These last few days I’ve been working on the driver stage and overall schematic for the new 6L6 SE-UL amplifier. While drawing up the schematic yesterday, I inserted a 250kΩ volume control at the input without much thought. While performing some preliminary analysis, I realized my mistake.
Continue readingFor the last few days I’ve been applying oil to the SET chassis. It now has four coats of oil, cured and buffed out. There’s only one decision left for the chassis.
Continue readingToday I was once again reminded of the perilous state of human fallibility and the risks of personal hubris. The cost of today’s lesson? One ruined KT-88. And a little smoke in the office.
Continue readingThis morning as I sat down in my office to check email and the like, I looked over at the amp in the corner of the room and made a snap decision. It was time to perform a SET swap.
Continue readingThis afternoon I’ve been working on another amplifier project. This particular one is the 6L6 SE-UL for which some readers have been looking since I published my Optimization of the 6L6 SE-UL page back in March of 2019. I recently realized that it had been three years since I published that data set and that it was probably time for me to get the project started. So this afternoon I’ve been investigating driver stages for the amp.
Continue readingIt looks like the weather has finally broken here at CascadeTubes and spring has arrived. Yesterday, the 6AS7 SET chassis got its first coat of oil. The purple heart used for this chassis is definitely much deeper in tone than that used on the The 6DJ8 Headphone Amp.
Continue readingAbout a year ago my television display died and I was forced to buy a new TV. I had been using the Lacewood V2.0 amplifier for the sound system and, when I plugged in this new TV, it formed a bad ground loop with the amplifier, introducing a nasty hum. This was not an insurmountable problem. I simply dug through my parts closet until I found a little line isolator I had built about a decade previous for some project I was working at the time. I installed this isolator and the problem went away. But that’s not the end of this story.
Continue readingI 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.
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