TUBELAB, INC.
MOUNDSVILLE, WV

Tubelab is both our name, What is the purpose of the Tubelab web site? The plan is for the web site and related activities become self sufficient in 2006 (still didn't happen, maybe in 2007), and generate some income later in retirement. At this time the web site hosting and related development activities are funded entirely out of my own pocket. Operating funds have been generated by selling some of my amplifiers, since I can't possibly use them all. We are cleaning out the warehouse and selling the stuff that we don't have time for locally and on E-bay. Our E-bay ID is tubelab*com. There are thousands of oddball tubes and components and several old amplifiers that are being sold. The proceeds from these items are used to fund the web site and development of more vacuum tube projects. E-mail to Tubelab We get several e-mails per week. Some of the e-mail is asking my opinion. Often it is asking for my opinion about something I have never tried. I try to answer these e-mails politely but this requires substantial time. These questions are better asked on one of the audio forums. Unfortunately some of the audio forums are frequented by "experts" that will gladly give (or sell) you their opinion as fact. Some of these people can become quite rude to anyone who does not agree with them. I refused to participate in any of the audio forums for several years because I thought that they were all like that. About a year ago I discovered the circuit has become the most popular topic of in my e-mail lately. I get e-mail complementing me for the concept, saying that it really wakes up their amp. I also got a few e-mails criticizing me for using silicon. Many write asking for component values for their particular amplifier design. I can't possibly calculate the values for everybody's design and test them, so I am doing the next best thing. I am working up a cookbook approach to assist you in perfecting your own PowerDrive circuit. We welcome your ideas, circuits, suggestions, and questions that relate to the material presented on this site. I can't help you decide which amp, speakers, tubes, or components to buy. Those questions ask for an opinion based upon personal choice. My personal choice is likely to be different than yours. I will try to answer e-mails when I can, and discuss recurring topics on this site. — Who is Tubelab? Tubelab is operated by George and Sherri Anderson. We have been operating an electronics design consulting service (G and S programming) for the past 25 years. Our consulting firm started with the microcomputer industry in the mid 70’s designing SS-50 bus boards, and has evolved to embedded system design featuring the Microchip PIC processors and the Motorola HC11 series. I (George) have worked for a large electronics company designing cellular phones and communications equipment for the past 30+ years. Before that, I ran the service department at a large stereo store. I have a bachelors degree in computer engineering and a masters degree in electrical engineering. I currently hold 3 US patents in the communications electronics field. Sherri also worked at the large electronics firm for several years in the test equipment lab. She stopped working full time while we had children at home. Our designs begin with an idea or a circuit which can be original or from an outside source. A rough schematic of one or more stages is drawn with first guess component values. Using tube manual or measured data, calculations are performed to verify or adjust the component values. If the design lends itself to simulation, then a simulation is often done. Then we use the Tubelab to prototype the design. Once built on the Tubelab the tweaking begins. Component values, bias points, power supply voltages, and other parameters are adjusted to optimize the sound. Different tube types or different output transformers can be tried, and the tweaking repeated. It should be noted that my optimum sound is likely to be different than your optimum sound. There are many variables to consider such as musical preference, speaker type, room size and layout as well as your ears. This is the main reason why an "expert" can not tell you what you need to hear. You must decide for yourself. Sometimes I'll just sit down at the Tubelab and "play with some parts" or try out some new tubes to see what turns up. If you try this approach, be careful, and be prepared to fry a few parts before you create a masterpiece. Never use your good speakers when experimenting or testing a new amp. If your amp oscillates the speakers could be damaged. We use a home built cabinet with a 6" X 9" car speaker in it for testing. Car audio speakers are relatively cheap, hard to blow out, and give reasonably decent sound. We briefly mentioned simulation. At work I am known as the build it guy. I use simulation sparingly in an environment where simulation is the norm. I am the guy who takes someone else's simulation and transforms it into a working product. What have I learned? The biggest thing to remember is that if the simulator tells you that something won't work it usually won't. If the simulator tells you that a circuit will work, it has a chance, success is not guaranteed. A successful simulation means that the circuit will work if all of the components closely match the mathematical models. This is not often the case with 50 year old parts, or new copies of 50 year old parts. You must be aware of this, and not be too trusting of any vacuum tube simulation. I have used simulation on vacuum tube circuits quite often. It can help you determine whether or not to build a design, and often accurately predict the performance. 1) You should use Amperex Bugle Boy 6DJ8's (or whatever particular tube that the "expert" is selling) I am sure that these particular tubes sound great in his particular amp. Will they give the best possible sound in your amp? Not necessarily. Every tube has a set of operating conditions (voltage and current) where it performs best. If your amp provides the tube with the same set of conditions that the tube was designed for, it will work well. Every amp, and every tube is different. I have been curve tracing a lot of tubes in the past year, and I have found a large variation in tubes of the same type. It seems that the common types 6SN7, 12AX7, 6CG7 are all over the place, even among several tubes of the same brand and vintage. If you are building a new amp, put in some known good tubes of a common manufacturer, get the amp to work well, then you can swap tubes. If there is a large variation in sound among different tubes, you are probably operating the tube too far away from its ideal operating point.