The AM Forum

O.K. guys, I've finally found a R-390A in good working shape. Any advice on things to look for before I plunk down big bucks? I'm going to try to get in a little research this evening, but I'm pretty busy not having expected this to come my way so soon. I took a quick look today and saw it has some funky antenna connectors on the rear. Guess I can clip lead on the inside for now. It has the Vernier for the BFO too.

Thanks & 73, Phil   
               

The antenna connectors are easily sourced.  The balanced one is the same as a twinax 110-Ohm job, as used on IBM computer networking.  The unbalanced one is a type "C" 50-Ohm.

73DG

Hey Phil,

Your best preparation comes from reading all the information out there on the R390A that you can find on the web. Hope you join the club, if not with this example, then some other you may find later.

What kind of shape, what kind of money ?

These two factors are more important than "what contract," these days, although some people prefer some manufacturers over others.

"Good working shape." SO I guess you have you turned it on and tuned it ?   If it runs and sounds okay, that's most of the test.  Otherwise you could be chasing down bad tubes and power supply capacitors before you can go further.

If it's running, (and I take it this is the case):

Check for whether the main kilocycle knob tunes smoothly, without a lot of resistance. Binding is not good.  

When tuned into an AM station, put it on 8Kc selectivity and further move the Megacycle knob off its detent. If the signal improves, you probably need an alignment. A high-mileage radio won't have a very pronounced notch, mechanically, as you rotate among Megacycles.  This could indicate commensurately worn cams in the tuning stages, making it tough to align.

All bands should produce a signal.  If not, you may have a dead crystal or two. Not fatal, but a bargaining point.

Chronologically, the newest radios likely to be found on the market came from Electronic Assistance Corp., with serial numbers above 6000 meaning 1967 or newer. These radios had Teflon insulated harnesses instead of the vinyl wiring of earlier models, and can help protect against scuffing-related shorts from going in and out of the rack all these years.

"Funky" antenna connectors might be stock or maybe not.  They're mounted on a module, not just a chassis bulkhead, and yes, you should pull the top and bottom covers off and look for signs of fire or modification.

Does the MUTE work ?  Important in station installation.

A couple of good modifications you may find include a substitute for the ballast tube on the topside, left front corner, RT510. You might find a 12BY7 in there instead, with only its filament as an active element, and a rewired socket underneath.

You may also find solid state rectifiers underneath, in place of a pair of 26Z5 tubes in the power supply module.

A little bit of reading here:
http://www.r-390a.net/Pearls/tubes.pdf

Mongrel versus purebred.  A bad module in the R390A was meant to be substituted by a repair depot to get the receiver back in service quickly. The bench would later fix the module for the next plug and go.  Consequently, if it's, say,  a "Motorola" mainframe (see serial number plate,) you might find Sterwart-Warner, EAC, Collins, and other modules inside. No big deal functionally, but it shows the receiver has been to the depot sometime in its life.

Every R-390/A owner should:

Subscribe to http://mailman.qth.net/pipermail/r-390/ Get on the e-mail reflector for lots of tips & help.

Read stuff from here http://www.r-390a.net/

Down load and print out the latest revision of the Y2K manual, now at revision three. Link can be found above.

Craig,

An R-390A is on my wish list. I gave a couple of R-390A s-meters away years ago --the ones with the radium paint-- and regret it to this day.

Here's some info about R-390A modifications, servicing, etc.:
http://groups.yahoo.com/group/thedallasfiles/files/Receivers/R-390A/

You have to subscribe to read it, but I think it's worth it. Dallas Lankford seems to know his loop arrays, and so I imagine he knows what he's talking about there also.

Hi Phil
It may seem like a daunting task to get a nice R390A. All of the points mentioned above are very good. Is there anyone who likes boat anchors close by you to assess this radio??? Some of these radios have seen very rough service. Some have had an easy life in a seldom used comm van from the military. I bought mine from a MARS Ham operator. They gave the R390A to him to say thanks for wiring their comm center. Brand new in a wooden crate. So mine never saw military service, but from old age, has had its problems. With the service manual, you can almost anything that is needed to that radio.
The audio from the Diode Load can't be beat.
Fred

I thought this was a good idea since my line voltage is high and I prefer not to tie up a variac for this.

http://www.r-390a.net/faq-HiVolt.htm (http://www.r-390a.net/faq-HiVolt.htm)

