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 Post subject: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Fri 12, 2018 9:02 pm 
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Location: Costa Mesa, California
I have finally built up enough back strength to hoist the 390A onto the bench. Now I have questions. First off, I pulled the cover off the PTO and worked the dents out. Next I cleaned up the 3-wire cord connection and removed the IF deck. C553 is readily accessible and will be changed to a modern capacitor. I have been reading how others have approached restoring this radio and the person I bought it from several years ago gave me his advice. He had restored and worked on literally hundreds of these radios--from the present day to going all the way back to his time in the service in Vietnam. As one can imagine, everyone has a different opinion as to what should be done to restore these radios. Mine is in what appears to be very good condition. Here are the questions:
1.) C553 (300 volt Gen Instr) replace with HV ceramic disc or 630 volt film?
2.) Replace electrolytics?
3.) Replace black beauties?
4.) Rectifier tubes--leave in and hope they work (my tester doesn't do these) and if they don't, pay the high price for replacements, or change to solid state with load resistors and inrush limiters?
5.) Take the entire gear train apart and clean and lube or minimal disassembly and clean and lube?

Undoubtably more questions will follow and I am taking photos to upload when I return to civilization. All and any advice would be appreciated.

Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Fri 12, 2018 9:54 pm 
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Location: Eagan, Minnesota, USA
Norm,

I went through my R390A a few years ago when I bought it. My approach was to rebuild one module at a time.
For that C553 capacitor, I used an orange drop. For all of the other 'paper'/black beauty types I used yellow Illinois Capacitor brand film capacitors. I replaced the electrolytic capacitors. For the pull out types, I bought sockets from AES and installed separate Nichicon capacitors in them. Then plugged them in. I saved the original electrolytic plug in types just to have them.
My set still has the rectifier tubes in it. I have a set of spares. The manual will discuss replacing them with diodes. When you remove the RF deck, you'll have complete access to the gear train. My set was very clean, and the gear train did not need total disassembly. I cleaned it outside by flushing it with cleaner and blowing it dry with air from my compressor. Light pressure is enough. Then I used synthetic oil on it. Once that was done and back inside on the bench, I removed each slug rack and cleaned and lubed the rollers. Do one set at a time. I would warn that total disassembly could be a challenge. Search the web for info on that. And there is a lot out there. Same for the R390A in general. Lots of info on the web for it. I was able to print out a manual compiled by a few very knowledgeable people - I think they called it the Y2K manual for R390A or something like that. It's what you need for answers to future questions you'll have.

Just a quick general summary of what I did.

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 13, 2018 2:13 am 
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Frank,

Thanks for the advice. Obviously, removing the modules is the way to get started on this thing. Why? Because it makes it weigh a lot less! I am starting on the AF deck first, then the IF, and then the others. It seems that replacing the paper caps and electrolytics is probably the way to go.


Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 13, 2018 6:22 am 
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Testing the tubes for the IF deck has revealed that V504 is a 6AK5 instead of a 6AK6 as the chassis and schematic are marked. The tube shield is a smaller shield and would not fit a 6AK6 so this was done with purpose and probably worked okay. They are similar tubes (same pin layout) but the 6AK5 has a max plate voltage of 180V while the 6AK6 has a max plate voltage of 300V. The manual shows the pin 5 voltage at 165V, which is right in the wheelhouse for the 6AK5. It also appears that the 6AK5 has more gain than the 6AK6. Was this done on purpose as a modification? I have some 6AK6's on the way for the audio module as output tubes so it will be easy to swap once the radio is up and working. I guess I can judge for myself at that time.

Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 13, 2018 6:55 am 
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Location: San Jose, Ca.
Norm, Welcome to the adventure. R-390A's are great.

Frank and Norm, I like what I see. There are 3 caps in the 390A that are problematic besides the electrolytics, C553, C609, and C551. You know about C553, and the other two go bad often. C551 on the agc line is a little tricky, it not only leaks between the plates, but also to ground (both ways are bad for the agc operation). I suggest wiring in a replacement under the chassis and leaving the original in place. But, be sure to disconnect both ends of it and don't use either terminal on it.

