specific receiver experience/impressions: National NC-100(X)A et al

[David, K3TUE]

More specifically, then National NC-100(X)A (NC-120 (RAO(-1-9)), NC-156).  The NC-120/RAO/NC-156 are military version with 2 RF preamp stages and no push-pull AF PA.  I'm not talking about the one that looks like an HRO with the Millen dial (NC-100, NC-101), but the later one with the centered half-moon dial.

Does anyone have any personal experience with/impressions of this receiver?  I have just been doing some reading, and was wondering if this croud had a opinions of it.

[w3jn]

Of course 

What do you want to know? I've had 5 or 6 RAOs over the years (the one with the 2nd RF compartment and single-ended audio).  Pretty decent receiver, some had S-meters and some didn't.  No bandspread.  Very easy to fix, has the National sliding coil catacomb.  Power xformer is a weak spot.  If you get one needing parts I have enough spares to probably build a whole new one except for the power tranny, catacomb, and filter choke.

73 John

[David, K3TUE]

Does anyone have any personal experience with/impressions of this receiver?  I have just been doing some reading, and was wondering if this croud had a opinions of it.

What do you want to know?

Mostly I just want to know what someone who knows them thinks of them.  Is it a receiver worth owning/using/keeping?  Does it have any notable of strengths and/or shortcomings?  Could you draw some comparisons with more well known receivers?

Just general stuff like this.

[n2bc]

I am up to my elbows in an RAO-9 now (two RF stages, no S-meter).  I've completely recapped it (almost all were leaky), and replaced many resistors (how about a 220K that measures 990K?).  I'm a day or two away from power.  It is easy to work on.

A warning....  The RAO-9 has an IF output feed, not sure about the other variants.  The feed goes directly to the plate of one of the IF amps, there is B+ sitting on the connector on the rear chassis.  I stuck a small 1KV disk in series.

There is good news / bad news from all the wax covered paper caps.  The good news - at least in mine - the entire chassis was covered with a thin film of wax, zero corrosion after 60 years.  The bad news is that most are leaky as I said, but worse is the horrific mess the wax makes on the top of the coil/cap tray.  The wax gets transferred to the contact fingers and makes quite a gooey mess.  I warmed everything up with a heat gun and wiped most of it off, then disassembled the coil tray and cleaned everything with acetone.  Looks like new.

There is a schematic for the RAO-2 on BAMA.

Enjoy!

73, Bill  N2BC

[Vortex Joe - N3IBX]

Dave,
       I have a NC-101X, NC-120, and RAO-5. All three are good receivers with the exception of the NC-101X, an early model with a 6E5 tube instead of an S/Meter. I have never been able to get it straightened out. The audio is distorted and sensitivity weak. I did a halfass recap job, and perhaps when I finish it, it'll be a good player. I've heard nothing but good reports about them.

Regards,
           Joe Cro N3IBX

[w3jn]

Mostly I just want to know what someone who knows them thinks of them.  Is it a receiver worth owning/using/keeping?  Does it have any notable of strengths and/or shortcomings?  Could you draw some comparisons with more well known receivers?

Just general stuff like this.

See my post above.  Of course it's worth owning and using if the price is right.  It's never gonna hold a candle to a Collins, but IMHO it's a cool old buzzard RX.  Not nearly as good a RX as its 1940 contemporary, the SP-400 but better buillt than a SX-28.  SHortcomings will be power tranny problems, drift, and too fast a tuning rate (as well as "where am I" dial calibration).  You'll almost certainly need to do plenty of lube work on the mechanical parts (the coil catacomb slides and gears, and the tuning gearbox).

73 John

[Todd, KA1KAQ]

Of course 

What do you want to know? I've had 5 or 6 RAOs over the years (the one with the 2nd RF compartment and single-ended audio).

73 John

Good thing I didn't know this when I was at Gaithersburg, John. I'd have burned your ear off whilst picking your brain for information. I have one of the later models with the one piece cabinet and no S-meter, I'm guessing RAO-7 or -8. It was my first 'real' SW receiver, second after the S-40B that got my feet wet. Moore's book lists it as the NC-127 I think.

