3A/167-801A Single Ended amp.

I must have built nearly a thousand preamps and maybe a hundred power amps when I was doing Supratek. 

Most of the power amps were push pull amps , the single ended amps I built were mostly using 6C33C-B Russian "Mig" tubes that are able to output 15 watts with low output impedance.

                                             Merlot 15Watt 6C33C-B single-ended amplifier.

15 watts is a good compromise for the majority of speakers . The lower power DHT tubes like the 300B, 2A3 , 6B4G, etc will drive a lot of speakers but with serious compromises in regards to dynamics , response , etc when asked to drive speakers that need some oomph. 

If you are going to run these low powered amps you need speakers with very high efficiency , at least 90dB , preferably higher .

Now that I've retired I've found myself with a lot of NOS tubes and some very good output transformers , and time on my hands. 

So here is a description of what will be most likely my last build of a Single Ended amplifier- an amplifier I'm going to throw everything at , and will reflect my many years of tube audio. 

I'm still very much in awe of SE amplifiers, the hype about their superior sound quality is quite true, and there are good technical reasons for it. 

BUT, you need a very good high-efficiency speaker , that is accurate, transparent and is an easy load for the SE amp. 

Or maybe use a low power SE amp to drive a high efficency mid or full range driver in an active 2 or 3 way system. 

(Use a high power tube or sold sate amp to power the bass drivers, as I do with my Open Baffle speakers.)

An 85-90dB  speaker will not bring out the best features of a SE amp - you will be better off long term with a DHT push pull amp built to the same level of quality .

The heart of this new amp build is the Tango X-10S output transformer (OPT) 

I swapped some original 1930's Western Electric 300B tubes for a pair of original Hirata Tango X10-S opt's many decades ago with Nobu Shishido , a highly regarded Japanese tube guru . 

The X-10Swas designed to be used with 211 and 845 DHT tubes, and I built 3 or 4 versions using these tubes and the X-10S

Then the opt's sat on a workbench for maybe 20 years . I was going to sell them- you see them advertised for ridiculous prices , but I kept them as I regarded them as state of the art devices even though they were +40 years old. 

The original plan was to use them with Australian manufactured 1930's VT25's, which weren't VT25s at all , but very close substitutes to British DET 25 and CV1025 tubes, able to take 1000 volts on the plates and probably a very good match with the X10-S ( there are no datasheets for the ancient Australian VT25)

However, much to my dismay I discovered that the filaments of these tubes were all open circuit , and no amount of careful surgery could fix them. 

There's not many tubes that work with the Tango X10-S primary impedance of 10Kohms. 

The 211 is the ideal tube to use with it, but I dont really fancy working with 1000+ again volts at my age. 

Most DHT tubes use 2kHz - 5Khz  opt's . But the equally ancient 10, 10Y, 801A and the American VT25 all need a high impedance opt , so I decide to use 801A tubes .

In Class A1 an 801A can give a maximum of 3-4 watts output with a plate dissipation maximum of 20 watts. 

However, with interstage transformer coupling between driver stage and output tube , and with fixed bias in this circuit, it can provide around 6 -7 watts deep class A2 , at the onset of clipping . 

Plate dissipation goes above the maximum at 22watts,  but these values tend to be conservative, and I have plenty of 801A tubes. 

I tend to prefer single tube driver stages for my SE amps - they have a purity that seems to become veiled with multiple tube driver stages.

You need a high gain tube , but it also has to have the swing and current to drive the 801A tube. 

The later generation frame grid tubes such as the 7788, D3a, E280F, 417A, 437, 6E6P, and others are all suitable tubes to use with transformer coupling , and I have used all of these over the years with the Sowter interstage transformer. 

But the finest driver tube I've used with the Sowter 8423 interstage transformer (IT) is the very rare and very expensive STC 3A/167  tube. 

The 3A/167 has enormous gain,  tremendous drive and works perfectly with the 5K:5K impedance of the 8423.

The measured 1kHz square wave is just about as good as you will get with a SE amp , and even more impressive as there is zero feedback used in the amp. 

A word about measurements , and square waves in particular: 

Measurements do not define the sound of an amplifier in absolute terms, but they do give a very good indication of how an amplifier is performing in a technical sense , and  provide real clues to the sound quality. 

A 1khz square wave will give you an enormous amount of information if you have the experience to understand the wave form. 

A perfect square wave does not exist , but its not too hard to get it looking almost perfect with a solid state amp loaded with lots of feedback , like this. 

The lean, tilt (either way) slope of the top edge (either way) , the roundness of the corners , the degree of roundness of the corners , ripple on the leading edge corner- these all mean something , and with a lot of experience , and knowledge of the circuits and components , you can pretty much tell how a tube amp is going to sound , within reason. 

Its a bit trickier to get a tube amp design with a perfect square wave, and in truth you really wouldnt want to. 

Tube amps have lots of resonances from the transformers , the capacitance , inductance and reactance interactions, and these all add up to bend the square wave out of shape , or more correctly into the shape of the response.

Have a look at this square wave:

Its taken from the measurements of a $350,000 dollar amp reviewed in an American audiophile magazine.

Frankly it's a shocking result , and I would be ashamed to sell an amplifier with this sort of response- it indicates a severe bass problem , and I would imagine it would be just about unlistenable if you were half interested in an accurate presentation.

In fact, its so bad I suspect the amplifier may have been damaged , or the measurer made a huge mistake - I cant imagine a third of a million dollar amp could be this bad. 

