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Home Brew Analog Computer System
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GK:

--- Quote from: TimFox on March 30, 2015, 04:37:31 pm ---I just remembered another article, where the editor must have been a young person.
This was in EDN, maybe 10 years ago.  It was on the history of the vacuum-tube operational amplifier.
First, it described the design by Julie during WWII, which used a 6SL7 (octal) dual triode as the differential input stage.
Then, it described the postwar commercial design from Philbrick, a very similar circuit using a 12AX7 (9-pin miniature) dual triode.
Both devices were referred to as "high-micron" triodes in the article, as a misunderstanding of "high-{mu}".

--- End quote ---


Hi Tim,

The full manual for the EC-1 is here:
http://www.analogmuseum.org/library/heathkit_ec1_operation_manual.pdf

The whole "library" of Bernd Ulmann's "Analog computer museum website" is worth checking out:
http://www.analogmuseum.org/english/library.html

It was my initial discovery of the EC-1 manual and then Bernd's site that got this whole project started.

T3sl4co1l:
Hmm, fascinating.  Nice test! :-+

Also, that's not a bad 8/20us pulse, crudely speaking.  If that puts any kind of perspective on it, relative to conventional surge protection diodes.

The datasheet says 4A I_FSM at 1us, so you're definitely well beyond that, but for the range between "yeah, it'll do this under continuous service for decades" and "it only has to survive a few hundred surges", who knows.  Those tiny diodes used for USB that claim 15A surge (8/20) and have lower capacitance than this one, can't possibly be holding up too well after their tests... but they only have to withstand 10 of them for the entirety of the test, or whatever.

Tim
GK:
Made a start on loading the Logarithmic amplifier PCB's, which arrived last week:



The thermistor mounted above the SSM2212 dual precision NPN transistor for ambient temperature compensation of the scale factor:



The original plan was to fix the Coke bottle cap down with Araldite and then fill from the bottom of the PCB. That's what the two (5mm dia.) holes are for - epoxy syringed into one and air out the other. However I'm now perhaps having second thoughts about filling with epoxy (a la Jim Williams) as that would make any future re-work (replacement of the SSM if necessary) a bit of a bother. Has anyone here ever looked into the long term conductivity/insulation properties of hot melt glue?


The calibrated log conformance and scale accuracy over the smidgen over 4 decades input (10mV to 100V) that the output is within its voltage swing limitations is within 0.1% by my preliminary measurements. Haven't got time to tabulate values and plot the error curve tonight so just a scope screen shot:

SeanB:
Use beeswax, as then it will still be a good thermal conductor and yet will still be easy to remove for rework.

I have an embarrassing amount of Tektronix wax blocks though, all black ( black is 'free' when you order the colour wax blocks) if you want the finest quality ultra pure wax to use in that application. All in nice easy open single shot packs. If you want some shoot me a PM and your address (again) and I will pop them in the post for you on Tuesday ( Monday is a public holiday) if you want to wait the 2 weeks.
GK:
Ooh... that reminds me, I still have a prezzie (a bit lame really) sitting on the shelf here to send in return. I don't know much about beeswax. Is it non hygroscopic and a very good insulator? What did Tektronix do with it? Google just brings up references to "Phasor" printers.
 
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