Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Feb Sat 24, 2018 3:00 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 52 posts ]  Go to page Previous  1, 2, 3  Next
Author Message
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 20, 2018 9:39 pm 
Member
User avatar

Joined: Sep Wed 10, 2014 2:01 am
Posts: 1602
Location: Costa Mesa, California
The manual has a drawing of the cam positions at 7 MHz. On the cam plate are marks for each cam position to line up with at that frequency. That is the starting point because at that position the slug racks are at a known frequency. The gears are obscuring several of the markings, but with a flashlight, one can just see the alignment. The final iF is 455 KHz and I have already determined that a signal of 10 microvolts at the grid of the mixer before this stage produces a tone at the speaker--so far so good. Feeding this mixer (called the 3rd mixer) is the the VFO (2.455 to 3.455 MHz) to the cathode of the 6C4 and tuned circuits between 2 and 3 MHz to the grid. I am now trying (unsuccessfully) to inject a signal that would replace either of these and get a tone.

I am about to connect a scope to see if there is signal at the grid or the cathode from either of the two sources.

Norm

_________________
KK6IYM


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 20, 2018 10:08 pm 
Member
User avatar

Joined: Sep Wed 10, 2014 2:01 am
Posts: 1602
Location: Costa Mesa, California
I tried one last time and was successful. The tone appears when the signal generator is at 3.267. Moving the dial either direction causes the tone to disappear. When I release the VFO coupling and leave it not moving (stays at one frequency) and spin the dial, the tone does not go away. Clearly there is no signal coming through the tuned circuits--this should be expected--because the tuned circuits operate between 2 and 3 MHz and I am replacing that component of the signal--but 267 KHz higher than the upper limit. Trying frequencies 910 KHz either direction gets no results. Hmmm.

More to come.

Norm

_________________
KK6IYM


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sat 20, 2018 11:37 pm 
Member
User avatar

Joined: Sep Wed 10, 2014 2:01 am
Posts: 1602
Location: Costa Mesa, California
Okay, the VFO tunes backward. After further testing, I found the end points. Then, when I went to unhook the antenna, WWV at 10 MHZ came in. I had left the VFO at one end point and the band to 10 MHz. Strangely, the antenna is partially unhooked and I am receiving well on just the coax, because the antenna switch is turned to a different radio. Rotating the KHz knob down, I get the country station just below WWV, so things are looking better. Now I need to figure out how to move the frequency display from 562 down to 0 and rotate the stops so that the knob is prevented from going lower.

On another note, this is a real good country station--Johnny Horton, Hank Williams, Jimmie Rodgers.

Norm

_________________
KK6IYM


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 21, 2018 2:09 am 
Member
User avatar

Joined: Sep Wed 10, 2014 2:01 am
Posts: 1602
Location: Costa Mesa, California
Much head scratching and I was able to get the bands from 8 up to 30 MHz working with the dial reading correctly, the stops where they should be, and the signal coming from the speaker with 100 microvolts at the antenna. This represented great progress. At that point, it became clear I would have to move some slug rack cams. The manual states that at the bottom end of the kilocycle dial, the slug racks would be at their lowest position--highest inductance point. The two at the top on the far right were not even close. So these I moved while listening to the tone from the speaker and watching the audio line meter. Setting them this way agreed with the manual and now with 2 microvolts (or less) at the antenna on all settings from 8 MHz up, I get good reception.

The radio doesn't receive signals below 8 MHz so there is more work to do on that end--but good progress has been made. Looking at the scope connected to the third mixer, there isn't any signal at these lower frequencies--or very little. However, the crystal oscillator is working on all frequencies with little variation between any of the bands.

Norm

_________________
KK6IYM


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 21, 2018 2:39 am 
Member

Joined: Sep Thu 01, 2016 3:56 am
Posts: 157
Location: San Jose, Ca.
Hi Norm, This is the fun part. As for the rack positions, the 2nd var IF is always at it's high point with KC readout = 000 on any mc. As for the 1st var IF, it depends on the megacycle band. At 8.000 mc, it's at it's highest, while at 00.000, it's at it's lowest.

As for no receive below 8mc, that points to the 1st xtal osc and the 1st var IF. The 1st mixer is turned on by a switch contact that makes contact only below 8mc. You can use a tube extender or just pull the 1st xtal osc and check voltage on pin 6, its screen. Should have +150 with mc = 0 to 7. My 1st step would be to verify that it's working. You can scope it or use an rx set to 17 mc and place the ant next to tube.

The position of the slug racks for the RF section (front group of 6 in a line) is dependent on the selected mc and kc readout values. Refer to the 'alignment chart', fig 91, page 117 in the tm-11-5820-358-35 tech ref.