Again, you can "fix" some problems with feedback, but there's a heavy price to pay for that.

Back to the  square wave response of the 3A/167-801A amp.

No feedback , there's a bit of ripple on the top leading edge , which indicates  a little bit of peaking at high freq >20Khz , but  it wont be audible , and can be adjusted to suit the ears with a damping resistor on the interstage secondary. 

Its nice and square , and indicates a very flat response from well below 15Hz to above 20khz. 

Its not perfect, but a perfect square wave usually indicates some , or a lot of feedback in a tube amp. 

This amp will have extended treble and a punchy , controlled bass . The Tango's are renowned for a nice midrange so that should be a given.

Power supply: 

The high voltage B+ supply uses UF5408 diodes in a CLC configuration, followed by a GZ37 tube rectifier used as a damper for a slow start.  All polypropylene caps, no electrolytic caps. 

The filament supply for the 801A is a voltage regulator , followed by a constant current source regulator for the 7.5V DC @1.25A . I find this configuration to be very quiet and it sounds better than a straight voltage regulator for DHT filaments.

The bias supply uses a voltage doubler CRC  configuration , followed by a 75 volt gas regulator , which is then in series with a pot for fine bias adjustment .

The 6.3V DC for the 3A/167 is a conventional voltage regulator. 

There's nothing revolutionary or special about the design - it's a good solid design that uses high quality components , is well built , performs very well on the test bench , is built to last a long time and be very reliable.  Each monobloc weighs 20kg. 

The components and tubes are worth over $5000 ( the Tango X10-S and tubes are very expensive) so to build this as a commercial venture would not really be viable .

I don't subscribe to the ridiculous prices amateur and AI guided unprofessional builders are trying to extract from ignoramuses these days. 

If your going to buy an expensive amplifier make sure its built by a person or company with many years of experience , and the cost reflects the components and engineering in it. 

Ask for a set of measurements , ask lots of questions - use the same thinking you would use to buy a car . Dont rely on forums or AI for unbiased facts- you'll only get opinions or rehashed info that means nothing.

Sound of the 3A/167-801A 

It sounds very much like a 211 SE amp , with a lot more grip and power than its 7 watts would suggest.

Its rich and organic sounding, very good bandwidth , but still very realistic and natural sound. 

They have turned out pretty much as I hoped for , and I'm enjoying them very much.

They have Supratek badges on them, but I'm retired now and not making any more power amps , these are for my personal use only. 

Update / 6B4G/302B Single Ended Amplifier.

 I'd like to thank all the people who have sent me good wishes the last year ,  its been very appreciated .

My lastest scans have shown the cancer is stable , and while I have mostly good days , its nice to hear from such nice people on the other days.

It's also been very humbling to hear how so many people are enjoying the Supratek products. I've had messages from across the globe, from New Zealand to Russia , from people who say the Suprateks have enriched their audio lives , and take great pride in owning a Supratek. 

One recent conversation was with a chap who has owned his Supratek since 2007 and is just now replacing a set of tubes - that's pretty good  going in 20 years.

He says he's tried many preamps costing many multiples the price and yet to find something as enjoyable.

That's a common theme- long term ownership that continues to deliver enjoyment from music. 

You can tell I'm quite proud , but it's also been an honour to be able to do this for so long , and to meet so many good people along the way. 

I've just started another preamp build , and while its a long process now , I hope I can make a few more people owners of Supratek preamps.

While I'm still enjoying the Lii Audio F-15/JBL2226/Raal 20-70XR ribbon OB speakers, I did have to spend a fair bit of time finding an amplifier to suit the Lii Audio F-15 driver.

This is what I finally decided on: a 6B4G Single Ended, with options to use the AVVT 302B tube.

The 6B4G tube is not the typical double plate usually used in SE amps, but the Sovtek single plate that was available back in 1990, or even earlier.

It's not a true 6B4G, it has a much bigger plate structure , possibly the 300B Sovtek plate.

It has a plate dissapation of 40 watts, much more then the double plate 15 watt maximum.

It can take a plate voltage of over 400 volts, and current of 100ma (not at the same time!)

 It has a clear, slightly warm tone , but without the tubby , somewhat congested tone that 300B tubes can suffer from.

The driver tube is also Russian, the 6E6P , a high transconductance, high gain tube in triode connection.

I like the single driver configuration when using a preamp, just have to be sure the driver tube can swing enough voltage to get full power from the output tube.

I've also set up this amp so it can use a pair of veteran AVVT 302B tubes. These are "super" 300B tubes, capable of much higher voltage and current than normal 300B tubes

Also higher power, and a cleaner, more engaging sound than typical 300B tubes, which frankly I find quite boring. ( I sold a big stash of original WE300B tubes about 30 years ago - no regrets)

To use both 6B4G and 302B I had to install a switch to change filament voltage, and adjustable fixed bias supply to suit either tubes bias requirements.

The bias supply is regulated with octal gas regulators- 75 volt OA2 for the 6B4G and 105 volt OA3 for the 302B. A simple pull and insert , adjust bias and a different amplifier!

As the 6B4G is an octal tube and the 302B is a 4 pin, I had to make a 4 pin to octal adaptor to use the 6B4G in the amp.

The driver tube has its own shunt regulater , using 6L6 tubes. 

I like regulated power supplies - they dont have the warm tubby sound of ancient tube designs you see everywhere these days , but a solid, detailed, yet natural tone that has significant depth and width .

