6550/KT88 SET amp aka "Uber Beam Machine"

DaveC113 · « **Reply #140 on:** 24 Jan 2008, 11:15 pm »

Also, as far as how hot the top plate will get... the power tube's dissipation is going to be about 30W, so I don't think thats going to be an issue, but I wonder how hot the transformers are going to run?.. Most spray paints are rated up to 200 deg F service temps, and I also have some 3/16" thick high-density felt that I was planning on using between the transformers and the top plate, (which will be 1/8" alum). The felt also has a service temp limit of 200 deg F. I guess I'm going to hope it doesn't get that hot, I've seen a few amps with hammered paint finish, which is also 200 deg F rated... hopefully the amp won't smell like burning paint and singed hair

Dave

nodiak · « **Reply #141 on:** 26 Jan 2008, 01:28 am »

Ordered Transcendar transformers - 5K, 100mA, UL tap at 50% (model TT-018-OT). $150 + 15 shipping, four weeks lead time. So I'm commited now! I'll make some choices for the rest of the parts soon. Big thanks to everyone posting what their using, that's helpful

.
The guy that built my amp reports that they are clean with smooth extended high end, tight bass, open and refined mids. He used Tamura's in the SE EL84 I'm using now, and has used Transcendar in similar models. So it's a bit of an evolutionary move for me.
Also will soon have the drivers and xo schematic for clones of Galante Rhapsody's. These are Radian cast frame 8" paper cone woofer with coax mounted Radian tweeter. From reports they sound like my kinda thing, and could be the ticket for my current amp as well as this one. I use a sub for 70 hz and below.
Don

Dmason · « **Reply #142 on:** 26 Jan 2008, 01:37 am »

Don

You are going to like the Radians. My Radian 508 are among my most prized drivers. These, mine, are abit older, and have the Emilar 1 inch compression driver, which is smooth as silk, easy on my tinnitus which tells you something. These go back to the Tannoy wing of Altec, here in California, and the original designer in Northridge. They share this common genetic, and they sound that way. I would be interested in seeing your XO schema... I have heard only good on the Transcendar irons as well.

This project is becoming very interesting. Large data points in favour of the Transcendars, Edcors, and I like the James, which are highly adaptable, and very well finished. THL Audio in Taiwan tells me James is indeed OEM maker for current Tamura of the variety that are offered as James, but for sale in Japan. Buy James and get Tamura, I guess.

Jim

I ordered the Fostii today. They, F120A, were in stock. Should have them next week. . I also have LEAP curves for three different cap values @ line level, if you are interested, email me. .01uF cap for 100Hz high pass @ speaker or line level. I prefer speaker level to give bass amps the ability to see the signal from the tube amp, which allows it to better mimic the characteristics. "Nuance," as Hillary Clinton might put it.

jrebman · « **Reply #143 on:** 26 Jan 2008, 04:04 am »

Dave,

If my transformers get anywhere near 200 F, I'm sending them back -- that is waaaayyyy too hot. Think more like 100-110 F as a more reasonable zone. The tubes are another story.

Don, very cool. certainly great to have a variety of OPTs to compare on similar platforms.

Dan, Yes, definitely want to take the sub signal off a full range speaker output. I'm going to be building the equivalent of a speaker level converter into my amp, so there will be two female RCAs located between the right and left channel binding posts. It's the only way to maintain perfect gain and phase tracking over the entire frequency band. When I get to building my preamp, one set of outputs will always be full range, and the other will have switchable 60/80/100Hz high pass, as well as full range, selections.

Good news on the F120As -- didn't think we'd be seeing any more of those on these shores again. There can't be that many of them left as they are supposed to be out of production now.

-----

Now a question for the gang, and maybe this is better asked in a separate thread. My Edcors, despite my best efforts to make sure I didn't get blue bells, came with... yes, blue bells. I wrote to Edcor today and they replied that they immediately put a set of the gray ones in the mail to me and said to just make sure that the new ones go on the same way the old ones came off, with the correct series of washers, etc.

Now, I had always heard that swapping end bells could disrupt the integrity of the laminations and introduce small gaps, which would ultimately compromise bass response. Does anybody know how true this is, and if there is a special method one uses for swapping end bells?

I suppose that there is now a spare set on their way to me that I can always have those powder coated to whatever color I want, or even plated, etc. Advice appreciated.

-----

Got a quad of cryoed TS 6550s on the way too. Ostensibly for my Cayin PP amp, but can easily see either these or the Gold Lion KT-88s ending up in the SimpleSE. I'm sure I'm just going to have to try some EL34/6CA7s at some point as well. At least I picked my operating points so that any of these tubes would be happy in the amp.

