All posts by George

New hosting service

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.

Data recovery

I have now recovered much of the data that was lost when the hard drive in my main computer died. I now believe that the drive just died, unrelated to my poor programming ability. The drive has become extremely temperature sensitive. I have discovered that If I put the drive in the freezer for a while to get it real cold, then put it into the computer, it will work for about 15 minutes. I have been running back and forth between the freezer and the computer for a few days. I have recovered most of the data that was not backed up. Some of the pictures for the assembly manual were corrupt. I have recovered my e-mail, and will be answering the unanswered mail as soon as I reload all the software on the new drive. I have got a new laptop (which I am using at this moment) that contains an image of the web site so that the web site exists in at least two places. All of my software writing experiments are being moved back to the old computer just in case they had anything to do with the crash.

Last week I learned why it is important not to use your primary Windows computer (the one that does this web page and stores all e-mail) for dumb Linux and “C” experiments. A program ran away and wrote garbage over much of the useful data on the drive. I am in the process of reconstructing the data for the new web site from back ups that were 1 month old. Email that was sent to the Tubelab address was trashed, I have recovered less than half of that e-mail. E-mail sent to the Bellsouth address was restored intact.

After this crisis is over, all Linux experiments will happen on a dedicated computer. I got a new Windows laptop that will mirror the Tubelab content of the main machine. This computer could do webpage support. It has been used for development of the big web page upgrade that is coming. Early in January, some of the changes will go live. As these are debugged and become fully functional, more will be added. The entire SE amp board manual will be on the site. Boards will be available at that time. New content is coming.

We are being told that tropical storm Gamma is expected to visit south Florida late Monday night. I had set back up 1 bench and was working on the second. Now it looks like I must pack it all up and hide it in the closet. Since the window behind the bench leaked about 4 gallons of water during the last storm.


The wife of a fellow engineer was killed yesterday while riding her bicycle in an appropriate bike path. The path had debris scattered across it, as do most of our roads. The debris likely caused her fatal crash. Another friend of mine was killed while working on a ladder to remove debris from his yard. The ladder fell over backward, his neck was broken.

Hurricane Wilma

Hurricane Wilma, the 7th hurricane in 14 months to visit us, has devastated this area. 98%of Broward county has no electricity, and it will be 4 weeks before it will be fixed. Without power, there is no gas, since it takes power to pump gas. I am creating a page of pictures of storm related damage. All of these pictures were taken within bicycle distance of my house (most are within 200 feet) since I am saving what gas I have to run the generator, and many streets are not passable by car. I can post these pictures since I have one of the few working phone lines in the area. Tubelab, and the SE amp boards are obviously on hold for a while. My work place is closed due to damage for at least a week. It will take about a week to clean up the mess. I have lived in Florida for 53 years, this is the worst hurricane that I have seen. Andrew caused worse damage, but over a much smaller area. Wilma has caused severe damage for at least 5 counties. There is a path of destruction that looks like these pictures that is 100 miles wide, and goes completely across the state.

Common PC board questions

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.

The 833A amp

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.

ISP has been down

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.

My first grandchild

My first grandchild (a boy) was born on 6-18. Unfortunately at the same time my father, who has been in the hospital (80 miles away) for almost a month, was moved into intensive care. Needless to say I have not had the time to finish the assembly instructions. I will get back to this as things return to normal. The safety and meter use pages continue to get few hits, 4 each this week. by contrast the 845 SE page got 55 and the 73 Challenger page got 60. Come on people, you asked me to write them, at least look.