Regards, Larry


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 21, 2018 4:28 am 
Member
User avatar

Joined: Sep Wed 10, 2014 2:01 am
Posts: 1602
Location: Costa Mesa, California
Thanks, Larry. You are right, below 8 MHz, the first mixer and first Xtal oscillator are used, but not on the higher bands. I pulled the oscillator tube, a 6AK5, and it was very weak, so I replaced it with the good one I had pulled from the 4th IF, which I had replaced earlier with a proper 6AK6. I then pulled the Xtal can which is mounted on an 8 pin tube base. It was pretty tight quarters getting the spring retainers off and getting it loose, but it finally came out. I tested the 17 MHz crystal and the 200 MHz crystal and both were fine. The test is simply placing the crystal in series between the leads from my signal generator and the RF voltmeter and with 1 RF volt applied, dialing up and down a few Hz to see what the response is.

My next test was to apply the RF frequency signal to the test points at the 2nd mixer and 1st mixer. The second mixer required less than 50 microvolts at the IF frequency (combination of the 17 MHz crystal and the dial setting frequency). The first mixer required millivolts at the IF frequency. I then tried setting the generator at the dial frequency. Eventually, after adjusting the slug rack between the first and second mixers and the transformer coupling the first crystal oscillator, I was able to get all the bands to 5 microvolts at the antenna--except the 7 MHz band which has yet to show any sign of working.

It may be time to go to the manual and follow the alignment procedure. I have everything but the 7 MHz band very close and from here on it is just peaking circuits. There are big questions still to be answered. The panel has a switch for the BFO, but it is a two position switch and the panel has markings for 4 positions, LSB, USB, AM, CW. I know this radio probably is just AM and CW, but when I turn on the BFO, I hear no squeal. I also need to reset the band stops, as I have no bands above 30 MHz and the switch can travel below 0 MHz.

Norm

_________________
KK6IYM


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 21, 2018 5:34 am 
Member

Joined: Sep Thu 01, 2016 3:56 am
Posts: 157
Location: San Jose, Ca.
Great work Norm. Sometimes the 0 to 7 mc switch is not adjusted right and the 1st osc is not getting power in the 7mc position. Or the 9 mc crystal in the 2nd osc for the 7mc band is not making contact. Try removing and reinserting it a few times. But if the 15 mc and 24 mc bands are ok, the 9mc crystal is probably good. See chart fig 8 on page 16, same book.

As for the ssb markings on the panel, I've heard that a small batch was modified for ssb reception, but it would have a 4 position switch installed. SSB can be received fairly well on a stock 390A, but requires riding the rf gain (unless the Langford agc ssb mod is installed). Sounds like there's something wrong with your bfo. Look for mods on the bfo tube.

Regards, Larry


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 21, 2018 6:33 am 
Member
User avatar

Joined: Sep Wed 10, 2014 2:01 am
Posts: 1602
Location: Costa Mesa, California
The BFO and the 100 KHz calibrator are both not working, but the 200 KHz crystal is good so that isn't the problem. I finally figured out the cam position diagram--7+000 comes after 7999. No wonder it didn't look anything close at 7-000. I will have to move the top far right cam to get it to match. That may be part of the problem for the 7 MHz band. These radios are complicated, but they really just require a person to put in time playing around with all the adjustments and seeing what makes them tick. doing the capacitor replacements helps familiarize a person with the radio and then working through the mechanics of the gear train and cam slug racks helps to demystify that part of the radio. There are test points at the mixer grids where a signal is injected for trouble-shooting and alignment. This is a different sort of radio than most others of its era, but the principals are the same, so as intimidated as I was by it before starting, it is now becoming a big lovable bear.

Norm

_________________
KK6IYM


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 21, 2018 6:56 am 
Member

Joined: Sep Thu 01, 2016 3:56 am
Posts: 157
Location: San Jose, Ca.
Norm, For the 7mc band, it uses the 3rd overtone of the 9mc crystal. Sometimes it's weak, even when the 2nd and 1st are good. Also, make sure that the trimmer caps in the 1st var IF and the 3 RF 7mc band can caps are adjusting correctly (not at end of adjustment).

Regards, Larry


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 21, 2018 5:15 pm 
Member

Joined: Jul Tue 21, 2009 1:38 pm
Posts: 748
Location: SW WA state
Norm Johnson wrote:
I finally figured out the cam position diagram--7+000 comes after 7999. No wonder it didn't look anything close at 7-000.
Norm


Norm,

Sorry I didn't make myself clear... That's why I asked you earlier if you were checking the cam position at 7.000 or 7.000+ (8 MHz)...
Glad to see you making progress!
On the BFO: How does the BFO tube filament look? Is the tube operating?
I make liberal use of those Pomona socket extenders looking for signals and voltages.
You should be able to rotate the BFO shaft both ways (gingerly!) until you run into the end stops on the unit itself... I can't remember if it's a single turn, or if it is multiple turn and just not set correctly and way off frequency.