-- Jim

nodiak · « **Reply #144 on:** 26 Jan 2008, 10:58 pm »

Jim, yes I agree the variety of trans and parts is cool, now where we going to meet to hear them all?

Not that NY, Colorado, So. and No. Cal wouldn't make for a great trip

. Just joking as the www at least allows these great discussions and we'll all point out comparisons we're aware of.
Can you just exchange your trans for the grey ones? I have no experience with these things in particular but it doesn't sound good to take them apart and expect the same pressure and alignment without the tools, jigs, and whatever they use.
Dan, good to hear of your 508's, these 5208's seem to carry the old world Tannoy heritage also from reports. I'm anxious to hear them. I hope it's a tweeter I can live with for audio, supposed to be Radian 465pb. This kit is from someone who reverse engineered some Rhapsody's to make a run of them, but the cabinet maker couldn't do the order so the drivers and design were sold, I just lucked into it when googleing around. I'll share the xo with you, apparently not the stock Radian one. A big part of why I went for them is so I can have a reference for monkeying around, will ob them eventually with ob bass - either Augies or the new Rythmik/GR Research ob systems. A carrot to chase.
Been hearing good things about KT77 with similar amp, JJ's are supposed to be nice as were reverse engineered from Genalex (via Bob at Eurotubes).
Don

jeffdavison · « **Reply #145 on:** 4 Feb 2008, 10:08 pm »

BUMP...

thread's beginning to scroll away into the recesses of the forum..

Where's everyone standing?

JD

jrebman · « **Reply #146 on:** 4 Feb 2008, 11:04 pm »

Right now I'm sitting... with a nasty intestinal virus

.

Just a few more odds and ends to get ordered, but for me the next big task is laying out the top panel and getting it machined and finished. After that will be the building of the chassis. We're all ready to stuff boards though.

A circuit breaker question for those like Josh who have used them before:

I got us a few 2 amp Potter and Brumfield (now Tyco) W28 series breakers that would serve both as breakers and power switches. However, what I got was push-to-reset types. I know the make, or least, Made, these with what they call an auxiliary switch so the breaker can do both, but I can't seem to find those any more -- digikey doesn't have them, nor does Mouser -- I searched myself and also called for assistance, and came up empty. FYI, these are the types that fit in a normal panel mount fuse holder opening.

-- Jim

JoshK · « **Reply #147 on:** 4 Feb 2008, 11:07 pm »

Good prodding Jeff. I have used the excuse of my two week long cold/flu to avoid doing any real work on the UBM. I just haven't felt well enough to sit in front of my bench for any length of time until later last week.

I started to layout a breadboard and that is where I left off. I was waiting on a few resistors and some sockets which I now have. So I need to wire it up and start testing.

In the interim I ran across Pete Millet's E-linear amp. The schematic and build details are on his site but the article surrounding the logic is in April 05 AudioXpress. I ordered a archive copy of this mag (actually all of 05 on a CD for $15) so I could have this article. It looks very intriguing and I have a few D3A's on hand, so I could possibly test this topology out too.

This amp is intentionally my experimenter's amp. There are so many cool ideas to try out, which is why I embarked on this project in the first place. Pete's topology gives high power using an ultralinear variation with something akin to plate-to-plate feedback instead of global feedback to lower the output Z. Its quite clever and I'd like to try it out.

Dr Dan, how's your build coming? He is probably still busy doing things much more noble than building audio amps.

JoshK · « **Reply #148 on:** 5 Feb 2008, 12:50 am »

I got the smaller amperage breakers from bgmicro.com, iirc. They mount with a round hole. I also recently bought an NTE 2amp thermal breaker from action-electronics.com. They have sort of a rocker switch which is why I bought them but I don't think it'll actually be that convenient as a switch now that I have it in hand. Glad I only bought one.

Took a quick look at bgmicro doesn't seem to have what I got anymore. I found a 2.5amp breaker on surplussales.com for $6. here. But it requires making a square hole and it doesn't look like it will cover the cut, so it needs to be nicely done. Kinda a pain for a diy'er unless you use FPE.

I found this while googling...
http://www.surplusshed.com/pages/item/r3042.html
Question for Paul/others. It says 1.5amp and shows a 250V rating, does that mean at 125V it is a 3amp breaker? Meaning, is it the watts heating the thermal element that trips the breaker?

nodiak · « **Reply #149 on:** 10 Feb 2008, 06:10 am »

Hate to see the thread get pushed off the front page

Have been going over parts to build up the board, should get an order out this week. Will have a new solder station in a few days too. Things moving along.
Also deciding on motor run cap. ASC has the reputation among amp builders but have only found their X386S in 60uF and smaller. Would need to parallel two 50uF's. No problem with cost ($30 for two, still cheapish), but would prefer a single 80 -100uF. Anyone know a source?
Don

