I did see a thread somewhere about using a cradle to hold your radio while working on it. I thought that was a good idea and decided to have a go at making one but then the scrooge side of me kicked in and I decided to try and make it adaptable to fit almost any radio to save making more than one cradle.The final idea used what I had to hand which was basically some 7.5" squares of paxolin and a few nuts and bolts.
My design required a visit to messers Block&Quail for two 1M threaded bars 8mm dia which were cut in half to make four bars half a meter long. The next job was to drill four holes 9mm dia in the corners of each of two sheets of paxolin half an inch in from the point of the corner, then I secured each of the four threaded bars to one piece of paxolin using nuts and domed nuts the other piece of paxolin was pushed onto the other end of the rods with a nut on each side of the paxolin so the paxolin could be locked in place and dome nuts fitted to the open ends of the rods for safety
The facing ends of the paxolin sheets have some of the non-slip rubbery stuff that is made to stop things moving around your dash-board, glued to them to provide a non-slip surface.
It is then just a matter of putting your chassis in between the paxolin sheets and adjusting the sliding one so they grip the chassis and locking it in place with the 8mm nuts just tight enough to hold the chassis in place. As no holes are used to hold the chassis it should be infinitely adjustable to put the chassis at any angle you want but with all four sides of the cradle being open the chassis should be available from any direction. Of course you can drill holes in the paxolin, to hold a more complex shape if you wish to but I think for most chassis just pressure will work quite well.
In the pictures you will see it holding my Pilot Major Maestro chassis I have removed the speaker because it gives me better access to the chassis but if I had needed the speaker on I would probably make some extension pieces for the paxolin to keep the speaker clear of the bench.
Of course should you want to make one of these anything would do for the end pieces like plywood etc I just used the paxolin because I had it to hand ..........
Now that's cunning - I like it!
- Joe
Very neat! I like the comment about using paxolin for economy because it was hand. If you check out the price of paxolin from stock it would make your eyes water!! A good idea to make it universal - for some years I've made a habit to make a cradle for any radio I'm going to be working on for more than just a quick repair. I just use scraps of wood and metal - whatever is to hand - bits of angle iron, flat iron, MDF, chipboard etc. Certainly a 'universal' cradle has merit in that it would save having to make a new cradle for each radio.
I've attached one or two pics - one of a KB FB10 'Toaster' upended for cap replacement, another of a Stella 105U, (which is similar in curcuitry to a DAC90A but with more refinements, such as bulbs that actaully glow, a couple of thermistors etc, and finally, a Ferranti 054 which I'm restoring for a nephew. A friend of his was going to take that and a Pye Fenman1 to the tip, but passed them on to him. He's given me the Fenman1 as a 'reward' for my efforts in sprucing up the Ferranti for him. And what an effort! The maker's service sheet looked comprehensive, in that it ran to seven pages, but it has no underside view of the 'rats nest' chassis layout, so I had to trace each component from its value and the valve pins etc to which each is connected. Some of the Hunts caps were almost inaccesible between two tagstrips which are back to back, and wider at the base than the top, rather like a tent. I've added some pics of the chassis showing the progress to date. Afrer reforming the three smoothing caps, replacing several caps and a couple of out of spec resistors, and easing a seized cam which operates the FM tuning, the set works well. However, I'm awaiting a UK sourced NOS ECC83 for the VHF tuner, and a NOS Russian made EM80 magic eye - on of four I've bought on e-bay for £20, hopefully wending their way here from Siberia! It had a flimsy sigle insulated mains lead, restrained as usual by having a tight knot tied it it, so I've replaced that with a 3-core lead.
Hope that's of interest.
David
Hi David, Yes it looks like I was pretty lucky with the Paxolin I got mine from a friend who has a Govmt surplus business so it looks like I'll have to keep on his right side
I haven't yet fitted any new caps etc to my Major Maestro chassis as I'm trying to make some replicas which are coming on quite well I'll post some piccies when I have something worth showing. You will also note there is a mains transformer on the chassis instead of the usual dropper resistor I think this is the last version made but the tranny only supplies 6.3 volts for the valve heaters and pilot lamps the 240v AC HT is still derived direcly from the mains so there is still a live chassis .................
(28-08-2011, 10:49 PM)Bluebottle Wrote: [ -> ]Hi David, Yes it looks like I was pretty lucky with the Paxolin I got mine from a friend who has a Govmt surplus business so it looks like I'll have to keep on his right side
I haven't yet fitted any new caps etc to my Major Maestro chassis as I'm trying to make some replicas which are coming on quite well I'll post some piccies when I have something worth showing. You will also note there is a mains transformer on the chassis instead of the usual dropper resistor I think this is the last version made but the tranny only supplies 6.3 volts for the valve heaters and pilot lamps the 240v AC HT is still derived direcly from the mains so there is still a live chassis .................
Yes, if it's the post-war T16/T17 AC only version they had 6.3V parallel heaters powered from an auto transformer, using an indirectly heated cathode on the rectifier valve, powered from the same 6.3V supply, rather than from a separate winding. An auto transformer is far superior to a mains dropper as it doesn't dissipate the heat that a mains dropper does, which is kinder to the cabinet and to other components, though as you say, the same precauions must be taken as an auto transformer doesn't isolate the chassis from the mains.
