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Old 27th Jan 2020, 3:54 pm   #1
Calmore
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Default New rear panel

I have a radio with no rear panel and no idea what the original looked like, so I'm going to laser cut one.

The photo shows the first prototype; would the original have looked like this?

I have a few tweaks to make and plan to cut the final one from a much darker hardwood.

Thoughts? I'm not bothered of its not 100% accurate, so long as the general ethos is there.
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Old 27th Jan 2020, 4:05 pm   #2
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Default Re: New rear panel

It looks pretty good to me! There is a picture showing a partial view of a PT36 back here https://www.radiomuseum.org/r/pilot_pt36.html
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Old 27th Jan 2020, 5:40 pm   #3
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Default Re: New rear panel

Ok, so short horizontal slots. I'd probably keep the chassis connectors hidden; the chassis is set back maybe 3/4" from the rear panel so sufficient space to plug things in internally.

I'll post a picture when it's finished.
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Old 27th Jan 2020, 8:00 pm   #4
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Default Re: New rear panel

Looks very, very good. How do you laser cut?
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Old 27th Jan 2020, 8:06 pm   #5
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Default Re: New rear panel

Did you do this with a professional machine or one of those ebay jobbies? I once repaired a laser cutter for the local high school who let pupils design and cut all sorts of banal things from MDF. I did think, this sort of thing is the future and I must get one, though the thought of programming a design puts me off.
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Old 27th Jan 2020, 9:32 pm   #6
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Default Re: New rear panel

That's actually superb, very well done.

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Old 27th Jan 2020, 10:54 pm   #7
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Default Re: New rear panel

Yes, it's a "professional" machine, but the cheaper machines will probably work, but will only handle thinner/smaller sheets.

Generally you feed the laser cutter with a DXF file that can be drawn in most CAD packages.

I chose plywood instead of MDF because MDF stinks when cut and produces a lot of sticky residue.

Most schools have laser cutters so may be able to assist. If you have a local MakerSpace it's worth talking to them as I'm sure they'd help for a small donation.
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Old 28th Jan 2020, 11:13 am   #8
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Default Re: New rear panel

Excellent result, and far less laborious and messy than using a router jig to cut the slots, which is what I've done to make replica backs over the last eight years in a router jig I designed for the purpose. However, I've always managed to get a picture, a 'rubbing' or at least part of a damaged back to use as a pattern. For a Portadyne Princess, I was able to scale the slots from a photograph from knowing the size of the cabinet.

So far I've only come across one radio with horizontal slots - a Murphy U198.

Across a range of makes and models that I've come across, there are variations in slot dimensions and spacings, but not too great. I've attached a picture below of the most common vertical slot dimensions and the spacings between each slot, and between each row of slots. (Those shown were the dimensions of the Pilot 'Little Maestro' back that I replicated as shown in the last pic bellow).

So far I've only come across one radio with horizontal slots - a Murphy U198, but I imagine that horizontal slots will generally have similar dimensions and spacings to vertical ones. I've expressed the dimensions in the diagram in mm rather than inches, but in fact the slot widths are almost always 6.00 mm, rather than the 6.40mm (1/4") which we might have expected in UK radios made in the pre-decimal era.

I hope that might be of some interest and help.
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Old 28th Jan 2020, 11:59 am   #9
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Default Re: New rear panel

Brilliant. Thank you.
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Old 29th Jan 2020, 10:54 pm   #10
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Default Re: New rear panel

There *may* be the opportunity in maybe five months time to laser cut a few back panels, if people can supply machine ready DXF files, subject to restrictions on size etc. Cost would be the cost of material plus postage. If anyone interested please let me know.
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Old 30th Jan 2020, 2:59 pm   #11
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Default Re: New rear panel

The Bush DAC90 (original version) rear panel with its burnt top corner immediately comes to mind.

If someone made a new thin rear panel that was heat resistant it could be hidden behind the damaged original rear panel. The ventillation holes would have to line up.
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Old 30th Jan 2020, 3:13 pm   #12
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Default Re: New rear panel

Wasn't the maximum size of the vent slots one of the things specified in a British Standard some time in the 30s? I remember something about a 'standard finger' that should not be able to pass through the slots.