Saw the note about what to look for in an R-390 the other day and just ran across this on that place:

http://cgi.ebay.com/polished-aluminum-R-390A-R390A-r-390-HF-receiver-/280713229562?pt=LH_DefaultDomain_0&hash=item415bcff4fa

Is this for real? Have a hard time believing all this about how the 390 is the greatest receiver ever built and how the NSA is still using them today! And I cannot think of any application where the government bought polished aluminum front receivers. The 390 a good receiver but this is almost to the point where I am surprised they are not offering it with oxygen free copper wire power plug for the significant improvement that only the most sophisticated operators will understand.
KA3EKH

You could ask him directly. He's a member of this forum. Some believe R-390's are better then R-390A's. The seller sounds like he came from a marketing background. Personally, I don't care for either one of them. Dumped my R-390A at Dayton several years ago.

The R390A still has some of the best phase noise numbers compared to anything with a synthesizer. The down side is the mixer stages. This is a weak link.
Tracking filters help the poor single ended mixers. This would be a cool radio to hot rod with better mixers. I almost did it, then found Racal and Cubic and lost interest.
Anybody can claim it is rebuilt but few know how to do a good job.

There are volumes of information and good advice out there, Phil. Plenty of snake oil BS too, so beware.

Aside from a geartrain that can be somewhat intimidating the first time around, it's a pretty straightforward rig, made easier by its modular design. Most parts are readily available. One of the more frequent failures is a broken gear clamp, causing the geartrain timing to be lost. Antenna connectors are easy enough to change if you prefer, adapters are available if you don't want to modifiy it.

No need to screw with rewiring sockets or any of that if the 3TF7 ballast is dead. Just stuff a 47 ohm resistor between pins 3 and 7 in the socket. Should be 5-10 watts IIRC. Easily reversible, too.  ;)

I've got a couple As here along with the original 390, if you're in the area stop by. Or if you get hung up on something, give a call. Otherwise we can chat at Shelby. Certainly one of the all time best receivers out there with so many possibilities for simple upgrades, like driving a big speaker with an outboard amp hung off the diode load connections on back.

BTW, that microdial on the BFO was used mainly for RATT/RTTY work with ASA and others. Makes resetting to proper frequency more precise and looks cool, but won't make any difference for AM use. Still, better to have and not need than need and not have.

The AD may be pumped up by a rug merchant, but some of that about the gummint using the old BA's might be true. They would be the only electronics working after an EMP event.

http://en.wikipedia.org/wiki/Electromagnetic_pulse

Back in the late eighties and early nineties was fortunate enough to be in the pipeline for NSA disposal for awhile. At that time they were dumping most of the equipment from the late seventies and early eighties and never saw one tube base radio. Think by the seventies with the exception of maybe military intercept everyone was using Watkins Johnson stuff or custom built receivers. Saw things like Interrad, Microdyne and many others including weird things like Bearcat programmable scanners mounted in tempeasted rack mount enclosures but never one R-390. The R-390 is a great receiver if you know where something is that you want to listen to, or if it's a static non changing circuit. I saw them used as WWV receivers where you can stick it in a rack somewhere and forget it as late as the eighties. But it appears to me that in the last several years they are reaching some form of almost mythical status. Now know that the receiver in question is a custom rebuild with the polished panel and can see where many would find this desirable and can understand that some may want to buy them who may not have the expertise required to work on or overhaul them but somehow, not cretin how maybe it's just my psychotic nature or that I was traumatized at a young age by suffering thru a mechanical alignment on a 390 that inspires me to rant agents them. Please remember that this is only my opinion on the subject and not meant to discourage the original poster from his wanting a R-390 Although I sold off my last 390 years ago it almost appears that you cannot be a serious AM operator without one these days.
Ray KA3EKH

Everyone seems to make such adoo about aligning a 390 or 390A. They may be a bit time consuming, but they are not all that difficult. Having done several of them over the years, I can think of a lot of things that are by far worse!!

I would much rather align a 390A than change a bandswitch wafer in an SX-42  ;D  ;D or some of the other szht details I have taken on over the years.

Aside from the weight issue, what turns you off about them Pete?

Hey Fred,
Don't be so sure about SS and EMP. I just shot 3/4 of a million watt pulse into one of our systems and it didn't even blink.

Bandswitching and tuning; as a band cruiser, it sucks. Never cared for the audio output, even off the detector feeding an outboard amp. The Hammarlund SB-600 always ran rings around this receiver in these categories. Used the 390A as a foot stool until I got rid of it. Still have the SP-600. I've never had a fondness for Collins equipment so its removal was insignificant in my shack. Of course, on the bright side, Collins equipment make great "flipper" material especially at large hamfests and Ebay.