-Tom


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 21, 2018 6:03 pm 
Member
User avatar

Joined: Sep Wed 10, 2014 2:01 am
Posts: 1602
Location: Costa Mesa, California
Thanks, Tom. Yeah, you were clear, but sometimes when I don't fully understand things (like what the + and - means on the dial), it goes right over my head. Fortunately, enough seeps in that the light goes on eventually. This radio had the dial way off and it required rotating the counter considerably to get everything where it should be. The BFO knob hits the stops on the front panel, so with the knob removed a person can rotate the shaft fully through the BFO possible range. I get no response. I do have some tube base extenders and they should tell me something when I check the pin voltages. The BFO tube is a 6BA6 which I tested. Those tubes are pretty fool-proof, but I have others if need be.

I spent more time going through all the bands last night after setting the cams to match the diagram (Fig.68). I adjusted the crystal trimmers and end up with several of the low bands not working. The band switch is a little problematic. It requires wiggling back and forth to get the crystals started for a couple bands. I will probably need to pull the IF deck and crystal deck again after a little more alignment adjustment. Fortunately this is not difficult and will not require messing with the dial, gear train, VFO, and cam alignment. I am pretty confident all that has been sorted out and I hope to avoid having to re-do any of it--although I am now quite intimate with its inner workings.

This is one of those radios where I say to myself, "Wow, that looks complicated. I hope I don't have to try and figure that mess out." Of course, I have just cursed myself and will then need to spend hours trying to figure "that mess out." In the end there is that sense of accomplishment when the learning process has run its course and I have acquired new knowledge.

Norm

_________________
KK6IYM


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 21, 2018 8:44 pm 
Member
User avatar

Joined: Sep Wed 10, 2014 2:01 am
Posts: 1602
Location: Costa Mesa, California
I just realized that the calibrator is working, but without a BFO it doesn't create a tone, just a dead spot. The pin resistance for the BFO 6BA6 is correct, however the pin voltages are not. The plate, pin 5, should be 86 volts and it is 19, the screen, pin 6, 82 volts and it is 69. Something is happening with the plate resistor, R530, or maybe one of the new capacitors I installed is opening up and leaking under load. I replaced the tube with no change.

Norm

_________________
KK6IYM


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Sun 21, 2018 10:35 pm 
Member

Joined: Jul Tue 21, 2009 1:38 pm
Posts: 748
Location: SW WA state
Norm,

OK on your lack of B+... Possibly look for a plate resistor gone high, or as you suggested, and cap breaking down.
IIRC, I had to lay in a good supply of 2.2K Ohm plate resistors...
The crystal deck (band switch) had a crap load of contacts, and alignment on them was pretty critical.
Hopefully, you're through the worst of it now.
Of course, I cleaned all of the switch contacts as part of the PM regimen...

-Tom


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Mon 22, 2018 1:46 am 
Member

Joined: Sep Thu 01, 2016 3:56 am
Posts: 157
Location: San Jose, Ca.
Norm, When cleaning contacts, be careful to not get much on the insulating material. Using deoxit is great, but it and other cleaners can make some material conductive and permanently damage them. And then there's the antenna trim knob shaft gear insulators - be careful with them.

Regards, Larry


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Fri 26, 2018 5:47 am 
Member
User avatar

Joined: Sep Wed 10, 2014 2:01 am
Posts: 1602
Location: Costa Mesa, California
Now I am stumped. I pulled the IF deck and inspected the BFO tube base, V505 a 6BA6. Everything looked normal, resistors tested in spec, no bits of solder, capacitors new or test at value. I returned the deck to the radio and the BFO did not function and the pin 5 (plate) voltage was still about 20 when it should be 86. Screen at 70 should be 82. Both the screen and the plate have a resistor to a connection point that is fed through a third resistor to the switch which is connected to the IF B+. The screen has a cap to ground as does the connection point feeding the plate resistor and screen resistor. The plate has a 12p cap to the detector.

I jumpered around the switch for a small improvement to 27 volts. I pull the tube and the plate and screen go straight to 200 as it also does at turn on before the tube warms up. I replaced the plate resistor and the 12p coupling capacitor. Other tubes connected to the IF B+ have full voltage. Resistance at the pins is as specified.

Final clue--the grid coming from the BFO sealed coil and capacitor package is -.15 volts instead of -4.8 so it isn't oscillating, but if the plate voltage is down as low as it is, this might prevent oscillation. I have tried several tube replacements.

