Jurassic Electronics: Audio with tubes, and discrete amplifiers

Long time member/lurker, first post on this board.

This may have been broached (many times) before, but are there any audio, pro audio, or instrument amplifier special interest groups that are alive and well at DMS? What about tube electronics? Or something more niche like discrete audio electronics? If not, what’s the level of interest?

I build pro audio and guitar/bass amplifiers, mostly classic designs or variants thereof. I was wondering, for example, if there would be any interest in me bringing up my Hickok 750 tube tester once a month for a testing day for those without a tester. Or a group project to design and build a DIY curve tracer (tubes and/or high power transistors). I can think of a lot of other group oriented projects or classes to suggest, but I have no sense of how many of us are at DMS. I may be the lone freak as far as I know.

Thanks,
Bryan

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I would be interested in this. I have a cache of tubes from the “warehouse” a while back. I’d like to know if they are good tubes. I’d also be interested in your build class.
I’m a novice electronics guy, but I would be interested in any classes regarding amps.

Here’s the warehouse reference thread:
https://talk.dallasmakerspace.org/t/a-treasure-trove-of-maker-goodness-hording-trigger-warning/6288/79

Also from @richmeyer donated a tube tester for electronics lab. New Donation to the Electronics Lab - Vacuum Tube Tester

VECTOR has a tube tester and some tubes since we occasionally work on old tube amps from jukeboxes and antique radios.

We have discussed having a vacuum tube technology 101 class and maybe a class to build something like a tube based headphone amp but the subject matter experts who were talking about putting the classes together have been busy with life and work and had not had time to do so yet.

Personally I want to know more about how they work and how to test and troubleshoot tube based circuits from the level of an amateur self-taught electronics hobbyist. Frequently the tube based stuff I do see is aimed for EE level understanding and not at a level I can pickup much from it.

The first part is simple.

Heat up a metal and it gives off electrons. Position an electrode nearby and it picks up some of them. Apply a negative charge it and it repels the electrons. Apply a positive charge to it and it attracts the electrons. What you now have is a diode; current flows on one direction and not the other.

Position a grid between and by applying a charge to it allows control over the current flow.

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For some reason, it says I don’t have access to the “warehouse of tubes” topic when I click the link.

I’d certainly be willing to both help out with testing and sorting the cache of tubes (by intended use and practical use - they don’t always coincide) and with teaching/co-teaching one or more classes on tube electronics. I’m quite busy with work/family, but I could certainly do workshops here and there on it.

And I agree with you Shawn that much of the learning material both online and in books out there go too high or too low for most hobbyist types. I’m confident I could address the DIYer’s needs on a more practical level.

If we have enough interest here, I’ll try to take a pulse on interested folks’ background knowledge level and goals and put together a proposal for a class or two.

Thanks for the feedback so far!

BT

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About a year ago, a guy named Fred, had a warehouse full of all manner of electronics that he needed to be emptied so he donated the whole lot, for the most part, to members of DMS to use any way we saw fit. Of course, much of it DMS couldn’t use so he allowed DMS members to take some of it.

As a result, many people helped him clean out the warehouse by taking stuff home.
I confess to hording some of it myself and that is where these tubes came from. Below are a few pics from the thread and a video of the place.

image
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Wow. Where was I when that went down! What a score!

BT

Maybe when we meet in your class we can discuss what you need for your classes and or personal projects and I can help you out. There were quite a few folks who helped with the evacuation process. Fred did a lot of contract work for TI, I think, and he had all kinds of tools, parts and components as well as complete systems. It was amazing just touring the place.

Fred’s warehouse opened up around November 2015 and lasted a few months as the 16,000 sqft or so was mostly emptied. Fred kept a bunch of the stuff he wanted, some stuff is at DMS, and a few of us helped give homes to a ton of stuff that otherwise would have ended up in the scrap guys truck or the dumpster. The first time I went it was very packed with narrow walkways wide enough to barely navigate while carrying something. By the end is was mostly cleared.

There was lots of old test gear, semiconductor wafer fab equipment, random parts from thousands of items that had been taken apart over the years and sorted out on a shelf. Just about anything and everything you could possibly think of it was probably there and Fred knew exactly where it was. The business had been a electronics testing lab for many years so they had all kinds of environmental test chambers, lots of unique lab equipment, etc. After that business closed Fred acquired the space and ran his business repairing Genrad test equipment. Fred also would buy surplus stuff from the electronics and semiconductor industry in DFW so there was lots of random stuff that came with the lot that he wanted to get certain items.

