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Old 28th Sep 2015, 3:53 pm   #1
RadioHist
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Default McMichaels Twin Supervox 20 years in repair

McMichael Twin Supervox 20 years in repair…

In the Fall of 1995 my Italian friend sent me a McMichael Twin Supervox. I hit problems in acquiring documentation and encountered some restoration issues I was not equipped to address properly. So… It has sat in silence till this very rainy week. It is now on the bench in pieces. I’m confident the conservation and restoration can be completed. I do however need some bits of information that I hope some of you can provide.

1. I presume that there was some sort of safety cover on the back of the cabinet. I have not found a photo of this on the Web. Any photos of this cover would be greatly appreciated so that I can fabricate a credible replica.
2. It is obvious that some sloppy repairs were done on the set. The Trader Service Sheet #557 Rev. 4 shows the Westinghouse Metal Rectifier mounted under the speaker… In my set the MR is precariously perched as shown in the picture and a 8 ufd. dry electrolytic is laying loose in the bottom of the chassis. (I presume this is a replacement of C23.) Are there any photos that show the correct arrangement of the rectifier and C23? How is C23 mounted?
3. Our sloppy repairman seems to have misjudged clearances and found he could not replace the chassis side bracket after doing his dirty work. It seems to me that this bracket is virtually identical to the other bracket except for the mounting of a small phenolic (?) board. Are they the same? If so I can easily make a replica.
4. The loudspeaker grill cloth in my cabinet is completely wrong. The Web pictures I’ve found don’t have enough resolution to show the pattern weave… I need better snapshots.

This radio is certainly scarce on this side of the Atlantic. But very interesting to me in that it shows the first attempts to make metal shell valves for broadcast receivers (Catkins) and has the Metal Westinghouse H.T. rectifier never used in the USA. I think my set is truly worthy of restoration so that I can exhibit it here at various conferences. So answers to this query would be greatly appreciated.

Yours,
Robert
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Last edited by RadioHist; 28th Sep 2015 at 3:58 pm. Reason: left out sentence
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Old 28th Sep 2015, 4:56 pm   #2
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Default Re: McMichaels Twin Supervox 20 years in repair

There aren't many of these over here either. It's a good example of early/mid 30s British design, before everybody started making superhets. Your chassis seems to be in good general condition despite the 'repairs'.

Some pictures at radiomuseum.org: http://www.radiomuseum.org/r/mcmicha..._rv8_rv_8.html
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Old 28th Sep 2015, 10:38 pm   #3
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Default Re: McMichaels Twin Supervox 20 years in repair

Hello Robert,
I have two of these awaiting restoration.
I have found one and it has a non original back cover but I am pretty sure the other one does have the correct cover.
To give you the precise information you require for an internal reconstruction I will need to remove the chassis from one of the sets which I probably wont be able to do till next weekend.
Looking in the back the missing side plate does seem to be the same as the other side but with a paxolin (phenolic) board held by four bolts to hold C23 insulated from the chassis. In the set that I have looked inside, C23 has been replaced by a more modern component but the paxolin board is still there.
I have attached two photographs but I will get you more including the back cover and speaker cloth when I find the other set and have removed the chassis.
Yours, Richard
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Old 28th Sep 2015, 11:31 pm   #4
Peter.N.
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Default Re: McMichaels Twin Supervox 20 years in repair

I haven't seen one of those Westinghouse rectifiers since I took my dads old Lotus radio to bits in about 1950.

Mounting it that way up is preventing it from cooling properly but I don't suppose its a lot of good now anyway.

Peter
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Old 28th Sep 2015, 11:56 pm   #5
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Default Re: McMichaels Twin Supervox 20 years in repair

I would strongly advise replacing the rectifier, as if it fails it's likely to emit disgusting and indeed poisonous fumes. You may be aware of this of course.
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Old 29th Sep 2015, 1:48 pm   #6
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Default Re: McMichaels Twin Supervox 20 years in repair

I’m excited!

Thanks gents for the feedback. I was restoring the power transformer yesterday afternoon. The paper covering was in terrible crumbles… Get to restack the laminations after lunch today.

Richard,
Photos would be VERY much appreciated! I guess we need some speculation about the mounting for what is identified as C27 in the 1933 Wireless and Gramophone Trader Sheet (C 23 on Trader Sheet 557 that I attached on my first post…) I think it was originally a screw base electrolytic just like the one in the center of the chassis (see attached photo). So maybe the Paxolin board had a sheet metal L-Bracket with a big hole for the electrolytic? Any chance either of your chassis still have that bracket to photograph?

I did download the radiomuseum.org photos that you can view without membership. Both chassis shown were repaired in various ways… One had PM speakers, the other a different mounting scheme for the audio output transformer.

I’m not interested in expedient repairs just to git ‘er goin’. I’m trying to preserve the historical accuracy of the artifact as much as possible.

I guess I’m one-up on those sets also since I have all four Catkins.

If anyone has a derelict 8 uf. electrolytic in your junk box, I might want to buy it from you. Of course these types of electrolytics were used here and I might get lucky and find its doppelganger in my own parts chaos. (I can easily recreate the paper label.)

Again thanks for the interest in my project.
Robert
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Last edited by RadioHist; 29th Sep 2015 at 1:50 pm. Reason: wrong photo attached...
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Old 30th Sep 2015, 1:12 am   #7
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Default Re: McMichaels Twin Supervox 20 years in repair

Hello,

Here are some pictures of the back. It looks as if it may have been cut out by hand as some of the sides of the holes are not square. It is made of plywood about about 9/32 of an inch thick.

It only covers the top part of the back leaving the metal chassis exposed at the bottom.

If you send me your email address by PM then I can send you the full sized pictures.

