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 Post subject: R-390A/URR " BAL " adjustment
PostPosted: Feb Mon 12, 2018 5:19 pm 
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Joined: Sep Sun 08, 2013 11:53 pm
Posts: 42
In the RF section we have on top the cans the coil and 2 adjustment caps . On the metal cover plate it defines the primary side adjustment as " BAL " For those who have the Y2K Chapter 5 page 39 C201A , primary side , a small 3-12 pf trimmer is the one i'm talking about . Chapter 6 Figure 6-6 shows these caps as BAL there too .. These caps do not figure in the RF alignment procedure. Why ? Is there a particular way that they need be set before the procedure is started ? It seems a mystery. I am puzzeled why they are completely left out the procedure.

Thanks :)

Ric


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 Post subject: Re: R-390A/URR " BAL " adjustment
PostPosted: Feb Mon 12, 2018 6:08 pm 
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Joined: Sep Wed 10, 2014 2:01 am
Posts: 1936
Location: Costa Mesa, California
Ric, I had no luck with those when I did my adjustments; however, looking at the schematic, I would say they would be adjusted last after the inductance and output trimmer are peaked. They appear to be for centering the input side after the output has been final tuned. How you would tell if they are correctly set is a good question--as they do not make much if any difference in audio output.

Norm

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 Post subject: Re: R-390A/URR " BAL " adjustment
PostPosted: Feb Mon 12, 2018 6:31 pm 
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Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1273
Location: Champaign IL 61822
The purpose is clear: to adjust for the best common-mode rejection.

Unless you are using a truly balanced antenna and feedline, they are immaterial.

IF you wish to set them, remove any balanced to unbalanced input connector
adapter, then attach some sort of pins to each of the two balanced
input jack holes. Attach them together and to any sort of long or short wire antenna.
Picking up noise is fine. Then go through all 6 input coil bands at
0.75, 1.5, 3, 6, 12, and 24 MHz (rough frequencies is good enough) and adjust
for minimum [sic] signal level.

BUT ... I advise you that unless you actually USE such a balanced
antenna setup, it is silly.


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 Post subject: Re: R-390A/URR " BAL " adjustment
PostPosted: Feb Mon 12, 2018 6:48 pm 
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Joined: Sep Sun 08, 2013 11:53 pm
Posts: 42
Thanks dtvmacdonald , now i can sleep in peace :D
The bal makes sense now.

At this point in time , i got way more pressing problems to solve with the radio. The adjustment being pointless ill concentrate to try get the beast back in service. Not to let myself be distracted by them good old " how does this work " at every corner and get the receiver working. Im curious and get in trouble a lot for it but this is a hobby after all and part the fun for me is not operating the radio , but to really understand it's inner workings.

Dead on all bands , modulated 455 kc at the rf input is heard in the line out / speaker.
Would have loved a good course on how to isolate faults like the guys had in the army .
My lack of knowledge is showing :D

Happy trails


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 Post subject: Re: R-390A/URR " BAL " adjustment
PostPosted: Feb Tue 13, 2018 6:06 am 
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Joined: Sep Thu 01, 2016 3:56 am
Posts: 271
Location: San Jose, Ca.
Ric, Don't worry about lack of experience. None of us knows everything. You will get all the help you need here.

Since it's dead on all bands, and you are hearing the 455kc sig, your IF deck is probably working and the RF deck is failing. One thing to look at is the 2nd crystal osc deck and vfo. These 2 tubes filaments are in series with a 14 vac current regulator that is on the IF deck. If the 3tf7 regulator is open (located on the front right of the IF deck), then both osc will not work. Be careful measuring in this area as the 3tf7 is easy to blow. Sometimes the osc tubes pins get corroded and a little movement can get them working again. Another thing to look at is the +150. It's only used in the RF deck and 2nd crystal osc. The RF deck is where all the fun happens.