The Lii Audio F-15 is a very fussy driver that needs a very good, very capable amp. 

LATER: 

After a couple of months of fine tuning and some minor design changes I settled on using the AVVT 302B tube exclusively in this amp. 

The extra power is handy, producing about 1.5 times the power of a 300B , but it is better tube for the sound I want from the F-15.  The 302B also lasts forever as it is just idling in this design. 

Taming the Lii Sound F-15 Coaxial.

 

The Lii Sound F-15 Coaxial driver must be the most perplexing driver I've ever come across.

It's sold as a full range driver, and the ears and measurement confirm it's doing a reasonable attempt at that, but its seriously rolled off both in the lower bass and upper treble.

But despite that it has a extraordinary ability to sound quite interesting with exciting dynamics that makes the sound literally jump out of the drivers. 

It sounds much more efficient than its rated dB . Its just an excited driver, extracting a lot more information than you'd expect from a 15" driver.

BUT, part of that excitement comes from a far from flat frequency response. It's nothing like the response graph provided by the factory, which is pretty much flat.

The F-15 has a huge boost and plateau from 6-8Khz , and a dip around 2Khz. 

This is hardly what you'd call hi-fi, although I suspect it might be something approaching the inverse of what a lot of older guys with limited hearing loss have.

Maybe it is a quite clever marketing ploy by Lii Song - give all the old hi fi guys a driver that restores their old ears , a sort of giant hearing aid?

Is that too skeptical ? 🤫

Nevertheless, despite it being quite interesting for a while, the brain/ear interface is too clever to be fooled for long , and the F-15 soon starts to sound a bit too detailed and eventually quite shrill.

It's too inaccurate to be called even remotely "hi-fi" , and I'd call it a novelty driver not to be taken that seriously.

Still I did recognise something in it that deserved a bit of work to see if it could be brought to the fore.

I was using a JBL 2226 15" bass driver under the F-15 for bass enforcement , but the problem of the brash upper mid/treble had to be solved.

First thing I tried was a notch filter , but that was mostly ineffective- the plateau is just too broad and high to be tamed by a notch filter , and I've never liked using them, as they can often do more harm than good .

Then I tried a low pass filter around 6Khz to see if would generate a reasonably flat response - it worked better than the notch filter, but still not the smooth response I was after.

Looking at the raw response, it really is quite hopeless and it was then I decided I had to totally remove everything above 2Khz , and use another driver to fill in the 2Khz-20Khz response.

I eventually settled on a 2Khz 2nd order low pass filter that worked satisfactorily , if not perhaps perfectly.

There's still a bit of a boost at 6Khz - it really needs a 24dB 4th order crossover, which I will build. 

Interestingly the values I used - 0.82mH and 9.4 uF are nowhere near what the crossover calculators suggest, but measurement confirmed they are reasonably close in achieving the desired roll-off.

Now I had the problem of what to use for the 2Khz to 20Khz range, and more importantly would it work with the difficult F-15.

I had some horn tweeters I could try but decided to try a pair of RAAL 70-20XR ribbon tweeters.

I was worried that the directivity of the ribbons would clash with the F-15 , especially as I was using the F-15 off axis , to avoid some undesirable beaming. 

The RAAL 70-20XR has a very good reputation , and I've used it very successfully in other speaker designs. 

Its expensive at over $1000 each , but I believe it lives up to the manufacturer's sales blurb:

This model is somewhat different from other models. The ribbon of 70-20XR is wider in comparison to the others, which is indicated by its label. Ribbon is 70mm long and 19mm wide. Housing is made out of 8mm thick steel. At the bottom of the chamber there is an adapter transformer, which is completely covered with resin. Net volume of the chamber in between the transformer and the magnet is reduced with wooden tiles to the required level and that space is very precisely filled with sound absorbing material. In this ribbon, the filling is made of finest medical cotton wool from pure cotton. The strong neodymium magnets are the same as those installed in all other models except for the 64-10.

The transformer in this model is special, also wound by hand and completely handmade. The primary is wound with a copper wire with a round section and high purity, while the secondary is being wound with copper foil of a 0,1mm thickness in three layers. The transformer is special because it has 3 outputs: 6,3 ohms, 9 ohms, and 12,6 ohms. In this way, the user can choose which sensitivity fits the best. The outputs of the transformer can have other values which can be chosen by the user himself on special request.

The next feature that sets this ribbon apart from the others is that the ribbon is made like a sandwich. It’s made out of two layers of aluminum foil with a thickness of 8 microns, which is ironed and stiffened by a very demanding process. In between the two layers of aluminum foil a special grease is extremely precisely measured and applied, which has the role of soothing the ribbon in an even shorter time after the impulse stops. This ribbon doesn’t have carrier foil made out of MYLAR, it’s in direct touch with air. This provides the smallest possible moving mass, several hundreds of times smaller than any classic DOME tweeter and far smaller than RIBBONS with a MYLAR carrier foil.

The result is shockingly rich, detailed, the sound image is unencumbered by any colorations.

The ribbon itself is fixated on the ends to the supporting frame via tensioners. After installation, the ribbon is being precisely tensioned in order to achieve optimal performance. In this model, the ribbon is the same length as in the 70-10 model. In all models, the first number indicates the effective length of the ribbon, and the second number indicates the width of the ribbon. Model 70-20 is user serviceable, which means that the user can replace the ribbon himself if necessary.

Like every other model, this one is characterized by exceptional openness, detail, spaciousness and depth of the sound image. The sound is fluffy, colorless, it will not hide or mask even the finest information read from the source.

