6550/KT88 SET amp aka "Uber Beam Machine"

DaveC113 · « **Reply #120 on:** 1 Jan 2008, 09:22 pm »

Can anyone say approximately how hot the top plate will get?

Thanks,
Dave

JoshK · « **Reply #121 on:** 1 Jan 2008, 09:36 pm »

well George would have first hand experience but you can probably estimate it from assuming 1) that the output tube is the major contributor to heat, 2) the output stage is class A so it is putting out some percentage of its output in heat (like 50%?). The KT88 is putting out 5-8watts which is likely about 20% of its power draw, so the rest is heat maybe. They are probably similar to 100watt lightbulbs, maybe more heat.

jrebman · « **Reply #122 on:** 4 Jan 2008, 11:25 pm »

Just an update on the trio of SimpleSEs getting built here in Boulder.

We have most of the parts -- save for a few switches, mounting hardware, and power supply chokes (and I still don't have my PT or OPTs, but that will have to wait for a while until I can afford them.)

We've been getting various pieces of wood and top plate materials. Dave and Mike are going to use aluminum plates and Maple and maybe bloodwood for Mikes. I snagged a few boards of highly figured curly Koa with a reddish tint, but the guy who sold it to me also offered me a nice piece (10" x 72" x 1") of a lighter gold color piece of Koa for $60, and that's the piece I'll probably use for this amp (and a preamp chassis as well.) I also picked up a 12" x 24" x .125" piece of copper plate for my top plate.

Next step is to have a board stuffing and soldering g2g, and then get the plates machined (Mike's dad owns a machine shop, so that makes it easy.)

I had a good discussion with ZJack Elliano the other day and it's looking like my amp will be all electra-print iron -- PT, OPTs, PS choke.

So, we're plugging away, but still see it being a while before any of these are making music.

-- Jim

JoshK · « **Reply #123 on:** 5 Jan 2008, 07:12 pm »

Sounds like a pretty good time. Its nice to have others to build with as you guys teach eachother a lot more than you might think.

I started to build a breadboard version of the amp but I am waiting on 4 missing resistors that I forgot to order and then they got backordered. The Aikido board is otherwise done and I made a plywood platform to build the "breadboard" version on. Then while I waited I took my momentum and finished up a pair of UcD monoblocks that had been sitting on my bench and a finished the TVC preamp (save for some reconfiguring of the HT bypass...I don't like how I have it set now).

jrebman · « **Reply #124 on:** 5 Jan 2008, 07:29 pm »

Josh,

So how is your aikido configured? I'm assuming you went with the octal version -- are you using 6sn7/octal 6h30? And if so, what PS voltage?

Just curious as I'm building my 9-pin version more or less the same with 6cg7 for gain and 6h30 (or also 6dj8) for output.

-- Jim

JoshK · « **Reply #125 on:** 5 Jan 2008, 09:09 pm »

6SL7 into 6H30 octal @ 300volt B+

6CG7 is only going to provide a gain of 10x or 20db, so you are going to have to have a medium gain preamp (high for a preamp) to drive the 6550 to full output.

jrebman · « **Reply #126 on:** 5 Jan 2008, 09:38 pm »

Josh,

Should have said that this is for a preamp, not for a driver stage for an SE amp. I'd like to be able to see the schematic because I'd actually like to cut the gain down to 10 dB or so. The 20 dB would be great for the F4, but that's a long way away (did you see that the boards are now being made and orders taken?) -- maybe switchable 10/20 dB gain -- don't know if the aikido will support that or not.

-- Jim

JoshK · « **Reply #127 on:** 5 Jan 2008, 09:56 pm »

Feedback would be the only way to cut gain with that tube configuration....or an output transformer with 2:1 ratio would do it too. I was thinking the latter 2:1 idea might be something I'll explore. It trades the excess gain for more driving current, which is nice for driving SS amps and longer cables.

I did see the F4 board order and ordered a pair for a later date.

I don't know of any lower gain dual triode noval tubes to be used in the first stage of the aikido. The 12B4 would be cool to try in the Aikido but it isn't a dual triode so it wouldn't work with the noval aikido boards without some adaptation.

When I finally fire up my Aikido line stage I was thinking if I really liked it I'd cut the gain in the amp accordingly. For the 6550 SET amp, with the Aikido driver it would be as simply as rolling in a 6SN7 in lieu of the 6SL7 in the first spot and change R2 & R4 to optimize, although it will work without the resistor change.

