29-08-2011, 08:01 AM
(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