Yours, Richard
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Old 30th Sep 2015, 1:38 am   #8
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Default Re: McMichaels Twin Supervox 20 years in repair

Wow! Great pictures of the back cover... Makes me think it will be a relative snap to reproduce. The easiest e-mail address is: Removed by Moderator
Got the power transformer back together and it is looking great.

Will pick up the sheet metal to make the missing side bracket tomorrow afternoon.

The twin speakers in my set are Magnavox and the little paper label on the back of the field coil pot is missing on one and the remaining one is awful looking so I recreated the artwork this morning.

I'll post pictures tomorrow.

I'm still excited

Robert

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Old 1st Oct 2015, 2:16 am   #9
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Default Re: McMichaels Twin Supervox 20 years in repair

The first attachment shows a replica tag for the field pot on the Magnavox speakers used in the Twin Supervox. I have started a web page on my project and you can download a .pdf of this Magnavox tag. My local print shop has silver paper on which to laser print the black... Cost me all of 23 cents including tax for a single sheet with six images....

http://kd4hsh.homestead.com/McMichael-TS-00.html

Making the replica side bracket was no big deal... Just realized I forgot to punch two holes... No problem.

As mentioned earlier, the mains transformer looked terrible. I was able to peel off the outside layers of insulation paper and recreate what was there. I got lucky in that I've had for nearly 40 years some of the old style Kraft paper with water soluble glue that used to be used in xfmr winding. What I did not have was any transformer varnish. The new stuff has a red dye in it. Did not want to go there.... Found out that the local auto parts store has spray cans of a transparent coating that is supposed to withstand up to 500 F. So I applied that to the dried kraft paper. THEN to get the original look, I figured out that I could use a little PVA veneer glue with transparent amber dye as an over coat. It dries to a great looking translucent effect. It is not going to discolor at normal operating temperatures.

I tried to find the correct font to use in recreating the paper tag on the back panel. After an hour and a half, I gave up. I then decided that I would see what would happen If I tried to clean up the low resolution image posted here and was rather surprised that it looks this good. If I get the full resolution image, I think I can come up with a tag I'll be happy to use.
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Old 1st Oct 2015, 9:16 am   #10
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Default Re: McMichaels Twin Supervox 20 years in repair

Fantastic work, I'm very impressed.
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Old 1st Oct 2015, 7:37 pm   #11
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Default Re: McMichaels Twin Supervox 20 years in repair

I thought I was going to be clever enough to use Mr Moose low resolution image to figure out the dimensions of the back cover. But I forgot that old bugaboo, parallax. So just for future reference if you have a general need to photograph something like this, there should be two snapshots made. With your scale placed on the object perpendicular to your first shot.... (I'm assuming two identical scales are not at hand...) Then a majority of parallax issues will wash out.

I did update my web page on this project a little. (link in posting below)

Robert
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Old 2nd Oct 2015, 2:18 pm   #12
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Default Re: McMichaels Twin Supervox 20 years in repair

I got a little lucky in that the T.C.C. electrolytic I need is made under license from Condenser Corporation of America so I ought to be able to find a can with identical dimensions over here without too much sweat.

I will need an appropriate label and it dawned on me that the round battery scanner I made last year would be ideal to grab the image on the can I have and then make a new graphic. Worked like a charm!

Robert
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Old 2nd Oct 2015, 2:21 pm   #13
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Default Re: McMichaels Twin Supervox 20 years in repair

Mr Moose

Just FYI - I sent you a private message with my e-mail address so you can send the high resolution photos of the back cover.

I presume the 9/32" plywood is 3-ply?

Thanks,
Robert
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Old 4th Oct 2015, 8:00 pm   #14
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Default Re: McMichaels Twin Supervox 20 years in repair

Got the paper label on the back cleaned up. Close inspection will reveal some parallax issues but maybe I can live with it... Will get printed on Oyster paper.

Interesting statement to see posted on a radio from my American point of view. I'm thinking it was the depths of the Depression and it was an attempt to prevent collapse of business for their dealers. I'm guessing it did really not prove very effective?

Robert
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Old 4th Oct 2015, 8:11 pm   #15
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Default Re: McMichaels Twin Supervox 20 years in repair

https://en.wikipedia.org/wiki/Resale_price_maintenance
https://en.wikipedia.org/wiki/Net_Book_Agreement
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Old 4th Oct 2015, 9:11 pm   #16
Mr Moose
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Default Re: McMichaels Twin Supervox 20 years in repair

Hello,
The label is not actually paper but some sort of thin, possibly ivorine, type plastic which has distorted a bit with time hence the wonky lettering and it is held in place by four little nails.
I have removed one chassis and will send you some more pictures later.
Yours, Richard
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Old 4th Oct 2015, 11:51 pm   #17
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Default Re: McMichaels Twin Supervox 20 years in repair

For more on price fixing by radio manufacturers see The Story of Defiants.

— Joe
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Old 5th Oct 2015, 2:17 am   #18
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Default Re: McMichaels Twin Supervox 20 years in repair

Very good collateral information! It is in my file just now.

Thanks,
Robert
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Old 5th Oct 2015, 2:26 am   #19
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Default Re: McMichaels Twin Supervox 20 years in repair

Quote:
Originally Posted by Mr Moose View Post
The label is not actually paper but some sort of thin, possibly ivorine, type plastic which has distorted a bit with time hence the wonky lettering and it is held in place by four little nails.
OK, Thanks for that clarification. I note that my cabinet has a tiny (maybe 4 sq. mm) fragment of the label shown in this radiomuseum.org photo. It does look like thin Ivorine (white celluloid that has turned cream color).

Bit-by-bit progress!

Robert
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Old 5th Oct 2015, 2:30 am   #20
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Default Re: McMichaels Twin Supervox 20 years in repair

Paul,

Ditto Thanks for your links as well.

Robert
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