6550/KT88 SET amp aka "Uber Beam Machine"

DaveC113 · « **Reply #340 on:** 4 Sep 2008, 04:10 am »

Beautiful! The layout looks great, as does the chassis... Do you know how much power it has? What speakers are you using it with?... and a pic of the wiring would be great too.

Dave

jeffdavison · « **Reply #341 on:** 4 Sep 2008, 05:20 am »

Here's a series of pics of the second one underway. I estimate 10 to 12 watts in pentode. I'm using a pair of open baffle speakers I built using the Sterling Silver Iris drivers from Hawthorne Audio in baffles and crossovers I built myself.

WARNING.. graphis intensive.....

JoshK · « **Reply #342 on:** 4 Sep 2008, 07:56 pm »

Wow, that is some work Jeff. You've been busy.

I like the aesthetics and your build quality looks first rate.

I'd love to hear more details surrounding how you potted those chokes and how you fasten them to the chassis after potting.

I finished drilling out my wood chassis on the back for the connectors and plugs. Its glued up and now I need to sand and finish. Then I can start to put the amp together.

My aikido preamp is in a similar stage. Then my Lambda TD12M Apollos arrived last night and my wife is out of town this weekend, so I feel I might be making more sawdust.

jeffdavison · « **Reply #343 on:** 5 Sep 2008, 01:11 am »

Once the first was done, the next one was a breeze, as all the r&d has been done and the drawings were finished. I use the toner transfer method to make my pcbs, so all I have to do is print them out with my laser printer and iron the drawing to the copper clad. If I get enough demand, I'll get some professional pcb's made up. Many places can make small runs for cheap, but nothing beats the convenience of just printing them up at home... very easy to make changes in the design on the fly if needed.

The top, front and rear plates are from Front Panel express, and since the drawings are done, it's a simple matter to hit the enter key in their program to place an order for them and wait a couple weeks for delivery. Table saw in the basement and gluing jigs I made for the first amp and router jigs I made as well make the going real easy once I have a nice piece of Rosewood in hand.

When I potted the chokes, I inserted some rectangles of wood between the choke ends and the wall of the case. You can see this in the pics. Just a fair warning... potting compund is not cheap!. About $40 for the toroid and two choke cases worth. After potting, I simply drilled some hole and they are mounted to the top plate with wood screws. For the big potted toroid, I used cut down maple dowel rods in the corners before potting as the round toroid in the square case left the room needed. Wood screws worked very well also.

I should have "S.E." (second edition) ready to fire up in a couple of days. Number 1 is traveling with an audiophile friend of mine who travels for sales, to demo at shops across the south between Georgia and Texas. Going to try to make this effort "semi" commercial.

JD

SET Man · « **Reply #344 on:** 5 Sep 2008, 01:17 am »

Hey!

Jeff, beautiful work there.

Take care,
Buddy

JoshK · « **Reply #345 on:** 5 Sep 2008, 01:32 am »

I thought the wood at the end was thick copper. Wood makes a lot more sense.

JoshK · « **Reply #346 on:** 9 Sep 2008, 02:34 am »

baby steps...

rough sanding done.

the back side with connector sockets drilled out.

I did a bit of chiseling so that the neutrix connectors are flushed into the back. I had to take quite a bit wood out in order to fit the breaker switch so that I can actually screw on the fastening nut, but it worked.

JoshK · « **Reply #347 on:** 9 Sep 2008, 02:37 am »

Now I gots to do some fine sanding and then learn how I want to finish this chassis. Thinking shellac. Not decided yet.

jeffdavison · « **Reply #348 on:** 9 Sep 2008, 05:21 am »

Josh,

I can recommend a good spray for the wood. I used it in my guitar building days..

It's called Deft and it lays down a really good finish that's , imo, It's a lacquer as pretty as Shellac and as durable as polyurethane.

Very easy to apply and you avoid the "glop" potential of brush on finishes and you can get a nice even coat with the cans fan pattern spray nozzle.

They have brush on, but I like the spray myself. Also I prefer the semi gloss (once dried and cured, can always be polished gloss)

Here's a link to Rocklers page for it...btw.. Lowes carries it ( at least the local one to me).

http://www.rockler.com/product.cfm?page=17624&cookietest=1

For my Rosewood base I took the wood down to 1000 grit and used Watco Danish Oil finish.

JD

JoshK · « **Reply #349 on:** 9 Sep 2008, 03:33 pm »

Thanks Jeff. I'll keep that in consideration. I wonder if it is anything like Crystallac which a lot of guys like to use on guitars for similar reasons.

