There have been far more questions about the Tubelab SE. The parts list has been modified to reflect the changes outlined below.
If you have a Tubelab SE and it is working OK, leave it alone. If you have any instability, or have experienced blown mosfets, make these changes. If you are starting a new build, or in the process of building one, make the following changes.
Increase the grid stopper resistors on the 5842 (R31 and R32) from 1K to 4.7K ohm. These resistors should be carbon composition if at all possible. The 5842 will oscillate if given the opportunity. The higher stopper resistor value will help. If you are using a volume pot on the board, make sure that the case of the pot is grounded. The cable from the board to the input jacks should be connected to ground on the PC board, and connected to ground at the input jacks. All ground connections to the chassis should be made at the input jacks. See the wiring diagrams for the Simple SE for details. The oscillation occurs in the 100KHz range which is inaudible, but may be heard as a hum or buzz. It can also cause the output tube current to rise unexpectedly.
R14 and R25 set the operating current for the mosfets. The parts list shows a value of 20K ohms. This is good for boards that operate from 275 to 325 volts of B+. Boards that operate from 325 to 360 volts should use 30K ohms. Boards that operate from 360 volts to 400 volts should use 36K ohms. This will reduce the dissipation at higher voltages. The B+ voltage may be considerably higher than normal during the time that the tubes are warming up. This is especially true with low cost power transformers. Voltages of 450 volts and higher have been seen, which combined with high mosfet current can lead to blown mosfets on power up.
C6 should be rated for the full B+ voltage, and the expected rise on power up. This means a 350 volt cap is OK for 45 amps that run at 275 to 325 volts. A 400 volt cap should be used if your B+ is from 325 to 360 volts, and a 450 volt cap is needed for boards that run from 360 to 400 volts. It is unlikely that a 100uF cap that will fit the PC board can be found in the higher voltages. It is OK to use an 82 or 68 uF cap.
I am posting this minor update (from a hotel room with free internet) to add the pictures from the 2006 Mopar Nationals including an entire page of pictures of the 2008 Dodge Challenger concept car. It was announced that production of this car will commence in April of 2008. I have done some minor reorganization of the site to make room for more pages in the future. Everything is still here, although some pages (and their links) now have their own sub page. I have been working on the assembly manual for the SSE amplifier. My return (and the manual) has been delayed by car trouble. Try to find an oil pan for a Volvo in rural West Virginia.
The break in my work schedule lasted for 7 days (I knew that it was too good to be true). The SSE boards are in and three amps are already up and running. I can build these boards in about 45 minutes each, they go together real easy. I am already working on the construction manual. I have gathered about 500 pounds of transformers which will all be tested and the results posted here (two transformers are already done). I will be out of town for most of August, so there will not be much activity until September.
I finally got a break from my relentless work schedule (it won't last) so I have been updating the web site every night. I have added (or finished) several pages in the Tech Pages and Tested and Proven Circuits sections. These pages were created to explain some of the experiments that began as a thread on the diyAudio forums. Some of the material is directly cut from my contributions to those threads. Some additional material has been added.
The SSE section has been updated, and will continue to be updated as more info becomes available. The PC boards are on order. My amp has been stressed tested in several ways, including me playing guitar through it, and plugging it into a Variac and cranking the input voltage to 135 volts while playing rock music at full volume! It is still going strong.
I have added some text and old pictures to the Tubelab SE assembly manual. I sold every assembled board that I had during the time that I was too busy to build any (the past 4 months). The pictures (text too) for the checkout and bias adjustment pages were lost last year. I have finished assembling a new board, and the new pictures will be shot this weekend. I will add them to the site ASAP.
I have added a few more updates and 2 new pages (in a big hurry, so I am sure I messed something up). The Budget SE output transformers and the 6AV5 testing page. I have updated the Tubelab SE assembly manual, but I won't have it finished for a few more weeks. Many of the final assembly and checkout pages were lost, and the board that I used to shoot all of the pictures was sold a few months ago. I have assembled a new board, and am in the process of shooting new pictures.
Tropical storm Alberto has reminded me that I must fix my roof before we get a serious storm. My roof got minor damage last year from hurricane Wilma. All of the roofing companies are booked selling complete re-roof jobs (15,000 to 45,000 dollars!). I can't get anyone to do my "small repair"( $1000), so I must do it myself.