I can still find stuff from Fred’s in nearly every corner of DMS. Much of the large and heavy items came over in my truck since I have a liftgate.

I have been slowly sorting through the stuff I picked up from Fred’s warehouse. Most of it is going to be used to outfit my home electronics lab and some of it will likely end up finding new homes with people who can put certain items to use.

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I would be interested in a simple “build a tube amp” class. It’s been something that I have always wanted to build for a home office setup

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Great story. That’s the kind of windfall electronics geeks dream of! Would have been cool just to see his space in all its glory.

Thanks Pearce. Got you on the tally sheet for “interest in a tube amp class”.

I missed the target on your question. I know there are a few audio nerds around here. I’ve always been fascinated by audio tech myself but feel like I can’t actually hear the difference. (What’s worse than a tin ear?)

I think you could easily make a special interest group under the electronics committee, and people would show up to your meetings or workdays.

Thanks, Pearce. Appreciate the perspective.

Some thoughts on “wave one” of possible classes I could put together:

  • Practical Introduction to Tube Electronics and Working Safely with High Voltages
  • Build a Single-Ended Tube Guitar Amplifier
  • Troubleshooting Tube Electronics Safely
  • Build a JFET Guitar Amplifier
  • Introduction to Jurassic Audio Electronics: Tubes and Discrete Solid State Amplifiers

I can think of a bunch. Let me know if any interest you and if you have other suggestions.

thanks,
BT

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If you want to use a hybrid module, I have 2 listed on Makertrade for free.

How about adding Vacuum Tube Testing to the list.

I have several different types of Vacuum Tube Testers, everything from a; generic filament tester, Emission Tester, Mutual Dynamic Conductance Tester, even the Military TV-7 which is the best one. Plus I have 100+ various tubes and many inline socket adapters that be used. The inline socket adapters allows one to measure the various pins with a Scope or Meter while under operation.

Raymond: yes, I’m interested in the modules. Don’t see those much anymore.

Rich, great idea. I think you walked by one day when I had my Hickok 750 up there to loan to another member. We joked around about it looking like the Project Mercury control room or something like that. Seems like between you and me, we could do a testing class and discuss the different types of testers (including the low-cost, newer curve tracers like the U-tracer and older ones like the classic Tektronics 576 ), how to pick the right kind, cautions (will it test the tubes you’re interested in? are the roll charts still available, etc). Hopefully there’s interest. I think there is.

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So it sounds like there’s enough interest to give a couple of classes a shot and see how much interest there is in the broader community. I’ll work on submitting two classes for the August/September time frame. Thanks to all who commented.

I’m leaning towards:

  1. Intro to vacuum tube electronics. Fundamentals and safety
  2. Choosing and using a tube tester for tube electronics projects (hopefully Rich can help out, or at least bring some of his testers up).

For the first class, I think it’d be a good idea to make that one mandatory for anyone new to tube electronics due to the high voltages involved. It would cover how tubes work, different types and uses, equipment needed, new manufacture vs old stock, basic tube circuits as used in audio applications, common topologies/architectures, and an overview of several good starter projects of varying difficulties. The safety portion would cover proper measurement techniques, using isolation transformers/importance of floating units under test/build, variacs vs isolation transformers, overview of the “death capacitor” and old, dangerous grounding techniques, adding a ground prong to old units, etc. There’s enough there that it might be a good idea to make the safety portion a class of its own.

For the testing class, I have three working testers, a Hickok 750, a Jackson 637 and a little Realistic emissions tester. I’m about to start work on a modern USB connected curve tracer based on a board/software from France. So I can basically cover true Gm testers, dynamic mutual conductance, cathode emissions testers and PC-connected curve tracers. It would be nice to fill in the gaps/show other examples from your collection, Rich. Happy to work with you as much as you’re willing to develop/teach the class.

Thanks again all.

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thats a great name for a tube company “jurassic electronics”

The newer Curve Tracer that was mentioned, the U-Tracer, is an unusual instrument. Instead of using true DC voltages it uses Pulse Width Modulated (PCM) DC for all the tube operating parameters. This process makes for smaller adjustable filament supply circuitry without the use of a heavy isolation transformer. The resulting sweep waveforms look okay. But, the older tubes filaments were never designed for PWM. The original response curve is therefore much different. That’s why the U-Tracer does not give a pass/fail indication like a tube tester does, it just displays a response curve. The operator still has to decide if the response curve is good or bad. Transconductance is based on a sine wave impossed on the grid, not a PWM signal. The U-Tracer is a great kit but it does have it’s limitations when testing vacuum tubes.