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TubelabSE - Anyone built?

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I just got back from a two week trip. I have about 100 emails in my inbox. I will go through them this weekend. There are 2 from Australia, if one of them is yours, I will reply with ordering info.

I have built dozens of tube amps, including several versions of these amps. I have an obviously biased opinion, but the TubelabSE is still the best sounding amp that I have for critical listening. My favorite one uses 45 tubes, which don't get very loud on my speakers but have excellent sound. The SimpleSE amp is a good compromise between simplicity and performance. It gives up a little detail in exchange for ease in construction and zero maintenance.

The TubelabSE has been around for two years. I have heard from several people who have completed their amps, and are happy with them. Comments range from "I like it" to " this is the first amp that I have owned that could startle my golden retriever".

I have only been selling the SimpleSE board for a few weeks. I have only heard from one person who has completed his amp (two days after he got the board). He was impressed, and had just ordered a bunch of different tubes to try in it.
 
Hi, tubelab = George?

Tubelab = George and Sherri, I would be George.

I assume the pcb also comes with various component lists?

I have placed the parts list with DigiKey and Mouser part numbers and the important criteria for each part on the web site. The SimpleSE parts list has been refreshed with the exact part numbers that I used in the latest amplifiers that I built. I am finishing up two TubelabSE amps, and I will post the updated parts list from those builds shortly. There are some parts on the published list for the TubelabSE that are no longer available. Substitutes are being tested this weekend. All of the build information that I have is currently posted on the web site.

I realize that people in other countries are likely to order parts from a local distributor. In this case you can look up the DigiKey or Mouser part number, call up the spec sheet and use it to find a similar part from your local distributor.

I also would like to get a Tubelab SE board (or a SimpleSE board - I'm not choosy - what the heck, maybe both) when you get ready to start selling boards. Will you have an announcement here, or should I watch your web site?

I had planned a big banner across my home page, when everything was ready, but in reality I have been selling TubelabSE boards for over a year and SimpleSE boards for a couple of weeks. People have convinced me that they could build their amplifiers from the assembly manual that is currently on the web site. I have not yet had the time to figure out how the " integrated shopping cart" feature that my web hosting company uses is supposed to work with Microsoft Front Page, so I have been doing business via email. These things will come in time.

People kept emailing and asking for boards, so I sent them. I have been using feedback from these "early adopters" to refine the assembly manual. Feedback from early purchasers and who wanted a second amp, and people who desired an SE amp, but didn't like the complexity or the prices of DHT's, led to the design of the SimpleSE. The TubelabSE was designed so I could build DHT amplifiers, and sell them. I didn't design it originally to be assembled by others. The assembly manual was written after the amp was designed. The SimpleSE was designed from the beginning to be a "kit" amplifier and the assembly manual was written as the board, and associated amplifiers were designed and built. It therefore is much easier to build.

Both assembly manuals are considered "works in progress" and will be updated continuously. The SimpleSE manual is fairly complete, and the TubelabSE manual will be improved and updated as I get time. Watch the web site, if at any time you feel that the assembly manual gives you all the information needed to build your amp, send me an email, and I will get you a board.

At this time I can only ship to countries served by the US postal service's Global Priority Mail service. It is the only economical choice. Paying Fedex $35 to ship a $35 board just doesn't make sense.

I can not answer Tubelab related email from work (a couple of forum posts / day are OK so far). I get home from work late each day (8PM) so I don't have much time for email. I answer email from purchasers first, so other emails sometimes don't get answered until the weekend. I have been away for two weeks, so I have some catching up to do.
 
Hi George,

I noticed on the schematic for the Simple SE that you are running the cathode feedback from the cathode bypass cap only. Do you find any sonic differences between this way versus running the cathode bias current through the OPT secondary?

Thanks,

Kyle
 
Do you find any sonic differences between this way versus running the cathode bias current through the OPT secondary?

I don't find any sonic or measurable differences. The feedback signal must go through the cathode bypass cap either way. The method I chose was used to eliminate the DC across the speaker leads that would result from passing the cathode current through the OPT secondary. I cave been assured by Lowther owners that even a few millivolts of DC would be unacceptable.

The cathode feedback can be disabled if desired. I tend to not use it in triode mode and turn it on in UL mode.
 
I have an amp very simliar to the Simple SE, using the EL34 in Triode mode.

