FrankCooter

Excellent explanation of often poorly understood power supply issues, particularly regarding the use of chokes. Like you, I'm also a big fan of "iron" in a HVDC supply. For many years, audio power supplies were more or less an afterthought to the audio circuitry. A lot of the mushiness and euphonics attributed to tube gear was directly related to the floppy, high impedance of cheap and under designed tube rectified power supplies. Conversely, a good portion of the flat, cold, harshness attributed to early solid-state gear was the result of power supplies that consisted of nothing but noisy solid-state diodes, a pair of giant electrolytic capacitors, and simple resistor. I'm curious to see your shunt regulator. On one hand, with the minimal and balanced current draw of the SRX circuit, one wonders if it would make any noticeable improvement over the already very effective LCLC filters you're employing. On the other hand, because of the minimal current draw of the amp, the SRX seems like an ideal candidate for a shunt regulator experiment. Generally, I prefer shunt over series regulators. Sometimes I think that solid-state series regulators can add add a glare or harshness to some circuits. Shunt regulators, whether tube or solid-state, don't seem to have this problem. One thing you might want to consider if space is no problem is swapping the electrolytic caps for some PIO motor-run types. At least with class A single-ended tube circuits, it can make a noticeable improvement.

When I was referring to the the SRX circuit, I meant Jim's SRX Plus circuit. The original is pretty good, but Jim has taken it to an entirely new level. I don't often build other people's designs anymore, but the original SRX always intrigued me, and the SRX Plus has renewed my interest. I have a reputation for building "over-the-top" tube projects, but I actually find it a lot more fun to see how much you can do with simple circuits and limited resources. In the not too distant future I'll be building Jim's SRX.

I have some spare power supply boards for the KGSS. You're welcome to one if you want. I second nopants recommendation for the SRX. It's easy, cheap, rugged, uses readily available common parts and can be built point to point. Any design can always be improved, but there's nothing at all wrong with the circuit as is.

What you're looking for is called "SOOW cable". It's very flexible and is designed for equipment where there is a lot physical motion. I use 16 gauge 8 conductor. It's rated for 7A/600VAC. Try "Wire and Cable to Go". They sell it by the foot. If you can't get it anywhere else PM me and I'll cut you a piece off my (ever shrinking) roll.

Thanks guys.

Really like what you've done with this circuit. I've come close to building the original several times. I've always had an attraction to dirt simple, but high performance tube designs that could be built in a weekend by a high school physics student using mostly scrounged parts. I don't have anything to add to to your extensive documentation except my output tube experience with several Egmont variations using simple 10M90 CCS. As has been mentioned, the 6BL7/6BX7 have huge section to section variations. Out of 30+ samples I could not get any that matched closer than 10V. Some varied as mutch as 50V. Too bad, because on paper, they look like excellent candidates for this application, not to mention they are cheap. By trial and error based on listening, I settled on 400V rails with 20mA current. Overkill I know, but I like small power tubes in non-traditional applications. I used triode-connected EL84's, 7591's, and 6v6. Running open loop, it was easy to hear the differences. I would bet your cascode CCS is a mutch better approach. The 50's era 6SN7GTA/B is a great tube, I've run them no problems at 400V at full dissapation. They are also still plentiful and a great bargain. I especially like the Sylvanias. Thanks for your contribution and let us know when you article comes out.

Rotijon, I have never seen Kerry's work in person, but judging from the posts and photos of his work on these forums, I consider him ( I've built electronic equipment myself for 40 years) the finest amp builder in this hobby. No slight to the commercial version, which is superb, but I would bet his construction sets a quality and artistic standard that can't be pratically duplicated in a commercial product.

HemiSam, pm me, I may be able to help.

