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THE AM BULLETIN BOARD => Technical Forum => Topic started by: NR5P on February 26, 2012, 08:04:50 PM



Title: Need some quick help on purchasing an r-392
Post by: NR5P on February 26, 2012, 08:04:50 PM
Please don't buy this haha.  I am thinking of getting this.  An r-390 is out of my price range.  This r-392 is very similiar.  It doesn't seem that to many of these come up for sale.  I like the ruggedness of it although this one looks like its been put to the test.  The guy says it works but that audio output is lower than it should be.  I don't mind doing some work to it and I have a power supply.  If there is a problem with it does anyone know just how hard these are to work on?  It seems to me this may be a little high on the price but it may be worth it to me unless it is a complete nightmare to work on due to complexity...I want to upgrade my receiver and was going to get an hro-50 or 60 and was set on it.  Then I found out about the r-392 and I love it.


Title: Re: Need some quick help on purchasing an r-392
Post by: NR5P on February 26, 2012, 08:16:55 PM
also it is missing some screws from the front so I think the likely hood of needing to do a little work is pretty good. 


Title: Re: Need some quick help on purchasing an r-392
Post by: k4kyv on February 26, 2012, 08:25:39 PM
If you can get a manual, the R-392 is pretty easy to work on.  Of course, you need the 28V power supply capable of several amps.  It uses special 28 volt filament tubes, and runs only 28 volts on the plates, but it performs remarkably well.  Like the R-390 it has no mechanical filters, and actually has good audio quality, since the final audio stage is push-pull, and rated at a couple of watts, since they were designed to be operated in a noisy jeep.


Title: Re: Need some quick help on purchasing an r-392
Post by: KA8WTK on February 26, 2012, 08:29:33 PM
Audio could be low if he hooked up the wrong impedance speaker.
I use an LS-166 which has a 600 to 8 ohm transformer in it and the audio is fine. Never tried it with an 8 ohm speaker.


Title: Re: Need some quick help on purchasing an r-392
Post by: NR5P on February 26, 2012, 08:37:46 PM
I went ahead and purchased it.  The guy has great feedback and I'm to impatient to wait for a cheaper one.  The coolness factor of this radio was to much.  Even if it takes work to get it running right, I'd rather do the work and keep it on the air then somebody else get it and part it out.  I feel so much better using a piece of equipment after I've put blood sweat and tears into it anyways.  Hopefully it doesn't need anything but a few panel screws though ::)  I'm going to look for a power cable now and I've got a power supply capable of supplying well over 3A.  I'd like to build a power supply just for this receiver though....maybe in a large ammo can.  I love that I can connect a couple batteries in series and run this if it was necessary.  At least until the filaments suck all the juice


Title: Re: Need some quick help on purchasing an r-392
Post by: W7TFO on February 26, 2012, 08:40:43 PM
There is a retrofit module used in the audio output stage to solid-state it.  All of them I have seen have a lower output level than the tube FWIW.

A 600-Ohm speaker is necessary to make it work right, as stated.

73DG


Title: Re: Need some quick help on purchasing an r-392
Post by: kb3ouk on February 26, 2012, 09:10:53 PM
One little tidbit of info that may be of some use, the filament and B+ pins on the power supply plug are seperate, i've heard that some people run the B+ at a higher voltage (probably something like 40-50 volts) and get a little better performance.


Title: Re: Need some quick help on purchasing an r-392
Post by: WA1GFZ on February 26, 2012, 09:23:03 PM
I had a very clean r392 from Fair radio. It tested quite well by today's standards. The issue I had was I could not buy tubes for it anywhere so I sold it. The guy I sold it to 10 years ago just told me that he still has it and never turned it on. Audio went dead and never looked into it. Audio output tube usually craps out. Easy to solid state the audio. 600 ohm output. I bet it would be a cool RX to solid state.


Title: Re: Need some quick help on purchasing an r-392
Post by: kb3ouk on February 26, 2012, 09:33:39 PM
it has been done: http://users.erols.com/mdinolfo/r392ss1.htm (http://users.erols.com/mdinolfo/r392ss1.htm)
actually, the neat thing about solid stating an R-392 is the low voltage it runs at is perfect for solid state devices, compared to the 300-400 or so volts that most tube receivers use.