Some radios/TVs from the era I remember had a sort of fabric mesh bonded to the inside of the cabinet over the vent-slots area for added protection.
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Old 31st Jan 2020, 8:53 am   #13
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Default Re: New rear panel

Quote:
Originally Posted by Calmore View Post
There *may* be the opportunity in maybe five months time to laser cut a few back panels, if people can supply machine ready DXF files, subject to restrictions on size etc. Cost would be the cost of material plus postage. If anyone interested please let me know.
Very generous offer.

I have a Rent a set (Strad) 551 that I have fully restored except for making a new back (the old one is missing. I do have a photo of what it should look like so will try and make a suitable drawing in the correct format.

Please put me down as interested.

Peter
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Old 31st Jan 2020, 8:56 am   #14
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Default Re: New rear panel

Quote:
Originally Posted by Calmore View Post

I chose plywood instead of MDF because MDF stinks when cut and produces a lot of sticky residue.
Have you tried hardboard?

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Old 1st Feb 2020, 10:54 am   #15
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Default Re: New rear panel

The topic of repro backs - especially for the more common radios - crops up periodically on the forum because they either go missing, or on live-chassis sets which use a mains dropper, the top of the back often carbonises and crumbles away, (EG; especially the DAC90, and to a lesser extent, the DAC90A). Then you are faced with either bodging in a piece of material of some sort or another, or making/buying a replica back. For a DAC90/90A 'corner bodge' repair, these CNC milled ones made from 3mm hardboard are currently available:

https://www.ebay.co.uk/itm/VINTAGE-B...-/143460718214

The only complete DAC90A repro ones that I've seen on e-bay were of 3.2mm MDF, made by forum member 'neil24-7', last on the forum 18 April 2018.

Neil runs a business making such things as slate signs, using a CNC router. In 2017 he made a batch of excellent repro DAC90A and Wartime Civilian Receiver backs in 3.2mm MDF which he offered on the forum at the very reasonable price of £12.00 each, given that the CNC router needed to be programmed and set up. However, though they were much admired, and some forum members enquired about the possibility of other panels being made, they didn't sell well, and Neil was left with most of them on his hands.

Neil’s ebay listing, (which has ended), for his DAC90/DAC90A backs stated:

Quote:

DAC90 REPRODUCTION REAR PANEL:

“Finding a complete unburned DAC90 Panel is impossible to find these days so I have reproduced these hard to find panels to make your restorations look Fantastic and as near as possible to original. CNC milled 3.2mm Black Hardboard. We also stock DAC90A reproduction panels and are trying to add more Radio makes all the time”.

End quote:

Neil's forum thread offering DAC90 back panels is here:

https://www.vintage-radio.net/forum/...d.php?t=136961

Though the backs were keenly priced and much admired, few were sold and Neil asked that the thread be closed.

DAC90s and '90As are money pits and often cost far more to restore than they're ever going to be worth. (possibly an OPT or rewind, a UL41 output valve, maybe a UY41, a set of caps, possible wave-change switch problems, volume control, maybe a twin smoothing/reservoir cap, pilot bulbs, etc), Maybe for some restorers, the cost of a commercially produced replica back is just a step too far?

We see that situation with requests for valves, where - when pointed to a link where a valve is available for say £10.00 - the response is sometimes: ‘But that’s as much as I paid for the set’, which may be so, but all hobbies incur costs and in this hobby, those costs often exceed the value of a restored set. That’s the price we pay for our enjoyment and fulfilment.

From feedback on the forum, Neil had understood that some members might be interested in replica backs for Wartime Civilian Receivers, so he made a batch and offered them at a very fair price of £12.00 each, complete with repro labels. The link to the thread on those excellent WCR repro back panels is here:

https://www.vintage-radio.net/forum/...0A+Back+Panels

They didn’t sell and Neil asked for the thread to be closed.