What am I missing?

Norm

_________________
KK6IYM


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Fri 26, 2018 6:26 am 
Member

Joined: Sep Thu 01, 2016 3:56 am
Posts: 157
Location: San Jose, Ca.
Hi Norm, Verify that the bfo unit is wired in correctly. If yes, check C526 if you can or replace it. If still not working, the problem is probably a cap inside the bfo. If you have another one, you could try a swap. If not, check the 3 caps inside. And, make sure the coil inside is not grounded when disconnected.

Regards, Larry


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Fri 26, 2018 10:29 am 
Member

Joined: Sep Thu 01, 2016 3:56 am
Posts: 157
Location: San Jose, Ca.
Norm, I forgot to mention that the cover on the bfo can be very difficult to get off. They're usually aluminum, so can be damaged easily. A little bit of liquid silicone on the joint overnight has helped me. Spray some on a q-tip and wipe it on all around the joint. And, carefully pry it off. Don't put any stress on the shaft, though. And when you put the cover back on, silicone the rubber seal, first. It will go back on much easier.

There are 3 caps inside. Two are NTC's to keep the frequency stable. They are very fragile. If they need replacing, they probably need a higher ntc value.

Regards, Larry


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Fri 26, 2018 4:28 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1524
Location: Canyon Lake, TX
Norm Johnson wrote:
Final clue--the grid coming from the BFO sealed coil and capacitor package is -.15 volts instead of -4.8 so it isn't oscillating, but if the plate voltage is down as low as it is, this might prevent oscillation. I have tried several tube replacements.
What am I missing?
Norm

I suspect that the low plate and screen voltages are an effect of the lack of oscillation, not the cause. With only -.15 volts bias on the tube, the excessive plate and screen currents will pull down the voltage.

_________________
What happens under the chassis stays under the chassis.


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Fri 26, 2018 5:01 pm 
Member
User avatar

Joined: Sep Wed 10, 2014 2:01 am
Posts: 1602
Location: Costa Mesa, California
Thanks, Larry and Ed. I pretty much had concluded what Ed said about the low grid bias causing the tube to draw excessive current. Which means I will have to inspect the BFO sealed can for problems. It is being held in place by two of the four screws--which--when I first spotted this--led me to think it was problematic before. Opening the can is almost a certainty now, so thanks Larry for the tips--I will need them.

To verify that the lack of oscillation at the grid was causing excess current and the plate voltage drop, I used the tube base extender and set my signal generator to about .455 MHz and turned on the calibration signal with the radio set at a 100 KHz point. I touched the grid (pin1) with the signal generator lead at 1 volt and checked the plate DC. It was 30 volts higher. Pulling the generator signal away caused the voltage to drop back down. I could hear the beat note from the speaker.

A final test was to connect 4 AA batteries together and touch the grid with -6 volts DC. This brought the plate up to 67 volts.

Norm

_________________
KK6IYM


Top
 Profile  
 
 Post subject: Re: Stewart-Warner R-390A/URR restoration
PostPosted: Jan Fri 26, 2018 7:45 pm 
Member
User avatar

Joined: Sep Wed 10, 2014 2:01 am
Posts: 1602
Location: Costa Mesa, California
The BFO lives! That was embarrassing. Had I done all the proper testing ahead of time, I would have known the problem from the start (but would have learned far less). A check of resistance to ground at the three sealed BFO terminals could have told me that the coil was open.

I removed the BFO from the IF deck and carefully pried the case off. I then needed two pair of eyeglasses stacked on top of each other to see what was happening with the wires. As a side note, whoever unhooked the BFO last had the cathode tap and ground reversed. The connection to the first winding was open at the terminal going to the grid wire input. The broken end of the magnet wire could just be seen with my multi-eyeglass vision. This was fortunate. A failure in the second winding, with the layered Litz wire, would have been difficult to correct. The magnet wire easily unwound a small amount so the end could be prepared (scraping with a sharp knife) and a short piece of bare copper wire soldered on. I used a strand of some #18. I then led this back to the original connection point and soldered it, then checked resistance to verify continuity, and finally reassembly and replacement in the IF deck. Larry's idea to wet the rubber O ring with silicone (303 Aerospace Protectant) helped the case slide back in place and gave new life to the rubber seal.

The BFO worked as soon as I tried it, so mission accomplished and on to the next problem.

Norm

_________________
KK6IYM


Top
 Profile  
 
Post New Topic Post Reply  [ 52 posts ]  Moderator: Sandy Go to page Previous  1, 2, 3  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: Big Harry, Thewasp and 10 guests



Search for:
Jump to:  






















Privacy Policy :: Powered by phpBB