DIY vacuum tube audio

[rcavictim]

DIY speaker design/building and tube amplifier design/build are a hobby I'm into in a serious way.  I could turn this into a cottage business if I were so inclined, which I'm not.  For anyone interested in tube audio I thought you might like to see an article I published in a Ontario Ham radio club publication on a single ended triode, Class A2 stereo amp I designed and built a few years ago.  I have come up with some very, very good amplifiers and speakers which I use at home through the DIY route.  My high efficiency speaker designs which I call UltorTM and Ultor-XTM, are uniquely my own and I'd put them up against speakers that sell for $100k even though I was able to accomplish amazing clarity and range with low cost drivers.

The tube amp article is found starting on page 8. here,

http://www.barriearc.com/Newsletters/BARC%20Issue%202007-3.pdf

If there is interest I'd like to recommend to the The Management that we add a new forum topic area to cover discussions about our membership's 'other' technological interests.

[mike90045]

Brass, walnut, glowing filaments. So Cool!

[clytle374]

Very nice work, I'm jealous.

I've looked around for a tube shortwave receiver kit, know of any affordable ones?

[rcavictim]

Very nice work, I'm jealous.

I've looked around for a tube shortwave receiver kit, know of any affordable ones?

You are about 40 years too late I think to find one of those.  Heathkit was your last likely hope.  There are still plenty of decent tube technology HF communications receivers available at Hamfests and on ebay, etc., just not likely you will find an unbuilt kit.  You could find a construction article in a 50's or 60's issue of the Amateur Radio Handbook, but that represents an enormous amount of work, not the least hard will be sourcing some of the coils and other scarce parts, then you need some basic RF bench test gear with which to align it.  I have all this necessary test gear and copies of the referred to handbooks but I'm likely too far from you to be of local assistance.

Thanx for the complements on my amplifier.  I have attached a picture of my large highly DIY'd amp showing the tubes visible with the safety cover removed.  The large tubes are 300B's middle rear and 805's outer rear.  Further discussion and a photo with cover on is shown later in this thread below.

[clytle374]

Just thought I'd ask about the kit.  I've got somewhat of an electronics bench, but it's all still in boxes since I don't have room yet.

 

[dubbleUJay]

rcavictim, great looking amp in the newsletter.
I always wanted one, but the key factor was/is always the output transformers.
You said in another thread that there are ways to get around the tx's, do you have any "free" cct diagrams of one?
I might just eventually be able to get myself one of these then! 

Thanks,
dubbleUJay

[Jedon]

Wow that's awesome! It sounds like your speakers are huge, funny to have a tiny amp to power them! I have plenty of room, I want some large speakers and a big amp for my home theater. Maybe build woofers into the floor?

[Henry W]

Here is a good site if you like to get into World Class DIY high end audio. This is where I started almost 10 years ago.
I belong to an audio club that is hosted by Kevin Carter from http://www.kandkaudio.com/

I built a few differant Transformer Coupled, Push Pull, 300B Mono amplifers.
My current ones are rated at 16 Watts Triode Connected. I tried to post pictures but I think the forum reached its limit. I will try later. The amps are a little dusty but I think you guys will like the pictures anyways.

I am thinking of using GM-70 Russian tubes in my next Amps. But 900 to 1200 volts for the main power supply is very serious. It is a big jump from the 500 volt power supplies in my 300B amps.

Here is Kevin Carters forum for high end audio.
http://www.audioasylum.com/forums/KandK/bbs.html

rcavictim, You should contact Kevin. I think you both would have lots to talk about. He is a great guy.


Henry

[admin]

give it a try again Henry, i have expanded the download space so it should allow more pictures to be
uploaded.

admin

[Henry W]

Thanks Admin.

[rcavictim]

Here is a good site if you like to get into World Class DIY high end audio. This is where I started almost 10 years ago.
I belong to an audio club that is hosted by Kevin Carter from http://www.kandkaudio.com/

I built a few differant Transformer Coupled, Push Pull, 300B Mono amplifers.
My current ones are rated at 16 Watts Triode Connected. I tried to post pictures but I think the forum reached its limit. I will try later. The amps are a little dusty but I think you guys will like the pictures anyways.