However, I didn't really expect it to work optimally with the F-15, as they are such different drivers.

To say I was pleasantly surprised is an understatement; I was shocked at how well they integrated .

To be honest this is the most natural, immediate, and vivid vocals I've ever heard, and I've had half a century playing around with electrostatic, horns ,  planar  and just about every speaker you can imagine. 

It has the positive attributes of all these speaker types , without any negative attributes .

Excellent imaging and soundstaging , utilising the best of well mastered recordings. 

I would never have thought that the combination of a Chinese 15" co-axial driver and a Serbian ribbon tweeter would make such a grand musical sound. 

The F-15 does a superb job restricted to upper bass/midrange , and the Raal 70-20 XR fills out the treble in a splendid fashion. 

I do think that the Loftin White 6B4G/2A3 SE amp driving the Raal 70-20XR would be contributing to the beautiful, smooth sound , as it is a gorgeous sounding amp. 

Technical description: a Supratek Grange preamplifier with dual adjustable level outputs - one output for low bass and the other for upper bass, mid and treble. 

JBL 2226 15" bass driver used in open baffle configuration. Graham Maynard T-Bass OB EQ. Minidsp digital crossover 10hz 48dB high pass, 180Hz 24dB low pass. Carver solid state amplifier.

Lii Song F-15 15" co-axial driver. Passive low pass passive crossover 12dB 2Khz , reversed polarity. 300B/6B4G SE amplifier.

Raal ribbon tweeter. 10uF capacitor in conjunction with inductance of internal transformer forms a 12dB 2Khz high pass crossover , with 24dB acoustical crossover- see Raal website for more info. 6B4G Loftin White SE amplifier.

The dual outputs of preamplifier allows me to make fine adjustment of bass to mid/treble balance of each recording. 

There is no perfect setting of this balance as every recording is influenced by the quality of the recording , the mastering engineers perception , and various other influences.

I like being able to make fine and subtle adjustments to suit my system, room  and ears, rather than being stuck with one "suits all" option.

It's amazing how much difference just a slight change to the bass balance can make to the overall sound. 

So a very surprising and satisfactory result, that I'm enjoying very much. 

Always something to learn in this peculiar hobby!

                                                              JBL 2226 Bass response

                                                  JBL 2226 Bass, F-15, Raal 70-20XR

New Email Address - Updates

 micksupratek@gmail.com

After 25+ years of using supra@supratek.com.au as my email address , it has become cluttered with spam , which my current email provider is useless at removing.

This has led to missed and confusing emails , and I apologise if anyone has been disadvantaged by this.

I'm now using micksupratek@gmail.com as my primary audio email address.

Please take note and advise anyone you know who is in the Supratek circle.

On other news , I'm slowly building a few preamps - just finished a Dharma , starting another and then will do a couple of Granges, and a pair of Malbec power amps. This will likely take a long time, so no promises on orders. 

Dharma with NOS 6J5 tubes  and Power supply with NOS 6F6G, 5V4G tubes.

All are using genuine early 20th century NOS tubes from my tube stash , apart from rectifier tubes , which are becoming harder and harder to find.

I've also treating myself to some new power amp builds .  Designs which I've wanted to try for decades, but have been constrained by time and the demands of Supratek. 

These are the power amps I'm using in my system at the moment.

I've had a half dozen CV1076 (DA41) for at least 30 years, but never had the opportunity to do something with them.

https://www.r-type.org/exhib/aaa1214.htm

They are somewhat between a 300B and a 211 triode .  From the transmitting triode family with a thoriated tungsten filament , they have the same "lighthouse" radiation of the 211, 845 etc tubes.  They get quite hot, but look very cool! They were designed as Class B tubes for high power PA audio , but we want to use them for Class A high fidelity! 

The circuit was originally designed by a Japanese guy back in the fifties , and although not popular , quite a few Japanese and some Western tube diy guys have built modified versions of it. 

It uses a small power tube like a 6V6, 6K6, 6F6 etc as a cathode follower, with the cathode tied directly to the grid of the CV1076. 

This way it can provide a POSITIVE grid bias and deliver grid current to the CV1076 so that it can run in Class A2 . 6-8 watts .

It sounds glorious , makes 300B SE amps sound like mud. Has a real 3D soundstage, deep imaging and detailed but still very natural and organic sound. 

One of the best SE amps I've built , very happy with it. 

Of the "conventional" SE tubes, the 2A3 is probably the most renowned.  As Joe Roberts said, back in the 90's - I've never met a 2A3 amp I didn't like" .

My Loftin White 2A3 SE amp is another beautiful sounding amp- just the bees knees for female vocals and music that is not too complex and dense. 

I'll do a write up of that later, but here's a description of my 6B4G parallel push pull amp .

The 6B4G is the 6.3V version of the 2A3 - the 6B4G has 6.3V filament v 2.5V  of the 2A3. 

This amp has seen many variations as I've used it as a test mule for various driver stage designs. 

This version I've made it as simple as possible - one driver tube , an interstage transformer and the output tubes and transformer. 

The driver tube is the Russian 6E6P - a high conductance/high gain tube with low impedance that can swing a lot of drive volts . The Inter-stage transformer is 1:1+1 and provides more voltage than the 6B4G will ever require, and will easily drive the 6B4G stage into Class AB2. 

The 2A3/6B4G tubes have very high transconductance and require separate biasing for both phases of the push pull output stage.

