[ARC5] ARC-5/R-25 tuning gang question

[J Mcvey]

Ok, sort of good news to report...The oscillator tunes a little below 2.3 MHZ to about 2.6 MHZ which turns out to be 1.6 to 1.9 MHZ . Not too shabby for hack job. At least it's useful!There were no calibration marks or overlays on the dial, so I don't know how the guy tuned the thing!
Now, for that noise in the RF section...
I don't think this is a candidate for full restoration since the tuning cable mount was removed.  We just have to take 'em as we find  'em sometimes.

 

    On Saturday, January 30, 2016 11:34 AM, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:
 

 On 30 Jan 2016 at 15:20, J Mcvey via ARC5 wrote:

> I was afraid that it got "ham-mered" ( very appropriate term)

Yes. I believe I'll use that term from now on. :-)

> and so it also
> seems to be the consensus here. I got as far as putting a scope on the
> oscillator yesterday and got a very clean looking sine wave, but didn't measure
> the frequency. The IF's are 705 KHZ which I think is correct for the R-25.

Yes. Absolutely correct.

> Had
> to restore this one back to 24V operation too. The plan was to sit it in a rack
> next to the BC453,for the lower frequencies, but now I wonder if it's still a
> 160M radio.

As Robert pointed out, if it is (and it very well could be) then there will be at 
least three caps, probably mica or silvered-mica, in parallel with each of the 
sections of what remains of the main tuning cap in order to "bandspread" the 
receiver.

At the low end of the band, (with the tuning cap fully meshed) the total 
capacitance of each section should be close to the maximum capacitance of 
the untouched original cap, values listed in the "Replaceable Parts" section 
of the appropriate Military manuals.

> I may as well finish this up and see what I have since I have
> already put a bit of effort into it already.

Yes. I know the feeling. As Robert reminded us, I did much the same thing 
with a BC-454 here before I thought to examine the tuning cap and coils. 
Once I started, I had enough work in it to try to complete the job. Besides, I 
was very curious...

>  The lesson learned is to
> COMPLETELY inspect a radio before starting a restoration/repair.

Yes.

> IF I had seen
> that variable cap, I probably wouldn't have put all those hard to find parts
> back in it. Otherwise it looks like new inside and out. I judged this book by
> it's cover....

Well, in my case, I started with what I took to be the worst-looking one of the 
"hammered" BC-454 receivers I had in the stack.

BTW, as Robert pointed out, there were several DIFFERENT articles in the 
Surplus "Perversion" Manuals on converting the receivers to 10 meters.

Mostly, they used the BC-455 or R-27s for this work, but sometimes they 
used others. 

The last article on doing this "ham-mering" was in the last volume, volume 3, 
by Bill Orr. At least in his article it was obvious that he had tested his result. I 
was not able to determine whether any of the previous authors had bothered 
with that. In at least one article of at least two in the first volume, it was 
painfully obvious that the author had not bothered to test his result at all.

I might add that after I had (painfully) completed the "conversion", what 
resulted was a very good 10 meter monitor receiver. I was quite surprised at 
how well it works.

In your case, since the R-25s are somewhat rare, I'd be trying to put it back 
to original. I have at least two R-25s here, both badly "ham-mered" long 
before I got them. :-(

Ken W7EKB
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