Collins R-390A/URR help?

[airboss20]

I just bought an old Collins R-390A/URR for my grandfather. He was a high speed decoder for the Army Security Agency during the Vietnam conflict era. I think he is going to cry when he sees it, but I need to make sure it works before I give it to him.

There are 3 antenna inputs on the back, and I would like to buy, make or acquire the proper antennas for it. I see that there is a 125ohm balanced input with a Twinax connector, an unbalanced input with a C connector, and an unlabeled input with a BNC connector.

Which one or ones are the best for listening to shortwave, ham, CB and anything in its receive range? Also, What is the best antenna suited for this radio?

Hours of online research has not turned up much information.

Any information would be greatly appreciated.

 

[rfradioconsult]

A boat anchor in the truest sense but a great receiver, certaintly helps with wrist strengh excercise!
Haven't had hands on for almost 40 years, I think the C conector is corrct the BNC I think is actually an IF out signal to a companion ISB detector. Something along the lines of the PAR SWL antenna would be fine for your glow-in-the-dark radio.

EF-SWL Antenna | PAR Electronics | Filters for the commercial 2 way market, MATV, FM broadcast, laboratory, marine industry, amateur radio, scanner and short wave listening enthusiasts

 

[airboss20]

Thanks for the info, looks like similar items are quite affordable on ebay. Would I port this to the unbalanced C or the balanced twinax?

 

[prcguy]

The 125 ohm balanced input is the best input to use, even with an unbalanced antenna. You can use a computer Twinax connector and ground one pin to the coax shield and the other goes to the center conductor.

The type C connector is the second best input and you can find C male to N or BNC female adapters on Ebay. The BNC on the rear of the radio is an IF output as mentioned earlier.

I acquired an R-390A about 2 months ago and there is a lot to cover bringing one up to specs. Many tubes to check, mechanical nightmares, leaky capacitors to replace, etc. Remember, these things are about 45yrs old at minimum.

For any adjustments or upgrades you want to download the R-390A Y2K manual, which is a completely rewritten military manual with tons of extra information gathered over the last 50yrs of tinkering with the 390A. Here is a site with lots of good info and a link to the R-390A Y2K manual.
The R-390A Frequently Asked Questions Page
prcguy

 

[rfradioconsult]

The 390 is a great receiver, especially if you don't do a lot of channel changing, that is were the term "390 wrist" comes from.

 

[W4ASZ]

I bought a restored R-390A from Rick Mish of Miltronix a number of years ago and it is a delight to use.

I use the C connector and an adapter and it works peachy.

This is a great gift. Good for you !

 

[kb2vxa]

"The 125 ohm balanced input is the best input to use, even with an unbalanced antenna."
If that were the case there would be no C connector for an unbalanced input. A little common sense should tell you that the balanced input is for a balanced antenna such as a dipole with open wire feedline while the unbalanced input is for an unbalanced antenna working against ground and a coaxial transmission line. The BNC is the IF output for the RTTY adapter which BTW contains a product detector needed for FSK reception and works a whole lot better than the BFO injection for CW and SSB.

Don't leave your grandfather stranded with a boat anchor and no way to work with it, that is modify and repair, get your hands on the service manual and both of you learn what makes the venerable R390 tick. It's not your run of the mill receiver, it's 25VDC mobile military which has quirks I'm sure you never heard of along with a few terribly hard to obtain parts like the ballast tube. Last but not least I'm sure there are a few things needing attention right off the bat to get it working properly again so get cracking the books, if you need help it's no farther away than the AM Fone web page. The AM Forum - Index

Oh and I almost forgot the rare as hen's teeth CV-116-TU RTTY adapter photo in case you get lucky.

 

[WouffHong]

Boat Anchors to love!

Or, you could use this receiver I owned back in the 60's

AN/FRR-3A - Complete with "dial-a-Channel whirring rotary step bandswitching!

6' high! :roll: :roll:

http://pixtoshare.net/anfrr3a.jpg

Da Wouff....

 

[prcguy]

With a little common sense doing research on the topic or having actual knowledge of the R-390A Warren would know the C connector input bypasses the first RF stage in the receiver and the balanced input usually works better, even with unbalanced 50 ohm coax.

A little more knowledge would be in order so Warren doesn't incorrectly call the R-390A a 25VDC radio, its 110/220VAC.

There are some simple mods for the R-390A (2 diodes and a cap) that makes SSB reception real nice, check the R-390A Y2K manual link in my previous post.
prcguy

"The 125 ohm balanced input is the best input to use, even with an unbalanced antenna."
If that were the case there would be no C connector for an unbalanced input. A little common sense should tell you that the balanced input is for a balanced antenna such as a dipole with open wire feedline while the unbalanced input is for an unbalanced antenna working against ground and a coaxial transmission line. The BNC is the IF output for the RTTY adapter which BTW contains a product detector needed for FSK reception and works a whole lot better than the BFO injection for CW and SSB.

