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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Fri 26, 2018 10:52 pm 
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Location: San Jose, Ca.
Great work Norm. Good save. It's too bad some previous person left you the mess.

Regards, Larry


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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 27, 2018 3:31 am 
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Location: Costa Mesa, California
I spent the rest of the day going through the full alignment procedure--this time with a better understanding of what I needed to do. The bands from 8 up were perfect. Bands one and two were very problematic, requiring a lot of RF at the antenna to get any response. The bandswitch had to be advanced and then slightly returned, sometimes needing a mid-band position for best reception, which was still poor. At last I concluded I would need to again pull the front panel and oscillator and RF decks.

The inside of the crystal oscillator deck looked fine. I carefully preserved settings and the switch was exactly where it should be for the band. The RF deck was my main question mark. There is a set of gears that engage for the bands below 8 MHz. These move the bandswitch inside the RF deck. After a lot of staring and rotating the switch this way and that, I have concluded it is off its proper index position when the lower bands engage. It is really obvious for band 0 and 1 that it should be slightly rotated, but then looking at the schematic and studying the switch wafers, it is not 100% clear. I really don't have much choice other than to reposition it and reassemble the radio to see if I am correct.

Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 27, 2018 9:14 pm 
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Many hours have passed since my last post. I set the bandswitch at 6, loosened the collar, and holding the wafer shaft so it wouldn't move, rotated the bandswitch to 7. I did a number of continuity checks and finally reassembled the radio. Band 0 and 1 worked very well for, really, the first time. Band 15 worked very well and that was it. All other bands did very poorly.

Like all radios, the bandswitch controls which transformers--coils and capacitors--are connected to the signal path. There are 31.5 bands, but only 6 sets of transformers. The first set handles half a band, the next one band, the next two bands, then four, then 8, then sixteen. This makes for some creative gearing and switch rotating. I believe that my gear assemblage has a little play, such that it won't positively find the exact right spot and has to be fiddled, moved slightly past the band stop to get to the right place.

Needless to say, I did not look forward to disassembling the radio again. So, I made a special tool. I took a 12" piece of steel 1/4" rod and carved a wide slot in one end so that it could slip snugly over the end of a standard 1/4 band shaft with the two flattened sides. I installed a large radio knob to aid turning it. I then made a LED probe light with two long wires connected to some batteries that could fit in the 3/8" hole at the back of the RF deck and the back of the radio. This allowed me to peer through the hole and inspect the back of the bandswitch. Sure enough, there was an extra 1/4" or so of shaft showing. I apparently was not the only one who thought access might be handy to the back of the bandswitch. The hole in the RF deck was needed to extract the shaft, but an extra hole in the back of the radio meant someone anticipated rotating the shaft while the deck was still in the radio.

I loosened the collar and returned the switch to the original position. Sure, had I conceived of this plan in the beginning, I could have saved myself a lot of work removing and then replacing the RF deck, but it was only the knowledge gained from that experience that made this new method possible and allowed me to understand what I was doing.

Currently, after much fiddling and adjusting of everything from the cams to the crystal switch to the bandswitch, I have reached a state of modest compromise where all the bands work, but some require the megacycle knob to be slightly rotated about half a band down to get a good signal response. The megacycle knob moves the cams, the crystal switch, and the bandswitch, and yet it seems like I am missing a fourth switch that I am not aware of that is slightly out of position.

Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 27, 2018 11:00 pm 
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Location: San Jose, Ca.
Norm, Nice job on your adjusting tool. But it sounds like there is still something wrong with the band switch. I assume when you had the deck out you carefully examined the center of each wafer. They need to fit fairly snugly on the shaft and not rotate very much at all without turning the shaft. I had one where I had to replace a switch segment because it was not right. It was in the antenna switching.

Which bands are currently not right?

Regards, Larry


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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 28, 2018 1:07 am 
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Larry, thanks for the help. I really need all the help I can get. I took a walk with my little dog, Dirty Ted, up in the forest and a voice said, "Norm, just read the manual." So I did. Paragraph 70, page 110, d. says to remove V207 (the most difficult tube in the radio to remove) and check the resistance between pin 6 and pin D of jack 208. It should read 56K at band 7+000 and go to infinity when switched to band 8. Mine didn't change. It didn't go to infinity for quite a few bands higher. The manual says to remove the RF deck and rotate the switch shaft until the condition matches the book, but I didn't see that as the solution. I did a lot of megacycle rotation watching the action of the intermittent gear and studying the position it should be in shown in Fig. 68. I also monitored the resistance the whole time. It turns out the intermittent gear was about 30 degrees out of position. I corrected this and then using my bandswitch shaft tool, rotated the shaft slightly for a final alignment that produced the correct resistance at band 7 and 8.

I then did a run through of the tuned circuits and they all peaked at the low end with inductance and the high end with capacitance. This is something the radio hasn't done since I started. I think I am about 95% there. I get pretty good response on all bands. Hopefully another time through with the first and second variable IF protocol and I will be heading down the home stretch. When one of these very complex radios is as screwed up as this one was. . . . .okay, just send it over here. I am having fun.

Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 28, 2018 3:00 am 
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Location: San Jose, Ca.
Great work Norm! I know these can be frustrating to work on, as you certainly had a right to be on this one (not saying you were), but success as you are seeing is quite a good feeling and well deserved. Congratulations!!

The last one I did had many, many issue, but the 2 most difficult were replacing a switch segment in the band switch and the Cosmos PTO (I spent a few months on it and ALMOST got it good enough, but not quite. I ended up getting a different PTO and fixing a couple problems in it). That R-390A is now a fine rx.

Regards, Larry


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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 28, 2018 3:10 am 
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Final details like VFO dial lock and such and then I put it on the air. First thing to pop up was some contesting on 40 where the BFO worked perfect for SSB. Then more contesting on 20. Then WWV at 2.5, 5, 10, 15, and 20 MHz. Looking good. What I should have realized at the start was that the intermittent gear is meant to change the RF bandswitch at 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz. It is kind of too obvious once a person thinks about it, but sometimes the obvious goes right past when it isn't in the manual and someone before has moved things they should not have. Of course, I do that all the time, but I just stick with it until I find my mistakes.

It looks like I am at the point where there are a few more small things to tidy up and adjust, S meter, filter, frequency zero adjuster, and then I will find a case for this thing and call it a success.

Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 28, 2018 11:59 pm 
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Here are the photo's. The first is the BFO repair, then the bandswitch tool.

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If you look at the photo of underneath the RF deck, you see that the bandswitch has 1/2" extra at the rear that can be used to rotate it from the back of the radio. In the photo, most of the bandswitch sits with the tuned circuits. They are above the chassis but we see the terminals in rows going side to side. The top of the photo has the .5 to 1 MHz row, then the 1-2 MHz row, then the 2-4 MHz row, then the 4-8 MHz row, then the 8-16 MHz, row, and the final row below the bandswitch is the 16-32 MHz row. In front of the switch are the gears. You can't see all of it in the photo, but there is a gear attached to the bandswitch shaft, then a small driver gear, then an intermittent gear. This is a gear with teeth missing for sections of the gear such that it only activates the switch at intervals corresponding to the band changes between the tuned circuit ranges listed above. That was the gear that was out of alignment in my radio and which the manual had no information, but the action is pretty obvious when you understand the purpose. All of this can be accessed without removing the RF deck--otherwise the process would be quite tedious. However, with the deck out of the radio, the alignment is much simplified and well worth inspecting.

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The R-390a needs only a handful of tools for repairing it. The most important of these is the hex-fluted #66 driver. I have a set of Xcelite drivers which has come in quite handy over the last few years--especially for Hallicrafters and Collins radios. Yesterday, about half way though working on the 390, I fumbled the driver and it hit the floor. The handle went one way and the snapped off driver the other. After some searching, I found the driver end. Without a good working driver, there is no way to work on this radio--so I set about to fix the tool. I found a couple lengths of brass tube, the larger-- 1/4" OD. I smashed the smaller around the end of my fluted driver and filled the area around the driver with solder. I then slipped the 1/4" section on and soldered it as well. I had such good success with the radio knob on my shaft tool, that I used another large knob for the driver tool. It not only worked well enough to get me through the rest of the radio work, but worked better than before. It will be a permanent item in my tool box going forward. It ain't pretty--but it sure can cook.

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Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Tue 30, 2018 12:42 am 
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Bravo Norm! Been reading along. I have never been inside of one of these beasts, but sure have enjoyed reading about it. Not sure I want to after the gear headache you just went thru! Keep up the good work, whats up next?


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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Tue 30, 2018 2:00 am 
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That is a good question. I have a SP 600 in pieces waiting for me, a rather decrepit SX 42--complete but in bad shape, a Viking 2, an Invader, and several more things--however, right now I am starting on a dual conversion, first tunable IF, with fourteen tubes not including the rectifier and regulator--home brew. Before it gets underway though, I am building my coil and IF transformer winding machine based loosely on the Gingery book. The receiver will be a modular version where I can test sections and mix and match. It has a 455 KHz final IF that will lend itself to multiple experiments.

So, not sitting still.

Norm

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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Tue 30, 2018 2:24 am 
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I'd like to add my kudos, Norm.

If you don't mind I'll be borrowing your fluted driver idea to make one for the knobs on these Halli's so I don't scratch the front panel when they're being stubborn. I could have used one earlier today as I was removing the SX-42’s knobs for cleaning.

I too am in the process of figuring out the next project.

I hope you'll do a thread on the coil winder as you design and build it.

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"The question is not what you look at, but what you see." Thoreau


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 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Wed 31, 2018 2:35 am 
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The winding machine is about complete with only a few tweaks left. It wound its first coil twenty minutes ago. I have a thread in Home Brew on it. But here are a few photos.

Norm


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