With George's board, I am sure you could roll in the 12AU7, 12BH7 or ECC99 in lieu of the 12AT7 but you'd need to change the cathode resistor and reset the CCS current assuming it has enough room to do so (I think it does). Still not too hard, but not like just rolling the tube.

nodiak · « **Reply #128 on:** 9 Jan 2008, 06:21 pm »

Jim, do you know which models you're going to get from Electra Print? Really appreciate the Boulder group's sharing their projects.
Also, I have thought maybe the 5965 might be a good alternative, just from what I've read.

jrebman · « **Reply #129 on:** 9 Jan 2008, 06:47 pm »

Don,

The choke is the model 2528 power supply choke and costs $34 in open frame configuration and Jack can add bells for another few bucks. I think he said they are about 2" x 2-1/2" x 3" and weigh 3 pounds each. Small enough for me to fit underneath the top plate.

My copper plate and Koa boards arrived, and in sorting through my stash of parts I found a 50k dual log taper PEC pot.

Josh, regarding output coupling transformers for the Aikido, it looks like the CineMag CMLI-4x150D will work nicely as a 2:1 or 1:1 with a simple switching arrangement using a DPDT to switch the two primary coils from series to parallel and with the outputs wired in parallel. Looks to be a very fine transformer. So, with a 4PDT switch I can have selectable 10 dB/20dB gain transformer coupled output for the Aikido -- I like the idea of that.

-- Jim

jrebman · « **Reply #130 on:** 13 Jan 2008, 03:51 am »

I was poking around DIYaudio yesterday and I noticed a post about transformers for the SimpleSE, and found out that there is a better model of the Edcor available, plus an Edcor power transformer that almost looks like it was designed for this amp.

The OPTs are the CXSE series -- 25 watters, much beefier than the XSE ones, closed design with end bells and lead-out wires, and not solder tabs, and with much better frequency response. I did some poking around and these seem to get pretty high marks from those who have used them, and at $83.50 each, they look like a real bargain. Drawbacks that I can see: they are single primary and single secondary only, the UL tap is at 40% if that bothers you, and they are some sort of blue color that to me sounds pretty gaudy. Given that, they do seem to offer a lot of customizations, and most new designs have a one-time setup fee of $20 and they'll do single unit quantities. If somebody has previously paid for the same design you want (as in, they have it in their design files already) the setup fee is waived. I've seen some references to OPTs with multiple secondaries, and will ask them about this when I call on Monday. It would also be very nice if they would do a black powder coat instead of the blue, but I'm not sure if that is an option or not.

The poewr transformer is not in their stock line, but is one that another person had done custom, and is configured as follows:

Primary: 120 vac 60 Hz (yes, not 115 like Hammond)

Secondaries:

380-0-380 @ 200 mA
6.3 v @ 5A
5v @ 3A

The PTs are in a light gray finish as standard, and cost about $65 or so. It appears that they don't stock these and all are made when ordered, so that's probably why customization is not a big deal for them.

So, assuming no custom options and not including shipping, it looks as if a decent quality set of iron can be had for $225 or so, and I've not seen anybody say anything bad about these, only that they were quite good, and an exceptional value.

-- Jim

So, as I said, I'm going to call them on Monday, and see what the options and pricing are like for a full complement for a SimpleSE, and I'll post a breakdown here for any others who may be interested.

jrebman · « **Reply #131 on:** 14 Jan 2008, 06:29 pm »

As promised, I spoke with the good folks at Edcor this morning and ended up buying a full complement of iron for my SimpleSE (except for the PS choke, which will be an electra-print).

They don't do the powder coating in-house so the best option they could offer was to get the light gray end bells on the OPTs to match the ones on the PT. They also told me that a lot of folks paint them with an epoxy or enamel paint and have no problems. Here are the part numbers and prices for anybody else who may want to go this route.:

Outputs:

CXSE25-8-5k $83.50 each
(25 watt, 5k primary, 40% UL tap, 8 ohm secondary)

Power:

XPWR-033: $59.48 each
(120 vac primary, 380-0-380 @ 200 mA, 6.3v @ 5A, 5v @ 3A secondaries.

They estimated shipping at about $15 from N.M. to Colorado.

I'll definitely let people know how these sound, and I hope this gives folks another option to consider.

