What is your R390A experience and suggestion?

[W1DAN]

Hi All:

So after all these years of being a National HRO fan I picked up an R390A.

I am getting used to the radio, and have read a fair amount about it.

So....

What do you like about the radio?

More importantly what do you not like about it??

What would you modify?

Do you pull the audio tubes when listening to the diode detector to lower heat?

Do you run the rx with the oven on?

Do you run solid state rectifiers?

Have you bypassed or solid stated the regulator tube?

Do you run a receiver that you feel is superior (tube or solid state).

Thanks!
73,
Dan
W1DAN

[w3jn]

This thread really belongs in the tech forum, but...

What I don't like about the R-390 is the looks, the tuning feel, the lack of a product detector, too slow AVC attack time, and crappy audio (requires use of outboard amp).

Likes:  it's bulletproof, one of the best front ends out there, good selectivity options, stability, frequency resettability.

Modifications I've done to mine is install a product detector, and bypass the stupid 3TF7 filament regulator.  I would like to do some work on the AVC circuit to increase the attack time.

I run with solid state rectifiers, no ovens (absolutely no reason to, it just increases warm up time greatly), haven't solid stated the OA2 regulator - again, no reason to.

The only receiver that comes close in performance that I own is a WJ 8716 - that radio has absolutely the BEST recovered audio of any receiver I've ever used.

73 John

[WA3VJB]

Dan,

You'll want to turn off the ovens, and think about swapping the filament of a 12BH7 to replace the ballast tube. I still have the 25Z5 in there, but there's a mod using another type of miniature rectifier tube that's more available and with better current handling capability.

I use the Line Output as a cue monitor, with the Diode Load as the recording feed. The Local Output goes to a spot speaker over by the transmitter.

The only thing I don't like about the receiver is wanking that MC knob to get from band to band. So I have more than one receiver.

[WA1GFZ]

I had a nice one once and traded it for a HP141. It is a mechanical work of art.
Hands down you cant beat a tracking RF stage. Hands down cleaner LO than any synthesized rig.

It is ugly but so isn't a sleeper hot rod.
I would ( now fire up the flame thrower guys) if I kept it
started at the audio output and worked my to the antenna solid stating one stage at a time with FETs. I would use U310s and CP640s in the RF stages and replace the single ended mixers with something like H mode.
I would also hang an I/Q converter off the 455 KHz and connect it to a computer.

Really, I went out and bought a spare set of tubes and enjoyed watching the gear chain

My unit went down the road when I got into the Racal RA6830.
Yes, John that WJ is a clean radio for the 70s. I checked out a couple 8718s and was impressed with the synthesizer. Cleaner than the Cubic

[W1DAN]

Hi All:

Thanks for all the replies and suggestions!

I experience the fact that it is stable, good audio from the diode detector and has good filters (wish it had a 6kc instead of a 4kc filter).

This is a radio that pushes me to make a synchronous detector for it.

So the problems I find so far on this particular rig:

AC power supply hum. Guess I gotta replace the filter caps.
FM hum..shows up when I turn to the side of a carrier.
After about 4 hours the radio overloads easily and the signal meter goes higher...guess a bad cap or tube in the IF?

I notice the limiter knob position affects the diode output level (I do not notice any distortion).

What I wanna do with this rig:
1) solid state the rectifiers.
2) pull the audio output tubes to save heat
3) replace the current regulatro tube to preserve it.
4) re-cap the IF and other parts as needed

So do you have a solid state rx that you feel is better?

Frank:
I solid stated an old HRO years ago...could not get the LO to track properly, but got great audio with an infinite impedance detector. How would you deal with the changes in signal levels with the FETS (i.e volta from a tube to a FET)? I am not gonna SS this one....

The R390A is a fun rig though...

Thanks guys!

Dan
W1DAN

[WA1GFZ]

Dan,
Use the K2CU AM detector that is about the best I have seen. It is stored on this site somewhere.
Don't waste your time with a sync detector do SDR interface and have variable bandwidth. It will work much better. Sync detector you are constantly playing with the loop filter constants PITA. I did a pll lock ahead of the sdr and that sucked  too.
The software can easily handle it so why make life hard. Just down convert the 455 KHz to around 10 KHz and dump it into the sound card. I did color burst crystals divided by 8 in my sdr project. This will give me 8.44 KHz into the sound card allow ing a bandwidth of just over 16 KHz maximum at the sdr.
I would get a spare PTO and make it track right. Solid state it on the bench then install it.
I've seen a number of articles doing that mod and you can fix the tracking if there is a problem.
My 390A overloaded also, I thought it was the single ended 6C4 mixers. I'm thinking the close in dynamic range is trashed due to the mixers. A good mixer with that clean lo would be cool. 9 pin 7360s would get you to single balanced.
I think there is some real performance hiding in all those gears.
The High z circuits would be fine using fets but I would replace the power supply with a low voltage supply. I had planned on building a new module and run 15 volts down the hv lead. All the heaters would become spare connections.  gfz

[w3jn]

The problem with R-390A overload is due to leakage in the AVC circuit, a misaligned AVC transformer, or a gassy tube whose grid is on the AVC bus driving the bus a bit positive.  Most likely the problem is the time constant capacitor. 

A properly working R-390A will NOT overload on anything you'll find on the shortwave bands, unless you have some bigassed xmitter in your backyard.