Title: Re: Need some quick help on purchasing an r-392
Post by: IN3IEX on February 27, 2012, 05:52:34 AM
NR5P:

I had the same inspiration last december and I purchased a working Collins first series R392 with a Switching PS and LS166 from an italian ham for 400Euro.
I am very happy with it. After some minor electrical fixes I will repaint the box and will use it.
Manuals (BAMA) are made for servicing, just follow them.
My R392 is full tube, no transistor and no semiconductor diode.
I discarded the switching PSU (because of  RFI) and built a linear PSU with 26V 4A current limited, this PSU has a 30V zener+SCR overvoltage limiter after a 4A fuse.
4A are not enough for filament current surge. The PSU takes 20 seconds for exiting the current limit of 4A, after this warm up phase, the PSU works fine (and filaments are not stressed at power on...).

Changed two or three 26A6 (IF and RF) for some gain in s-meter reading, previously installed tubes worked fine indeed.
Increased the BFO coupling capacitor with a 68pF in parallel to C618. Now I do not need to reduce the RF gain in SSB-CW. After this mod, retune T601 for maximum audio output - T601 does not affect the S-meter.
Follow the manual on how to remove the lower deck (very easy - set BW to 8 kHz, few connectors, green screws and lift).
Fixed overshoots of ALC in SSB with a 20k trimmer resistor in series to C103 (this capacitor is on the front panel near the BFO switch - very easy to access)..... In 1950 they apparently had no idea of pole-zero compensation in control systems.
I added a trimmer to the cathode of one of the IF tubes in order to follow the schematic of the second series. (the first and second series also differ in the number of slugs in the RF coils - see the two manuals available on the internet).

Reduced the ALC operation on first RF amp 26A6 with a 1 Megaohm resistor wrapped on test point E201 near V201 and ground. This mod increases sensitivity and improves ALC dynamics in SSB.

The receiver may require touch-up alignment (if it already works)...

Read this if needed:
http://www.antiqueradios.com/forums/viewtopic.php?t=58404

The receiver is very sensitive on any band. I can receive BC without any antenna (the antenna is the antenna connector). I never perceived intermodulation by tuning BC bands, or 40m Ham near BC edge, or MW, using SW full size dipoles.
Audio quality in AM is very high, much better than most receivers I have, if using a wide band loudspeaker. I have found a 600 ohm dual cone speaker made by Philips in the '60.
Frequency stability is surprisingly high.
The R392 is a masterpiece, no doubt.

Tubes are here:

http://stores.ebay.com/K5SVC/TUBES-/_i.html?_nkw=26&_fsub=8&_sid=14089412&_trksid=p4634.c0.m322

Giorgio


Title: Re: Need some quick help on purchasing an r-392
Post by: WA1GFZ on February 27, 2012, 09:08:45 AM
I seem to remember the R392 dynamic range over 90dB. It would be a very cool RX to solid state. No synthesizer phase noise. No ringing filters. Perfect front end for a softrock.


Title: Re: Need some quick help on purchasing an r-392
Post by: IN3IEX on February 27, 2012, 09:55:06 AM
Yes, 455 kHz IF output on front panel....  and keeps the table in place.


Title: Re: Need some quick help on purchasing an r-392
Post by: WD5JKO on February 27, 2012, 10:49:21 AM

The tube center has most of those tubes for $5 each:

http://www.thetubecenter.com/vacuumtubes_tubelist_tubes_13CW4-90c1.html


Title: Re: Need some quick help on purchasing an r-392
Post by: The Slab Bacon on February 27, 2012, 11:38:18 AM
With the somewhat odd tubes they used in 392s, if you plan on keeping and using it often, I would emass a good collection of spare tubes. Those are somewhat similar to the ones used in mid 60s hybrid car radios. But those were 12v fils and 12v plate supply as well.

