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 Post subject: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Sat 11, 2017 7:51 pm 
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I picked up this RCA Stratoworld III today inexpensively, and thought it would be a fun project. My experience with TO's and others that are transistor based portable radios has my general expectations set - small spaces to work, etc.

Anyway, the only thing I could see out of order was that the battery pack was missing and the wires for the pack were hanging out the back. I pulled it apart and found a mess... I'm betting someone thought these wires must be 120v AC...

Both 2N270 outputs are bad, but the others I tested are okay. Now the decision is to fix or part out. I love a challenge so leaning towards fixing. Aside from finding replacement output transistors, I don't know what other hard to find parts I'll need. Two resistors in the power circuit have disintegrated... Guess I'll know more when I get in to it.

Wish me luck!

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Imagine applying 120v to the battery connection! Surprisingly, the 2N407 is fine.

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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Sat 11, 2017 11:38 pm 
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Location: Valencia, California
If you would like the RCA Service Manual and/or the Photofact Manual, PM me with your e-mail address and I'll be glad to send you the scans. I also think I may have a battery holder for this if you are interested?
Considering the apparent condition, I'd vote for fixing it.......good luck! :)
Bob


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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Sun 12, 2017 12:12 am 
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Bob - very much appreciate the offer. I have scans of the RCA service data and Sams set 436, folder 13. What I could use, is a sharp scan of the Chassis Bottom View (page 2 I think) with the parts call-outs. My scan is really fuzzy. Between the schematic and surrounding parts, I think I have it figured out - but a clear view from the Sam's would be helpful.

So far, along with the outputs only R37, R38 and R42 are bad. These are the resistors that were blown apart. Otherwise, nearby components are checking good. Testing the interstage transformer (T1) is next...

Sams's partial schematic below. Partial schematic above is from RCA service document.
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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Sun 12, 2017 3:05 am 
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Anyone have any experience using the NTE102 as a replacement for the 2N270? Criticality this application?


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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Mon 13, 2017 8:55 pm 
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Do NOT part it out.

The typical answer I would give for this dilemma is to find a common beat-up Zenith AM-only set from the same era and use that as a parts donor. I've resurrected several TOs with missing transistors that way. The transistors in this RCA radio are fundamentally the same and would likely work just fine with the Zenith transistors.

If someone really did apply 120 volts directly to that set, things could get dicey, though. If coils or transformers got blown up in the process you may have to improvise.


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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Mon 13, 2017 9:16 pm 
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Location: Indianapolis, IN
I agree---that radio is way too nice to part out and surely would be worth the effort to repair !

I also agree about using common Zenith parts if available and there are other lower-end RCA sets which could be harvested for the audio transistors as you do want a matched-pair for the output.

And thanks much for the pics---have always liked that set and great to see the "innards" !

Best of luck and will be following along...

John


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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Mon 13, 2017 11:37 pm 
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I've moved ahead with fixing it up. I've replaced all the obvious parts to just get it running. The transformers ohm out to around what I'd expect - and I've ordered NTE102's to use for the time being. Once I test and validate basic operation, I'll dig in.


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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Thu 16, 2017 1:17 am 
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Success! I replaced all the bad components, all wax caps (except those embedded in the tuning switch) and electrolytics. I popped in the NTE102's and off it went. Lots of stations on all bands to boot. I'll probably just do the 455khz IF alignment and call it a day.

On the NTE102's... I read a beta of 32 on one and 64 on the other. I believe they should be more closely matched for the output circuit. Thoughts?

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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Thu 16, 2017 2:02 am 
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Congratulations & great job---glad it turned out well ! And good to see the additional pics---looks very clean inside...

I've never found any manufacturers' info stating exactly what criteria they use in matching transistors for push-pull outputs and sure would like to know ! Would think that gain difference would affect audio quality---how does it sound with those transistors in place ?

Looking forward to seeing it back together & a final performance report---are you going to detail clean it ?

John


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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Thu 16, 2017 7:49 pm 
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I wonder if just sticking in a pair of silicons the circuit will self bias and work ok?


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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Thu 16, 2017 8:27 pm 
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I would be inclined to use NTE-102A's or equivalent for the output transistors. The "A" version seems much more robust.

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Dave


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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Thu 16, 2017 8:39 pm 
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I'd be very interested if the silicon's could be made to work with little modification. And for the germaniums, the 102A's are easier to find so maybe I could buy a small pile and more closely match.


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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Sat 18, 2017 1:39 am 
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Beginning to clean and detail, and thought I'd run this by you guys. The finish on the main bezel/frame is a little rough. It looks like a casting that was chromed in some spots and maybe painted to detail.

Any recommendations on cleaning this up? Short of re-plating the whole thing, which is probably too expensive, maybe clean it up best I can and leave it alone?

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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Mon 20, 2017 4:37 am 
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Your thread has inspired me to extract my 1MBT6 out of storage. The lighter part of the front of the frame casting seems to be some kind of silvery/white paint. Mine was somewhat dirty in spots which I was able to clean with Q-tips and my favorite cleaner (ArmorAll Auto Cleaner). I had to push the cotton down into the tiny grooves with a jeweler's screwdriver.

Does your frame have sections where the white paint has worn off or are the discolored areas just dirty?

Dave


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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Mon 20, 2017 7:47 pm 
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Joined: Apr Fri 30, 2010 7:16 pm
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With regard to cleaning up the front bezel. It is an all brass casting. It was never "plated" with anything. The original finish was highly polished brass with a clear coat lacquer sealer sprayed on it to prevent tarnishing. after that, the brass was masked off and an argent silver paint was applied to the ribbed areas.

I have restored many of these bezels and it is a time consuming process but can be brought back to like new condition. I used paint stripper and a brass brush to remove the bulk of the clear coat and silver paint. I then got out my bench mounted 1hp polisher with two types of 10" buffing wheels and rouge. Its tricky, but after an hour or two the bulk of the brass is highly polished and any residual clear coat gone. Some of the very tight corners that aren't accessible with the wheel are polished out by hand. Once the brass shines like new, it is masked off and the ribbed area is re-sprayed with an argent silver automotive wheel paint. You can remove the masking and leave it as is or re-spray the entire bezel with a high gloss automotive clear coat to protect against tarnishing. Doing that slightly dulls the bright brass gold color but you'll never have to do any maintenance.

Good luck!


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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Feb Mon 20, 2017 9:22 pm 
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Excellent info - thanks.

I'll need to make a plan...

And Dave, as Froggy mentions, the ribbed area is paint and is flaking off on mine.


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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Jun Mon 05, 2017 8:44 pm 
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Just got my hands on one of these as a multi-radio deal last week.
If you still have any of the service or other documentation available, I would be grateful if I could get a copy.

Mine is working, but could use new caps for sure.

Thanks!


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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Jun Mon 05, 2017 8:59 pm 
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Skyliner218

Not sure who your post is directed to.........I would PM the member you are directing your inquiry to.


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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Jun Tue 06, 2017 2:19 am 
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You can view and/or download the Sams service information for the 1MBT6 here: https://app.box.com/s/21z2ex6mbbeqkf8jd10nt89eroxhq1tq

Dave


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 Post subject: Re: RCA Stratoworld 1MBT6 (Wish me luck)
PostPosted: Jun Tue 06, 2017 2:36 am 
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In addition to the "Sams" information that Dave posted, I also have the Genuine RCA Service Manual and the Genuine RCA Users Manual should you have an interest.............


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