Hi As we go joyously bashing the poor guys that designed this beast, it’s worth noting just how old the design is. 741 op amps were indeed “modern” when they did much of this and quite possibly to modern to be trusted. Most of the design would have been right at home in the late 1960’s at a conservative design house. As time has shown, in a lot of cases that mistrust of the early linear stuff was well founded ….The 741 only was designed in 1968….The 5065 design dates to roughly that time.
Bob > On Aug 30, 2015, at 8:08 PM, Magnus Danielson <[email protected]> > wrote: > > Poul-Henning, > > On 08/30/2015 09:54 PM, Poul-Henning Kamp wrote: >> -------- >> In message <[email protected]>, Bob Camp writes: >> >>> Since they needed to calibrate the voltage swing, there aren’t a lot of >>> options >>> with the technology they were using at the time. Today there are a lot more >>> choices of how to get this sort of job done. >> >> It's not just the swing, it's also the shape of the curve: >> >> http://phk.freebsd.dk/hacks/HP5065A/20150828_c_pot/index.html >> >> If it were just the range things would be a lot simpler. >> > > Ehm, eh... that transistor pair you have there. How *tight* together is > really the transistors thermal connection? I bet not all that good. > > The reason I got involved with counters and atomic references was originally > my interest in analog synthesizers, and there we use a transistor pair for > exponential conversion, which has scale and offset issues and thermal issues. > The use of a Q81 +3300 ppm/C resistor in the division network helped to > compensate the thermal properties of that transistor pair, and you wanted > stuff like MAT-01 where the two transistors is thermally ties to each other > and the put your tempco resistor to that for good performance. All this > requires good measurement and good reference, so that what motivated me > towards that step. Anyway, the take-away is that you should look at that > discrete op-amp and see if it is not causing you the thermal dependence you > are trying to locate. Maybe replace it with a more modern op-amp like the 741 > or something (irony may have been used). > > Cheers, > Magnus > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