As for using tube rectifiers, I like them, but if you want to leave your 390A powered on for days at a time, then consider the SS recs. If you do, be sure that the B+ is not higher than it should be. If you're concerned about warm up time for stability, there are ways to improve that.

The 390A has the vfo and bfo filaments wired in series off of the 26 vac source with a current regulator (3tf7) in series with them. This is a good method to stabilize the current, but it's easy to blow the 3tf7 when playing around. If the vfo fil is accidently grounded, it's blown. I recommend doing the 12bh7 mod and using 1 in it's place until your ready to do the final alignment and button it up. I run with one in place of the 3tf7 all the time, and my stability is quite good.

Be careful cleaning the split gears. If you get dirt in between them, it's hard to get out unless you take them apart.

As for the 6ak5 in place of the 6ak6. If there are no mods on it for this, I'd put in a 6ak6.

Regards, Larry


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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 13, 2018 4:58 pm 
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Location: SW WA state
Norm,

I have restored a number of R-390A's as well (I have one on the bench right now)...
This last one, I've gone deeper into disassembling it than others.
Still, I have yet to pull apart a gear train.
I follow the "spray or brush on WD-40" routine, and clean all of the gears that way.
I bought a gallon of the liquid, and only used about a cup...
I lube the gears afterwards with either a synthetic oil or grease.
As far as IF deck capacitors go, I replace ALL of the paper foils with the yellow tubular 630 volt caps.
And I do this in all the decks.
I'll pull the decks, and carefully wash and dry all of them.
Cleaning agents are 409 and Simple Green, except where Nicotine is involved, where a concentrated Ammonia is necessary.
In that case, I use an 80% solution of 30% Ammonia with the other 20% being either 409 or Simple Green.
I found out that the Ammonia itself cleans the Nicotine, but may not clean other stuff.
The Ammonia/cleaner solution seems to get both the normal grunge and Nicotine.
Decks are individually cleaned, then dried in the oven at warm so drying is accelerated, but the parts aren't damaged by the heat.
By all means, replace the nasty Tantalum cap (I think it's 8 uF) on the audio deck! If it leaks, you're SOL. It will eat the circuit board.
I don't replace filter caps unless they are bad.
I go so far as to pull all of the IF/RF cans on the chassis, and all of the modules, then clean the bare chassis itself.
One the last rig, I even took off the side plates.
And I pull all of the guts out of the IF/RF cans, clean the can, and the pins of the assemblies.
I normally don't run into radios with the 3FT7, so I wire in a series resistor combination to get exactly 6.3 volts onto the (I think) BFO filament: The value needed can be different between chassis, so what I do, is have a bunch of these flat pack high wattage resistors that look like TO-3 transistors: They heat sink onto the IF deck chassis using one existing hole, with the addition of only one new hole.
Values are approximately 44-48 Ohms, so I usually take a 24 Ohm resistor, and add in a 22 Ohm, and see where to go from there (too much filament voltage, add a bigger resistor. Too low, drop the resistance a bit). I've seen some pretty high voltages (7 volts or more) on that tube with other conversions, so this works well for me.
BTW: On your IF deck, do you have caps to trim the mechanical filters, or are your padders fixed?
I have a process of using a "gimmick" cap consisting of a fixed and variable cap to get the right value for the fixed padders.
It's straightforward, but a PITA as it is time consuming, as you need to do one cap at a time, and there's eight that have to be done (4 each total, on input and outputs).
But then, R-390A's are time consuming, if done RIGHT. And there's a lot of schlubs out there that cut corners...
Then we eventually get into massaging 5749/6BA6's to find the lowest noise ones to put into the earlier IF stages...
I think I have exactly one pair of NOS 26Z5's... Nearly all of the R-390A's I have seen have been solid stated.
This is a standard field modification, and I support doing this. All of the ones I have worked on are solid stated.
Yes, I would use an inrush current protector. I install them on all of my equipment.
I've been using the CL-60, but I believe there are better ones out there, as you want to match the current rating as close as you can to the current drawn by the device (radio) for maximum regulation effect (without going over the part's rating).
Congrats on your find, feel free to chime in when you have questions.