DaveC113 · « **Reply #350 on:** 9 Sep 2008, 04:51 pm »

I used the Deft brush-on semi gloss laquer for my amp and speaker stands with very good results. It dries fast and polishes up really nice. I just go over it with some fine grit paper after its dry for a nice, smooth finish. It dries to touch or so you can put on a 2nd coat pretty quick, but you want to wait overnight before sanding or buffing it out.

jeffdavison · « **Reply #351 on:** 30 Sep 2008, 08:37 pm »

Just a friendly bupt to the top o the forum

Newest trick I'm trying out are grid chokes on the driver and power tubes...the let DC go to ground and the AC signal pass.. Have to be wired in place of the grid leak resistors. Using a Lundahl Ll1670 after the input 6SN7 as a grid choke / 2:1 autormer (to reuduce gain a bit) into the 6H30 driver. And will be using a Magnequest BP-16 NI as a grid leak into the 6550.

Have read good things about grid chokes, tho the may be sensitive to noise pickup.

JD

Niteshade · « **Reply #352 on:** 2 Oct 2008, 01:15 pm »

I'm not a fan of printed circuits- but this modular design is exceptionally nice! The company that makes the boards does a fantastic job too. Something to think about: Having the tube sockets directly mounted to the top chassis plate. I never liked watching boards flex while installing/removing tubes. Also- having to remove a defective socket that's soldered to plated-through holes could cause problems. The chassis designs are A++! Some beautiful work is going on...

jeffdavison · « **Reply #353 on:** 2 Oct 2008, 03:57 pm »

The boards really dont flex that much, the standoffs aren't that far apart and the 1/16 thick fiberglass is fairly stout. Also the tubes are always inserted gingerly and removed gingerly as well.

The boards aren't made by a commercial company, did them up myself using what is called the "toner transfer system"... What you do is layout the circuit on any drawing program of choice, widen the traces to where you want and finalize it as a graphic drawing ( I never got around to using any specialized PCB design software - I've been making boards this way for over a decade). The drawing is then printed out with a laser printer onto "Staples" Photo Basic Gloss paper. The picture is cut out and ironed with a clothing iron, onto copper-clad pc boards... The toner is actually very fine plastic particles that are melted / fused on to paper by the laser printer... what the iron does is remelt the toner onto the copper. After the ironing, the board is soaked in water and the paper removed.. all that is left on the board is the toner / drawing... this acts as a perfect etch resist (occasional touchups needed tho). I etch the boards with ammonium sulphate ( any Fry's electric store carries the chemicals) and presto... I have a pcb... albeit a one sided pcb. Just drill the holes with a micro carbide bit (various sizes available at McMaster Carr) in a drill press and stuff the board. Can be designed and fabricated in an afternoon or evening.

This makes it very fast so you don't have to wait on any design/fabrication house, and you can make any change in layout or parts spacing to your hearts desire.

The signal is all point to point

Only the power supply boards are pcb, so there is only a little "rat's nest" inder chassis. I perfer the sound and parts swapping is a breeze

Jeff

Quote from: Niteshade on 2 Oct 2008, 01:15 pm

I'm not a fan of printed circuits- but this modular design is exceptionally nice! The company that makes the boards does a fantastic job too. Something to think about: Having the tube sockets directly mounted to the top chassis plate. I never liked watching boards flex while installing/removing tubes. Also- having to remove a defective socket that's soldered to plated-through holes could cause problems. The chassis designs are A++! Some beautiful work is going on...

Niteshade · « **Reply #354 on:** 2 Oct 2008, 10:33 pm »

Thanks for the technical info Jeff! I'm going to look further into it- as I said, the modular approach is enticing. I would like to know how these single ended KT-88 amps sound! Will they take away the 300B's thunder? Has anybody who built one of these AB'd the two? 300B's are too expensive- unless their sonic quality justifies it.

DaveC113 · « **Reply #355 on:** 3 Oct 2008, 12:31 am »

Niteshade, if you haven't seen tubelab's web site:

http://www.tubelab.com/

He has a pcb (which I used) for a KT88/6550/EL34/etc SET amp called the Simple SE, and a more complicated DHT SET amp for 45/2A3/300B tubes using a mosfet to augment the driver tube. He makes some comparisons, saying the SimpleSE is "almost" as good, but prefers the sound of a DHT slightly more.