Many smaller table top/bedside radios used auto transformers - the KB FB10/2 ('Toaster') and Pye R33 for example. The use of a mains dropper rather than an auto-transformer in the Bush DAC90A is just one of many shortcomings of that model, and it's rather a pity that of all the radios that could have been put out on rental, the rental firms chose the DAC90A, probably the one post-war set which looks like it was designed using parts from Pandora's box. To be fair to the designers, I think we have to assume that they were probably constrained by the design brief they were given so soon after the war when they were skint, and in a hurry to get back into peacetime production, which must surely have been: 'make it quick, make it cheap, make it for rental, make it AC/DC' (which would preculde the use of an auto-transformer). Many homes still had DC mains well into the late 1950s - our house in Nottingham wasn't converted to AC until 1960. Well into the 1960s were still quite a lot of DAC90As in daily use, and back then I attended a year's night school for radio and TV servicing, the tutor being the proprietor of a radio and TV workshop. He often used to get DAC90As in, and his theory was that Bush designed a set that worked OK, then started taking parts out of the set till it stopped working, then put the last part back! Not a 'classic' radio but certainly an iconic one, which for those of us who lived through that era, is an omni-present reminder of post-war austerity. At least it was an improvement on the Wartime Civilain Radio!
Given the amount of work needed on the DAC90A - replacing the waxies etc, I wonder how many restorers bother to make a cradle, or if they just balance it on the bench as best they're able? Very few would be my guess, given that it's often a first restoration, as they abound at car boot sales and on t'internet.
Opined David
universal cradle an exelent idea
rob t
(29-08-2011, 08:01 AM)Yorkie Wrote: [ -> ]Yes, if it's the post-war T16/T17 AC only version they had 6.3V parallel heaters powered from an auto transformer, using an indirectly heated cathode on the rectifier valve, powered from the same 6.3V supply, rather than from a separate winding. An auto transformer is far superior to a mains dropper as it doesn't dissipate the heat that a mains dropper does, which is kinder to the cabinet and to other components, though as you say, the same precauions must be taken as an auto transformer doesn't isolate the chassis from the mains.
David, According to my Trader service sheet the Transformer is a conventional double wound isolation type transformer and on test the windings do appear to be seperate, but both primary and secondary windings are connected to earth which would negate any isolation, so just as dangerous just a little cooler. The Bakelite case also doesn't have the Asbestos heat shield built into the top, which was probably more dangerous to life than anything else ...........
Mike
This looks a great idea but I'm not the best person just to knock one up without a design to work from as I usually find that I start on something like this and then encounter a problem only to find that one of my colleagues has found a cunning way to get around the problem that I have just found!
Any bright sparks out there have a quick design for me to follow please?
Many thanks
Rob
(29-08-2011, 10:33 AM)Bluebottle Wrote: [ -> ] (29-08-2011, 08:01 AM)Yorkie Wrote: [ -> ]Yes, if it's the post-war T16/T17 AC only version they had 6.3V parallel heaters powered from an auto transformer, using an indirectly heated cathode on the rectifier valve, powered from the same 6.3V supply, rather than from a separate winding. An auto transformer is far superior to a mains dropper as it doesn't dissipate the heat that a mains dropper does, which is kinder to the cabinet and to other components, though as you say, the same precauions must be taken as an auto transformer doesn't isolate the chassis from the mains.
David, According to my Trader service sheet the Transformer is a conventional double wound isolation type transformer and on test the windings do appear to be seperate, but both primary and secondary windings are connected to earth which would negate any isolation, so just as dangerous just a little cooler. The Bakelite case also doesn't have the Asbestos heat shield built into the top, which was probably more dangerous to life than anything else ...........
Mike
A rather belated response to your comments Mike, but having looked again at the circuit I see that I was mistaken - it doesn't in fact use an auto-transformer - just a heater filament transformer, with the HT straight from the mains. An auto transformer is one in which the primary is tapped part way down so that although the HT is still taken straight from the mains (so all the same precautions as with live chassis designs are called for), as it's from a tapping on the primary the HT voltage is dropped to the required level rather than wholly relying on a dropper resistor in which the mains voltage has to be dropped to a suitable level for the HT - perhaps 100V less than the mains. Some radios use droppers which generate so much heat that it would be more accurate to describe them as 'electric fires' rather than 'radios':D
Maybe by now, you've successfully used your cradle to good effect, and have completed the restoration of your 'Major Maestro', in which case, some pics would be of interest!
MOD NOTE: Quotes tidied up.
Hi All,
Its been really bugging me to work on a chassis that is difficult to hold in one position without it falling over (numerous times!!!). I know that David made a cradle but I never got around to, or felt good enough to come up with a suitable design.
Hunt on google for ideas I cam across this that someone had sold on ebay (Mods - I hope I'm safe here, no price mentioned and its not a current bid).
I wonder how difficult it would be to make one??
What do you think - good idea??
Regards
Rob
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