~ OT: have been running the Radian 5208c coaxials (Galante Rhapsody clones) about a week and they are very nice! Smooth and detailed, big soundstage and space, and the coherence of any single drivers I've heard. Will go for some better caps soon. Missed out on some used Mundorf silvers, so am researching options - Obbligato looks nice, as does a Clarity SA with Obbligato or Mundorf blend. Only need 2.7uF and 3.0uF pairs. Really impressed with the speakers and have decided not to pursue some of the other speaker ideas I was working on.
Bit of a bummer as my computer locked up a couple days ago and won't start. I bought this cheap used one but am having trouble setting up my email account. Also miss all those convenent favorites I had going. But there is something to a fresh start. I think a mac might be in my future, maybe.

jeffdavison · « **Reply #150 on:** 17 Feb 2008, 06:41 am »

well, just tryng to keep this thread up near the top...

Anyone look at this?

http://diyaudioprojects.com/Tubes/KT88/index.htm

jeffdavison · « **Reply #151 on:** 17 Feb 2008, 04:58 pm »

http://webpages.charter.net/porkchop/tubeamp/se_kt88-full%20schematic.jpg

JoshK · « **Reply #152 on:** 17 Feb 2008, 06:26 pm »

Hi Jeff,
Thanks for the links. Those schematics you point to are part of Mikkael's KT88 SET project. Its a quite popular project and pretty simple for beginners. Its also an affordable project that doesn't use hard to find or expensive boutique parts. I mentioned Mikkael's design at the beginning of this thread as one of the possibilities. I think it is a simple and sweet design.

Don,
Keep us up to date on those Radians. They piqued my interest more than a couple times.

On a slightly tangent note, I've picked up a box full of GE 6FW5's. George of tubelab.com, who designed the SimpleSE amp that many here are opting for has been participating on a couple of threads that aren't directly related but have inspired me to try a couple other ideas when doing this project.

George is working on a cathode follower amp (SE) and has tried a lot of different finals. One of the outputs he used were 6LW6's which are a different base version of the 6LF6. These tubes are getting quite expensive. But the idea is experimenting with some of the transmitting pentodes from the end of the tube era. There is also some chatter about a PP class B amp that uses two 6LF6's in screen driven mode (enhanced triode mode) to achieve a linear, lower distortion amp with ability to hit 150w. This with 2 output tubes and relatively little heat for a tube amp!

Well, it got me poking around. I found the 6FW5 (not anywhere as giant as the 6LF6), which is similarly equivalent to an EL36, which is said to be a much more linear pentode than the EL34, particularly when triode strapped. The EL36 was the subject of a screen driven pentode stage in another project. That got me researching what enhanced triode mode/screen driven mode was and its requirements. It won't be something I'll use with this amp, at least not in first iterations, but I do want to compare the 6FW5's I got to the 6550s.

I read some things about the 6FW5s. Mine in particular were made by GE and as similar in internals to the GE 6DQ6s. There is an urban legend that Sylvania used their 6FW5 pentode model as the basis of their 6B4G when asked to make 6B4Gs for a military contract. The 6B4G, as many of you already know, is a 6volt equivalent to the 2A3, which need no introduction. Well I've also read that when triode strapped the 6FW5 is similar, electrically, to the 6B4G. Except the plate dissapation seems to be a tiny bit higher, meaning probably 5-7watts (guessing based on plate dissapation specs) in class A1 triode instead of 4.

Now I don't know if the 6FW5's urban legend of being related to the 6B4G is true, but it does look to be quite linear, which the best triodes from the 2A3 era were. Also, the 6FW5, when found, is pretty cheap, unlike the 6B4G, the 2A3 and the 6A3. I got a box of 38 for $4/ea. The GE brand is also one of the better makes it seems. Recent prices on ebay have seen the 6FW5 spike to around $20/ea now that people are starting to play with them, which is a bummer. They aren't plentiful.

The bad news is that they aren't pin compatible with the 6550/KT88/EL34/etc, so I will have to wire up sockets differently for these. But the good news is, I am using octal relay sockets for my breadboard amp which have terminals for all the pin contacts. This makes changing the pinout quite easy. FYI, the pinout is the same for the 6AU5 and 6AV5 which are slightly smaller versions of the 6FW5, but also very robust and linear pentodes. The 6A*7 might be easier to find if anyone else is intrigued enough to try breadboarding one of these too. Another similar tube is the EL36/6CM5 which I mentioned earlier, but it has a anode cap, so be careful around pets/children with these amps as the top cap is carrying the high voltage. That is one of the reasons why I chose the 6FW5 instead of the 6CM5.

So that concludes the tangent.... I find all this a great deal of fun. Discovery new tubes, different topologies and ideas is what keeps the excitement and momentum going in all my projects. It also have inspired me to try out high performing but cheap tubes.