Cathode feedback helps the bass alot, however it seems to make the frequency response even less flat than my $35 Output Transformers make it already.

I put a Switch in, so I can turn it on and off as I please
 
I have sent an emai to Mr TubeLab (George?) asking the questions below, but I realise that he is busy and thought that someone else may have had similar questions as me and might be able to provide some feedback.

I am looking at building the SimpleSE amp. I have a pair of Lynn Olsen Ariel transmission line speakers that I built a few years ago, which I think are around 92db. I am currently powering them with a solid state chip amp that I built. The designer of the speakers recommends a tube amp to power them. I have also built the recommended base units for these speakers, with an active crossover at 80hz.

I am looking to dabble in tube audio, but do not want to spend a fortune, hence the SimpleSE choice. I have built several simple chip amps, active crossovers and several other non-audio electronic projects, but have never built a tube device.

My first question is regarding the choice of output transformer. The transformers by Edcor seem to be good value. My question is should I go for the XSE15-8-5K ($19 USD) or the CSXE25-8-5K ($79 USD). Considering that I am crossing over at 80hz, does this make a difference? Happy to spend the extra money for a noticeable improvement, but not wanting to spend the extra if it is not required in this application.

Second question is regarding the power supply transformer. I might have missed something on the site, but I could not find a reference to power transformer spec, or a recommended transformer. Does anyone know what I should be looking for? As I live in Australia, it will need to be 240 volt compatible. I know that the Hammond 300 series transformers can be wired for 240 volts, but seem expensive. Would something like this be suitable? http://www.edcorusa.com/products/transformers/xpwr/xpwr106-240.html

Also, the schematic calls for an optional choke in the power supply, but I could not see the required value. Any recommendations here?

Any help would be greatly appreciated, especially since transformers are very expensive in Australia (over double what you pay in USA). I have just found out today that I will be travelling to Los Angeles on Friday for five days, so if I get a quick response I will be able to order the transformers and have them delivered to my friend in LA for me to pick up when I travel there.

Once again, any help and advice greatly appreciated!

Cheers,

Chris H
 
I just made it to the computer, so I will answer the questions here so that everyone sees the answers. I often get the same questions multiple times via email.

Considering that I am crossing over at 80hz, does this make a difference?

If you are using active crossover most of the deep bass frequencies will be attenuated before reaching the main amp. With the crossover set at 80 Hz, the energy below 70 Hz should be minimal. I have tested the $19 Edcor transformers, and the $79 Edcor thansformers. I prefer the sound of the midrange and highs from the little transformer over the sound of the large one. With seperate amp (the chip amp?) for the low frequencies, the problem of the little transformer saturating on deep bass is removed. I would use the small one, it just sounds better.

The small transformers tend to distort when asked to produce over a watt or two below 75 Hz. If used in a situation that does not demand very low frequencies (like yours) or operates at low power, these are real nice transformers. The high frequency response goes out to over 40KHz, so there is no phase shift in the upper audio range. The big Edcors have problems with this. I have a SimpleSE amp with 6V6's and the $19 Edcors that sounds real nice even on strong bass, but it only makes about 2 watts.

The SimpleSE is a fairly flexible design, which can be used with a wide variety of tubes which each have different voltage limits. You did not indicate which tube you want to use. The choice of output tube, and the expected power level will determine the choice of power transformer. For example, the 6V6 amp that I mentioned above uses an Allied 6K56VG transformer that puts out 540 VCT. The B+ voltage with this transformer is 320 volts. This is just about right for the 6V6, but too low for most other tubes.

For the common audio tubes (6L6GC, EL34, KT88) I use an Allied 6K7VG which is 750 VCT. This gives me about 430 volts of B+. I use the Allied transformers because they made by Hammond but cheaper, and I have never had one fail in about 15 years of amp building, unfortunately they are 120 volt primary only. The 6K7VG is similar to the Hammond 274BX, but is $15 cheaper. Transformers with "universal" primaries tend to cost quite a bit more than 120 volt only transformers, due to the added winding, and the extra iron required to handle 50Hz. This is not needed in the USA, so I have limited experience with them. The Hammond 374BX has similar specs to the 274BX (which I have used) but as you have found out, costs more. People on this forum claim that it is a much better transformer, but I have not tried it.

