About one third of the e-mail that I have recently received is from people desiring to build their first vacuum tube amplifier. It has become apparent that there is tons of vacuum tube related information on the Web. Unfortunately there is little information related to electrical safety. Most DIY web sites just have a warning notice. Some of the questions I have received indicate a serious lack of electrical safety knowledge. I have received questions from people that are already building (or about to start) their first amplifier, who don’t know how to use a voltmeter. Even though I had stated that this site was intended for experienced builders, it has become obvious that inexperienced people will (and have) purchased our board. Many of the questions and fears involve powering up the board, checkout, and setting the bias. I have decided to rewrite the sections of the manual that detail these operations, before any more boards are sold. The procedure is being changed to use multiple meters that are connected to the board before powering it up. This makes the “scary stuff” much safer for inexperienced users. Digital meters have become ridiculously cheap, so there is no reason not to own a few. Read the safe meter usage page for details on which meters to use and how to connect them up.
Since there is little safety information available on the web or in print, I have decided to write my own. There will be three initial pages, electrical safety, safe meter usage, and amplifier grounding. These will be added to the web site as they are finished. Most of the information is based on my 40+ years of electronics experience, and some common sense. Much of the material should be obvious to the experienced tech, but everyone should read it at least once. The material is written in a simple, easy to read format. If you do not understand EVERYTHING presented on those pages, you should not be working on high voltage electronics.
I intend to continue the series on safety because I believe that the information is not well covered on the internet. Electronics can be a safe and rewarding hobby if you have the knowledge and the skills to practice safe electricity. I DO NOT intend to cover introductory electronics, and basic vacuum tube theory. I have only limited time to spend on this site, and I choose to spend it on new and unique amplifier designs. I WILL continue to search for this information and post links to it on the information sources page.
There has been an increase in e-mail lately, with a few common questions which I will address here:
1) What is required to build your Tubelab SE amplifier?
To build the SE amp board, you will need to be able to solder. The instructions are written for someone who has never assembled a PC board before, but soldering skills (and equipment) are assumed. You will also need a digital meter capable of measuring up to 400 Volts. You will need to make several voltage measurements during initial board checkout. This is easily accomplished with 3 cheap digital meters. See the safe meter use page for a preview of the setup. You will also need to manually set the bias for the output tubes initially and every time the output tubes are changed. This requires taking voltage readings on a live amplifier and adjusting a trimmer potentiometer to get the right reading. These steps are fully explained in the manual, but if you have never done this, you MUST enlist the help of an experienced person. All vacuum tube equipment operates on potentially lethal voltages.
A computer is needed to view the instruction manual CD. I find that it is helpful to have the computer located near the assembly workspace. The instruction manual is heavily supplemented with digital photographs of many steps in the assembly and test procedures. The instructions are in web page format so they can be viewed using a web browser like Internet Explorer. The images that are included in the pages have been adjusted such they fit in the web page and can be viewed on any monitor at 800 X 600 or higher. The original high resolution images taken with an 8 megapixel camera are included on the CD so that intricate details can be viewed if needed. I am in the process of making a movie file of the initial checkout and setup of a new board. This will be a .mpg file which is viewable in Windows Media Player. I may be able to provide a Mac viewable movie but this is not known at this time since I do not own a Mac, and they have been banished by the IT department at work. Several other files relevant to the construction and operation of this amplifier are provides on the CD. A text version of the instructions are included, so it is possible to print these and build the board, but this is not recommended.
2) Why is bias adjustment required? My friend doesn’t have to set the bias on his SE amp.
Your friend’s amplifier probably uses “cathode bias”. This does indeed require no adjustments. It also restricts the amp to one type of output tube. Our amplifier has a bias adjustment so that you can run different types of output tubes, usually with only a readjustment of the bias control. Some experienced SE amp users often set the bias differently for different musical situations. This amplifier design was conceived as an extremely flexible SE amplifier of very high quality. It was never intended as a beginners amplifier. There is a beginners SE amplifier in the works though.
3) There has been more than one person who has said that the web site is “confusing” or “hard to follow”. Some have asked for more information for ” a tube amp newbie”. Some have asked for me to do a 300B – 6SN7 – 5AR4 amp. Others have said “Why all of the car pictures?” or “Where are the rest of the car pictures?”
Ok, I can see how this web site has become disorganized over the past two years. I plan to do a reorganization of the whole site after the SE amp board is all finished. This site was never intended as a “newbie” site. That has been stated on this page since the first day it went live. Look below under “A word about this site”. I also state that I didn’t want to do the same designs that are already all over the web. A300B – 6SN7 – 5AR4 amp has definitely been covered well on the web. I have built amps like this and I was not all that impressed. 6SN7’s all tend to be microphonic. That is why my amps use the 5842 input tube. Since I get several questions from newbies, I will try to find some good “newbie” sites and books and list them on this site. The car pictures are simply an outlet for two of my other hobbies, muscle cars and photography. I have thousands of photos from years of car shows. Each one must be processed to be used on the web. More pictures will be added as time permits.
4) A beginners SE amp? Tell me more.
Yes, there is a “plug and play” SE amp in the works. I have had several requests for this, so the amp is beginning to take shape on my Tubelab 2 prototype system. The output tube will be a 6AQ5. The input tube has not yet been chosen, but will likely be some type of dual triode. Why a 6AQ5? I never heard of that. The 6AQ5 was chosen because it is a true audio tube, it can be run as a triode for 2 Watts or as a pentode for 4 Watts. Millions of them were produced so they are cheap ($3 to$5), and they were produced by just about every tube manufacturer so there are several popular brands to choose from. It also happens to sound good. Some other low cost amplifier kits use TV vertical output tubes, or tubes that were only made by one vendor. It is too early to set a price for the kit yet, but the target is for a complete SE amplifier kit (circuit board, parts, and transformers, no cabinet) in the $200 range.
There have been several e-mails lately asking questions about the SE amp board, the Tubelab SE amplifier and the costs involved in building a complete amplifier. I have updated the SE amp board page with the answers to many of these questions and some new information.