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Forum 141

[Closed] Restoring a Beau Decca Mirror-Lid TV and remaking the PSU

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Brian Cuff
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I've split this thread off my original "spot the theft" thread as this will be concerned only with the PSU fabrication and the restoration of the complete set (the mirror-lid variety) after the PSU/Amp has been completed (if this is not to your liking Chris, please attach it to the original thread).
I started with the pictures that Till posted in the other thread and have now been able to borrow a coplete unit so the path has eased somewhat.
Firstly, I drew the chassis in Autocad for the sheet metal company to work from. They can go straight from the .dwg file to their NCC coding so any mistake is down to me - and there will be some! :qq1

As the transformers etc. have arrived, I decided to do a "let's see what fits" excersize. With a little bit of persuasion on the mill, the transformers and choke fitted fine (I forgot to allow for the lead-out wires in the width of the drop-through hole) so did the EHT rectifier bracket. The caps (not re-stuffed yet) have been placed in position and the valve-holders fitted. Unfortunately, my pair of PX4s have the wrong envelope for the spacing of the holders (52mm) so I will have to do a trade with someone - Gerry at Crowethorne Tubes perhaps. Anyway, this is what it looks like so far - time to start the wiring :thumb .

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Posted : 21/03/2014 6:22 pm
neil1974
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Looking good so far Brian :aad .

Cheers
Neil.

 
Posted : 21/03/2014 7:36 pm
freya
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Very nice, look forward to more pictures :aad

 
Posted : 21/03/2014 7:39 pm
mark pirate
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Great work Brian, it certainly looks good :aad , I used Autocad at work for 12 years prior to retirement, I must install it on the workshop PC and see if it all comes flooding back!

 
Posted : 21/03/2014 9:12 pm
Brian Cuff
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I must install it on the workshop PC and see if it all comes flooding back!

It will Mark, and it is a really useful tool for all sorts of designing from benches and workshops to steam locomotives (if they're your thing!!). Thanks for the nice comments guys.

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Posted : 21/03/2014 9:56 pm
Katie Bush
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I shall watch with bated breath.

Your "scratch build" restorations are absolutely phenomenal and truly amazing.

Marion

 
Posted : 21/03/2014 10:36 pm
Brian Cuff
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I was able to get down to some serious wiring today. That included mounting the sound output transformer. I was fortunate enough to buy a couple of 10W P-P transformers with a lodaing of 2000R a-a from 3 or 8 ohms. A common loading for a pair of PX4s is 4000 a-a and, as there are 3 off 5R speakers in series in the set, I reckon that will make 4000R a-a using the 8R secondary. The transformers weren't very expensive and have masses of iron so could make for a good sound!
I have decided to fit new electrolytics instead of re-stuffing some as all the other stuff is new - it seemed a bit stupid to use old capacitor cans! Unfortunately, I don't have any so I have ordered some which should be here next week.
All the wiring is complete as can be seen in the picture. I find it very difficult to make the wiring really neat using silicone rubber insulated flexible wire. It would be nice to be able to source solid core - say 20swg as it would stay where it is put!
As soon as the caps arrive, I will install them and test the PSU. I will not, however, check the rest of the set yet as I need to make some progress with the Pye 12C that I am working on.
The vertical steel bars on the top of the chassis are to protect the transformer bobbins - a bit late as I have already damaged them! The chassis is so heavy now with the iron mounted, that I needed to be able to keep the chassis level during wiring. These three bars were already in stock as I made them for when I was restoring a Marconiphone 709 as that, too, has an extremely heavy chassis.

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Posted : 23/03/2014 8:16 pm
Anonymous
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Cooker wire is solid with fibreglass sleeve.

 
Posted : 23/03/2014 10:11 pm
FRANK.C
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Superb work Brian :thumb

Frank

www.electronics.frankcuffe.ovh

 
Posted : 23/03/2014 10:22 pm
Anonymous
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I find it very difficult to make the wiring really neat using silicone rubber insulated flexible wire. It would be nice to be able to source solid core - say 20swg as it would stay where it is put!

To beautify your work even further you might be interested in this, if you've not encountered it already:

http://www.mullardmagic.co.uk/mullard/p ... olour.aspx

Although this is stranded tinned copper, it is genuine vintage, is cloth covered, keeps its shape very well and can be laced into very neat cableforms.

Best wishes,

 
Posted : 24/03/2014 3:29 pm
Brian Cuff
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Thanks for the link, Dave. I am following that one up.

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Posted : 24/03/2014 4:43 pm
Cathovisor
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Also, Brian....

http://www.radiodaze.com/category/306.aspx

This stuff really looks the bee's knees! I use Radiodaze for a lot of things and I can thoroughly recommend them.

 
Posted : 24/03/2014 9:51 pm
Brian Cuff
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:bbd I've ordered some of the cable that Dave recommended from Mullard Magic. It does look good. I will also try the Radio Daze some next - I quite like the solid core aspect of it!
I am still waiting for the caps for the PSU so I thought that I would use some old caps which I re-stuffed for my HMV 1804 which I started an age ago but seems to have been sidelined by more interesting stuff! In order to finish the phase inverter wiring, I had to have stand-in caps as a lot of the wiring uses their tags. So in they went and I finished the wiring - no picture because I haven't trimmed any components ore wires because of the transplant I will do when the proper caps are delivered. On powering at half mains voltage, there seemed to be no problems so up it went to 250V. The phase splitter worked OK so in with the PX4s - not a very good fit due to the fat envelopes. I measured 100Vp-p across 20R before clipping which means I'm over-runing the PX4s a bit so I will have to look into the bias (derived using a separate rectifier). The pictures show how the finished product looks and I must say, I'm very happy with it. I can't wait to finish it properly and get the Beau Decca working again.

The transformer bobbin cheeks were damaged in the post :bbd - I have most of the bits and will repair them as best as I can.

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Posted : 26/03/2014 9:47 pm
mark pirate
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That looks excellent Brian, shame about the PX4's being the wrong size :ccb
The chassis looks so much better for a coat of paint.

 
Posted : 27/03/2014 12:52 pm
Brian Cuff
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Thanks Mark. I am going to swap, with a friend, my pair of PX4s for a slimmer pair at the NVCF so that problem is solved.
The PSU is now finished and working apart from adjusting the PX4 bias which I can't really do without the PSU being loaded properly so I will have to wait until the rest is going. This is the last picture I will post in this thread - unless a query is raised - showing the new PSU in its rightful place in the set. One thing I've noticed is that the thief has left the mains lead and fixing bolts in the bottom of the set!!

I will start a new thread once I get onto restoring the Beau Decca, starting with the radio.

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Posted : 28/03/2014 6:59 pm
Cathovisor
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You could always use AC044s - RGD used them in one set because the PP3/250 was physically too big: model 925 IIRC.

 
Posted : 28/03/2014 7:21 pm
Brian Cuff
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That's true, but as I have access to a narrow pair of PX4s as a swap, that seems the way to go!

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Posted : 28/03/2014 7:41 pm
Lloyd
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New chassis looks great, and looks right at home in there too :aad

Lloyd.

 
Posted : 28/03/2014 7:49 pm
Refugee
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That was a quick build.
Is that the tuner looking lonely to the left of the tube framework?

 
Posted : 28/03/2014 10:41 pm
Brian Cuff
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No, Ref. That's the gram preamp. The radio chassis is mounted above the PSU. There are, I think, 3 different EQ settings built into the radio chassis. I don't know why, as in 1948 there were only 78s for the general public - although I have a couple of dozen 331/3 records from the late 1920s!

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Posted : 29/03/2014 12:35 am
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