On 6/14/2014 6:18 PM, Robert wrote:
CZ, I fix old watches too, a Hamilton 992B anyone? Computers from the 80's, how about an HP71B, I still have one and use it along with lots of programmable HP RPN calculators like the mid 80's 11C (which is still going strong in my machine shop). I think it's not that those old computers broke, it's that they got obsoleted by software and newer technology. There are guys still looking for old stuff, I built a Sinclair in the late 70's that I later sold, nothing wrong with it, just outdated.
Very nice. Most of my work is on the Elgins; I have an 1871 era slow train HH Taylor model and it's quick-train peer the BW Raymond. The Taylor is cased in 18k gold. You can always tell because the case is dented; clad cases will not dent, real gold will. Likewise I'm restoring a pdp8/e right now, much simpler than the older 8I I had 20 years ago. By the 1970's they got a lot better about making a 50 pound supply instead of a 100 pound supply (yes, I am powering it with a Corsair/500; working on a 12 to 15 volt DC-DC converter)
As for reversing the field, think about it, how were they going to reverse the field back then? With an 'H' bridge circuit, not then they weren't. The relay was the easiest and probably most reliable solution.
The right way to do it was to lock the field on and reverse the armature. That's what they did on the E20, and I think the E20 came before the E15. Also why the original E12 had a 3 speed version of the E20 control without field weakening.
I thought the E15 came a bit later as a reduced cost model. It had fewer main speeds (3 vs 4) and less field weakening and the dopey card controller. The E12 started out with the armature control then seemed to move to the E15's type of controller.
C