I spend a lot of time experimenting with various vacuum tubes circuits. It is a past time which I really enjoy. It also gives me an outlet for my creative tendencies when the workshop is too cold to make custom furniture (and amplifier chassis). As a consequence I have amassed a fair amount of test equipment and miscellaneous cables, adaptors, probes, and other odds and ends over the last decade or so. And regardless of the fact that I want to concentrate my attention on my vacuum tubes, sometimes it’s the other things that demand my attention.

On this cool and rainy afternoon I spent some time and attention on probably the most overlooked and neglected of test equipment items; patch cables.

This afternoon I assembled seven new patch cables (4mm banana plug to 4mm banana plug) and did some much needed repairs on some older low voltage cables. I usually don’t buy pre-made patch cables for single wire connections; they’re just too expensive. I generally buy bulk banana plugs from wherever I can get them and assemble my own. Years ago I bought two 50 foot rolls of test lead cable; one red one black. This is a link to the wire I used. I’m still working on those two spools of wire.

I have had a lifelong tempestuous relationship with patch cables. I cannot count the number of hours I’ve spent looking for circuit problems only to subsequently discover that the issue was with a patch cable. This was a regular occurrence in my younger years and it forever colored my relationship with this lowly species of test equipment.

Warning – Rambling “Old Guy” Story

I did not realize how much it had affected me until my first circuits lab in college. I think I was about 18 years old. The first lab quiz was on equipment usage and lab procedure. Now I had been tinkering with all manner of electronic test equipment for so long by this age that the quiz itself was trivial. The particular lab in which we were working was a repurposed room of some type with old wood benches along it’s periphery and a few tall cabinets of miscellaneous equipment. And next to the entrance was a rack with about 200 test leads dangling from chest high to the floor.

When we arrived, appropriate test equipment had been placed on the benches and we were to go to the cabinets to get the various bits and pieces required to complete the lab. Along with this we were to collect some patch cables and test leads to use. So I dutifully collected my components and a generous handful of patch cables and test leads and retired to my bench. And this is where my particular tendencies singled me out.

While everyone else in the lab started dutifully working through their quiz, I turned to my bench and began testing leads and probes. Using the bench VTVM (yes the lab equipment was that old) I proceeded to perform a continuity check on every patch cable and test lead I had retrieved from the rack. Now to say that these leads were well used would be an extreme understatement. These leads looked as if they had been abused by classes of freshmen engineering students since James Clerk Maxwell first wrote his equations.

As I worked through my checking of the test cables, I had about a 30% failure rate. This was either a simple open circuit (not very common) or a continuity problem which responded to shaking wires or playing with connectors. Knowing that intermittent cables are the bane of experimenters everywhere (I had already learned the lesson the hard way), whenever I got one of the bad cables I simply dropped it on the floor behind where I was standing. The last thing I wanted was to have one of these bad cables get mixed up with the good ones on my bench. When confident that I had good functional equipment and test leads, I turned to the quiz and was the first in the class to finish it. What I did not realize was that the whole time the lab instructor was quietly watching exactly what I was doing.

When I finished the quiz, I returned the supplies I had used to the cabinets and the functional test leads to the rack. I then picked up the quiz papers from my bench and picked up the handful of bad test leads off the floor. I went to the instructor’s desk, turned in my work and I placed the bad leads on his desk. He just looked at me with a funny look on his face. I told him the leads I placed on his desk were faulty and needed to be repaired. He then wrote a 100% on the front of my quiz and handed it back to me without even looking at it. He said that I obviously passed.

The serendipitous benefit of my performance with the test leads was that the following week when we arrived in the lab, the rack contained what looked to be about 100 brand new test leads. This didn’t dissuade me from always testing my leads at the start of a lab but it was nice to have some new equipment. A few of my lab mates even adopted my practice. Sometimes I wonder if they’re still doing it.

Back to Today

So this testing of the cables is a practice I still follow. It only takes a few minutes and it gives me real peace of mind when circuits start doing the unexpected. And I still occasionally find a cable that’s bad. It was a few of these cables I was fixing today. It’s truly amazing how having real confidence in your test equipment can make working at the test bench so much more enjoyable.

As always, questions and comments are welcome.