This web site is in the process of a complete makeover. I have about 6 months worth of new information (and some old stuff that I found) that I haven’t had time to post. It will take a while to get it all posted. The Tubelab SE assembly manual is being uploaded first. The Tubelab 3 prototyping system is finished, a few pictures are here, more will be added as soon as I can get them processed. Complete assembly details will follow. Several new amplifier designs are done, and will be added also. The PowerDrive circuit has become quite popular, and I constantly get requests for unique designs. There is no way that I have the time to design, prototype, and test each one of these. I am finishing up a new page that should help you design your own.
I plan to put a lot of new and old content on this site over the next few months. This requires some better site organization. It will no longer be possible to have a link to everything from this home page. The menus (links) on the left bring you to secondary menu pages that have links to the individual pages. The news that formerly occupied this space has been moved to the news page.
All of the old pages are still here (some are updated) and they are still in the same location, so all old bookmarks and links should still work. Email me if I broke anything. I don't claim to be an expert web designer.
I have concentrated on functionality and content, I will make it look nice as time permits. Some of the new pages may have little or no content. That is because I mapped out the design of the web site before I finished the individual pages, and I needed to make sure that all of the hyperlinks work. Content is being added as I have time. I sit in front of a computer for 8 to 10 hours a day at work, when I get home, I would rather play with tubes.
Family matters and other commitments have required me to be out of town for many of the weekends so far this year. This will continue for the near future. I have tried to set aside one or two evenings per week to answer e-mail. I am currently running about one week behind responding to e-mail.
I have got a new internet hosting account with far more bandwidth than I had before, for the same price. I can now put all of my ideas on the internet without worrying about the cost. Many have requested the Tubelab SE PC board assembly manual, so it will happen first. The PC boards will also be available at this time.
Just when I had the SE amp board ready for launch, Digi-Key discontinued the line of resistors that I was using. I have replaced the smaller ones with metal film resistors and the larger ones with a different line of resistors. This required re - shooting most of the pictures in the resistors section of the manual. This is almost done. I am in the process of setting up my internet account for payment via PayPal. This can be done by credit card without a PayPal account. When these things are complete, boards will be available.
I have received lots of email lately. much of it related to the PC board. I have answered each one individually, but in the process I have discovered several common questions. These comments are intended to answer some of these questions:
1) The board contains TWO complete amplifier channels, and ONE common power supply. One board is needed along with three transformers and a suitable enclosure to build a complete stereo amplifier.
2) With this board you can build an amplifier that is optimized for 45's OR 2A3's OR 300B's. Since these tubes have different characteristics, it is not possible to build ONE amplifier that is COMPLETELY OPTIMIZED for all three tube types. The primary differences between the requirements of these tubes is load impedance and supply voltage. This means that the transformer set is chosen for each tube. It is possible to build ONE amplifier that will work well with all three tube types. To do this a compromise must be made. I choose a transformer set that supplies the output tubes with about 310 to 320 volts. This is above the recommended maximum for 45's and 2A3's. I have built 5 amps with this configuration and ran about 20 different tubes through all of them, without issue. I have not tried any globe 45's. 320 volts is a bit low for a 300B and you will give up a couple of watts on 300B's compared to an amp optimized for 300B's. If you are uncomfortable with these compromises, build your amp for your favorite tube type. There is a chart in the manual that outlines all of the choices.
3) Unfortunately 50's will not work in this amplifier without modification. They require 7.5 volts for the filament, which is above the maximum for the filament regulator IC. Unlike tubes silicon really does not like being fed too much voltage. It would be possible to use an external power supply if you really wanted to use 50's, but these tubes are out of my price range, so I have not tried them.
4) I know that the price of 5842's has gone up several fold since I started using them. I used to get them for $3 to $4 USD each. Several people have e-mailed asking if there is a suitable substitute. Unfortunately in this board there is no substitute other than the WE417 which is usually even more expensive. I have been searching for a different tube that is just as linear, with good gain, for use in my next design, and I have not found it yet.
