One of the nice features of some vintage hifi was its very neat and tidy layout - all those brightly coloured components, laid out on tagstrips or turret boards and connected together with beautifully laced wiring looms. But what do we know about the components themselves ? Often not much.
Sadly, I have an interest in Erie carbon composition resistors - specifically in why they degrade with age. In an attempt to learn what I can I stumbled across a reference to a film of them being manufactured, way back when. The film was in the care of the Imperial War Museum and when I asked them I found that it hadnât been digitised, so basically I couldnât see it 
. However if I was sufficiently interested then they might be able to digitise it for me and sell me a copy. âOKâ, I said, âgo aheadâ. They got in touch on Friday and said theyâd finished it. Iâve now learnt that because they are a keeper of public records they feel obliged to make available for free on their website anything that theyâve digitised. So now you can see this wonder too !
Actually you learn next to nothing about the resistors. But you learn a lot about just how primitive wartime manufacturing really was. The sequence where someone asks for 5kohm resistors, which was not a standard value, so they go through a batch of 4.7kohm ones hand-measuring them to find those near 5k, then they âtumbleâ the paint off in a dustbin full of sawdust and solvent and repaint them, again semi-manually, with the 5k colours has to be seen to be believed !
Enjoy
VB
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Greta stuff 
Amazing that it was filmed in colour (rare at the time) but has no soundtrack!
I had it in my (stupid) head that carbon comp resistors used a phenolic compound like Bakelite for the element (which is hygroscopic and degrades over time when subject to heat), but when I checked, most supposedly use a âclayâ binder, and drift is claimed to be a function of different thermal expansion coefficients disrupting the carbon particles. Phenolic might actually have been better in that respect FWVLIW⌠Anyway, âclayâ covers a multitude of evils in terms of source, purity and thermal behaviours being a natural material, so something like smectite is going to behave very differently to kaolinite, and even different batches and source locations for any one type would still vary in content. Without knowing in detail how they sourced components, you may never know - albeit if you have any contacts at the uni, clay mineral analysis is pretty routine workâŚ
Lovely film!
Iâm confused as to how the paint / masking machine didnât clog up.
Having seen the resistors I suspect the paint might have been pretty âthinâ. So the nozzles, which are in almost constant use, would have been OK. The discs with the slots in look like they rotate through a cleaning wiper or bath or some such. I think the things Iâd be most worried about would be the rotating spindles. Presumably their bearings are shrouded by the design of the rotating part and the jet from the nozzle is kept fairly tight, which would also save paint. The cutout behind the resistor tubes also stops the paint âbouncing backâ onto the moving parts.
VB
Curious, it looks to me like the paint flies all over the show, it is a small marvel my grandfathers beard wasnât dysentery brown and he lived in Rhodesia.
Believe it or not we think that paint colour is actually red (I donât know how stable the early Kodachrome stock was). The colour scheme was âbody tip ringâ which would make these resistors red violet yellow i.e. 270kohm. Brown violet yellow - 170kohm - wasnât an E-series preferred value. And later on in the film we see them hand-painting some 5kohm ones (definitely green black red) and the red there is brown too. The overspray behind the resistors in your still pic might well be several hours/days/weeks ⌠worth of course.
VB
1 Like
Amazing how many they were able to make without any badgers being involved.
. However if I was sufficiently interested then they might be able to digitise it for me and sell me a copy. âOKâ, I said, âgo aheadâ. They got in touch on Friday and said theyâd finished it. Iâve now learnt that because they are a keeper of public records they feel obliged to make available for free on their website anything that theyâve digitised. So now you can see this wonder too !
Amazing that it was filmed in colour (rare at the time) but has no soundtrack!