Don't leave your grandfather stranded with a boat anchor and no way to work with it, that is modify and repair, get your hands on the service manual and both of you learn what makes the venerable R390 tick. It's not your run of the mill receiver, it's 25VDC mobile military which has quirks I'm sure you never heard of along with a few terribly hard to obtain parts like the ballast tube. Last but not least I'm sure there are a few things needing attention right off the bat to get it working properly again so get cracking the books, if you need help it's no farther away than the AM Fone web page. The AM Forum - Index

Oh and I almost forgot the rare as hen's teeth CV-116-TU RTTY adapter photo in case you get lucky.

 

[Fast1eddie]

Go get 'em, prcguy!!

 

[kb2vxa]

PRCguy, why do you insist on arguing "lack of knowledge" with I who has refurbished and repaired several R390s using the full service manual, the original as supplied to the Army and my experience operating them? It only goes to show that you among others know little to nothing about people's background yet argue out of sheer ignorance of it, seemingly to brag about your "expertise" at the expense of others.

"Go get 'em, prcguy!!"
Ah, a cheerleader. Well, you're not alone in giving RR among other web forums a bad reputation but don't expect me to join you down below as I have matured beyond the schoolyard nyeah nyeah crowd.

'Nuff said, move along, nothing to see here.

 

[prcguy]

Warren,
I had no problem until you highlighted one of my comments and tried to shoot it to pieces with your bubbling fountain of knowledge so I bit back.

I guess you could have breezed over the OP and mistaken the R-390A with the 28VDC R-392 vehicular receiver and I occasionally make similar mistakes when I read in a hurry. I also suffer public humiliation when my gross mistakes are pointed out and sometimes it helps us learn and pay attention to details. Welcome to the club and I hope you understand its nothing personal, its just life on the Internet.

I have no real expertise in anything special and am probably a lot like you with a little knowledge about a lot of different things. Then there's that east coast/west coast thing but I think we'll be ok if you stay on your side there and I work on stuff from over here.

BTW, you don't really think the R-390A is a DC powered radio now, do ya?
prcguy

PRCguy, why do you insist on arguing "lack of knowledge" with I who has refurbished and repaired several R390s using the full service manual, the original as supplied to the Army and my experience operating them? It only goes to show that you among others know little to nothing about people's background yet argue out of sheer ignorance of it, seemingly to brag about your "expertise" at the expense of others.

"Go get 'em, prcguy!!"
Ah, a cheerleader. Well, you're not alone in giving RR among other web forums a bad reputation but don't expect me to join you down below as I have matured beyond the schoolyard nyeah nyeah crowd.

'Nuff said, move along, nothing to see here.

 

[ka3jjz]

Enough with the personals, gentlemen. Take it off list if you wish to argue. You're welcome to add facts to the discussion about the 390 series - let's keep it on topic, and professional

Mike

 

[Fast1eddie]

It's very simple Warren. Your arrogance and perceived superiority shows in your writings. No doubt you are a very smart man, but you turn me off, sir.

Nuff said, I am done. Have a nice day.

 

[kb2vxa]

"Enough with the personals, gentlemen. Take it off list if you wish to argue."
No argument here, that's water under the bridge.
"You're welcome to add facts to the discussion about the 390 series - let's keep it on topic, and professional."
That's exactly what I intend to do here this time around ignoring all other comments.

I'm not confusing the R390 with any vehicular receiver as the unit was built as a mobile unit by several manufacturers under contract with the Army which calls anything you can move with a forklift "mobile". Since it has no internal conversion from 24VDC (Army battery systems) it requires an external B+ supply. Please note that all heater strings add up to 24V and are connected to the external input allowing mobile operation in a radio truck which usually pulled a generator trailer, it also operates as a temporary base receiver off the 115VAC mains and was often used this way. One very interesting thing about the Black Sheep Squadron TV series is all the props were authentic right down to the radio equipment at the Army Air Corps base including the R390 teamed up with the transmitter made by Hallicrafters, unfortunately it's military designation escapes me at the moment.

Two things I found right off the bat that may help today's users, being the ballast tube only comes into play in regulating heater current when operated off 24VDC and mains power being quite stable it really isn't needed so replacement isn't a problem. There are two tubes in series with it, jumper it out and replace the 6V heater tubes with 12V and you're in business. Rather often some of the T-R changeover relays fail to operate because the selenium stack rectifier under the AC power supply module has failed due to age. Simply replacing it with modern silicon diodes fixes that and being under the chassis nobody will be the wiser. Oh, hang onto the ballast tube and the 6V ones you replaced, never irreversibly modify a classic as it reduces the collector value to just about nil.

 

[jackj]

I'm not confusing the R390 with any vehicular receiver as the unit was built as a mobile unit by several manufacturers under contract with the Army which calls anything you can move with a forklift "mobile".

