Retro Gadgets: Make Your Scope Dual Channel

We dwell in a time when acquiring an oscilloscope is only a minor luxury. But for a lot of decades, a great scope was a big cost, and nearly no hobbyist experienced a model new one particular except if it was of really lousy good quality. Scopes were significant and hefty and, at the selling price most folks ended up eager to fork out, only experienced a one channel. Granted, having just one channel is much better than getting practically nothing. But if the relative gain of acquiring a solitary channel scope is 10 points, the reward of having two channels is very easily at minimum 100 points. So what was a poor hacker to do when a twin-trace or higher scope price far too significantly? Why, hack, of system. There had been many styles that would change a solitary trace scope into a lousy-high quality multichannel scope. Heathkit manufactured various of these more than the years like the ID-22, the ID-101, and the ID-4101. They called them “electronic switches.” The S-2 and S-3 were even before designs, but the notion wasn’t special to Heathkit and had been all-around for some time.

For $25, you could adjust your scope to dual trace!

There ended up two prevalent ways. With substitute or alt mode, you could induce a sync pulse and draw one trace. Then induce once again and draw the second trace with a fastened voltage offset. If you do this speedy plenty of, it appears to be like like there are two traces on the monitor at just one time. The other way is to speedily switch in between voltages through the sweep and use the scope’s Z enter to blank the trace when it is in between alerts. This necessitates a Z enter, of study course, and a quickly switching clock. This is occasionally known as “chopper mode” or, basically, chop. This was not just the realm of adapters, though. Even “real” analog scopes that did dual channels utilized the identical approaches, though usually with the reward of currently being integrated with the scope’s electronics.


The aged ID-22 was tube-centered and rather easy. The S-3’s internal design was nearly specifically the identical.

The ID-22 made use of 11 tubes and a rectifier

Heathkit was not the only supply of these electronic switches. We noticed one particular from Sylvania in a [Mr. Carlson] teardown.

[Jeff] has a seem at an previous S-3 in an additional online video. out?v=BTqsPekyQGw

Just one trace, 8 knobs, and 16 pounds.

Why Trouble?

It is hard to remember just how unaffordable scopes had been in the past. In 1969, for case in point, you could get a solitary channel 3″ display screen scope with a 5 MHz bandwidth that you had to develop — from Heathkit, of training course, for about $80. Altered for inflation, that is above $650 currently, and maintain in intellect, this is for a scope with insane minimal specs. It didn’t even have a probe connector. The scope’s inputs ended up binding posts. You could, having said that, spend $8 a thirty day period for some period of time if you couldn’t locate $80 all at a person time.

A superior scope — nevertheless solitary channel — but with a 5-inch display and 8 MHz alongside with matters we consider for granted currently like exterior sync inputs expense $259 as a kit ($399 ready-to-go the equivalent of $2,000 and about $3,330, respectively). Hold in thoughts that the regular income in 1969 was about $500 a month. So a $250 scope was two weeks’ pay out — far more if you seem at acquire-household spend.

If you imagine about it, that is $283 per trace!

If you required a actual dual-trace scope from Heathkit, you experienced to hold out for 1971. The EU-70A price tag $565 and was all sound-state (besides, of training course, for the CRT). It experienced a relatively little monitor (about 4″x3″) and a 15 MHz bandwidth. It supported both alt and chop modes. You did not even have to construct it! In 1981, a 15 MHz twin-trace Tektronix T922 retailed for $1,090! Based on the year, you could get a 10 MHz scope from a model like B+K, Leader, Eico, or Conar for a small less.


In Operation

[KB9RLW] has a fantastic movie about the ID-4101 in use that you can see down below. Granted, considering the fact that his Dad’s aged scope blew up, he hooked it to a modern day scope, but you can continue to see how it labored.


There ended up plenty of models for related adapters revealed. [Leslie Solomon] of Well-liked Electronics fame applied four normal CMOS ICs to show four traces concurrently. The schematic underneath does not clearly show the result in technology, which needed a 4009 or a transistor.

Very simple circuit from April 1974 Well known Electronics to get 4 traces on a one trace scope

When you assume of a $60 scope these times, you may assume it is not very excellent, but take into account what $60 purchased in 1969, and you’ll enjoy the cheap scope of now. If you want to practice your scope capabilities, dust off an Arduino and check out out this trainer from [Bald Engineer].