In addition, the output transformer is a toroid design , and they dont like any imbalance between the two primary windings . With the separate cathode bias configuration, balance between the windings can be adjusted as low as 1 mA .

This amp starts to clip at 20 watts , which is far more than my high efficiency speakers need, but it has good solid bass , and the typical 2A3/6B4G sweet sound. 

Such a simple circuit gives an unencumbered , pure sound . The interstage does produce a bit of ringing , but the typical loading to reduce it does more harm than good , its minimal, and virtually inaudible. 

6B4G PPP amp. Monoblock - one channel. A bit untidy but it has been many amps over the years! 

I've had some rare and very expensive Tango X-10S output transformers for at least 40 years.  

These were most often used for 211 tube SE amps and sometimes 845's, although the 10K impedance is a bit high for 845 tubes.

I made a number of 211 amps with them,  and then they sat on the shelf for a good number of years. 

I found some very ancient VT25 tubes in my stash, that were used in aircraft radios post WW1 .

I realised that the VT25 tubes and the Tango OPT's could be used to make a very nice Class A2 6 watt SE amp , with a 3A/167 (WE437) tube driving an interstage transformer.

This build is underway, but will be a long-term project - I'll do another write up when it's finished.

                                                   Initial Circuit design VT25 SE Amp

The Loftin White circuit goes back to the 1930's , nearly a hundred years old! It was pretty much forgotten till the Japanese DIY guys started using it again, around 1970.

It's an all direct coupled circuit, no capacitors between stages. It's tricky to set up , but sounds great. 

It really works well with the 2A3 tube , highlighting the purity and beautiful tone the 2A3 is capable of. 

It needs a single high gain driver tube, the 12AX7 is often used , but the octal 6SL7 is a true audio triode and sounds much better .  The ancient 6SF5 is also a good choice.

Not much power, you're lucky to get 3 watts from it, but you'd be hard pressed to find a more intoxicating and beguiling sound.

Simple 6SL7/6B4G Loftin White SE amp . Power supply not shown.

SUPRATEK IN 25/26

UPDATE JAN 2026

So what is happening with Supratek ? 

In 2023 I was diagnosed with neuroendocrine cancer - Grade 3, Stage 4 . Metastasised to liver and bones , so, at the moment uncurable .

I underwent some pretty serious chemotherapy and radionuclide therapy and am now stable for the moment.

I'm feeling quite good, but have retired .  

I'm trying to get the last orders for preamps done,  and am still available for repairs in Australia and Asia.

Johhny Slate in North Carolina can be contacted at supratekrepairusa@gmail.com for repairs and all things Supratek in the US.

I'm enjoying life , listening to music , keeping fit and building the occasional piece of audio equipment to keep my hands and mind active. 

After nearly 50 years of audiophile nonsense, I have quite a collection of audio equipment and parts.

Amplifiers, speakers, speaker drivers, preamps, transformers( power, output and interstage), components etc. Thousands of audio tubes. 

Too much and I want to clear my workshop of most of it.

I'll soon begin to list it all on this blog , so keep an eye on this page .

It will all be at bargain prices - I've had some of these goodies for a long time and I'm not aiming to make a profit on it, so prices will be bargain basement - NOS tubes for $10  etc. 

Give me a good reason and I'll give it away! 

Please don't contact me before the lists go up, it's a big job and I probably won't reply while I'm doing it. 

Pix below of my end of game system - well that is what I tell myself, but it does sound great and I'm grateful for the time I have listening to it.

At the heart of system is the Grange preamp .

  Bass amp is one of Bob Carvers Load Invariant amps - I'm using a T-Bass device which basically gives sub woofer extension to a conventional bass driver in Open Baffe configuration. But its a 1-2 ohm load so need to use a solid state amp to get the necessary voltage - The Carvers can do that while sounding like a big powerful tube amp. 

The mid or full range amp is one of many I use depending on my mood or the season.  Single ended 6C33C-B , 300B, 6B4G or 6B4G , EL34 push pull amps.

The tweeter amp is a Loftin White 6B4G (my favorite tube) Single ended amp .

FOR SALE

I've an Ebay Store (Supratek) on which I will list items under these categories:

Tubes/Valves

Speakers/Drivers 

Preamplifiers

Turntable/Accessories

Amplifiers

Tube Audio Books

Transformers

And more as I uncover items. Rock Bottom Bargain Prices .  Make me an offer. 

Ok Lets start the list with tubes I have available for sale .

Minimum order is $AUD100 . Its not worth my time for less after testing and close matching for emmission , packaging and sorting etc.

Contact me with what you want and we'll sort it out.

supra@supratek.com.au

POWER TUBES

6G6G

6F6

EL32

7027A

6V6

EL34

EL37

6336

6AS7/6080

S12E1

S11E12

807

6K6G

6Y6G

DHT PREAMP TUBES

33

101

4P1L

6P2L

3A/110A

19

30

26

71A

DHT POWER TUBES

805

211

6B4G

801A/10/10Y

CV1076/DA42

830B

809

300B

OCTAL PREAMP

6J5 

6H9C/6SL7

6SN7

6F8G

5 PIN PREAMP

37

76

56

RECTIFIERS

CV187 

8020

3B28

VOLTAGE REGULATORS

OA2

OA3

9/7 PIN PREAMP TUBES

12B4A

6E6P 6E5P

6H23

5693

12AU7

6C19

5965

SV83

12AX7

6N2C

12BH7

12AY7

6J6

12AT7

6BQ7

6CM7

6GK5

6N1P

6AL5

417/5842

EF86/6267

6C4

6CB6A

6CW5

6211

6CW7

6BM8

6CG7

6U8A

6072

e180F

E810F

ECC88/6922/E88CC

5687

and more ..... 