Put a handle on that forklift and it becomes a portable forklift according to Army/Navy nomenclature.

 

[prcguy]

Warren,
Could you please supply a link or some other info on this elusive mobile R-390A? What external B+ supply does it use? Any model #s or links?

The "regular" R-390A does not have any external DC connections for the heaters anywhere on the radio and none of the other R-390A experts I can find in this country has ever heard of such a beast. The R-390A is known only for fixed station and shipboard use from AC mains.

Also, if you replace the two 6BA6s wired in series with the ballast tube you usually have to recalibrate the PTO end points since one of the tubes is in the PTO and its much easier to replace a bad ballast tube with a 43 ohm resistor or outboard 12v regulator. If the original 6BA6 PTO tube is good its best to leave it there since any replacement should have a lot of hours on it to avoid another PTO recalibration.
"Your friendly" prcguy

"Enough with the personals, gentlemen. Take it off list if you wish to argue."
No argument here, that's water under the bridge.
"You're welcome to add facts to the discussion about the 390 series - let's keep it on topic, and professional."
That's exactly what I intend to do here this time around ignoring all other comments.

I'm not confusing the R390 with any vehicular receiver as the unit was built as a mobile unit by several manufacturers under contract with the Army which calls anything you can move with a forklift "mobile". Since it has no internal conversion from 24VDC (Army battery systems) it requires an external B+ supply. Please note that all heater strings add up to 24V and are connected to the external input allowing mobile operation in a radio truck which usually pulled a generator trailer, it also operates as a temporary base receiver off the 115VAC mains and was often used this way. One very interesting thing about the Black Sheep Squadron TV series is all the props were authentic right down to the radio equipment at the Army Air Corps base including the R390 teamed up with the transmitter made by Hallicrafters, unfortunately it's military designation escapes me at the moment.

Two things I found right off the bat that may help today's users, being the ballast tube only comes into play in regulating heater current when operated off 24VDC and mains power being quite stable it really isn't needed so replacement isn't a problem. There are two tubes in series with it, jumper it out and replace the 6V heater tubes with 12V and you're in business. Rather often some of the T-R changeover relays fail to operate because the selenium stack rectifier under the AC power supply module has failed due to age. Simply replacing it with modern silicon diodes fixes that and being under the chassis nobody will be the wiser. Oh, hang onto the ballast tube and the 6V ones you replaced, never irreversibly modify a classic as it reduces the collector value to just about nil.

 

[kb2vxa]

"Could you please supply a link or some other info on this elusive mobile R-390A? What external B+ supply does it use? Any model #s or links?"
Ten year old memories are fuzzy at best so I refer you to a group far more familiar than I. You'll need to register on the site to gain posting privileges of course but I'm sure they can answer your questions far better. The AM Forum - Index I wouldn't be surprised to find out I'm wrong about a few things, it wouldn't be the first time nor the last so keep me posted if you will.

I never saw the need to recalibrate anything after changing the 6BA6 to a 12BA6 since the only difference is heater voltage and current. The only thing that affects calibration is inter-electrode capacitance which does not change unless the tube suffers catastrophic damage, the only thing that suffers with "age" meaning hours of operation is cathode emission. Electrolytics and carbon resistors are one thing but I've never seen an NOS tube go bad. (;->)

Oh one other thing, those B+ regulator series pass tubes are hard to come by and although I never needed to replace them I'm sure they're very expensive. I guess you already know that's rapidly getting to be the case with all tubes as only high power transmitting tubes are still being made overseas for replacement purposes only. There will come the day when new ones will become unavailable too and all boat anchors will become museum display pieces... -<)

Video Killed The Radio Star was the first played on MTV, MOSFET Killed The Power Tetrode will be the last.

Post edit:
I just had a look at a partial schematic and found the power connector and supply, here it is in a nut shell. J104 pins A & D are AC input fused for 3A by F101 and B being DC fused for 20A by F103, C being chassis ground. I saw no provision for B+ input but then again it may be on another page if there is one. My best guess is one may be on a rear panel strip along with the other inputs, outputs and T-R switching but tracing out the schematics is driving me buggy so I'll leave that to someone else. (;->)

 

[iamhere300]

The R-390A Frequently Asked Questions Page is a link with information about the R390A, and clearly showing it a 115/230 VAC item.

Rovero's R-392 Page is a link with information about the R392, and clearly showing it to be a 24-28 VDC item.

I loved the 390A that I used to have. I believe I even have a 3TF7 ballast tube floating around here somewhere.

Either the C or the 125 ohm input worked great for me, used just a long wire antenna.

 

[kb2vxa]

"The R-390A Frequently Asked Questions Page is a link with information about the R390A, and clearly showing it a 115/230 VAC item."
Yes, but why then does the power socket have a 24VDC input to the heater strings? I'm still waiting to hear if there is a B+ connection on one of the rear panel strips but that should come in time. Oh and BTW I just remembered its mate was the BC610 transmitter.