RobH Posted February 25, 2017 Report Share Posted February 25, 2017 Yes, I think Watts Radio in Kingston used to advertise in magazines like Radio Constructor. Living out in the sticks my main source for bits was the Shop On The Bridge in Reading, otherwise it was mail-order. Home Radio of Mitcham and Radio&TV Components spring to mind. That was long before the original Maplins started up of course. Quote Link to post Share on other sites
stillp Posted February 25, 2017 Report Share Posted February 25, 2017 Yes, but there is a big electrochemical difference. It's analogous to electroplating. Reverse the polarity, and you get way different results. Ed That is relevant to the corrosion, but not to the insulation. Quote Link to post Share on other sites
ed_h Posted February 25, 2017 Report Share Posted February 25, 2017 Corrosion is what we were talking about--whether polarity of the return had anything to do with it. Ed Quote Link to post Share on other sites
OldBob Posted February 25, 2017 Report Share Posted February 25, 2017 negative earth is universal these days, it is useful to convert to negative because it allows the use of alternators, sat navs etc. Bob. Never had any issues with my Sat-Nav or any other 'device' for that matter in my +ve earth TR2. Use an inline 12v socket and wire it up to suit : http://www.ebay.co.uk/itm/Hard-Wire-12V-Cigarette-Socket-Fused-with-Inline-Fuse-5amp-NEW-/201420468223?hash=item2ee5986fff:g:MVEAAOxy7MtRvc08 Also very happy with my Dynamo, Wide fan belt and steering box - who needs progress! Progress is fine as long as its 'Positive' (oops sorry). Bob Quote Link to post Share on other sites
stillp Posted February 25, 2017 Report Share Posted February 25, 2017 Ed, I did refer to the leaky insulation theory. Pete Quote Link to post Share on other sites
RobH Posted February 25, 2017 Report Share Posted February 25, 2017 "That is relevant to the corrosion, but not to the insulation." Pete - Its the effect of wet insulation that may allow erosion to happen as the wetness can act as an electrolyte. Once that is happening the polarity would have a big effect on the outcome. With the copper cable positive (anode) the cable will erode and deposit on the body (cathode). If you reverse the polarity so that cable is the cathode, the cable doesn't get eroded. Maybe that is why positive-earth was preferred for a while? Obviously if the insulation isn't wet and does not conduct that cannot happen. Just a theory and maybe total nonsense but I haven't heard a better explanation yet. Quote Link to post Share on other sites
ed_h Posted February 25, 2017 Report Share Posted February 25, 2017 Pete, if your point is that the polarity would make no difference in the insulation getting leaky, I'd agree with that. Ed Quote Link to post Share on other sites
RogerH Posted February 25, 2017 Report Share Posted February 25, 2017 Paul - yes the old red-spot, white-spot things were production line rejects for sure, as were the MAT gold coloured transistors and other bits that Clive Sinclair use to sell. Remember the 'power' amplifier Super IC 10 with the finned heatsink? The real full-spec deal was a Plessey part. Ah the days when Henry's Radio was Shangri-la. Nostalgia. Hi Rob, what an odd strange world. I was flitting through Googleland and decided to hunt down an amplifier that I built in the early 70's PW Texan. It would appear that I bought the kit of parts from Henry's. One of the Rega amps is still based on this 40 odd year design. http://www.angelfire.com/sd/paulkemble/sound8h.html Roger Quote Link to post Share on other sites
RobH Posted February 25, 2017 Report Share Posted February 25, 2017 Small world Roger, as you say. The Texan is a bit modern (!) - the first half-decent amp I built back in the 60s was a Mullard 3+3 (3 valves, 3 watts) - and the speaker cabinet was home made too. Quote Link to post Share on other sites
tthomson Posted February 26, 2017 Report Share Posted February 26, 2017 (edited) I think the change was more to do with electron flow. Thermionic valves worked on generating electrons through heat and then accelerating them across a vacuum using a positive voltage applied to an anode. It made more sense (at the time) to do this with the electron generating cathodes being tied to ground (making them easier to control). Hence the prevalence of negative ground electronic devices, driving the historical use of negative ground for all purposes including vehicles. Electrons being negatively charged "flowed" from negative to positive, whereas traditional current flow had been thought to flow from positive to negative. (They guessed wrong and we have lived with it ever since). In the 50s there were attempts to change this current flow to reflect the actual electron flow and in consequence it made more sense to have positive earth. Since then, so many devices have been designed for negative earth that very few are available for positive earth vehicles. In addition, any attempt to alter the coventional view of current flow has been ignored, so negative earth is the norm. TT Edited February 26, 2017 by tthomson Quote Link to post Share on other sites
DaveR Posted February 26, 2017 Report Share Posted February 26, 2017 Small world Roger, as you say. The Texan is a bit modern (!) - the first half-decent amp I built back in the 60s was a Mullard 3+3 (3 valves, 3 watts) - and the speaker cabinet was home made too. I agree the Mullard amps were good plus the documentation, the green book, they produced to build them. The 3/3, 5/10 and 5/20 series. I also built a 3/3, 5/10 and the later PW Texan. Also no internet then, if you wanted to listen to the world it had to be on Short Wave. Dave Quote Link to post Share on other sites
ed_h Posted February 26, 2017 Report Share Posted February 26, 2017 (edited) I'd been an electronics hobbyist for years and learned via conventional flow (pos to neg). But in military training in late 60s they taught electron flow. Got used to that, but then it was back to conventional flow in college. You might be on to something,TT. Ed Edited February 26, 2017 by ed_h Quote Link to post Share on other sites
DaveR Posted February 26, 2017 Report Share Posted February 26, 2017 TT is right, I too can remember the confusion on current flow. I believe change from valve to transistor may well have it kicked all off. Dave Quote Link to post Share on other sites
RobH Posted February 26, 2017 Report Share Posted February 26, 2017 Electron flow? Hmmmm....not sure TT. Don't forget this was not something new - electrons were first recognised in the 1890s and it was apparent from the start of the 20th century that 'conventional current flow' was actually incorrect so why wait 40 years? Somehow I just can't see a hard-headed car production engineer spending money on changing things just because of a nuance of theory. There had to be a practical reason for the change. Quote Link to post Share on other sites
DaveR Posted February 27, 2017 Report Share Posted February 27, 2017 The reason stated by the car industry, at the time, for the change in polarity was to reduce erosion/corrosion at the battery terminal. I guess whether it achieved this is or anybody got the electron flow correct is another matter. Now let go onto hole flow theory in semiconductor! - Help. Dave Quote Link to post Share on other sites
RobH Posted February 27, 2017 Report Share Posted February 27, 2017 Ooh don't start that one Dave. Hole-electron pairs, valency bands, h-parameter equivalent circuits; I remember learning all of that stuff.... never really needed to use it once I passed the exams though, Ohms law and Kirchoffs law were enough for most practical things. Quote Link to post Share on other sites
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