McMichaels Twin Supervox 20 years in repair

[Mr Moose]

Hello,
The back appears to be made of veneered 5ply not 3ply.
Yours, Richard.

[RadioHist]

OK 5 ply it is....

On a minor note..... You kindly provided a side view of the chassis which shows the side bracket with a notch to provide clearance for the basket of the loudspeaker. I note that my chassis does not have these notches. The 1933 Wireless & Gramophone Trader - 9-December-1933 definitely shows the Magnavox (G.B.) speakers as in my chassis. There was no need for a notches in the chassis to clear the baskets.

So obviously, I think, McMichael changed vendors for loudspeakers during various production runs. Maybe Magnavox (G.B.) went belly-up at that time or got bought out? I know that Magnavox in the USA started out their major manufacturing in Oakland, CA and moved to Ft. Wayne, Indiana about 1931. Maybe they shed overseas relations at that time?

In any case... Do you know the manufacturer of the speakers in your chassis?

Just another tid-bit I'd like to insert when I write a narrative of this project.

I think a guy has solved my electrolytic condenser problem, it should arrive in the post in a couple of days.

Robert

[RadioHist]

Well today I made my first attempt to make a replica of the missing 8 uf electrolytic. A guy here in the USA had a junker can that is made exactly the same way except that it was 1/4" too short... A little hacksaw work and I 'stretched' it.

This is the first attempt to print the label... I could get the tan hue a little closer but for now I'm pretty happy.

I did put a 10 uf. 450 VDC radial cap inside so it would work.

Robert

[RadioHist]

All the parts have been cleaned and parts fabricated. I've started to put the chassis back together and should have pictures to post on the weekend.

This got me to thinking about supporting documentation I might be able to collect for the notebook I'll have at hand when I exhibit this radio in 2016. (I have the two Trader sheets on the set.)

A web search shows no additional documents - just this one great image. I would really like to see photos or scans of a users manual. Specific sales brochures. Adverts.

Got anything to share?

Thanks,
Robert

[RadioHist]

After about three weeks on the bench, the chassis is back together!
The best I can determine, the chassis is virtually identical as it left the factory thanks to help from Richard and others. My replica side bracket and mounting for the missing electrolytic are the correct dimensions.

Since the back panel was in terrible shape, I had to go down to bare metal and paint with a nickel colored paint that I 'doctored' with an over-glaze of black and gold paint applied with a gauze pad. The top of the chassis was so good, I chose to clean it with a mild acid and an over-spray of clear lacquer. I would rather have the viewer see the original satin nickel plating.

More pictures later when I can get better lighting and stop the lens for better depth of field.

So in the next day or so I'll be on to the cabinet... I hate woodwork!

Robert

[HamishBoxer]

That looks superb without a doubt.

[RadioHist]

Thanks....

I don't know if anyone has mentioned this, but note the three cord flex in the two pictures. A couple of years ago I was looking for better ways to clean exposed cloth covered wiring such as the lines going to field coil speakers that generally turn an ugly yellow/brown or some such. I hit on this method if you have access to an air compressor with small aperture blow gun.

1. If there are any loose braid ends, use some embroidery floss to whip the ends so they will not fray.

2. Drop the wiring into a container and pour in low VOC mineral spirits. You might call them white spirits... Slosh around for a minute or two. If you have a natural hog bristle brush you can gently go over the wire but don't actually do any scrubbing of the wire.

3. With my blow gun with 1/8" aperture and 60 or 80 p.s.i. pressure, I blow off the wiring while it is dripping wet with the spirits. (You should see an atomized spray coming off the wire.) After repeating 3 or 4 times I'm done. The results are often very gratifying as you may be able to see in these low resolution snapshots.

My observation is that the spirits won't make the wire any less flexible than it already is.... Whenever it stops raining, I'll do the same to the mains cord and try to show the results.

Robert

Robert

[RadioHist]

The last step in putting the chassis in the cabinet was dealing with a problem around the hole for the volume control.

There is a thick brass washer with countersink holes for tiny screws that attach it to the cabinet and act as a bushing for the control shaft. The problem is that the cabinet apparently never did have the proper spacing to line up with the chassis. The net result is that one of the tiny screws just barely could bite into the cabinet face. And over time it simply broke out on the side. What to do

It dawned on me that I could take a 3/8" (or 10mm) wood dowel and wrap it with a few layers of Mylar film. On top I could the wrap a strip of cotton sheeting and on every second layer apply water thin CA adhesive to soak into the sheeting. I continued the wrap to match the diameter of the hole in the cabinet. Then I could drip on the CA curing agent and allow time to harden.

I used a fine tooth hacksaw to cut out a section to the thickness of the cabinet. The Mylar film allows your work to slip off the dowel and does not stick to the CA saturated cotton.

This bushing then is glued in place with yellow wood glue. The net result is a hard fibrous insert that can be pilot drilled and then the tiny screw installed for a 'bulldog' grip that is never going to pull loose. My thinking is this is much stronger than a daub of Plastic Wood and can be worked sooner.

My 2 cents (er.. 2 p) worth
Robert

[RadioHist]

For the first time in 20 years this Twin Supervox is whole again !

First off, my apologies to Richard. After all the business about needing to make a replica back for my set, I am walking into my old workshop in the house a few weeks later only to find the original back cover siting on its short side on a shelf only two feet (0.6096 M) from arms reach whenever I'm in the room! I simply could not recognize it as such.... The same place it has been for 20 years!

On the back I was surprised to see that it does not have the Ivorine tag with the warning. In stead is a paper label printed in red ink with the same warning.
Leading me to think again that my receiver must be a early production run.

Two friends have told me that they intend to give me a Osram branded MH4 Catkin to switch out the Marconi branded valve. One even claims to have a valve box I can use in my exhibition of this set in 2016.

I'll be assembling my usual notebook of restoration/conservation and history sometime before the end of February.

I'm really happy to have this, to me very interesting, bit of UK history to show at conferences here.

Robert

[HamishBoxer]

Great restoration job.I restored one of these but it did not look as good as yours.

only two feet (0.6096 M)

I have spent hours (not 20 years) looking for something that was on the kitchen table.

[RadioHist]

Forgot to mention the mains cord....

For years the mains cord was a helter skelter mess too rigid to make up into an orderly loop. I saw some references to using heat to soften the rubber insulation. I thought I had little to lose so tried it.... With my hot air gun adjusted to maybe 150 C I was surprised to find that I could flex the cord back to orderly loops.

Problem solved....

I am still a little puzzled about this set because it arrived from Italy with, what I regard as, a USA style 2 blade plug. I thought you guys used round pin mains plugs before advent of the modern plug schemes... Right/wrong

Robert

[SpiggyTopes]

I'm jealous!

What does it sound like through the two speakers?

[RadioHist]

I can't tell you what it sounds like.

I'm one of those crazy museum curator types that are more interested in preserving as much of artifacts as possible. With this restoration/conservation it is very close indeed to being an accurate historical record of the day it left the factory. No parts substitutions, rewiring or 'improvements to make better than new' for me. I'll write an article describing all that was done that will be available when it is exhibited. I might even see if Carl Glover wants to publish it.

An examination of the schematic and commentaries in period publications will tell you how it works and how well it was regarded in the marketplace. That's good enough for me.

Robert