5) Several people have asked me to put the construction manual on the web so they can determine their ability to build this amp. I can not do this since it is over 50 megs in size, and it would use up my bandwidth allotment in a few days. Web hosting plans are like US cell phone plans, you get charged by the megabyte (minute) when you exceed your plans allotment. The difference is that I must guess how many megabytes YOU are going to look at for a year in advance, and plan accordingly. This also limits how much NEW stuff that I can add each month, since the new stuff gets the most page views. I will put SELECTED parts of the manual on the site in the next few weeks, but I must process EACH picture first to reduce its size since I have been near my bandwidth limit for the last two months.
6) This board can be used as a driver board for a large SE amplifier using 845's, 211's, 833A's or other large tubes. There are two ways to do this. The board can be used without modification by substituting interstage transformers for the output transformers. The interstage transformers then drive the large tubes. A separate power supply is needed for the large tubes. The other way is to use PowerDrive. This requires a PowerDrive board to drive the large tubes. I have been convinced of the virtues of PowerDrive since I discovered it, but others have started e-mailing me, telling me how it did wonders for their amp. The Power Drive board is not ready yet, but you could build it on perf board, or point to point wiring.
I had to finish the testing of the prototype 833A output transformer in a hurry. I spent two hours trying to blow the 833A prototype amp up by playing guitar through it at extreme volume levels, complete with feedback and hard clipping. No dice, the amp just kept putting up with my S***, although I did blow the bench circuit breaker twice. I started a new 833A page to present these results. There are pictures and some data from an 833A amp that was temporarily assembled to test a prototype output transformer. The amp took up all of one work bench, and part of another. I put it together in a big hurry (3 hours) and it shows. I got over 200 Watts RMS from this thing, and it took some ridiculous abuse without complaint. All good things must come to an end, and this is no exception. I have already disassembled the amp.
The revised SE amp instructions are finished and an amp is being built currently. I will be out of town for most of August. The SEamp boards will be offered for sale when I return. This will be in early September. I will be working a zillion hours a week before I leave so this might be the last update for a while.
I was asked, " Why did you need to rewrite the manual. Was it too hard to follow?" No the manual was (and still is) easy to follow. The original test and adjustment procedure required making voltage measurements on a live board, and simultaneously adjusting the bias. This is no problem for an experienced builder, the original target user. It became apparent that many inexperienced people wanted this amp. I worked with two of the early consumers to devise a test and adjustment procedure that first timers are comfortable with. This is the multiple meter method outlined on the safe meter use page. This procedure separates the user from the electricity, making the procedure safe for newbies and experienced users alike. Now that digital meters are as cheap as screwdrivers, there is no reason not to have a few.
I have not had computer access for the last two weeks. Bellsouth (our ISP) was down most of this weekend. Even though I live in a major metropolitan area, all I can get is SLOW dial up, and that doesn't always work. I just got to my email. I have tried to answer everyone as best as I could. The answers to the common questions about the board status is below.
I sold a few boards to some inexperienced people at work to get their feedback on the assembly manual. I gathered their inputs, and made revisions. The revised manual is almost finished. The safety and safe meter use pages were done at their request, yet these pages get few hits. I will have some one build an amplifier using the new instructions before putting the boards back up for sale.
Unfortunately, my father became ill before I was done and I spent each weekend at his house (80 miles away), or at the hospital. He passed away last weekend, hurricane Dennis visited this weekend, and the funeral is now scheduled for next weekend. My mother needs care, and the legal arrangements need to be taken care of. Since the weekends are when I usually work on this, not much has happened. I can't say exactly when I will get it all done.
I plan to upload most of the basic assembly and checkout instructions to the web site, so that a potential builder can see what is involved before purchasing a board. I can't say yet when the assembly video will be done since I am new to digital video editing. I will post the progress on the web site.
I got a question about the picture of the amplifier shown above. Won't the transformers interact since they are so close together? Yes they did! Since that picture was taken I have rotated the power transformer 90 degrees to correct a hum that could be seen on the FFT analyzer when the amp was first switched on. Oddly enough the hum disappeared as the rectifier tube warmed up. Sooner or later I will take new pictures. The hum was only barely audible with my ear to the left speaker, but might have been a problem with more efficient speakers.
I have plenty of new information to add to the site, just no time to do it. I have an 833A SE amplifier running on my bench. It puts out over 200 Watts RMS at 4% distortion. It uses the same SE amp PC board. I will put the details up when I get caught up with all of the ugly stuff.
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.