As for the bal ant input adjustment, as already stated, you don't need to worry about it unless you are using a true balanced input. Most of us use normal coax feed (ground 1 pin and coax center to the other), so adjusting the bal will have no effect. The only doc on how to adjust it is in this book:

http://www.r-390a.net/TM-11-856A.pdf

on page 172 paragraph h. You must make a balance input adapter in order to do it. They are fairly easy to make (I made one for a friend enclosed in the normal twinax plug a couple years ago). I think you are right that the y2k book should talk about this a little.

Don't forget about C553. If you haven't already, there is one thing you should really do before powering it on again. Verify it's good or replace the 'mech filter killer cap' C553. You don't want to accidentally damage a filter.

Regards, Larry


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 Post subject: Re: R-390A/URR " BAL " adjustment
PostPosted: Feb Wed 14, 2018 4:29 pm 
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Joined: Sep Sun 08, 2013 11:53 pm
Posts: 42
Thanks Lar

Yep the killer cap has been replaced in this radio , the electrolytics in the audio deck also.
I do have the +150 and it's deadly accurate at 150.0 on a good fluke DMM.

E209 is totally off sitting at -17.5 v That's the first mixer test point , receiver on standby , set to 1.510 MHz
The manual says -4 to -6.8 so it's totally out of range.
E210 is -2.49 low from rating at -3 to -8 ( alignment off ? )
E211 is -3.78 -1.3 to -4.3 so that's fine
E402 is dead .. 0 .. yet shoots out 20.996 Mhz at the output on the counter.

Any ideas at this point will be welcomed.


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 Post subject: Re: R-390A/URR " BAL " adjustment
PostPosted: Feb Fri 16, 2018 3:06 am 
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Joined: Sep Thu 01, 2016 3:56 am
Posts: 271
Location: San Jose, Ca.
Ric, good news on what you see there so far. I wouldn't worry about the voltage being off on e209 and e211 at this point. E402 = 0 might be that your meter needs to be decoupled from it. Try a 200k to 300k res in series. As long as your counter sees cycles, that's good. I'd suggest starting by injecting an appropriate signal into the mixer grids at the test points. EG: 2.5 mh at tp e210 with the dial at xx.500 mh. The vfo should be putting out 2.955 mh. You can see that on the cathode of 3rd mixer with a tube extender. A visual check of the 2nd variable IF should show it midway in it's travel. If the vfo is very far off, you won't get any output into the IF strip.

Regards, Larry


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 Post subject: Re: R-390A/URR " BAL " adjustment
PostPosted: Feb Fri 16, 2018 4:55 am 
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Joined: Sep Thu 01, 2016 3:56 am
Posts: 271
Location: San Jose, Ca.
Ric, so if the 3rd mixer is working ok, then go to the 2nd. Because of the way our beloved 390A works, it's easiest to check it at frequencies above 8 mh. So on these bands, the 2nd xtal osc needs to put out a signal 3 mh above the band it's set to. IE: when the rx is set to 9 mh, the 2nd xtal osc needs to put out 12 mh. So you can inject 9.abc into tp e210 with the rx set to 9.abc (the same frequency). Then when that works, inject that same frequency into the antenna. You should notice a significant lower level of signal required there. If all is working correctly and aligned correctly, it should be 1-2 uv. If not, start with the cam alignment. Remember there is a difference between 7.000 and 7.+000 (which is at the very high end of the 7 mh band).

Regards, Larry


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 Post subject: Re: R-390A/URR " BAL " adjustment
PostPosted: Feb Fri 16, 2018 3:32 pm 
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Joined: Sep Sun 08, 2013 11:53 pm
Posts: 42
Joy :)

Found some browned out components under the deck , one of which is going to keep me busy for hours figuring out how to replace it cause it's lead goes to a contact on the switch between the wafer and the chassis :D \0/

After all .. what's a hobby if it dont make us cuss everyonce in a while ;)


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