None of the sets I've made DIY replica backs for would have been worth spending much money on, which is why I took the DIY approach and made a universal router jig. (I've seen some excellent examples by forum members at the top of their game who've laboriously made backs for People's set ('444') and round Ekcos by hand).
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Old 1st Feb 2020, 12:12 pm   #16
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Default Re: New rear panel

That's the age old problem though, isn't it? When you are spending maybe £20 on an almost complete set then £12 for a panel, a tenner for a valve and maybe another fifteen for a new mains cable and other components makes it a labour of love rather than an economic proposition.
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Old 1st Feb 2020, 12:15 pm   #17
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Default Re: New rear panel

I haven't tried hardboard but it will probably cut similar to MDF.
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Old 4th Feb 2020, 6:27 am   #18
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Default Re: New rear panel

If you go to a supplier to auto body or upholstery shops, you may find the board used to build upholstered door panels. It is paper impregnated with wax, and about 1/8 of an inch thick. You need sharp tools to cut it. I've used it to make radio backs. Here is one example: http://cejaupholstery.com/WaterProofDoorPanels.aspx
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Old 4th Feb 2020, 11:00 am   #19
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Default Re: New rear panel

In the UK, that's called 'millboard', and is closest to what the original radio back panels were made of.

The problem is that it's made of several plies of paper, which, when holes or slots are cut with either a drill or a router, from my limited experience the results are unsatisfactory as compared to MDF or hardboard as the plies tend to delaminate and its very 'fluffy' when drilled or cut with a router. The results using a CNC laser cutter might be quite different of course. I guess that originally, the panels would have been die stamped in their thousands.

Millboard is readily available in the UK from suppliers of classic car restoration products, notably a family firm established 40 years ago called 'Woolies' (the nickname of the founder, Ian Woolstenholmes). They supply sheets which are roughly 5 ft x 4ft for £17.50 + post. They will post it, rolled into a barrel shape, but it's only available in black, whereas many, if not most, radio backs are brown.

They describe it as being:

Quote:

2.3mm thick Compressed card consistency.
One side faced black and lightly grained.
Ideal for trim panels.

Unquote.

https://www.woolies-trim.co.uk/product/1648/millboard

As to the cost of restoring a radio, it's unrealistic for anyone to get a set maybe 60 years old, of unknown provenance, then fully restore it, and expect to recoup what they've spent on it. Sets such as the DAC90A were rented out in their hundreds of thousands by the likes of Radio Rentals. Though many people seem to think they're 'classic' or 'iconic', they're commonplace and it's unlikely that they'll appreciate in value. As I mentioned earlier, with such sets you can't just 'do it up a bit, mend it, get it going' - they're 'money pits'. (From a functionality perspective, it's just as likely that a future prospective purchaser outside of the hobby would rather than the guts would have been removed and it converted to Bluetooth).

There are countless threads on the forum about the work involved to restore such sets, but as with restoring anything old, the gap between what you spend and what the set might be worth if sold, isn't an 'investment' - it's the price that we pay for our enjoyment. Who is likely to buy a restored set - few people on this forum would be interested in buying a set which it's claimed has (allegedly) been 'fully restored'. I doubt I'm alone in saying that my hobby is radio 'restoration' - not radio 'collecting'. I only restore radios which are in a poor state, and having done so, I like to keep them, so I'm a 'collector by default'.

Back on the topic of replica radio backs, some designs lend themselves to only needing a few DIY tools - a saw, a drill and a sanding block for example. The first hurdle is to find a pattern, and having done that, you need skill, time, patience and the inclination to see it through. For anyone who enjoys such things, it's a challenge and a pleasure. Otherwise, it's a chore.

I'd cite as an example a back for a 444 'People's set'. The one below was gifted to me by a friend. It has eleven hexagon shaped vents, each consisting of 61 holes - 671 in total, plus 15 larger holes at the top, and a rectangular cut-out a the bottom. Not one hole is out of place because as a first step, it was necessary to make an accurate steel drilling jig for the hexagon - no easy task in itself. Clearly, several hours work in all. ('Low tech - high skill').

The only way to obtain such a back is to either make one, or buy one from a supplier such as Ben Dijkman who can supply them (price on request). Ben sells many replica radio backs, knobs, dials, speaker fabric etc, mostly for continental sets at what, to me, are quite reasonable prices. At least a People's set has some value, so there is 'headroom' between the cost of a new back and the value of the set.

https://www.bendijkman.nl/index.php?...oduct&ipath=11

The fact that Neil's CNC milled backs for DAC90/90As, and Wartime Civilian receivers offered on the forum attracted no interest at £12.00 each speaks volumes about unrealistic expectations.
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