I am thinking of using GM-70 Russian tubes in my next Amps. But 900 to 1200 volts for the main power supply is very serious. It is a big jump from the 500 volt power supplies in my 300B amps.

Here is Kevin Carters forum for high end audio.
http://www.audioasylum.com/forums/KandK/bbs.html

rcavictim, You should contact Kevin. I think you both would have lots to talk about. He is a great guy.


Henry

Henry,

Nice job there.  I like the damper tube bridge in the back.  IMO that is the better way to do a delayed B+ supply.  In my amp the 5V4 provides the delay portion of a hybrid bridge.  Are those 300B's the Kron ones that cost as much as a car?  P-P triode is a very good low distortion format while offering improved power and efficiency.  Who's output iron did you end up using?

BTW, you wrote,
"I built a few differant Transformer Coupled, Push Pull, 300B Mono amplifers.
My current ones are rated at 16 Watts Triode Connected".

Triode Connected? How else could you possibly wire a 300B?    

For the benefit of our readers, a 300B is a large glass triode that was invented early in the last century and used in the very best theater sound system amplifiers of the era by a company called Western Electric.  This very good sounding tube only makes about 7 watts max in single configuration so in order to get adequate SPL's (Sound Pressure Levels) needed for large theaters very high efficiency and subsequently large horn loudspeakers were developed.  Such speakers are capable of very low distortion.  They have been re-discovered by audiophiles in the past 20 years or so with the Japanese who call themselves 'audio maniacs' discovering and promoting their virtues early in the game.  The use of a single triode output stage in what is called class-A can have a almost magic tone and clarity that it's fans love. The old triodes that emit electrons directly from an open wire filament rather than a sleeved cathode, and light up like a light bulb are considered to have an extra magic quality to their sound.  The mechanism for this is not clear but I have heard it and my amp was built based on these DH tubes for this reason. The Japanese love of this triode sound when used with highly efficient WE loudspeakers.  This led them to start buying up all the old theater speakers from North America and related WE amplifiers, tubes and related paraphernalia.  This phenomena spread around the pacific rim to other Asian countries.  By the time North American audiophiles caught the SET (Single Ended Triode) bug most of the vintage theater amp and speaker equipment had already been sold out from under our noses to overseas and now there is precious little left here to be had.  Sound familiar?    Prices have gone to unreal amounts for some of this stuff.  An original WE 300B tube can sell for upwards of $2k US a bottle, and some plywood horn speakers sell for $20k US each without the driver component that generates the sound.  

The triode output tube I used in my amp described above is similar to the 300B in power specs but is a WW-II era industrial transmitting tube which is pretty much not yet 'discovered' by the audio crowd.  As such guys like me can still afford to buy them.  One of the popular challenges to modern tube afficionadoes is to try to find by experiment, off the beaten track transmitting and TV type tubes that happen to work really well in audio amplifier aplications but were never originally designed for that service.   My 809 is such a tube.  This is helpful with the world's stockpile of old stock vacuum tubes getting more scarce.  There are newly manufactured tubes for guitar amps and hi-fi being made again in reopened tube plants in the former Soviet  bloc countries and China but they are generally not up to the very high quality standards that were applied to the tubes made the first time around.  They are short lived and unreliable in comparison with few exceptions.  This puts extra pressure and higher prices on increasingly scarce NOS (New Old Stock) vacuum tubes.

Seeing the market for hi-end tube amps re-emerge in the 1990's a number of Chinese companies have risen to the demand and there are some very fine amps now available, some junk too.  The prices on the good stuff are actually very good.  I bought a couple from MingDa and I am very pleased with what I have although one has been completely customized by myself with a complete replacement of the original power supply and a new larger custom cabinet to hold all the extra transformers and capacitors needed in the upgrade.  This amp now weighs about 130 lbs. I have attached a photo of my handiwork. That hard maple case has 18 coats of hand rubbed black and clear lacquer piano black finish.  The inside is all copper lined.  Much labor of love in that project!  Henry, it uses 300B's as cathode followers to drive SE 805's.  B+ is 1060 volts.  Each tube dissipates 120 watts, the max CCS rating for an 805. I use vintage RCA, Westinghouse or GE output tubes. Sound is wonderful and 40 watts RMS is available.  My 300BC's are Chinese carbon plate from Shuguang. They have been totally reliable.  I bought some ElectroHARMonix  gold grid 300B's and they are garbage.  Grid to heater shorts on 2 out of 3.