If you intend to use any of the popular audio tubes (6L6GC, EL34, KT88), I would look for a transformer that produces 720 to 750 VCT at 175 mA or more. You would also need a 6.3 volt winding, and a 5 volt winding if a tube rectifier will be used. The 5 volt winding is not needed with a solid state rectifier. The Edcor transformer shown in your link does not have the voltage or the current capability to work with these tubes, however it would work with 6V6's, producing 1.5 to 2 watts in triode mode and 4 or so in UL mode.

I have had good luck with Antek toroidal transformers sold on Ebay. They do not have a 5 volt winding, but do have 240 volt 50 Hz capability. I use the AN4T-360 for most amps. It is total overkill, but far cheaper than the Hammond.

http://cgi.ebay.com/720V-CT-360V-40...11199021QQihZ017QQcategoryZ4660QQcmdZViewItem

I have also built several amps with surplus transformers. That is why I put the tables on the web site to estimate the results obtained by using whatever transformers you can find. I found about 20 Hewlett Packard audio oscillators sitting in a scrap yard waiting to be crushed. The transformers from those work just fine, and I got them for $2 each! (240 volt capable too)

http://www.tubelab.com/AssemblyManualSimpleSE/TubesAndApplications_SSE.htm

Also, the schematic calls for an optional choke in the power supply, but I could not see the required value. Any recommendations here?

I use Triad C-14X choke for most amps. It is so ugly that you will want to hide it under the chassis. I use it because it works, and it is cheap. Allied sells it for $15.16! Any choke of 5 henries or more that can handle 200 mA will work. I stuck a C-24X in the Industrial amp because the C14X wouldn't fit. It is only 1.5 henries, but the hum is so faint that it is not noticed on my speakers.

http://www.alliedelec.com/Search/SearchResults.asp?N=0&Ntk=Primary&Ntt=c-14x&sid=466B3F004D4BE17F

I have just found out today that I will be travelling to Los Angeles on Friday for five days

Really long plane ride! I will send you an email with PC board ordering info. I usually send boards out within a day or two after geting payment. I use Priority Mail from the US post office, again because it is cheap. They will usually get to California in 3 or 4 days.

Shipping to Australia is only $6 more for a PC board, so it may be better to stuff your luggage with heavy things like transformers!
 
Thank you so much for your detailed response, I very much appreciate it!

As for tube choice, I have no pre-conceived ideas or biases. I am guessing with the efficiency of my speakers (about 92 db) that I would want something towards the higher end of the power capability of this design? Looking at the Tubes and Applications page of your site http://www.tubelab.com/AssemblyManualSimpleSE/TubesAndApplications_SSE.htm this would indicate that with the recommended Hammond transformer 374BX B+ of about 430 volts with an EL34 tube I should get about 5 watts?

So how does this look:

EL34 tubes
Edcor XSE15-8-5K output transformers
Hammond 374BX (375-0-375) power transformer
Hammond 193J (10H 200mA) choke

Does this sound like a good starting point?

Like I said, I am new to tubes so happy to go with a recommended design.

I will email re the board...

Thanks again!

Chris H
 
chrish said:


EL34 tubes
Edcor XSE15-8-5K output transformers
Hammond 374BX (375-0-375) power transformer
Hammond 193J (10H 200mA) choke

Does this sound like a good starting point?

Chris H

Looks good, you just need some tweaking.....

I have a hammond 272HX, which is 300-0-300, and my B+ ends up being close to 380 volts, so you're looking at (375*1.41)~500-530 volts! so then I would make sure all caps are rated at at least 600 volts (to be safe)

What is the current on the power transformer? my 272hx is 200ma, and I wish to all that is holy that I would have spent the extra 5 dollars to get the 250ma version. This gives you headroom should you switch to KT88s down the road. I have a 193J choke, and it is fantastic, however once again maybe 5H at a higher current would be a better idea.

I personally would go for the EDCOR XSE25-8-7.6k. Now with 8 ohm speakers, this would put the EL34s at a robust 7.6k, which has its advantages, a higher dampening factor, and a little less distortion, it reduces your power out, but its well worth it (My El34s run at 10k on the primary

As well the XSE25-8-7.6k gives you "10 watts" of extra Iron to saturate which will help with bass response. As well, Should you fancy a pair of 4 ohmers (as I currently do). It puts the primary at 3.8k, which is low, but not unheard of for the EL34.

In reality speaker impedance varies vastly as a function of frequency. So the values of primary impedance are ideal.

But Your plan looks great, it just needs a little tweaking
 
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