap with a hammer, and know for sure 
what was inside.  Paper, almost certainly.  82000 pF would be big mica.

I'd expect bypassing the first tube could be done by disconnecting the 
common low-side connection to the first RF transformer primaries from B+ 
and grounding them.  Then connect the antenna where the plate of V1 is 
connected now.  Input impedance wouldn't be optimal, but there's a lot 
of gain and you'd only notice on the higher freq's.  Getting rid of that 
stage would probably be a good idea if you were going to use the 
receiver in earnest on a large antenna.  Gain before selectivity is 
always a problem when strong unwanted signal are coming off the antenna.

However, I wouldn't ham hack the thing at this late date.  Get it 
running the way the Signal Corps intended.  The "anti-radiation stage" 
has a broadband hi-Z input.  Attach a short whip and you've essential 
got a built-in active antenna.  Lube the mechanics and get it scanning 
for enemy radio traffic!

Be a little careful re: what DC voltage is required by the motor, and 
where it comes from.  I think you told be the original power supply had 
been modified.

Best regards,
Al

On 3/27/2012 11:05 PM, Joe Connor wrote:
> Just a note on the .0082 mfd bypass caps in this receiver. I pulled one out and it was made by Micramold. Given the lousy reputation of Micramold caps, I plan to replace them with .01 mfd ceramic disks.
>   
>                              Joe Connor
>
>
>> ________________________________
>> From: Joe Connor<joeconnor53 at yahoo.com>
>> To: "hallicrafters at mailman.qth.net"<hallicrafters at mailman.qth.net>; "milsurplus at mailman.qth.net"<milsurplus at mailman.qth.net>
>> Sent: Saturday, March 24, 2012 10:08 PM
>> Subject: R-45/ARR-7 Questions
>>
>>
>> I just picked up a pretty nice R-45/ARR-7 (the airborne SX-28). It came with the PP-32 power supply. Thankfully, a prior owner replaced the power xformer so the set can operate on 60 cycle power. With a little tinkering, the set now works pretty well.
>>
>> I have some questions that I hope you can answer:
>>
>> 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?
>>
>> 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.
>>
>> 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.
>>
>> 4. I know this is probably a needle in the haystack, but might anyone have a front-panel cover for the scanning mechanism?
>>
>> 5. Is there anything else that I should watch out for?
>>
>> With this set, I got some paperwork that shows how good we have it today with the Internet. The fellow who owned this set in the '60s apparently tried desperately to find a manual for it. I have the letters that Hallicrafters and the ARRL wrote to him politely stating that they couldn't help. Now, we click on Bama and there's a manual on our computer screen. It's pretty amazing, when you step back and think about it.
>>
>> As always, thank you for your help.
>>
>>                                          Joe Conno
-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/