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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 13, 2018 5:32 pm 
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Tom and Larry, good advice as always. This radio is quite clean and the decks do not need more than a cursory wiping down. The gear train and slug racks will require a little more clean-up, but aren't terrible. Your specific tips are much appreciated. The R-390A is one radio where there is almost too much information out there. Trying to read all of it would be very time consuming and then a person has to decide which advise to follow--because some conflicts depending on who has had success with what.

It is a good thing Tom and Larry mentioned the 8 MFd cap in the audio deck. I had seen it on the schematic, but when I did the paper caps on the component board, I just assumed the weird looking metal thing was a diode. It is not! Obviously if it is labeled C609 it is a capacitor. So far I have been very happy with the 390A construction. The easily removable decks, the labeling of all components, the construction engineering such that repair is not hindered, all of these are welcome for such an involved receiver.

Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 13, 2018 7:39 pm 
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Hi, Norm... Go to R-390a.net, and you'll find the Y2K manual, as well as the "pearls" (information) and more. It's all free for downloading under References.

I have my own 390a project to get back to, once I clear a spot on the bench, and get my son to help lift it!

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 13, 2018 8:44 pm 
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Tim, thanks for directing me to that website. I had it on the radar, but had not gone to it before. There is some good information there including the manufacturing information.

My radio is a Stewart Warner #1250. Some of the sub-assemblies (like the entire IF deck) are Teledyne Systems Corp. but other assemblies are Stewart Warner with components labeled Stewart Warner. The audio deck has a part marker MFD Nov. 8, '60. This doesn't mean the radio was from that date, but is an indication that it wasn't produced before that date.

Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 13, 2018 11:25 pm 
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For the 2 MFd capacitor between the grid of V506A, the time constant tube and the AVC switch, S107, I had intended to use an electrolytic because of size constraints. Which end does the negative connect to? At different switch positions different ends of the capacitor are connected to ground. My inclination is connect the negative to the grid.

Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 14, 2018 12:22 am 
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Norm,

It's uncommon to find R-390's that haven't had decks swapped.
The best indication of age is by contract number (if the tag is original to the receiver!), and by marks and other indicators on the chassis...


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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 14, 2018 2:02 am 
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Norm, It should be ok to use an electrolytic, but be sure there is absolutely no leakage. I've seen new ones that have too much for this. It should be less than 1 microamp. The negative side should go to pin 2 and the + to the switch.

When switching between agc slow speed, there is a 'moment of silence'. There are fixes for it and can be read about in the y2k ref or 'pearls'.

Have fun.

Regards, Larry


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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 14, 2018 2:50 am 
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Thanks, Larry. I have both film and electrolytic on the way, so if the film will fit the space, I will use it. I left the potted can in place and there was just enough room beside the power resistor (still giving it some room to breath) to insert a two terminal strip. I moved the leads from the potted cap to there and I should have enough room for a fairly large cap as well.

Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Mon 15, 2018 1:12 am 
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Here are the photos. I had some "tops" of capacitor cans I had saved and I also had some bad octal tubes. I broke the tubes and cleaned out the bases, which I used to mount my capacitors. Then I cut the can tops down to match the original and slipped them over the tube bases with some tape to position them and glue to hold them in place. I also added two small flat-head machine screws so that pulling or pushing on the can wouldn't separate it from the base. Of course one of the bad tubes I chose was a 5Y3 which I soon discovered had three of its five pins in the wrong holes to match the capacitor. That meant I had to carefully bend the flanges back to straight and pull the pins and reinsert them in the right holes.

I really appreciate the engineering that went into the R-390A. For a complex radio these are very easy to work on.

