In one of the page comment sections, Dave K asked this particular question:
You have both SET and UL pentode amps, from the listener’s standpoint, what are the audible differences in sound between the two types?
From a tech standpoint, I know that triode = even harmonic distortion, pentode = odd harmonic distortion
UL pentode = ??
And this was the simple answer I provided:
A big part of building custom vacuum tube amplifiers is layout. Even when the schematics are finalized and parts are ordered (and even delivered) the preparatory work is not over. With this phase comes the arranging and rearranging of transformers, tube sockets, potentiometers, switches, jacks, terminal strips, and all the other miscellaneous parts that make up the final amplifier. And this is where some simple quality tools can make all the difference.
A little background. I am a thirty year Electrical Engineer. I have spent those thirty years woking on some of the most amazing pieces of technology ever built. I have worked with cutting edge technologies before most people knew they even existed. I have had a phenomenal career. And I’ve spent that entire career with one company. That company has treated me very well, and I am grateful. But times are changing.
So, CascadeTubes now has a Twitter feed. The link is “CaliSuncalc”. The link is also on the left side of the Blog page.
If you ask me what that means for the site, I can’t really say. There are a few tweets there already. This is going to be a journey of discovery. So I guess we’ll see how it goes.
Feel free to take a look or even follow my tweets.
There is something very satisfying about seeing a project really start coming together. I finally got some time today to start working on my 6V6 Marblewood amplifier project.
It now looks like an amplifier instead of just a pile of boxes and parts.
So, this morning, I got a little reminder about the nature of the technology we all use. I currently have the 6EM7 Vertical Amp in my office at home connected to my computer sound card. When I reached over and turned it on this morning I got an interesting surprise.
I imagine that some folks have been wondering where I’ve been since the end of May. The truth is it’s been a very busy summer. Shortly after my last blog post, I learned that I was being transferred for the second time in less than two years. So far this summer I’ve bought a new house, moved ≈1500 miles (≈2400 km), totally packed and unpacked an entire house, a complete workshop, and an electronics lab, started a new job, and basically just tried to keep my head above water. However, in the process of unpacking things at my new house, I found something interesting.
A while back, I was at my local hardwood supplier and found a plank of wood of a species with which I was unfamiliar; marblewood (zygia racemosum). This is a South American hardwood with a golden yellow to orange color and large dark streaks of deep brown throughout. This, I thought, would make a very interesting chassis.
Well, my blog seems to be quickly becoming a list of things to avoid doing. I’ll get back to the more technical stuff soon but in the mean time I have one more blooper to share. I hope there aren’t too many objections.
So I have a new amplifier I just finished which will soon be added to the ever growing list of amplifiers on the web page. But when I was putting it together I managed to destroy a couple of expensive tubes due to a very simple error early on in the design process. Let me explain.
Sometimes I feel like an idiot!
This is a copy of a comment I made during a forum discussion on “improving” the response of an amplifier.
So lets talk feedback for a minute. There are lots of ways to apply feedback and all feedback performs the same function. Any differences in feedback response are usually due to the different impedance functions applied to the feedback loop. Contrary to popular opinion, there is no magic in any feedback function. The effects of feedback are to reduce gain, increase bandwidth, reduce circuit induced distortion and noise, and decrease gain function sensitivity to circuit parameter variation. And it works. We’ve been using feedback amplifiers widely since Harold Black introduced the concept back in 1934.
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When writing for a webpage or a blog it is sometimes very difficult to get a feel for your audience. You never really know if you’re talking to a few friends over coffee, standing in front of a classroom of twenty, or lecturing to an auditorium of two hundred. I know there are a few people with whom I regularly converse, but my web traffic suggests that there may be more. So in order to help me get a feel for all of you, I am proposing a CascadeTubes version of Groundhog Day. Allow me to explain. Continue reading
Everyone knows that you need to be careful when working with metal. Corners are sharp, shavings get everywhere, power tools can spin and throw pieces of metal; so it’s kind of obvious you need to be careful. But how about handling the other materials? Continue reading
Lately I’ve been looking at a project that’s been sitting on the back burner for quite a while. It’s a stereo power amp for which the 6EM7 Vertical amp chassis was a proof of concept. This amp uses an 807 tetrode in a triode strapped configuration. Now the one thing that I didn’t care for in the load line design was the level of distortion. From the load line paper design, distortion peaked at around 8% at 4.31W output, yielding a Ds of 1.8%/W. This is larger than I generally like in my amps. Then I had an idea. Continue reading
There are a lot of opinions out there considering what’s acceptable for low frequency amplifier performance. It seems like everyone has their own very strong opinion about how low the frequency response must go for an amp to be “acceptable”. And it seems that usually these opinions range from somewhere between 40Hz and 20Hz as the minimum acceptable “roll off” frequency with definitions of “roll off” ranging from “no loss”, to “-1dB”, to the Engineering standard of -3dB. And strangely enough, virtually no one ever addresses the technical performance of amplifiers at their low end rolloff frequency. Amplifier distortion is usually only measured (when mentioned at all) at 1kHz and not across the frequency band. Continue reading