View Full Version : Heathkit EC-1

March 3rd, 2009, 07:34 AM
I got a "new" Heathkit EC-1 - Complete with manuals, cables, tubes, etc. As I test it and hook to an oscilloscope I will post updates.



March 3rd, 2009, 09:06 AM
Very nice... I know that cost a pretty penny!

March 3rd, 2009, 10:07 AM
Cool. I was pointing out that system to my girlfriend a week or so ago when surfing through some auctions. Definitely let us know how it goes.

March 3rd, 2009, 11:53 AM
Don't forget to put in coins for the meter!! :p:rolleyes::cool:

Dwight Elvey
March 4th, 2009, 07:45 AM
Hi Bill
Someplace I have a drawing for how to do the bouncing
ball in 7 amps instead of the 8 amps in the manual.
This leaves two amps unused, enough to make a sine/cosine
This means you don't need the hokey external 60Hz sine/cosine
generator to make the ball round.
You can still run the simulation with just a dot on the scope.
Also remember that there are two places to zero an opamp.
One is for zero volts out and the other is for zero current
in. For integrators, you want the zero current in so they
have minimum drift.

March 4th, 2009, 08:48 AM

I am going to work on this machine over the weekend, but first I need to test the electronics. I may not get very far, but if I do I will work on the bouncing ball as they have with the 8 amps to start. Whenever you get the chance to send your mod, no rush, and thank you very much.


March 4th, 2009, 08:09 PM
Very cool, Bill!

I remember coming home from college over the holidays and visiting my old high school physics teacher, who showed me the EC-1 he'd just bought. Hadn't even been powered up yet. I spent the entire weekend getting the bouncing ball to work.

He thought it might be useful to teach the kids about computers, but I don't think he realized that he'd bought an analog computer--not the sort of system that you saw in Desk Set.

It's a shame that I didn't get to play with it for more than a weekend.

March 5th, 2009, 05:36 AM
Chuck - If you're in my neck of the woods, stop by and you can experiment with the EC-1 all you want. :-)

Dwight Elvey
March 5th, 2009, 06:55 AM

I am going to work on this machine over the weekend, but first I need to test the electronics. I may not get very far, but if I do I will work on the bouncing ball as they have with the 8 amps to start. Whenever you get the chance to send your mod, no rush, and thank you very much.


Hi Bill
To test, connect a resistor from input to output and then a same sized
resistor to the input.
This make a unity inverter. Use one of the voltage sources to make sure
the output tracks and goes the oposite polarity.
If this works in both polarities, your done.
The resistor values should be large, remember the output swing +-50v and
only a ma or so.

Dwight Elvey
March 5th, 2009, 07:16 AM
Hi Bill
One thing I forgot to mention. Ground reference is really rare.
I forget if it is the meter negative or the ampout negative.
The three initial condition sources are floating and need
one end or the other tied to ground or could be used as
a floating offset.
The coefficient pots all have one lag tied to ground but it
is not pinned out to the front panel there. I always thought
that if I'd bought one new, I'd have punched some holes
and added a few ground reference jacks. It is a real pain
to need to daisychain all the grounds from one reference
I don't want to drill my classic but if I'd had it new, I know
I'd have modified it.
Pomona banana cables work well for this because they
can be stacked.

March 6th, 2009, 10:37 AM
Thank you for the info. I will post an inventory of the resistors I have, etc. when I get the chance. It's such a nice weekend, I may have to wait until next weekend to make significant progress.

March 14th, 2009, 10:17 PM
Progress. YouTube video soon.

March 15th, 2009, 11:33 PM
Progress. YouTube video soon.

cool! that might give me some inspiration to work on my to analog EAI's

March 16th, 2009, 06:03 PM

The first illustrative exercise in the manual is titled "The Falling Body Problem." I had a vintage hacking get together this weekend. Bob and Mike brought tube testers and fortunately the tubes were all OK. We cleaned all of the plugs and connectors with soap and water. Dan hooked up a Variac in series with an incandescent light as a current limiter, so we could monitor the reaction of the EC-1 to current load. Bob used a volt meter to test the electronics and cleaned up a few things (solder joints and a loose wire), but nothing major was needed to get the old girl back up in running order. Fortunately I had the two N-2H neon lamps needed to replace the failing lights on Amplifier #4. The bulbs were impacting the voltage flow. You'll see from the video that my oscilloscope is about trashed. I have one at work, but I forgot to bring it home.


Detailed wiring pictures and info:

Thanks also Dwight for your tips, I printed them out and will keep with my manuals. Do you have a source for those input sockets? I have a few but I will need more to do the later exercises.


P.S. I don't like to use people's full names without their permission, but if you want your name revealed and you're mentioned here, just let me know.

Dwight Elvey
March 17th, 2009, 06:24 AM
Hi Bill
The sockets are actally crystal sockets but finding enough
old style crystals to destroy would be hard.
What came with the EC-1 was half of the older 300ohm
TV twin line connectors. I've looked a bunch for these
without success.
I found that the Pomona mini-banana plugs work. These
are about half the size of the regular banana plug, compared to
the larger terminals of the EC-1. I saw a bunch of the dual pin
ones on ebay about a week ago. They may still be there.
These are a little tight and may stretch the socket connectors.
I thought about removing the spring part of the plugs to
make them more like the original connectors but never
tried it.
There is a fellow selling a bunch of the larger ones and
I may buy some of these for my Comdyna. It uses the
regular size and spacing bananas.

March 17th, 2009, 06:42 AM
I guess I am lucky to have what I have. Thanks again.

Dwight Elvey
March 17th, 2009, 07:12 AM
Hi Bill
The crystal holders are cool because one can mount the
resistor or cap inside. One can then flip the cover over
and put a nice lable on it ;)

March 17th, 2009, 10:36 AM
I dug around a bit and found this guy (http://s88932719.onlinehome.us/FT241_crystals.htm) who's selling 20 FT-241 crystals for $10. Reworking them may be just the ticket.

The 300 ohm twinlead connectors seem to be history. Clear polystyrene with screw-clamp type wire connectors.

March 17th, 2009, 08:11 PM
Thank you. I would not have found this on my own.

April 11th, 2009, 06:21 PM
Today I switched to a better oscilloscope and was able to get a clearer output, do some experimenting. I am going to start working on the 2nd or 3rd exercise in the manual. I will post an update when I get one. I have not yet ordered more supplies.

April 15th, 2009, 09:13 PM
I took a bunch of new pics of the underside of the EC-1
they're the ones with the new file dates

I want to make a new movie with the better scope display too, asap.

Dwight Elvey
April 16th, 2009, 06:47 AM
Hi Bill
When I first got my EC-1, one of the three caps to the left
was shorted. I had to find a shop that carried the higher
voltage electrolyics to get a replacement. Luckily, I bought two.
I soldered in the new one, replaced the fuse and started
to play with thing. Then there was a pop-fizzzzzzzzz.
I'd put the new one in upside down. I don't know how
I did it. I'm usually quite careful about such things.
As I said, luckily I'd bought two.

April 20th, 2009, 04:56 AM
This video shows the Heathkit EC-1 re-assembled and attached to a Tektronix 7313 oscilloscope.