Norm


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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Mon 15, 2018 1:52 am 
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By far the best way to cure the "moment of silence" is to simply not use the
tube as an AGC amplifier. I.e. no cap between plate and grid at any time.
Just use it as the meter amp.

Rewire the switch to switch between the one permanently
placed cap and two larger ones that can be switched in. I use 0.47, 2, and 6.8 uF but
it up to your taste. Doing this means that the caps just go to ground so leakage is less
a problem and electrolytics work fine. See my article in this forum about my
full AGC mod for SSB.


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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Mon 15, 2018 2:02 am 
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Thanks. I found your modification post--

viewtopic.php?f=5&t=291360&hilit=r390a&start=20

I will give this some consideration. I do want to get the radio running first to see what the performance is as designed.

Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Mon 15, 2018 2:08 am 
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Norm,

I like how you did the electrolytic can!
I'm going to remember that trick.
Thank you!

-Tom


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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 20, 2018 5:59 pm 
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The final capacitors arrived from Mouser and some EBay 6AK6's. This allowed me to finish the parts replacements and assemble the radio. For the 2 MFD IF detector cap, I used a pair of 1 MFD multi-layer caps. These are quite small and fit the space better than anything else, as well as avoiding having to use an electrolytic capacitor.

I did some quick resistance checks, hooked up a speaker through a 600 Ohm transformer and flipped the switch. I heard static and, after attaching an antenna and working the dial, I eventually found a station. The radio worked! Until it didn't. More dial twirling and signal generator fiddling caused me to come to the conclusion that the one and only frequency I could receive was a result of an accidental alignment of various stages.

When I bought the radio, the seller cautioned me that I would probably have to do some slug rack alignment. The VFO was separate from the radio and looked a little beat up. Clearly I wasn't buying a "working" radio. The price was right. Once I started the restoration, I saw that the crystal deck bandswitch window read 20 and the dial band selector read 20. I assumed that I could just move the VFO around until it synchronized with the dial at an injected signal from the generator. This now appears not the case. At 7 MHz, the cams do not align with the diagram in the manual and rotating the KHz dial through its range doesn't bring them close to aligning. It is hard to see the lower cams, so exact 7 MHz position agreement is difficult to determine.

I think my next step is to see if I can find any combination of KHz and MHz gear settings that brings the 7 MHz cam position into agreement with the manual diagram. At that point, I would inject a 7 MHz tone at the antenna and rotate the disconnected VFO until I heard the tone at the speaker. This may or may not be possible depending on how out of alignment the slug racks are.

Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 20, 2018 7:47 pm 
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Well, I did find the apparent 7 MHz cam position point, set the crystal bandswitch to the line between 6 and 8 in the window on the crystal deck, and connected the signal generator with a strong 7 MHz signal to the antenna. I then freed the VFO collar from the gear grain and rotated the VFO through its full ten-turn range. I did not get a response. There is -6 volts at the crystal test point so the crystal oscillator works.

This is discouraging and I will need to re-think my strategy. These radios are somewhat difficult to trouble-shoot as access under any section chassis is not possible. Signal injection seems to be by using tube base extenders-which I do have.

Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 20, 2018 8:44 pm 
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Norm,

The R-390A is an interesting radio, and can drive one buggy... If I remember correctly, there are three variable sets of frequencies that move when you rotate the dial, so if one of them is not tracking properly, you're SOL... They ALL have to work together, or you get nothing!
I remember having an R-390A back in my Novice or Tech days... It was a $100 purchase, and I had zero test equipment or documentation... Like yours, it was misaligned, and did nothing until I lifted up on one of the slug racks, and it came to life on only God knows what frequency...
I sold it shortly afterwards.
I suggest you read the various manuals.
BTW: Are you looking for rack alignment at 7.000, or 7.000+ (8 MHz)?
You're probably going to have to painfully go through the thing, and verify EVERYTHING. Assume nothing is correct, and that the alignment and any switch orientations are suspect...
Best of Luck!
Remember that we are here for you!


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