[ARC5] 10-Meter 274N RX - The 20-27 RAT-1

Fri Feb 8 22:27:33 EST 2013

David,
I've probably had over a hundred ARC5/SCR274N type receivers, Xmiters, etc., go through my hands over the past 45+ years, yet
 your pictures of your RAT-1 and R-13 are the first I've seen of them.

I'm a little surprised that someone hacked the RAT-1, even way back then when we all did it. At that time it seemed as if there was a limitless supply of surplus gear, especially the ARC5/SCR274N gear. 
I still have a few receivers and transmitters that are in the original sealed boxes. By way of example of how ubiquous this gear was, I remember paying $5.00 each for the receivers and $10. each for the xmiters (with tubes). The accessory items, like the three receiver rack and control heads were almost free. I think I paid $1.00 each for used ones and $2.00 for sealed in the box ones. It seemed like no one wanted them because one could hack together something that would work for free or nearly so. 
I remember the owners of the local electronic distributer / amateur radio dealer / surplus store telling me many times what "cheapskates" hams were, lol.

I applaud you restoration efforts on your RAT-1! I actually did the same exact dynamotor-deck replacement you've performed. I'm sure I spent at least 15 hours on it using two-part epoxy, bondo and "red lead?" scratch filler. Finishing off the interior was even harder then the outside, but it came out remarkably nice.
At least the set you're restoring is worth spending the time on. I did it on a broadcast-band model that I think I gave away at a hamfest long ago.
I get a lot of joy bringing someone else's hacked-up basket case back to life.

I'm interested in seeing the finished product. I'm also curious as to how the R-13 sounds like if you find a station or two at the top-end of the FM broadcast band.

I actually make use of a broadcast band command receiver as my hi-fi AM DX tuner. I've been using it for at least a decade and at this point I'd like to find another
mil surplus/boat anchor receiver (a pre-hacked unit, of course) to modify/convert into a replacement for the command set am tuner that would out-perform it.
I'd also like to find a mil surplus BA-type receiver to do the same thing for the FM broadcast band. Given a production run of 50, I doubt an R-13 would be the basis for such a project!
Any ideas/suggestions?
73,
Rick

On Feb 8, 2013, at 8:52 PM, David Stinson <arc5 at ix.netcom.com> wrote:

> Well we're all interested in Ken's ongoing adventure
> with the modded 10-meter radio.  So I thought I'd present some "OEM" info from the RAT series.
> 
> I have the last 20-27 MC "Command Set" receiver produced:  CBY-46109 RAT-1 serial number 50.
> 
> http://home.netcom.com/~arc5/RAT-1/RAT120-27.jpg
> http://home.netcom.com/~arc5/RAT-1/CBY46109plate.jpg
> 
> Normally, I would not consider disassembling an authentically "Rare" (vs. "Ebay-Rare," lol)  RAT receiver,
> but this one had already been badly goobered by some doofuss.
> 
> I've got it working but man, was it a MESS.
> Drill holes in the front and back- he even wallowed-out the index peg on the dial rather than just align the poor thing.
> Worst of all, the nit-wit chainsawed-out the entire top
> of the dynamotor deck.  I used a junker to "graft" a new deck on the back.  I got it "off center" by about a millimeter on one side.  Probably no one but me would notice- it bugs me
> but I'm not going to hack it back apart again:
> 
> http://home.netcom.com/~arc5/RAT-1/RAT1rear.jpg
> 
> See all those grey spots on the back?
> Those are filled drill holes all around the replaced connector.
> As you can see, I still have lots of "backing and filling" to do.
> And, as I have come to expect from this kind of VANDALISM,
> the thing never played again and did not one lick of useful work
> after all this needless, thoughtless abuse.
> Anyways.... I digress.... Sorry  ( not really.... snicker ;-)
> 
> As someone previously mentioned, the variable cap is part number 4606,  44 pFd per section:
> 
> http://home.netcom.com/~arc5/RAT-1/4606Varicap.jpg
> 
> The little oscillator padding cap is one of those cute
> A.R.C. "hand-thrown" jobs made of little sheets of mica and conductor assembled on a nut-and-bolt
> armature which they tightened until it was "right."
> Should have made a photo of that.
> 
> One very cool thing:  The tuning cap is date-stamped
> and also stamped by the person who did the alignment.
> God rest you, "RV," whomever you were:
> http://home.netcom.com/~arc5/RAT-1/RAT1Date.jpg
> 
> In contrast, the varible cap for the 6-9.1 MC rig is 65 pFd per section.
> The modded unit uses one plate, doubtless to give you some bandspread.   Tuning is kinda "touchy" when the dial covers 7 MC.
> 
> The IF is 4200 KC.  The IF coils are still sealed and
> I don't want to open them.  The seals on the RF coils
> were already broken but, thank the merciful Almighty
> and for a wonder, doofuss had not boogered with them.
> 
> All coil forms are .69 inch outside diameter ceramic.
> (Thank you, Mike Hanz, for the "right tool" to measure this).
> Slugs are in place.
> 
> Here are the coils:
> http://home.netcom.com/~arc5/RAT-1/RATCoilset.jpg
> Top to bottom:  Antenna, Mixer, Osc.
> 
> http://home.netcom.com/~arc5/RAT-1/RAT1Antcoil.jpg
>     6 turns single winding.
> 
> http://home.netcom.com/~arc5/RAT-1/RAT1Mixcoil.jpg
> I cannot count the turns on the top winding; it is "pie-wound"
> and at least a couple of layers.
> Bottom winding is 6 turns.  Winding starts where you see it
> at the top right (yellow area of the screwdriver).
> 
> http://home.netcom.com/~arc5/RAT-1/RAT1Osccoil.jpg
> Top winding is 5 turns.  "Tickler" winding is 2 1/2 turns.
> 
> Operational notes for those interested:
> I've got this set fully operational as-designed on an RAT-1 dynamotor,
> but it's been many years since I last worked on it- like, maybe 1997!  So I went back through the alignment, fired it up and checked for
> gremlins.  All OK after IF, BFO and RF alignment, but very dead bands. Even fairly stable after a good warm-up. Using the 12SK7 RF amp (if you can call it that at 27 MC),
> sensitivity is considerably less than that of the modern receiver
> to which I compared it (sorry- my service monitor signal generator
> calibration is busted).   I saw that someone mentioned the higher-
> amplification 12SG7 and I just happened to have one.  Popped it
> in with no circuit changes and the improvement was significant.  You could use this on 15 meters if the band would ever really open.
> For "giggles," I stuck-in a 717A from the VHF rigs (yes, I know the filament is wrong; this was just a short trial) and that really made
> the few signals on the bands jump-up.  Is there some RTTY contest going-on today??  Strong CW signals from a K6 station,
> but only one lonely "Chicken-Bander," comparable to what I could hear on the Racal  RA6790.
> 
> Hope this has been of interest.
> GL ES 73 DE Dave AB5S
> 
> 
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