The 26 and the 6080 are about as far apart as you can get in the tube world. Neither is really suited for phono use. I own about 30 type 26, none of them are quiet. The type 112A is similar to the 26, and usually a little quieter, but not much. The only thoriated tungsten tube that I can think of that MIGHT work in this application is the 10y, which is expensive. Any DHT will be difficult and problematic in a phono application. If you're determinined to try it, I'd look at the Russian 4P1L or 6P21S. They both work well as the output of a headphone amp, and are dirt cheap. Lots of options if go for an indirectly heated type. I like small power tubes anytime low gain is required. Not much beats the tonality of a triode-connected 6V6.

Doug, I hear you about the Dynaudios. The best small speaker I ever built was a simple two-way based on the 21w54 woofer .Absolutely the best 8" woofer I ever heard. Simple 2nd order crossover and some Dynaudio tweeter I've forgotten the model number of. Quite efficient, but had some real balls. Ran just fine off a small push-pull 6V6 amp. So unless things have changed a lot in the speaker world in the last couple of decades I'd be looking hard at the Dynaudios. You might want to consider vintage JBL's, Tannoy's, Altecs, or Klipsch. If you do it right it's actually a profitable investment. A few years ago I had a pair of Klipsch "Belles" ( furniture grade LaScalas). I bought them cheap because of some fairly minor cosmetic issues. I refinished the cabinets, used them for a year or so ( my listening room wasn't really big enough to take advantage of them), and then sold them on Ebay for substantially more than what I paid for them. Another alternative is your own cabinets filled with TAD components. You won't lose money here either. I don't own any speakers at the moment, ( kind of done with the horn thing) but I'm beginning to think about some vintage high-end JBL's or Tannoy's.

Your work looks great. I particularly like the way you've handled the heatsinks and the chassis in general. My only criticism is that you can still work on the wire dress a bit. My projects always look like a mess at first pass. It usually takes me three revisions before I'm satisfied, and even then, there's always things you would change if you did the project a second time. It helps to wait a few days before each revision. Putting the project aside for a while clears your mind and gives you a fresh perspective.

Greetings Mario, There are many people much more qualified to answer your question here, but I'll give it a shot anyway since my tastes and expiences somewhat echo your own. I currently own SR-007Mk2's and have have owned 303's in the past. I have heard a lot of 007Mk 1's. The Mk 1 has a subjectively more even and neutral overall presentation. The Mk 1 responds best with solid-state or very neutral tube amplification. The Mk 2 has a bit of a mid bass bump and a slightly more forward presentation. The Mk 1 is preferred by most here, but the Mk 2 is a very fine headphone in it's own right. With some amplification (primarily tube) the Mk 1 can sound a little recessed and dark. I build tube amplification and listen to rock music. In my system I actually prefer the Mk 2. I also prefer the Mk 2 to the LCD-3 ( also a very fine headphone), which I also own. I was very fortunate to get a one time shot at a brand new U.S. Mk 2 with warranty at essentally a used price. Like you, I was hesitant to purchase a 10 year old headphone in unknown condition for the kind of money we're talking here. Many of the Mk 1's I've seen at meets are starting to show their age. If you ever need new drivers from Stax, they will be M 2's. If I had to pay full list priceI for the Mk 2's i might have made a different decision, but I have no regrets and greatly enjoy my Mk 2's.

Best post I've ever seen !

They do sound nice. Slightly fuller overall and with a less harsh treble than comparably priced Stax. Maybe one day they'll fix the "squeal" issue. Mine are on their 4th set of drivers (all supplied under Koss warranty-superb unlimited "no questions asked" service} and could use a new set. Perhaps someday Koss will attempt a genuine world-class product. I'd bet it would be very interesting.

