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 Post subject: RCA Strato-World 1MBT6 repair and strange behavior
PostPosted: Nov Wed 15, 2017 8:37 pm 
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Joined: Sep Mon 14, 2015 3:11 pm
Posts: 24
I have started working on the Strato-World that I picked up last spring, and there were several issues to straighten out. I'm positive that it has been worked on in the past as the antenna connections were cut and patched, but I could not find any components that looked to have been changed. The audio was quite weak, and the lower half of the broadcast band had no reception. Each of the SW bands yielded at least a weak signal or two.

I pulled the chassis and replaced all of the capacitors, including those in the band switch. Pretty tight quarters with a few buried caps, but not horrible if you just take your time. I almost skipped the non-polarized 4uf electrolytic, but as luck would have it found one at a local store that still had their Radio Shack parts bin.

After double checking everything, I powered up and found the audio to be much better. The top end of the broadcast band had my only local AM station fairly close to where it should be at 1410 kc. As I worked down toward mid band, I started hearing a garbled mix of AM stations along with WWV and Brother Stair. The lower half of the band is all SW stations. A quick check of the SW bands found stations pretty much where I would expect them, so it only seems to be an issue with the broadcast band.

My bet is that the clipped antenna wires mean someone pulled the chassis to try to touch up the alignment, screwed up and realizing they were in over their head just packed it up.

It was late at that point, so I did a quick attempt at pulling the lower end of the band back into line, but with no success decided to leave it until I had more time tonight.

My question is this. Since I had it out of the case, I attached it to my longwire antenna rather than the loop in the lid. Is it possible I have SW stations overloading the lower end of the band because of that? I have seen it the other way around, but never like this. I also have heard these were notorious for having strong local FM stations interfere with the SW bands, but have not experienced that at all.

I don't have a signal generator yet, but there are a couple of reliable regional stations between 600-750 kc that I should be able to use to get things close if it is simply a matter of trying again with the built in loop. I don't believe the IF cans have been messed with since this only seems to be affecting the broadcast band.

The other question is how people deal with getting stations aligned on the display when the chassis has to be out of the enclosure to access the adjustment points. I am thinking I may need to try scanning the frequency scale and print a copy to use for reference. The factory must have had some kind of jig to accomplish that when doing alignment before installing the chassis in the case.


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 Post subject: Re: RCA Strato-World 1MBT6 repair and strange behavior
PostPosted: Nov Thu 16, 2017 1:50 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 11542
Location: S. Dartmouth MA 02748-1225 USA
For the Strato-World an RF generator is a must.

Also will need the correct alignment instructions from a Sam's or RCA handbook on the model.

The alignment instructions also call for an aluminum plate under the coil area as well as the bottom plate on.

The alignment will also show how to tic the dial plate with station alignment markers. Strict attention must be paid so the correct peak on the oscillator is used so the band will only calibrate in one location per band. The wrong peak will make the band off as well as insensitive at the other end as the RF and ANT will not track.

The correct broadcast antenna coil must be in place, either the ferrite rod or the loop in the lid, they are part of the RF tuning. Incorrect loop or trimmer setting in the external antennas will make the BC band very weak.

The alignment may require the "rocking" technique. If so it will be explained in the alignment instructions if not the procedure could be found online...

GL

Chas


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 Post subject: Re: RCA Strato-World 1MBT6 repair and strange behavior
PostPosted: Nov Thu 16, 2017 3:31 am 
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Joined: Jan Tue 31, 2012 1:55 am
Posts: 2953
Location: Mountains of Mourne. Ireland.
http://www.antiqueradios.com/forums/vie ... 8#p2697448
http://www.antiqueradios.com/forums/vie ... 5#p2697475

Greg.


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 Post subject: Re: RCA Strato-World 1MBT6 repair and strange behavior
PostPosted: Nov Thu 16, 2017 2:29 pm 
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Joined: Sep Mon 14, 2015 3:11 pm
Posts: 24
"The alignment instructions also call for an aluminum plate under the coil area as well as the bottom plate on.
The alignment will also show how to tic the dial plate with station alignment markers"

I have both the service manual and Sams, and neither one shows this information. Would you be referencing the earlier tube version of the Strato-World rather than the transistor model?

Last night I connected to the loop antenna in the lid and was able to slide the bottom of the broadcast band back into alignment. I also peaked the antenna and rf for both ends of the band and it is receiving very well. In fact, I would say it is right up there with my solid state Trans-Oceanic. I will leave it there until I can get my hands on a signal generator to do a proper alignment.

The last issue I am seeing is with the tone control. It does not have a gradual change of tone, but goes from the low to high with nothing in between. I did not have time to dig into it last night so that will go on my list of things to do.

Fortunately my dial cord was in good condition and was able to be taken off intact, so getting that put back on was not the exercise in frustration most people seem to encounter. I would not want to have to recreate one from scratch though!


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 Post subject: Re: RCA Strato-World 1MBT6 repair and strange behavior
PostPosted: Nov Thu 16, 2017 4:04 pm 
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Joined: Feb Wed 17, 2016 2:38 pm
Posts: 113
Location: Cottage Grove, Minnesota
I have a 1MBT6 Strato-World that I have not been able to complete since the volume pot is extremely noisy when adjusting the volume. The carbon tracing in the pot is severely worn and it is a very unusual design that I haven't found a replacement. This may be the same issue you are having with the tone control. Its possible the carbon tracing in the pot is worn out.

I had to recreate the dial strings since mine was totally screwed up. The instructions for replacing the dial string are not very good, but once you figure out how it was designed it isn't too difficult. I did have to remake one of the strings because it was a little to long and I couln't get full dial and tuning cap movement.

I found that every single original electrolytic cap in the radio was completely open. All of them were replaced. I left the band switch alone other than the electrolytics and it seems to work fine.

_________________
Andy


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 Post subject: Re: RCA Strato-World 1MBT6 repair and strange behavior
PostPosted: Nov Thu 16, 2017 5:01 pm 
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Joined: Sep Mon 14, 2015 3:11 pm
Posts: 24
Replacing caps in the band switch was not too bad, outside of one that was buried in there pretty deep. I did not bother testing any of them since my plan was to replace any electrolytic and paper caps regardless. I also ended up changing the .05 disk cap on the volume control.

I will be interested to see how the radio performs after a proper alignment. Reviews I have read were somewhat mixed, but so far it is doing a nice job on the broadcast band. I only have 1 local station, and the next closest are 100+ miles away in Winnipeg, Grand Forks or Fargo, ND. I would say this stands up very well vs my Royal 7000.


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 Post subject: Re: RCA Strato-World 1MBT6 repair and strange behavior
PostPosted: Nov Thu 16, 2017 5:33 pm 
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Joined: Aug Sat 16, 2014 2:19 am
Posts: 987
Location: Palos Verdes, CA
Matt (50sTransistorRadios) has produced a you tube video on the RCA 1-MTB-6 that I believe you would find interesting:

https://www.youtube.com/watch?v=YgOsCJzsULM


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