Change is Good

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I want to start by rolling the clock all the way back to March 6th of this year. It was Friday and I had just returned from a business trip the night before. That afternoon (Thursday) my employer had decided that everyone was to start working from home immediately. Not wanting to try performing complex engineering tasks with only a laptop screen, I immediately ordered two nice high definition 24″ monitors. But the question was where to put them. The “answer” was, on my office desk where I usually do tube work, including prototyping and assembly. This gave me a good spot to do my job, but with two large monitors and their ample stands, it left little space for power supplies, oscilloscopes, signal generators, and other such trappings of my vacuum tube amplifier work.

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A Productive Day

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So I usually have multiple amp projects going on at any one time. There is a rather large project that I’ve been working on but it’s going rather slowly and I was hungry to make some progress on something. As such, I decided to tackle a smaller project I first prototyped in 2011 and that has been on hold since 2015. I spent the better part of today turning an 11″ x 58″ plank of Zebra Wood {Microberlinia brazzavillensis} into an amp chassis.

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Revisiting Past Endeavors

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So, I was sitting here on this rainy Sunday morning going through some amplifier designs and looking through my stash of tubes and various amplifier building supplies. While standing there looking at the shelves of vacuum tubes, transformers, and various piece-parts, my eyes drifted up to an amplifier sitting on the top shelf. It was my 6AS5 µ-power UL amplifier documented here. But why was the little amp sitting on a shelf collecting dust? Then I remembered.

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Single Purpose Jigs

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For those that are paying particular attention to my amp builds it will come as no surprise that I think the #44 and #47 (0.9 and 0.5 candela respectively) indicator lamps are a little bright to be used on tube amps. I just think that they tend to overpower the look of the amplifier when the room gets dim. However, as these lamps are ubiquitous, it pays to use them in our builds. So, on the 6DJ8 Headphone amp and the 6EM7 vertical amp I included a small adjustment potentiometer to tame these power indicators. And on the Marblewood amp, I chose a fixed 25Ω 1W resistor to dim the indicator.

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Grounding Philosophy

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I keep getting questions about amp grounding so I thought I would consolidate some of my previous notes on the subject. The first is a reprint of a forum post I made back in 2013 on the DIYAudioProjects Forum.

Warning: It has been brought to my attention that some people reading this post mistakenly believe that I am advocating the override, disconnection, or elimination of the safety ground (or bonding) connection in some pieces of equipment. This is not correct! The safety ground or bonding requirement for every piece of equipment is a firm requirement. At no time should any signal cable or independent wire be expected to fulfill the safety ground requirement for any piece of equipment. The process of “ground lift” is simply to provide a different signal ground reference in a piece of equipment.

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Singleton Power Tubes

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Being a proponent of single ended topologies, I am constantly on the lookout for singleton power tubes. Since I’m working on designs with all single ended signal chains, things like matching and bias points as less important to me than tubes which test strong and are reliable. One source containing lots of singleton “New Old Stock” and “Used” power tubes is Ebay. Often I can get a single power tube for far less than buying from one of the more established vacuum tube business on the web. But I have begun to wonder about whether these are really such a great deal after all.

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Loudness?

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Anyone who has taken a look around this site should soon realize that I really like my low power amplifiers. What this means is that most of my listening is at lower volume levels. Now the only problem with this is that the sensitivity of the human ear to different frequencies is dependent on volume level. So at low volume levels, the ear has relatively poor sensitivity to both low and high frequencies. And the quieter the music gets, the worse the mismatch becomes. Traditionally the answer to this conundrum  was the humble “loudness” control.

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Interesting Discovery

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So I was sitting down today to prototype a new 6SN7 preamp with a buffered output. As I was getting equipment arranged and pulling components I looked over at my dedicated prototyping station and something didn’t look right. As I looked more closely something jumped out at me that was unexpected and frankly, more than a little surprising.

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Tube Sound – Power Stage Topology

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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:

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Amp Layout Tools and Ideas

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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.

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What is Wrong With Tech Companies Today?

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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.

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