I agree on this. Other than band switching, i don't find the others objectionable. There are some simple mods to make the audio sound better. I may try those but I find the audio pleasant the way it is. Never tried the diode approach because I didn't want to run a separate audio amp for that purpose. Nowadays with a small solid state audio amp in line with it, it may be an improvement.

Back when I was sixteen or seventeen I saved up all my money and bought an R-390 at a Hamfest for around $250.00 or so. It was a Frankenstein radio built from several different radios and many had attempted to repair it before I got it, funny thing is the guy I bought it from said  "O, it works perfect. Just wiggle the band switch every now and then if it doesn't work" turned out that several of the clamps were broken and just about every gear was out of alignment. All the little alignment marks are great if the shafts that attach to the switches are correctly aligned but when they are not look out. Took forever to get the radio to work where you can start at the bottom and work your way up thru all the bands and have all them work. That was all over thirty years ago and I have owned, operated and worked on the family of radios since but still have no love for them. The ARR-41 is almost as difficult but the R-388, 75A series or 51J are easier to deal with and will stick with the Watkins Johnson or other manufactures that are minim of gears and switches and leave the fifties technology of clockwork radios behind. I have an R-1051G on the bench right now and with all the chains and gears on that would rather work on that then a 390
KA3EKH

Thanks to all for the advice. It's really hard to determine likes/dislikes and checking for problems in just an hour or two of operating, so I knew I'd get some great input from others that have been there. I checked everything I could remember.

Well, I think I'm going to take it. Collins build w/ nomenclature plate, s/n 67; looks very clean inside and out. I'll post some photos when I get it home.

73, Phil

 

Cool, you’re a true hard core AM operator now! Next you need a T-368, BC-610 or old broadcast transmitter.

Why or?

And works too.

I suspect it's like the SX-28 recap, Slab: once you've been through a few of them and have a system down, it's nowhere near as intimidating, as you know. The R-390 family is just intimidating to look at as you contemplate having to re-time one. It's pretty straightforward though, as long as you follow the instructions (Navy manual is the best). I think a lot of guys got into trouble back in the 90s when they joined the R-390 list, read about folks rebuilding a geartrain, and dove in for a complete tear down. Then again, it sure ain't no S-38!


I always kept the R-390 and A models in a rack with the trusty SP-600 for band cruising duties. R-390s were meant to have the ability to tune other frequencies, not necessarily to be easy to tune. Many spent their lives set to one frequency.

SP-600 is much easier on the wrists and the crystal filtering is smoother on strong signals than the 390A. Though the 6AQ5 audio output of the 600 doesn't hold a candle to its predecessors from the Super Pro line. And for pulling out the really weak ones, the 390s always excelled. Cruise around with the 600, pull 'em out with the R-390s. If you're all that serious about it.

For AM use, the A should be just the ticket for dealing with those noisey nights with QRM. Jay/W1VD had a good post on here a while back about using an outboard audio amp with his.

Here's some pics of the 390A. Couldn't get them to upload the other night.

Phil

One more... wonder what the mod is on the L.H. side?

Looks very clean. What are those small trimmers caps about on the chassis to the left?

Looks to have a vernier drive in there too. Never seen anything like it.

Here in the old continent the 390 is a myth. Every boatanchorer have to own one, and so i did. I decided for a collins 390 sn 51. It is in very good shape and aligned, but for me it is not the best of mine vintage receivers. Without the diode output to amp trick the audio is mediocre. The 8khz filter is too wide sometimes and the 4 khz too narrow for Am. it is not a bancruising receiver, and without the tmc-590 the ssb reception is ugly. I am sure that is a great receiver for point to point applications, but my recently restored RCA ar-88 receives the same stations but with a really better out of the box audio.
And you have to ear the R&S ek07d. Anyway the 390 is a very nice receiver

The new/different potentiometer upper bracket: The original one turn pot was too course! The carrier level meter would not hold zero. So a 10 turn wirewound 2 watt pot is the answer.

Those trimmer caps, don't have a clue.