Circuits

During the course of my 40+ years of audio (5 years to get to 50!) I've designed and built many hundreds and hundreds of preamps, power amps, speakers etc .

Of these, the prototypes were very exotic and dedicated designs , using all sorts of vintage and modern components , with design elements coming from the early 1900's up to the present day state of the art.

The amplifiers and preamplifiers I've released as commercial offerings have to offer great sound, but also have to be very reliable , and use parts and components that are, and will be available now and into the future. And I've always believed in a fair and realistic price , value for money , not the ridiculous prices many relatively inexperienced manufacturers hoodwink customers into paying. 

But I've always enjoyed pushing the limits with design and building - sometimes just to see what will, and wont work in the quest for sonic nirvana.

90% of these never get public attention - I'm somewhat of a "lone wolf" in audio, partly because of where I live ( the most isolated state in the world - and we like that just fine) and I mostly do this for myself, I'm not that interested in forums and handclaps.

But recently going through my files of circuit designs I realised just how many interesting designs I had stored over the years. 

Tube audio design seems to have stagnated a little over the last decade - I guess we're almost at the summit , and there's little that hasn't been investigated and tried. 

Early on in my audio career I was obsessed with finding the "best" amplifier or the best preamplifier and doggedly built device after device trying to find that holy grail.

After many years I came to the conclusion that there is no "best" . The ultimate goal is to find the sound that suits your ears, a sound that comes together with the synergy of all your components -sources , amps and speakers (and importantly room) that brings you satisfaction and joy . 

Enjoying the music - that's what it's all about eventually , and you dont need the "best" equipment or the most expensive equipment to get there. 

In that spirit I'd like to present some circuit designs that I have built and enjoyed, and even some designs that maybe didnt quite work out, but were interesting and were part of the journey.

This is mainly for the more technically minded audioholics , not everyone can make sense of a badly drawn circuit diagram, but maybe a little of the zen of tube audio design will come through. 

I'll put up photos if I can of the completed amps .

This will be ongoing and will eventually be a very long page, so keep checking back if you are so inclined.

Incidently , I have thousands of audio tubes , transformers and components collected over my long audio career.

I'll be putting up a list of these soon ,  for sale , at very reasonable prices - I've had them for a very long time , and wont charge the ridiculous prices some vendors are seeking these days.

Email if there is something your after, and no I dont want to sell any 300B, 45 or 2A3 tubes, but I do have many other fine audio tubes. 

The 6C33C-B tube and the Supratek Merlot SE amp. 

The 6C33C-b tube is perhaps one of the finest audio tubes ever released , although it was never designed for audio- it was used in the power supplies of Russian fighter jet electronics.

With a plate resistance of around 100 ohms , many times lower than any other triode , its relatively easy to design and build a suitable output transformer with very good bandwidth - its possible to easily get 10hz to 100Khz flat response , and I've built OTL 6C33C-B amps that got to 250Khz easily. 

But with that response comes very low output impedance , so that response can be transferred into a complimentary speaker with little or no feedback. 

A good 6C33C-B SE (single ended) will be very transparent and  detailed with high clarity . They are often described as being powerful sounding , for the power they produce , around 18 watts , but also with an elegance that is unique in audio amps.

They have drawbacks though- they produce a lot of heat , they need substantial power supplies, and they can vary quite a lot from tube to tube, which makes biasing them a bit of a chore, although there are ways around that. 

   

Tube curves- vey linear .

Supratek Merlot . I started building these in the late 1990's and turn of the century .

The first ones used 6SN7 or variants (76 ,6J5 etc) driving a 300B , which drove the 6C33C-b through an interstage transformer , in either grid or cathode drive. All the Merlots had a second 6C33C-b acting as a regulator for the power 6C33C-b tube. 

I built some using Plitron toroidial interstages and output transformers- these were fantastic transformers, and sadly no longer available - I'd love to get a pair of these amps back,  they would be prohibitively expensive to build these days .

Back then I also used transformers from Bob Lancroft in Sydney and Sowter from the UK. 

Later on I switched to using 6SN7 SRPP circuit to drive the 6C33C-B .  The SRPP driver isnt so fashionable these days , but its still a very capable and good sounding driver stage.

These versions had an even clearer and more defined sound , without the 300B DHT euphonics.

Here's an interesting design from Bob Lancroft - it's an interesting direct coupled drive stage .

This is a ideal circuit, no capacitors in the signal amplfication , but it would be a nightmare keeping it running consistently with the varying plate voltages , especially as tubes were changed or aged.

Very courageous and innovative design though - I like it! 

I then went on the build the high power and push pull Burgundy and Mondeuse monobloc amps . Also very heavy monster amps . Most had adjustable negative and positive feedback- they could be fine-tuned to drive just about any speaker. 

I will try to get some circuits of the push pull amps up onto the blog. 

One of the last Merlots I kept for myself , with quite a lot of mods I called it the Super Merlot , and I still use it often. 6EM7 input tube, 10Y driver  into 6C33C-B with a custom Sowter output transformer. 

It solved the biasing problem with the 6C33C-b as it used a servo that sensed the current through tube and adjusted for individual tubes and as the tube aged. 