He also has plans for an 845 SET using the DHT SE board as a driver... I'd like to build one of those someday.... I think it makes over 40 watts of pure SET power aa

Dave

JoshK · « **Reply #356 on:** 6 Oct 2008, 01:49 pm »

By the way, it should be mentioned that this thread encompasses more than one design. jeff's design is his own. Some are building Tubelab's SimpleSE and I am building Pete Millett's E-linear design.

I am not using PCBs in the E-linear...it is point to point.

JoshK · « **Reply #357 on:** 13 Oct 2008, 12:57 am »

found this link that has a great tutorial on padding shellac.

http://antiquerestorers.com/Articles/jeff/padding_shellac.htm

i am going to give this a try for my chassis. that is basically what i have left to do on the chassis, then i get to start constructing the amp.

the other finish option was crystalac, but i think i'll save that one for another amp.

slbender · « **Reply #358 on:** 13 Oct 2008, 09:29 am »

Hi Josh, et al-

My latest SET Amp (almost 18 months in the making) had its initial listening test last weekend October 5th, 2008 at the Audio Syndrome / Gotham Audio Annual BBQ, which took place on the South Shore of Long Island in Seaford, NY. at the home of Jimmy Marks. While the amp is "almost finished", I decided to bring it along, despite not having run a complete set of objective or listening tests on it. My initial tests were completed barely 5 minutes before I was picked up to go to the weekend BBQ.

My initial testing showed an undistorted output of 18vp-p across 7.5 ohms which is around 5 Watts per channel; the -3dB points were around 24-27 Hz. on the low end and well above 20kHz. on the high end as seen on the scope. These initial quickie tests were taken using an old homemade audio generator I designed and built many years back, it has nine step frequencies: 20, 40, 100, 333, 400, 1K, 6.3K, 12.5K, and 19.8K. I was also using an 80 MHz Oscilloscope to see the 3 dB down points, and a pair of 15 ohm / 1% / 2 Watt wire-wound resistors across each channels pair of 8 ohm outputs. Gain was such that just slightly more than 1.0 volt was required for full output, and the Signal to Noise was on the order of 64dB. The fan is somewhat audible, I need to get a quieter fan, or run this one at a slower speed than it is now, the fan is way noisier than the noise of the Amp. So while the Amp still needs to be tweaked and a few things checked, and a full set of distortion tests to be done later this week, and perhaps it needs to be optimized and maybe bypassed a little more, but still, I figured it was ready for prime-time listening.

At the meeting, we first listened for about an hour to the original (vintage) system which consisted of: a Playstation1 as the CD Player, modified Dynaco PAS w/o tone controls, a moded Dynaco Stereo 70, and a pair of Dynaco A-25 speakers, and a smallish AR Subwoofer. Then after eating and deserts, we again listened to the original system for a half hour, then someone had a new Digitally Controlled Preamp prototype (using fast IC's and an external power supply) which was hooked up in place of the PAS. Listening again for about a half hour, the system was both pleasant and detailed.

Finally after about 7 PM, my little SET Amp was hooked up, and the Digital Preamp remained connected. All of a sudden there were Oh's! and Aaahh's! and smiles all around. And now, nobody wanted to leave, some three hours later, our host finally kicked everybody out as it approached 10 PM. Of the dozen or so CD's played in the last part, only one didn't sound good, its dynamics were constantly clipping my flea-powered SET. The rest of the CD's sounded great. The soundstaging, musicality, clarity, and detail were better than the typical SET or other amps. This amp was designed and intended to be the equivalent of a 2A3 Triode at around 3.5 - 4 Watts per channel and it nicely meets that criteria. The stereo amp is small and rather light-weight at only about 12 lbs. without its carry around suitcase. So I'll probably bring it to several of the Raves and Meetings I go to in the next year or so. I'm already building the next two higher power versions of this SET amp, but they won't be ready for quite a while yet. Tried to insert an image, but it didn't work...

-Steven L. Bender

Quote from: JoshK on 6 Oct 2008, 01:49 pm

By the way, it should be mentioned that this thread encompasses more than one design. jeff's design is his own. Some are building Tubelab's SimpleSE and I am building Pete Millett's E-linear design.

I am not using PCBs in the E-linear...it is point to point.

JoshK · « **Reply #359 on:** 18 Oct 2008, 03:21 am »

Cool Steve,

Are you going to give us any details? Like what kind of amp is it, other than tube?

I started the shellacing of my chassis. Here's hoping it turns out.