Sorry for the ramble but some here might find this interesting history.

I am active over at DIYaudio.com.  I have a couple of friends who frequent the ETF (European Triode festival) just held as a matter of fact.

Henry your plan to build around the GM70 is a good idea.  These have caught on recently. A friend is embarking on that route now as well.  I am going to be trying an amp using 813's in the future and I have also gathered the parts to build a big monoblock subwoofer amp using a pair of 450TH eimac transmitting triodes.  B+ will be in the 2000-2500 volt range (output xfmer insulation limiting factor).  I have determined that a single large vintage Hammond plate xfmer which fortunately has followed me all across country on a number of moves since I was in my late teens is suitable to serve as a 1 kW to 8 ohm output xfmer with good fidelity to beyond 10 KHz.  It should work well in this limited frequency application.  This project is a bit over the top but it gives the artist in me a chance to sculpt another piece of performance art and would make a great space heater in the living room in the winter time.  I need a way to convert all that free electricity I'm gonna be making from the wind into heat.  

The picture of tubes below are L to R. KT88 (common high power hi-fi tube), 805, 833A, 450TH.  There is a fine 150 watt monoblock amp from Japan called the Wavac that uses the 833A. Price?  Don't ask.

Good luck with your GM70 amp and let us know how it goes.  Thanx for sharing.  Any other tubeophiles lurking out there?

P.S. Just had a peek at your audio club website.  I recognize several of the names.

[mobile_bob]

when you get to where you can't find that much needed tube, there is always this

http://www.youtube.com/watch?v=9S5OwqOXen8

always fascinates me how some guys won't take no for an answer!

bob g

[Mad_Labs]

Nice looking amp! RCA, have you ever made a Plasma Tweeter? I have made one small one and have the tubes to build a larger pair. It's the sweeter tweeter!  Bummer is I live off grid now and just the wattage of the heater makes me wince. I also have some nice glass to build a Tesla coil as well. Just got my sisters 1934 Atwater Kent going again, but it still needs more caps replaced.

Jonathan

[rcavictim]

Nice looking amp! RCA, have you ever made a Plasma Tweeter? I have made one small one and have the tubes to build a larger pair. It's the sweeter tweeter!  Bummer is I live off grid now and just the wattage of the heater makes me wince. I also have some nice glass to build a Tesla coil as well. Just got my sisters 1934 Atwater Kent going again, but it still needs more caps replaced.

Jonathan

Thanx for the compliment on my amp.  The output of a vacuum tube Tesla coil may be modulated the same way an AM broadcast transmitter final can be with audio for interesting sound effects.  I have done this in the lab many times.  I have built a number of vac toob TC's and still have a lab prototype on one of the benches ready for demo.  It uses three 810 transmitting triodes and makes a brush discharge about 16" long.  I made a magnifier type TC once on the bench using a 833A and got 22" brush discharge with a microwave oven power xfmer as the power supply.  This and an 833A was a super performer!!!!  Picture attached.  That pair of RCA broadcast transmitters I mentioned in another post furnished parts to make a 15 kW vacuum tube power oscillator that ran at 100 KHz and could be coupled to a tesla coil resonator.  That was quite fun.  I also made rotary spark gap driven, pole pig powered disruptive discharge TC's for a few years about a decade ago, some ending up in commercial use.  My very first big prototype and still my largest single resonator machine sits quietly in a corner of my lab. I haven't fooled with it in many years. It can throw an 18 foot long lightning like discharge into the air. Pretty awesome to behold close up! Yikes.  