( Its very handy to use a combination of fixed and cathode bias in 6C33C-b SE amps as it results in a more stable bias. 100R on the cathode ) 

The Super Merlot is here somewhere on the blog , I'll try to find the link. 

SATYA INTERCONNECT CABLES

 Over the many years I've been producing amplifiers and pre-amplifiers I've often been asked to recommend interconnects .

I tend to decline to do this as I just don't think there are a lot of interconnects that are either good value, or do what they are supposed to do. 

There is so much hype around interconnects and speaker cables- its possible to spend thousands on interconnects , for little discernable improvement in sound quality.

There are some preposterous claims made for some of these expensive cables , and they can certainly sound different .

Mostly because they have been engineered to act like a filter or tone control , but this is not the purpose of a good interconnect.

A good interconnect will let the signal through and do nothing more and certainly nothing less. 

It will allow the excellent frequency and phase responses of a good preamp to travel unhindered through to the power amp , with no detraction or addition to this signal.

It will be quiet ,  providing a barrier to any external hum or interference.

Presenting the Supratek SATYA interconnect , a high quality, high value interconnect that will do exactly what it should do , maintaining a perfect transmission between preamp and power amp.

The SATYA is constructed from a twisted pair of teflon jacketed, solid core , silver-plated pure copper cables. 

This is the same wire that I use in the Supratek preamps , so it will be a perfect match for the Supratek, and indeed any preamplifier.

 It has a copper shield over the twisted pair for shielding purposes and a plastic covering over the shield for durability. 

Quality Amphenol connectors. 

                                                                   Construction detail

                                                                  

The SATYA will match any cable for performance and will be a great partner for your Supratek Preamp. 

Aligning with the Supratek reputation for extraordinary value for money the SATYA costs $100 for a pair of 1.2 metres cables .

Also available in custom lengths at an extra $10 per 150mm extension.

Also available in balanced XLR configuration.

Please send email to supra@supratek.com.au to order. 

 

DUAL GRANGE WITH 12SX7 TUBES.

 The 12SX7 tube is a 6SN7 with a 12 volt heater , as opposed to the 6SN7's 6.3 volt.

Its been tested to have the lowest distortion of any 6SN7 , and sounds very good, with attributes beyond current production 6SN7 tubes, and amongst the very best NOS tubes.

I have a stash of unopened General Electric 12SX7 tubes, enough to build 4 Grange preamps with spares.

The first one will be a Dual Grange. This configuration has two line level outputs, both with the famous Supratek quality. 

This enables the use of a subwoofer, or for use in a bi-amp system.

As an example, one of my systems is a three way, with a 15 inch bass , a midrange horn and a tweeter horn.

The bass driver is driven by a solid state amp, which is connected to one of the Granges outputs, with level control to adjust gain.

The mid and tweeter horns are connected to the other Grange output, also with a level control.

The crucial mid range is driven by a wonderful 2A3 single ended amp, the tweeter with a small Class A solid state amp.

With a powerful amp on the bass , and a tube amp that is very synergistic with the mid horn i get the best of all sounds, and the abilty to do very fine adjustments to the overall balance , this is critical to getting optimal sound in each individual room, and to suit taste.

A master voume control sets the overall sound level.

Crossovers are passive on each driver, I personally prefer this to active crossovers, many speakers are bi-amp capable, which means the internal passive crossovers can be connected to seperate amps.

Ive been using this bi-amp method for many years , as  I find it is quite superior to one amp driving multiple drivers. Impulse or transient recovery speed is much improved. 

In such a system 2 or 3 reasonably priced amps will easily outperform an uber expensive high end amplifier.

The Grange preamp is built in a 1.2mm copper chassis with Australian Jarrah hardwood cabinets.

It has a state of the art tube phono stage designed for moving coil cartridges, which uses very high quality frame grid tubes designed at the end of the tube era - these are ideal for phono stages which need low noise and linearity. 

The line stage of this particular Grange uses 4 x 12SX7 tubes as noted above.

They are run conservatively,  and will last many years. A spare set of boxed tubes is included.

There are 10 expensive Lundahl transformers in the preamp, along with high quality components. 

The power supply is separate from the preamp and is the key to the superlative performance.  

It has a power transformer that is strong enough to power a big tube amplifier,  with seperate constant current source and tube regulation for each of the phono and line stages, so 4 in total.

40 years of tube design and build experience results in a tube preamp that is as fine as can be built , a custom built unit that will provide a lifetime of musical bliss.

This individual preamp will be available sometime in January 2024. 

Expression of interest to supra@supratek.com.au 

DHARMA LineStage

Just in time for Xmas '23 the time is right to announce a new Supratek product- the Grange Signature Linestage.

For the first time, a Supratek product won't be named after a wine variety - I've decided to call this preamp DHARMA, which is Sanscript for TRUTH . 

Appropriate I think , as this is the finest preamp I've built .

Based on the Grange Signature, the DHARMA is minus the phono stage, but has the same linestage circuit using 1944 NOS 6J5 tubes and the same power supply with constant current source tube regulated circuit.

The best linestage I've ever built, and the NOS 6J5 tubes are wonderful preamp tubes.

Combined with the Supratek Signature circuit , this preamp is warm and natural sounding, and yet still so insightful and revealing. 

Its the preamp to end your days with and the feedback from Dharma owners is very positive and rewarding.

Its only available with 6J5 tubes or if a Dual version is required (for biamping) it can be built with NOS 6SN7 tubes.

A spare set of boxed 6J5 tubes are supplied (4) which will last many decades.