VERY solid, well-designed and built radio. I can't begin to count the hours I spent listening to mine until 3, 4, 5AM. Once you figure out all of the controls (I was a newbie with no idea what B+/MVC/AVC meant), it's a knob-twiddler's dream. The front handles are deceiving when it comes to lifting it, though. Unless you have two people, you'll have to lift from under the cabinet to carry it any distance. The OT who sold it to me for $5 at his garage sale claimed it came out of a B-29, but I've never seen anything to back that up.

If anyone has a decent original manual for the -7 or higher, I have a nice RAO-6 manual that includes a pouch in back with additional documentation that I'd be willing to trade. I also need three of the captive screws and their holders from the front panel.

Definitely worth having if the price is sensible. Eat your Wheaties before going to pick it up.

[WBear2GCR]

I've owned a NC-100A for >30 years now. I think I'm the second owner. First was W2UO.

I got the optional xtal filter from him and installed it - I think the tone control is displaced to a vacant hole below... has the S meter and the sliding IF drawer. Dunno about the RF stage.

This one needs to be re-capped for sure, and have the dial string replaced. I did that once before.
It's missing the top cover.

I think it wants an external ooutpoot xfmr for the audio, iirc.

Worked great before I parked it for 15 years... (is it that long??).

I'll sell it if anyone wants it - saw one on epay go for a good $ recently.
Will trade for AM xmitter of the >100watt class (approx), working or not (but not trashed totally).

Yeah, I know this isn't the For Sale area...

Also have one of them with the HRO dial, that one worked ok too last time checked. Same rig inside as far as I can tell... would sell that one too - don't recall the nomenclature right off the top my my swiss cheeze head.

         _-_-bear WB2GCR

[w3jn]

There is no dial string in a NC-100A.  It's all gear-driven.

[k4kyv]

I have an NC-101XA and NC-100XA.  Haven't fired them up in years, and need to replace one of the i.f. cans in the 101XA that I attempted to modify about 20 years ago (was experimenting trying to get better passband characteristic).  Have several spare National i.f. cans but have never put it in the receiver.

I found it a very nice receiver, in some ways better than the HRO, except for images, since it has only one rf stage.  Mine has the directly calibrated dial with the pointer, and the xtal filter.  It drifted while warming up, but I managed to vastly improve that with temperature compensating capacitors inside the coil catacomb section that contains the oscillator coil.

My intentions were to use it my main station receiver instead of the HRO, but I acquired the 75A4 first.

I have one original National speaker to go with it.

Picked up the NC-100XA later, but have never done anything with it.  The same as the 101XA, except is general coverage (no bandspread capability) instead of ham band only.

Once those things warm up, they are almost as stable as the 75A4.  From my experience, none of the SuperPro series is stable enough for anything except AM.  The mechanical design of the main tuning capacitor causes it to vary with temperature changes no matter how long the receiver has been running.

The problem with the HRO is that when you change bands and insert a cold plug-in coil into the receiver, it drifts until the coil unit comes to temperature.  When I used the HRO as station receiver I always stored the most often used spare coils on top of the receiver so that they were always pre-heated if I decided to change bands.

Once warmed up, the HRO would copy slopbucket nets and QSO's on 20m for hours at a time without drifting.  I did have to run the receiver off a constant voltage transformer, since even slight changes in line voltage would make it shift frequency.  But I have noticed the same thing with my 75A4.  It runs off a constant voltage transformer.  It is a modern one, designed to run a PC, and is much quieter than the older ones.  Those things buzzed like a chainsaw.  I placed mine in the loft and ran a long extension cord to the receiver.

[w3jn]

Would a replacement IF xformer motivate you to get that thang back on the air, Don?  I have a whole box full... yours for the asking.

73 John

[Steve W8TOW]

I have a NC101 X with S meter. Nice rx, great AF and quite surprised the
selectivity is pretty darn good too. Recently acquired a NC-2-40 C...this
was a post war version GC rx, with no band spread or extra bands dedicated to
amateur freqs...like the NC-200 and NC-2-40-D had...
But, once again, the "C" version is no slacker...selectivity is fine and WOW the
AF is just fantastic!
gl es 73 steve
8tow

[k4kyv]

Would a replacement IF xformer motivate you to get that thang back on the air, Don?  I have a whole box full... yours for the asking.

73 John

I already have a stock set of National i.f. cans from an HRO of the same vintage that I parted out years ago.  Just need to swap them out with ones I attempted to modify.

Thanks for the offer anyway.