I have not yet built any plasma tweeters but have studied them.  That is another project I'd like to find time to pursue someday but larger than just a tweeter so as to bring the sonic excellence of the plasma transducer down lower in the audio range.  I hear you about the off-grid and power hunger issues of some vac toob projects.  My 805 SET amp draws 400 watts from the mains.  That clearly impacts air conditioning load in the summer, a time when I don't use it.  In the winter it is a welcomed heat source however.

[Henry W]

Hello rcavictum,

The tube manufacture is KR Enterprise in the Czech Republic. Back in 2001 The audio group I belong to got a great deal from KR. I got two matched pairs four $400.00!!! I believe at the time they were going for $800.00 a pair at tube dealers. So it was a big savings. I have been running them since 2004 almost every day and they are still very closley matched. Great tubes. They make Western Electric 300B tubes look like whimps. They sound different than Westen Electrics. Sounds like KR's has more guts (Dynamics), Very deep bass, Great detail yet not harsh at all. I like the sound of the KR's better then the WE tubes. But from I remember in listening sessions WE tubes have there place and that is vocals.

As you know lots of it is in Amplifier design, Speaker design and Line stage. My CD player is a Marantz CD6000OSD not a very high end CD player in my book but it is ok for now. I been working on a new line stage with DAC built in for 2 years. Someday I will get it done. Speaker Cables are bi-wired 12 ga. romex. I had some people laugh at my system when I bring them over to listen. But when I start playing CD's there jaws are on the floor. One person said he never heard anything like it in his entire life. He listened to $56,000 + audio systems and he said they sound like Sh*t compaired to mine.

Well back to the Amps. Your right with your coment.  How else could you possibly wire a 300B? I guess I was not thinking.

I guess I did not do to bad not having an electronics degree. I knew nothing about electronics 10 years ago. All I learned was from people in the club I belong to. Kevin has been a great instructor and he makes us students think.

I also like the 6CJ3 damper diodes. They are pretty much indestructible, last a long time, and cheap!!!!
I was goint to use a hybred design but I have a life time supply of 6CJ3's so I decided to keep it simple.
I also think slow turn on is most important for tube life.

I also found a good stash of nos Novar tube sockets back in 2001. I guess I was lucky.

All stages are transformer coupled. I will see if I can post the schamatics. The tubes are as follows: The input stage tube is one 6SN7.  Two 6BX7's for the interstage. And two 300B's.

The reason I went with two 6BX7's is it was hard at the time to find perfect matched pairs. We thought it was easier to match tubes this way. So all I am using is one side of the 6BX7.

The chassis was my own idea. Back when I first started everyone was venting there chassis to displace the heat from the cathode bias resisters. I ask Kevin about making the chassis out of all aluminum and heat sinking the resisters to the chassis. We figured out roughly the surface area needed and I ran with the idea. The chassis frame is made out of 4" 6161-T6 Channel tig welded and machined on a bridgeport type milling machine. Top of chassis is 7000 Series heat treated 1/4" aluminum. The bottom plate I think is 0.90" 6160-T6 aluminum.
Well the idea worked out fine. Running the amps 24 hours a day and it only gets warm to the touch. The finish is a silver hammerite powder coating.

I had absolutly no problems with them. All I ever done was miner upgrades like constant current sorces and Jfets.

If I get a chance I will open one up and take pictures.

Speakers will have to be another time though. Oh, the speakers are roughly 92db. effecient, biwired with external crossovers.

I would like to go on but it is getting late. Here is info where you can read about the ME-2 speakers and Ariel crossovers that I built.

http://www.nutshellhifi.com/Ariel.html#index
http://www.nutshellhifi.com/ME2txt.html#me2
http://www.nutshellhifi.com/Arieltxt2.html#top
http://www.nutshellhifi.com/Arieltxt2.html#xt
http://www.nutshellhifi.com/Arieltxt2.html#top
http://www.nutshellhifi.com/Arieltxt1.html#hota

Check out the PDF file below. It is the prints for the ME-2 Cabinets.


I will check out DIYaudio.com

Take care,

Henry