SUPRATEK MERLIN

 Many years ago I made a Single Ended amplifier that bordered on the ridiculous. It measured  650mm by 650mm (one monobloc channel) and required two men to lift it. 

The text from my web site said:

"The V1505 and it's equivalent the 212E has been described as the ultimate audio valve. 
An imposing 270 mm high and 90 mm in diameter it is a spectacular tube by any standards. 
A valve of this quality demands  preceding driver stages and power supplies of the highest calibre. 
I decided that I would make absolutely no compromises in any way in the design and building of this amp. Each monoblock amplifier (two for stereo!) measures 650 mm x 650 mm. 
There are 5 power transformers, 4 chokes and 5 signal-circuitry transformers on each chassis. 
It is finished in hammertone silver and black and with the Ediswan V1505 valve alight is a beautiful statement of industrial art. 
It certainly causes comment and wonderment from all who view it.
CIRCUITRY  I chose what I believed would be the best valves for each section of the amplifier- a 3A/167(WE437) for the input stage( but recently went back to a SRPP 6SN7 ) transformer coupled to a 1930's vintage, directly heated 50 valve as the driver, transformer coupled to the V1505. 
I don't know why transformer coupling sounds so good; it may be the oldest method of coupling valves, but it's re-emergence as the premier audio coupling device is long overdue. (Thanks to Mr Shishido and Mr Sakuma) 
It has been suggested that transformer coupling's low harmonic distortion is partly responsible for it's sound. 
The output transformer is a Japanese Tango, very expensive- very good! 
The power supply uses four U19 directly heated rectifiers for the V1505 plate supply, buffered by a GZ37 in the ground rail for soft start. Another GZ37 provides voltage for the 3A/167 and 50 and a 6X4 provides adjustable bias for the V1505. Each V1505 and 50 can be kept in perfect bias with individual bias controls and meters."

It performed very well, both on the oscilloscope and to the ear, but it exhausted me building it, and it was so impracticable that I didnt build a matching monobloc for stereo.

But it was a good learning vehicle,  and I resolved to one day build a more practical version.

Over the years I assembled the parts needed and I am very close to putting everything together.

First, let me explain the naming of this extraordinary amplifier.

The amp uses very ancient and extremely rare tubes that were designed for and used by both the British Royal Air Force (RAF) and the Royal Australian Air Force (RAAF) as transmitting tubes in their military aeroplanes.

Around the same era, Rolls-Royce made the monstrous 12 cylinder Merlin motor which was famously used in the Supramarine Spitfire fighter airplane which figured prominently in the Battle of Britain during the Second World War.

The Merlin motor was used in other fighter and bomber planes and was even used in some USAF fighters, including the Mustang.

Putting  such a huge motor into the relatively small frame of the Spitfire really highlights the engineering expertise of that era, and explains the amazing performance of the Spitfire,  due to its very high power to weight ratio.

There are very few Spitfires still flying, and likewise very few of the tubes I'm using in this amplifier are now available,  so the name Merlin appeals to me .

This will be a long project , hopefully taking around 6 months to build, and I will do regular updates on the progress as I go along.

If you are interested in the truly exotic , and an amplifier that is so rare and unique that only one set of monblocs will ever be built , then please enjoy the journey.

So to start, the Merlin will be a single ended amp of around 40 watts. 

Lets firstly get into a description of the tubes used .

The input tube is the STC made, Northern Electric branded 4310A . STC (Standard Telephone Company) was the British arm of Western Electric (WE) which initially used Western Electric designed tubes before they become more independent from WE.

The 4310A is the same as the WE 310A , a pentode tube used in the famous 1930's era WE91 amplifier, which used a 310A driving a WE300B triode. Fabulous tone.

The 310A drives an AWA branded (Amalgamated Wireless Australia) VT25 triode.

This tube is so rare that its been almost impossible to even find the correct documentation for it.

VT25 is normally the military designation for the number 10 triode , a very old 1920's triode which later evolved into the 801A.

There is also a VT25A , which starts to get confusing , but these versions are well documented , and while they are getting expensive , still obtainable. 

The Australian tube I'm using has a box plate much bigger than a 10/801A which suggests its an entirely different tube, desite it having a VT25 stamp on its base.

There are suggestions that it is a CV1025 . Documentation of the CV1025 claims a mu of 0.4 and Rp of 300 ohms. 

This is unlikely and its possible the tube is a DET25.

Using it in circuit will determine what it is, but regardless it will make a very fine driver for the output tube, which is the also very rare Ediswan V1505.

Similar to the WE 212E , this huge tube is a high voltage triode that can output high wattage single ended sound.

The minimum plate voltage for the V1505 is 1200 volts, which is getting into the scary side of voltages, good insulation and careful design and construction will be needed to ensure safe useage.

The output transformer needs to be of the highest quality to match the tubes used, and in keeping with the rare and expensive theme , I'm using a pair of Tango X-10S output transformers. 

These are designed for 211 triodes, and the 10k impedance is high for a V1505, but using an 8 ohm speaker on the transformers 16 ohm tap should be fine.

As I use high efficiency horn speakers I'm not after high power levels , and a higher load will deliver even lower distortion. 

Here's a mock up of the chassis , they are built in mirror pairs so this is the left channel.

Power transformer and chokes to go alongside the output transformer.

There will be a pair of ammeters and a level control in the 3 round bevels on front panel. 

Transformers and some other bits to arrive, come back in a month or so, to see how I'm going.

And in stereo.