That was the one really nice thing about 390As, other than the ballast tube and the rectifiers, they used all common, easy to find tubes.


Title: Re: Need some quick help on purchasing an r-392
Post by: NR5P on February 27, 2012, 01:23:30 PM
thanks for the help.  I did notice a few people have solid stated them but I'm going to leave this all tube.  I'll buy up some extras while I can get them.  I was hoping I had a 600ohm speaker in an old german shortwave radio I have in a little building i store parts for but it's low impedance.  Im sure I'll find one at the Belton hamfest coming up.  Or I may just build an outboard audio amp because I like to turn up the volume loud to hear around the house.  I don't know whats wrong with me I'm 27yr old and hardly have any piece of equipment without tubes!


Title: Re: Need some quick help on purchasing an r-392
Post by: WD8BIL on February 27, 2012, 01:55:03 PM
You can also try this little transformer. I put one inside my Navy Scott Model RCH (not again, Slab!.... You know what I mean!) and it works great.

Of course, connect the 8 ohm side to your speaker and use half the 1000 ohm primary to the radio. It'll work great!

  Audio Output Transformer  (http://www.radioshack.com/product/index.jsp?productId=2103254)


Title: Re: Need some quick help on purchasing an r-392
Post by: WQ9E on February 27, 2012, 05:45:21 PM
Fair Radio used to be a good source of those tubes and that is where I bought the spares for mine.  You might check pricing/availability there as you are looking.  I picked up my R-392 from Fair around 15 years ago while passing through the area.


Title: Re: Need some quick help on purchasing an r-392
Post by: IN3IEX on March 01, 2012, 07:10:17 AM
This is the speaker that I am using with my R392 with the 26A7 audio tube:

http://hupse.eu/radio/speakers/AD3570.htm



Title: Re: Need some quick help on purchasing an r-392
Post by: KA3EKH on March 01, 2012, 09:05:41 AM
If you want to be hard core now you have to get the T-195 transmitter to go with it and have yourself a GRC-19! The T-195 is only about one hundred twenty five pounds and if you donít find the newer one with the solid state inverters you have to supply 28 volts at around 250 amps for start up and around 50 amps while in operation but that will give you at least 60 watts of real plate modulated AM or 100 watts of teletype providing you get the modem and teletype unit to go with it.  Also the T-195 is a completely automatic transmitter (auto tune) and that along with being almost imposable to work on once removed from its case make it a real joy to try to repair!  I have a 1965 M151-A1 jeep and installing a GRC-19 on the back of it is a project that I have been working on for a couple years now.


Title: Re: Need some quick help on purchasing an r-392
Post by: NR5P on March 04, 2012, 12:10:56 AM
I got the receiver and no audio out  :-\.  I did fix the bright dim switch right away though that was an easy fix.  Looks complete except for tool kit missing and a missing tube shield which I had one that fit.  It should be easy to trace I'm getting 0 audio out even checking with a scope there is nothing.  db meter is reading between 10 and 20db for some reason no matter if antenna is hooked up or not when b+ is supplied.  I'm impressed with the way this is designed with all of the modules it looks like it won't be so bad narrowing it down at all.  I haven't taken one out yet though.  The digital readout assembly is not something I would want to mess with however, but I'm sure I'll never need to.  Man that is a lot of moving parts.  I guess that is the same no the r-390's or similar. 


Title: Re: Need some quick help on purchasing an r-392
Post by: NR5P on March 04, 2012, 12:13:49 AM
btw after chatting with the seller I believe he was telling the truth about receiver in the description.  He did say he was getting very low audio out and that was through the r-392 military speaker so impedance was correct.  I have no issues with the seller.


Title: Re: Need some quick help on purchasing an r-392
Post by: NR5P on March 05, 2012, 12:16:30 AM
I got it working!  It just seems to be a dirty bfo switch and agc switch.  It's clean on the inside but the contacts must not be making good connections on the switches.  I will take the panel off and clean them and I think it will work FB.  The smeter still sits between 10 and 20db for some reason with no signal, I know it's not the meter as it drops with rf gain control.  That should be another easy fix though.
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