Replica backs for Portadyne Princess & Noble TRF

[Yorkie]

In other threads I've mentioned that I've been restoring a Portadyne Princess, and a Noble - both TRFs, both using an identical cabinet, and though a different valve line-up having many similarities. Neither of them had a back, but luckily, Howard Craven had a Princess compete with back and kindly e-mailed me a picture.

Most UK valve radios seem to have the same sized vent slots the same distance apart, albeit different numbers according the size of the panel. Some also have horizontal slots, as did the Princess and the noble. Whatever the final shape of the back is to be, the blank sheet of material from which it is made needs to be rectangular to suit the router jig in which it is held while the slots are cut.

I already had a jig that I'd made for making a back for a Wartime Civilian Receiver (AKA 'Economy' receiver) so was able to use that to cut the vertical slots. I then made a jig to enable the horizontal slot to be cut. The same requirements apply - the jig consists of a means of holding the blank in position, and a router guide to allow the router to move back and forth to cut the slot by plunging the router into the blank, while limiting the length of travel of the router to the length of the slot to be cut. In use, the router is placed in position, switch one, plunged into the blank then move along inside the router guide to the end of the sot. The router is then switched off, the panel is moved along for the next slot to be cut.

I won't repeat all the stuff I wrote in an earlier thread about making backs - I've just appended pics of the blank with the vertical slots already cut in the Wartime Civvie back jig, then the additional jig to cut the horizontal slot, then the blank cut to shape, then painted brown ready to fit on the receiver. I'm not too enamoured with the label I've made and glued on, but it's a reasonable attempt at replicating the original, a pic of which is also shown.

The two radios are now finished, and I'll post a pic of them side by side.

Hope that's of interest.

[Retired]

Hi,

A very professional job indeed David and many thanks for sharing.

You've got this job off to a fine art with your home made jig producing first class copies of radio back panels. Many radios appear to lose their back panels so this thread is very useful and gives practical advice on how to make a top class copy rather than simply slap a lump of sheet material onto a radio with no style.

The cheapest of routers will do this work easily and once a router is bought it opens up other fields of interest such as your excellent comb/finger jointing again with a home made jig.

I'm sure this thread will encourage others to have a go at making correct back panels.

Kind regards, Col.

[Geaney]

Fully agree - vey useful info. The Siemens set I'm working on does not have a back so I'll be looking into a replacement once I get the thing working.

Cheers, John

[Yorkie]

Thanks for the kind comments guys.

These backs were made from normal 3.2mm hardboard as I couldn't find any oil tempered hardboard locally. Lots of timber merchants sell it, and having made these from normal hardboard, it's reaffirmed my view that oil tempered from which my first backs were made is far superior, and it's no more expensive either. I think I just struck lucky with the first lot I got from B&Q - the same bar code only brings up standard hardboard. I can only guess that it was a batch that their suppliers sent as an alternative at some stage.

I'd endorse Colin's view that for little jobs like this, the cheapest of DIY routers will cope happily. It only has to plunge into 3mm hardboard (or MDF) for a few moments while each slot is cut, using a 6mm or 0.25" router bit. Best to get a decent bit - Trend or whatever. Routers in untrained hands can be vicious items with an unguarded bit, but used in this fashion they're very safe as the bit retracts when the slot has been cut.

Whatever the size of the radio back, the same basic principles apply - some means of holding the blank in place, such as strips of scrap hardboard, and a means of advancing the blank along into the next cutting position for the next slot to be cut, then repeating the process till a whole row has been cut, then repositioning the router guide for the next lower row of slots. The router guide itself has an aperture cut in it to suit the size of the router sole plate, and to allow the sole plate to move up and down by just the extent of the slot to be cut.

Admittedly it take a couple of hours or so to make a jig, but the costs are minimal, and once made it's a lot less laborious and neater than other methods, such as cutting a hole at each end of a slot then using a chisel or fretsaw to cut from one hole to another to make the slot. Something such as a Wartime Civilian Receiver has getting on for ninety slots - the thought of cutting all of those without a jig of some sort doesn't bear thinking about!

As I said earlier, I'm not enamoured by using matt emulsion paint to finish the backs, but can't think of any other finish that is as near to the original as can be had. I use cheap 'tester pots' - I guess vinyl 'silk' might be better, but they seem not to do that in dark brown colours.

The Siemens looks to be another monumental project John, and you've done well to extract the caps from the 'rats' nest' of under chassis wiring and to replace them!

[Aerodyne]

That is a great result, David. I never used a jig as such when cutting a new back for a wartime civilian receiver and can endorse your feelings regarding the effort involved (though I did use a router table with a sort of rough jig arrangement consisting of limit stops). Your method is definitely the one to use.
Tony