I took some time this week to get several coats of oil on the chassis for the Dual Triode Test Station. Even though I’ve already used it for the mystery tube investigation and to compare some 12AU7s, it’s good to have it finally complete.
Continue readingI 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.
Continue readingBack in November, in my post concerning Tubes and Tube Testers, I talked about how I was not really a fan of generic tube testers. In that post I sited a statement from the RCA “Receiving Tube Manual”, RC-30, about testing tubes.
The tube tester cannot be looked upon as a final authority in determining whether or not a tube is satisfactory. An actual operating test in the application will give the best possible indication of a tube’s worth.
So I thought that as a simple demonstration I would collect some data from a couple of tubes; one new and one rather ‘used’. The results are really kind of surprising.
Continue readingThis has happened to most of us at some point or another. You come upon a tube with no markings whatsoever mixed in with a bunch of miscellaneous tubes. Or, like I just did, you get a “lot” of tubes from a reseller and most are marked but a few are wiped clean. But how does one go about positively identifying the mystery tube? Especially with the numerous types of 7 and 9 pin miniature tubes in existence this can seem to be a rather daunting task. However, just like a game of “20 Questions”, it is actually simpler than one might think.
Continue readingThis is a topic that rears its head periodically on vacuum tube forums and discussions. Just a couple of days ago I was reading a forum thread on preamps and someone threw out the suggestion of using a triode strapped 6V6 as a preamp tube. Now this is nothing new. I’ve been hearing this suggestion, on and off, for at least ten years. But using a triode strapped 6v6 (or any beam power tube) as a voltage amplifier is a poor idea which simply doesn’t hold up to technical scrutiny.
Continue readingNow that the color preamp is done (knock wood), I’ve been trying it out on different amplifier and speaker combinations. But there is a little issue. Unknown to most people is that your brain can really only hold onto an unadulterated memory for a minute or so at the very longest. Most of the time you’ve got less than about 30 seconds. After this interval your brain starts throwing out what it considers to be extraneous information leaving only impressions. And this is a big issue when attempting to make subjective comparisons.
Continue readingThere are a variety of sayings, axioms, proverbs, or quips which could apply to me this afternoon. A few which come to mind include:
“How wayward the decrees of fate are” – Vanitas Vanitatum – William Makepeace Thackeray
or this one:
“Pride goeth before destruction, and an haughty spirit before a fall” – Proverbs 16:18
or just the simple axiom:
“It ain’t over till it’s over” – Yogi Berra
In any event, it would seem that “Final Chapter” or no, I have one more post concerning the Color Preamp.
Continue readingSo I decided today that I really needed to close the book on the color preamp. This means that I couldn’t just prototype a new buffer and leave it at that. The preamp needed an end-to-end test in it’s final design configuration. So that’s what I did. The results were even better than before.
Continue readingLots of work has been going on the last couple of days working on an alternate buffer design for the 12AU7 “Color” preamp. As readers should know, I was not particularly pleased with the performance of the previous buffer circuit. It was bottoming out at too low a voltage. Now however, I have a simple change which yields much better results.
Continue readingThis afternoon I completed the “color” preamp and tried it out. I am very happy with the results.
Continue readingThe “Color” preamp has been checked out on the test bench and everything is working per design. Bias points are good and the gain stage is operating exactly as designed. However, the buffer design I used was from a different project, and it operates differently in this project than the last one.
Continue readingI had thought that the coupling capacitors I ordered on Tuesday would not arrive until this Saturday. However, the gods of DIY decided to smile down upon me and the capacitors showed up in today’s mail delivery. In my opinion, two days from order to delivery is exceptional. I spent some time this afternoon with a soldering iron in hand and the Color Preamp is now fully assembled.
Continue readingAs you may know I’ve been waiting on components to finish my “Color Preamp”. I thought that I’d have my output coupling capacitors by now, but I was mistaken. It seems that my parts supplier, after promising to get the parts right out to me, spent three days trying to find the parts in their warehouse, then sent me a refund. But I thought I’d outsmarted them.
Continue readingSince I’ve been at a standstill waiting for parts, I’ve been going over my parts supply and getting things organized again. It seems we’re all constantly working against entropy. While doing this, my bagged and sorted capacitors reminded me of a short article I wrote back in 2013 about component tolerances. I’ve decided to reprint it here for reference.
Continue readingI made significant progress today. Most of the signal stage wiring is done. I could finish it up in about half an hour, but there are two little blockages in my path; one due to a supplier problem, one due to me.
Continue reading