Craig,

I never saw the extra stuff on the Left Side like that. (trimmer caps, and  trim pot?)
The BFO "counter?" on the front panel is new to me.

nice clean condition !!!! Any documentation on the mods??
Looks like a nice receiver to me
Fred

An easy cure for the "carrier meter won't zero" problem is a 100 ohm or so resistor in parallel with the outer legs of the pot.  It carries part of the current so the pot doesn't heat up and drift, and puts your zero on a new place in case you have a dead spot in the pot right where you need it.

The best way to use an R390A is with a Rycom R-1307 at the IF output to receive the station you want, after finding it with an SX-28 or whatever fast-tuning set you like. If that sounds like a lot of trouble, it is said that nothing worthwhile is easy.

The turns counter on the BFO knob is rather common,  it's an RTTY depot mod.  The other items are ham creations.  The trimmer thing might be described in Hollow State Newsletter but I don't recall it.

Thanks John..........solved a LONG problem here. DONE!!

A couple of simple mods and they (390As) receive SSB like they were made for it. Just reduce the size of the plate dropping resistor for the BFO, and increase the size of the BFO injection coupling cap and they will receive sideband like a pro without installing a product detector. Mine has been that way for over 20+ years. 2 components to change is not a lot of work to do for what you get back.

Tell us more please. Is there a spot on the WWW where I can find this mod?

And where do you purchase a Rycom R1307?

Terry,
        I'm at work, so I dont have the skizmatic here. Without looking at the skiz for the IF deck I dont remember what the the resistor and cap numbers or values were. I'm sure someone has it posted on one of the R390 reflectors somewhere. It used to be a pretty common mod. But it is very simple to do and mine receives SSB like it is made for it. You rarely ever have to back down the RF gain, if you do, it is only on the strongest needle-pinning signals. Just set the BFO +1kc for lower sideband and -1kc for uppa sideband and the tuning dial stays the same.

IIRC, the BFO only runs with 12 or 20 volts on the plate. So dramatically reducing the resistor and doubling the size of the coupling cap should get you somewhere in the ballpark. JN might remember what the values of the parts were.

IIRC, the old "rule of thumb" was that you needed to have BFO injection = to 10X the IF signal to the detector for "distortion free" SSB reception.

I have seen that on some of the ones I have worked on over the years. Hmmmmmmm.........

I always wondered what the full scale meter rating and was. They are something wierd, and a standard 1mA meter movement or universal "S" meter wont work right in them.

A good working R390A s meter is pretty accurate. Full scale is .1 volts, 100dBuv.

Cool!  Glad it worked for you Fred.

Or just use a HRO-500 to start with; it will hear stations with a 30' wire that is buried in the 390 mixer noise.

IMO a slightly improved 51J4 is a better cruiser than either the 390 or 390A

Peeked inside my 390A for some maintenance needs and see a 22 ohm across the pot...is that good enough or 100 ohm better?? I might find a 10 turn pot also. Possibly my carrier pot has bad spots. Meter never settles. One day on zero next two hours on 20.
Thanks

That should be fine, Fred.  The problem is that there's a fair amount of power dissipated in that pot and it drifts, gets bad spots, etc.

That pot has been a source of problems forever, as Johnny sez. There's a precision ten-turn pot available that addresses it pretty well along with the other suggestions.


Sounds a lot like the Dallas Lankford AGC mod, Slab:

- one diode in parallel with R547, cathode as follows

  ---]<--- pin 2 V506A

- one diode in parallel with R546, cathode as follows

  --->[--- pin 1 V509A

- one 47 pf cap in parallel with C535

Quick and easy, easily reversible, and gives excellent results. Assuming that SSB reception without riding the RF gain is important, of course.

Phil, you got an excellent receiver. Looks pretty clean and complete. Should give you many hours of enjoyment and utility. Still the best receiver buy out there IMO. The microdial on the BFO is a mod for RTTY/RATT use as someone mentioned. ASA and a couple other groups used this. Wonder if you have a sticker on the back apron from one of them? Could be someone just added it for the coolness factor. They do make fine tuning of the BFO quite smooth along with adding a measure of logging.

R390As are for people who actually get on the air.

I better get my ARSE in gear........thanks Dave

Not meant for you Phred. It's just anyone who operates at night on the lower bands knows how useful those wrist twisters really are.

True story, though the passband tuning on the 75A-4 sure comes in handy, along with the mechanical filters, in such conditions. They've come down a lot in price, a decent one just sold for $660 on epay t'udder day. If you're not a collector, it's a $500 radio.

The 390s aren't as easy to tune, but then - they were never meant to be band cruisers. I seldom tune around when in conversation with others anyway.  ;D