[WA1GFZ]

Imagine a R390A tracking RF amp and a stage of conversion ahead of a SDR interface.

[W1DAN]

Hi John:

Thanks for the tip on the leaky timing cap.

From what I remember, changing the release time switch does not bring back the gain to normal. Is there a cap before this switch? It is interesting that it takes about 5-6 hours for the problem to kick in.

Frank:

Yes I am dreaming of an SDR interface. I also am thinking of an I/Q mixer and either a PC or a sync detector at the 455KC IF out. Sorry about abandoning the QSO on 75M Sunday. I got an important phone call. It was good to chat!

73
Dan
W1DAN

[WA1GFZ]

No problem Dan I needed to do more testing.
The board was found to be very sensitive so now considering moving the interface ahead of the 455 khz filters allowing a wider spectrum display equal to the roofing filters.

[WQ9E]

Hi Dan,

To add to the other great advice you have received on the R-390A, don't forget to change the blocking cap that keeps B+ off of the mechanical filters.  I am at work and don't have the schematic with me but it is obvious from the circuit which one you need to replace.  I have heard horror stories of this cap shorting which will take out the mechanical filter currently selected, the unlucky owner may then switch to other filter positions taking out the remaining filters-not a good outcome.

I was lucky enough to find my R-390A at the Princeton IL fest several years ago.  I made one last tour of the fleamarket and was returning to my pickup.  A car pulled up next to me, the driver opened the trunk and there was an R-390A inside (actual Collins manufacture)  complete with dust covers, original glow-in-the-dark meters, and the full military manual.  I asked how much and he said $50, no negotiation.  Sold!  Its only oddity is a vernier/counter on the BFO control.  I did pick up a couple of spare ballasts from Fair since I wanted to keep this one completely original.  Not quite as good a deal as a $10 garage sale SX-88 but a pretty good boatanchor buy even several years ago.

Enjoy the R-390A, it is a neat looking receiver.  Of course I also own 4 cuckoo clocks so I may be a little biased given the tuning mechanism.

73, Rodger WQ9E

[Steve - WB3HUZ]

Its only oddity is a vernier/counter on the BFO control.

Not really an oddity. I've seen the vernier on tons of R-390As.

[w3jn]

Legend has it those were the special NSA "sex slave" version.  Or maybe it was for ASA.  Anyway, I've had several with the turns counter on the Beef-O.

73 John

[WA1GFZ]

Check out Sherwood engineering. Rob has a list of a number of receivers he has tested. I have duplicated his numbers on a couple units.
The R390 is one model he has checked out. It does not have great dynamic range numbers but the lO is very clean.

[W1DAN]

Hi Frank:

Yes I have been there...good site to learn things.

Dan

[flintstone mop]

Hi Dan,
I might be duplicating what has been posted. If you are going to listen from the front headphone jack then, there are worthwhile mods to get hi-fi audio out of that jack. If you are going to monitor from the DIODE LOAD, don't modify the audio deck, leave the tubes in there, the heat build up isn't detrimental to the radio. Those radios were designed to operate in horrible environments. A ham shack is no where near that.
Follow other folks suggestions for the ballast tube. When  was rich I bought a couple of spares, so I stick with the 3TF7. Keep up to date with hard to get a hold of tubes and bite the bullit and buy the rare ones, so you have running spares. The more the radio stays on, the longer it runs perfectly. During the Summer whene get lightning storms, unplug your antennas and power down the shack, so the power surges don't kill your goodies, especially the plastic stuff.

If you are very critical about the audio from either the audio deck or the diode load, you might want to consider the Curry filters, if you have lottsa money to burn.
If you have the complete military manual tear into the radio and just give an eyeball at the maintenance points. You can even do an alignment.
If you do not have the test equipment to do these neat things, then prepare to spend some money and send the unit to Rick Mish. He is on the WEB. Do a google for Rick Mish R390A. He'll perform his service for whatever money you want to spend to bring the radio to original specs. If you want the radio to look like it just came out of the box, he can do that too$$$$$$.
I have all the alignment tools, bristol wrenches(very important!!), Sig Gen, etc and my radio is .5 micro volts sensitivity across the entire .5-30 mcs.
Replacing the B+ caps on the audio deck did wonders for my radio. It acted like a completely different radio. It just performed like new.
It's heavy, maybe ugly, but it will beat the pants off of any table top Ham receiver, and it's been around a looong time.
NEVER turn it off and connect to a transformer to assure that the R390A gets an AC voltage of 115 only. It wasn't designed for the 130 VAC we get in our homes today.
If you have the dollars, keep the original rectifiers in there. Don't solid state, now you have higher DC voltages and there are more mods to get the B+ back to factory specs.
I keep Hamdom alive and well with the many dollars I have spent over the years. Don't be cheap with the investments you have made in your shack. Keep the electronics happy and protected from Mother Nature and you will receive many years of trouble free service.
Sorry for the BW, just talking my head off here.
G'day
Fred MOP radio

[WA1GFZ]

our power bill is running about $130 now just 2 years ago it was 80.
Sorry I turn stuff off when I'm not using it because i was never rich
but always cheak. if I was worried about turning things on and off there would be a variac on it. 
Yup the R390A will go 24/7 but so doesn't the meter on the wall.