Capacitor upgrades are kind of like tube rolling and cable swaps. There are differences but they are usually small. Most of the differences are more the result of the type of cap ( PIO, polyprop, teflon, etc.) than price or brand difference. The biggest improvements come with the first jump off the bottom. You can usually easily hear the difference between a $1.00 coupling cap and a $10.00 cap of the same type. You'll need to strain to tell the difference between a $10.00 and a $100.00 cap. For a cheap comparison of different types, try the different Russian military surplus types. The teflons and the K40 PIO's are excellent. Bottom line is serious money is better spent elsewhere. That said, I did find the above review interesting and useful in a subjective sense. I've used a number of the capacitors mentioned, and the author's opinions roughly correspond to my own. Power supply caps, at least in single-ended tube amps, seem to make more of a difference. Motor-run PIO's are a definite sonic upgrade to traditional electrolytics. Same story with cathode bypass caps. All caps are necessary evils. In the end, if you can do it, the best cap is no cap.

I have a couple of extra KGSS power supply boards if you're interested. The amp section looks like a good candidate for point-to-point construction.

Since we've strayed into tube rolling, here is a list of the tubes I've tried as outputs for a simple two stage transformer coupled electrostatic amp. Absolutely no science or engineering here. Impressions are totally subjective and may have absolutely no relevance to any other design. Caveat, disclaimer, etc., etc.. All tubes were run in triode mode with 400V on the plate, and all were run in a linear portion of the curve, Besides the output tubes, the rest of the system stayed the same. EL84/7189 -Russian 6P14P and NOS RCA 7189 EL34 -generic Chinese, German RFT, Mullard XF-2, 60's Japanese Mullard copies 6550/KT-88 -vintage Tung-Sol 6550, vintage GEC KT-88, new production Gold Lion KT-88, briefly also tried the "Treasure" Chinese KT-88. 7591 - vintage Westinghouse, also tried the 6GM5, which is a 9 pin version of the 7591 7403- 50's Tung-Sol and Bendix 6P21S - A Soviet era directlly-heated 4 element tube , 2E22- another directly-heated 4 element tube some claim can substitute for a 6550/Kt-88 EL156- 60's Telefunken 6BX7 and 6BL7- RCA paralleled 6SN7GTA 845 - generic Chinese Output transformers for all but the 845 are purpose-designed Electra-Print 1:1+1 with a 3.3k primary (below optimum for several of the above tubes) The 845 transformers do not have a step up in the secondary and have a nominal 5k primary. Disappointments first: The EL84's, the 6SN7's, the 6BL7/6BX7 were not up to the job. All could be made to clip on peaks and otherwise sounded constriained and flat. The low primary impedance of the transformer may have been a factor. The directly-heated 2E22 and 6P21S. Major dissapointment here. Not bad, but no DHT magic. Transformer primary slightly low, but I think it may be more a factor of running the screen grids way beyond thier 220V ratings. I don't have a problem with running screens substantially beyond thier ratings from a safety standpoint, but I've been told that this will distort the triode cuves. All the KT-88's and 6550's. They vary, and they aren't bad, but they all seem a bit less refined and musical than a good EL34. The good: Mullard EL34 XF-2. The most musical of the large power tubes, incrementally better (but a worthwhile increment) to any of the 6550 types. Honorable mention to the Japanese Matsushita Mullard copies - I can't tell the difference The clear all around winner is the Telefunken EL156. This is the finest non-DHT power tube I've ever experianced. It has a large, open, yet very detailed and precise presentation that sets it apart from any of the others. Perhaps a little cooler than the Mullards The surprize of the bunch is the 7403. This is a regulator tube with a plate cap. You're on your own using it for audio purposes, but it seems suitable as a 6550/KT-88 substitute and it sounds comparable to the best of the 6550's. The 845 is different breed of cat from any of the above and deserves seperate consideration. Hopefully, I'll get to share it with some of you.

I'm not a fan of rolling different types of tubes in commercial amps ( or somebody elses established DIY design) either. At the very least, you've randomly altered the designs established operating points. At worst you may be making dangerous electrical demands on the amp that it was never designed for. For example, the EL156, while a great tube, takes less drive and biases up substantially different from an EL34. DIY is another story. Part of the fun, as long as safety and electrical parameters are properly accounted for, is to throw anything and everything that might roughly work into a circuit and experiment with different operating points. Most of the time the results are predictable and disappointing, but every once in a while you stumble on to something exceptional.