JoshK · « **Reply #153 on:** 17 Feb 2008, 06:35 pm »

One thing that bugs me with all my research. The name "uber beam machine" doesn't seem fitting though. The Uber doesn't fit, as the 6550/KT88 has around 40watts of plate dissipation, yielding around 8watts in class A**. This is dwarfed by some of the large beam pentodes used in transmitting applications such as the 813, 3E11, 6LF6, etc. A better name might be "beamer". Since this tube is a 5 series BMW, not the 8 series.

**In general, that rule of thumb works well...take a tube's max plate dissipation, in this case 40 watts and multiply it by 1/5 and you get what you might expect from a class A amp. In theory you should get about 1/4 of the plate dissipation in class A, but you also need to back off the max dissipation some in order to spare the life of your tubes, so 1/5 works out well.

nodiak · « **Reply #154 on:** 24 Feb 2008, 05:41 pm »

SimpleSE guys, little help please.
I'm working through cap choices. Bought Sprague motor runs for PS. Looking to order Sonicap G2's for C3, C11, C21. These are all affordable, and changeable later, but from taste reports should be a good start for me.
For C10/12/20/22 I am thinking of Elna Selmic II for the smooth and creamy or Panasonics for more neutral. Interested in choices for these 4 caps that aren't electrolytic also. Solen fast caps are also recommended but are pricey at that value ($25-50 each).
What caps are you guys choosing, esp.for C10/12/20/22?
Here's a thread with some Eddie Vaughn thoughts on resistor and cap flavorings.
http://www.hawthorneaudio.com/forums/viewtopic.php?f=8&t=1797&st=08sk=t8sd=a&start=15
Scroll down to Roberts post's, especially the last one of thread.
The EV amp I'm using is on the smooth and creamy side with Tamura opt's, Elna Selmic II's, Mundorf Silver Golds, motor runs. Overall I'm going to move a bit more toward the neutral and transparent side with the SimpleSE. Also not going to extreme $pending with V-caps, etc...right away.
Copied down Daves resistor list (pg. 12 this thread) and will make some choices on res. asap - been losing alot of time on this project, d&%@it. But I'm cool, I'm cool man...
Don

nodiak · « **Reply #155 on:** 26 Feb 2008, 07:59 pm »

An interesting thread about cathode resistor bypass cap values:
http://www.hawthorneaudio.com/forums/viewtopic.php?f=8&t=1659
I've decided to go in the 100-220uF range for mine. Which also makes better caps more affordable, if desired. I've chosen to try some of EV's ideas on the amp. Which will also help with discussing results at the Hawthorne forum with EV. There's a couple guys there that have built SimpleSE with 5K Transcendar opt's like I'm using, should be helpful.
Don

jrebman · « **Reply #156 on:** 4 Mar 2008, 05:53 pm »

Don,

Interesting.

BTW, where did you get those elna selmic caps?

Sorry I've been out of the loop for a while -- my computer died, and I'm still waiting for my new one -- revived this ancient laptop in the mean time.

Ah, it's always slower going than we'd like it to be.

-- Jim

nodiak · « **Reply #157 on:** 5 Mar 2008, 04:49 am »

Hey Jim, sorry about the computer problems. Having pc problems too, and bought a cheap used one to get by after mine locked up.
I haven't ordered yet but it looks like Handmade Electronics carries Elna Silmic II's which are what I will try.
http://www.hndme.com/productcart/pc/viewcategories.asp?idCategory=13
They're out of 50V 100uF . Is it ok to get 100V instead? I'm guessing it's ok to get higher V, not lower, but dunno.
Picked up Mullard CV4024's and Gold Lion KT88 reissues. Will start on chassis soon.
Don

JoshK · « **Reply #158 on:** 5 Mar 2008, 02:25 pm »

Higher voltage is ok, but they usually get bigger and more expensive with higher voltage which is why people only go a bit higher than high enough.

jrebman · « **Reply #159 on:** 6 Mar 2008, 08:04 pm »

Don,

Saw that Josh answered your questionh about cap voltage ratings -- and the same way I would have

.

Ok, I'm a space cadet and seem to have forgotten what the sinmplese uses for a filament voltage? I don't remember how the filaments are connected. I'm going to order a PT from Jack -- because I just ordered a pair of custom OPTs from him and want a cooler, quieter running PT than the Edcor will be.

So, my recollection on the filaments was 6.3 vac @ 3..5 A? Until I can retrieve all the files from my dead computer I have to rely on my overloaded brain.

Anybody want a good deal on a full complement of Edcor iron for the SimpleSE -- PM me. I'm still confident that they are very good, I just decided to go for something a bit better.

-- Jim