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

[john rose]

Dave, thank you for the pix. I always wondered how the '4606' tuning cap looked.
The ARC 5 manual AN 16-30ARC5-2 lists which series are/are not interchangeable with the ARC 5. It says, "The receiver units of Model RAT (13.5-27 mc) equipment were designed for 12-volt operation, and therefore may not be used in the receiver racks of the 24-volt.....". Is this correct?
----------------------------------------
> From: arc5 at ix.netcom.com
> To: arc5 at mailman.qth.net
> Date: Fri, 8 Feb 2013 19:52:10 -0600
> Subject: [ARC5] 10-Meter 274N RX - The 20-27 RAT-1
>
> 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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