It would be a freak show, but if you were really motivated, something similar ( but with much higher voltage ratings) that could probably be made to work is the 13E1.

The output tube I've always wanted you guys to play with is the El156. It's a clear step up from any of the El34 or KT88 types.

Yo, Birgir! Me and the bro's are ABSOLUTELY, TOTALLY, AWSOMELY, STOKED, PUMPED, and JACKED that you've become a reviewer dude!!!!!! On a more serious note, I think the $10k Woo mono blocks (cheap, generic tubes included) deserve a place on your list.

I was thinking of sort of a "poor man's" all DHT amp. 4P1l directly coupled to a 6P21S, then interstage coupled to either an 845 or a GM70. 845 then drives a 1:1+1 output transformer.Run the 845 at a relatively low 600V, 60mA plate current, and 100V fixed bias. A few years ago I talked Jack Elliano into making me a pair of 60mA/1KV rated transformers that could swing 600VRMS.It took him several attempts to come up with a finished product that he was happy with. Used them briefly for an 813 amp. He put a lot of work into the transformers but only charged his standard "off-the-shelf" price. Probably ought to put them to work again. To do this right, a 300B is marginal.Really there's no smaller substitute for an 845 type in this application. Power supply would either be something like a "21st Century Maida Regulator" or something tube regulated with a big pass tube like a 13E1. As an alternative, I was thinking about something balanced with direct-coupled outputs. CCS loaded 801's for outputs. 1st and 2nd stage 4P1l's.1st and 2nd stages direct coupled, caps between the driver 4P1l and the 801's. The EML's would be great here, but at $1k per quad, out of the question for me.

I've always been curious what a Stax/DHT combo would sound like. Might be an interesting joint project.

Here's a mock-up example of how I start my p to p builds. I start with a raw .090 aluminum top plate. First lay out all the major components, If you're using transformers, place the power and output transformers in diagonal corners to maximize the difference between them. Try to keep all power components in a tight area around the power transformer. Signal wires shoud be tight, short, and as far removed from power components as possible. If you have to cross power and signal wiring, do so at a 90 degree angle. Use DC for all filaments. Good AC filament wiring is an art in and of itself. Be prepared to take several different attempts at your wiring. Do not leave connections unsupported or hanging in the air. Don't be afraid to rip things out and start over. As you progress, you will always see things that you could do better a second time around. Remember always to think about safety and heat dissapation. Everybody that builds like this has a slightly different style. Rather than planning in advance where each particular small component or connection will be, I like to build a square of tie points around each tube socket and have a sort of connection point grid to work from. I like to keep everything at 90 degree angles if possible. For tie points, I like to use Soviet era Russian military connectors. Seller Sovcom on Ebay is a good source. I use a combination of 6 and 10 position connectors. They are pretty cheap, yet very high quality. Order 3 times as many as you think you'll need. I like octal tubes rather than 9 pin miniatures. The sockets are much easier to work with. They also usually sound better. Many miniatures have octal equivalents that can be used without any circuit modification. A 12AX7 is a 6SL7, a 12AU7 is a 6SN7., etc.. There is no direct octal equivalent to a 6S4, but half a 6BL7 comes close. Better than either of these would be to use a real power tube as an output device. A triode-connected EL34, or a trioide-connected 7591, which would be my personal choice (hey, it was good enough for McIntosh). There's lots more, and I'm sure others have points and considerations I haven't even thought of. Eventually you need to go ahead and jump in. Post your progress or problems here. Don't be embarressed if it's not a work of art at first pass. We're here to help and keep you safe.

Shoot me a PM Ken. Definitely interested in hearing your stuff. I have an LCD-3 and a Metrum Octave to add to the mix.