-- Jim

nodiak · « **Reply #132 on:** 14 Jan 2008, 09:11 pm »

Wow Jim, that's a good price. After George's assessment of the cheaper ones and the comments at diyaudio, it will be good to hear how these sound to you. Nice to see the build doesn't have to break the bank!
Don

jrebman · « **Reply #133 on:** 14 Jan 2008, 09:19 pm »

Don,

I did a lot of googleing and found all kinds of comments about these, and they seem to be significantly better than the XSE series, and people just had nothing but good things to say.

And if you ever consider selling that EV amp, you know who to call, right?

-- Jim

nodiak · « **Reply #134 on:** 16 Jan 2008, 04:57 pm »

Jim,
The EV amp is coming around lately (~ 250 hours on it), recently went back to 8" Hemp based speakers, they work very well together. I'll take good care of it and let you know if such a thing crosses my mind, (stranger things have happened). Am looking for a good preamp so I can have more inputs and sub at line level, TS Grounded Grid is recommended by Eddie to not change his amps signature.
My amp uses Tamura transformers, other similar EV amps use Transcendar's, would be nice to hear the difference. I am still leaning towards Transcendars for the SimpleSE based on the satisfaction of the EV crowd.
Don

jrebman · « **Reply #135 on:** 16 Jan 2008, 05:12 pm »

Don,

You might want to look into an Aikido kit. I've seen a few people who replaced their TS GGs with them, expecting no change or worse and who were pleasantly surprised. I'm going to be building one for my AKSA 100 N+ in my main system, and have a pair of CineMag 2:1 line output transformers on order that will let me cut the gain a bit, and which can easily be setup with a switch arrangement for either 20dB or 14 dB gain choices.

And who knows -- by then I may already have built a set of SE EL84s of my own

.

-- Jim

nodiak · « **Reply #136 on:** 16 Jan 2008, 05:40 pm »

Everyone seems to like their Aikidos for sure. Have considered it. The TS GG would be a fast build and leave me more time for the SimpleSE tho. Still since I need a preamp asap (sooner than another amp) I'll look at the Aikidos again.
Eddie put alot of gain in this amp, really wouldn't need much if any from a pre.
Don

jrebman · « **Reply #137 on:** 22 Jan 2008, 11:53 pm »

The Edcor iron arrived today, so without the holiday it would have been one week from the time the order was placed -- not bad.

They are pretty substantial -- the PT weighing approximately 7 pounds, and the OPTs are 10 pounds each. The bells have a nice gloss powder coat finish and they feel very wel made. All the transformers have leads that are at least 12" and the wire itself is well insulated -- definitely not wimpy wleads.

The laminations are nicely punched and stacked, very tight, and lots of them. Ok, not the cleanest punched laminations I've seen, but very close, and a lot better than a good deal of what's out there -- nothing to complain about at all. Very respectable, and considering the $83.50 price tag, excellent would be the word that comes to mind.

Of course we'll still have to see what they sound like, but George likes them enough that he's building them into a "permanent" amp, which should say something.

So, for the curious, total price for all three transformers and shipping came to $248.

-- Jim

DaveC113 · « **Reply #138 on:** 24 Jan 2008, 09:42 pm »

I asked George at tubelab about the ecc99 for a driver tube, and as a result I'm going to adjust the plate voltage and current for the tube. The 10mA of plate current meant for the 12at7 combined with the higher plate voltage didn't put the ecc99 in the ideal operating range (not even close actually...). George suggested 175V, and from the JJ website and searches on diyaudio, I've decided 22 mA of plate current will best optimize the operating point of the tube. This puts the grid voltage at about -5V, and at 22 mA, I get a 227 Ohm cathode reistor, so I'm going to go with the original 220 Ohm value there. The plate resistor will be changed from 330 Ohms to 150 Ohms to allow for the 22 mA plate current. I checked the CCS datasheet, and this will not be a problem. From the datasheet it looks like I need a 140 Ohm plate resistor, which is very close to the 150 I calculated.

The plate characteristcs of the ecc99 are more linear than the 12at7, and I expect it will outperform the 12at7 when the amp is driven with my high-gain preamp. I doubt the amp will have enough gain to use as an integrated amp with the ecc99, but I'll try it, and I'll also try the 12at7 with and without a pre as well.

Dave

JoshK · « **Reply #139 on:** 24 Jan 2008, 10:54 pm »

Good work Dave and good news Jim.

I got an email from a lurker today that is interested in building this amp. He said he has build many other projects before and has used the Edcors and likes them a lot. More data points in favor of Edcors.