6550/KT88 SET amp aka "Uber Beam Machine"

jeffdavison · « **Reply #240 on:** 2 Jun 2008, 05:05 pm »

Email George directly...
http://www.tubelab.com/PCB_order.htm

Jimmyd53 · « **Reply #241 on:** 3 Jun 2008, 03:42 pm »

How does it sound?

JoshK · « **Reply #242 on:** 3 Jun 2008, 03:44 pm »

Quote from: Jimmyd53 on 3 Jun 2008, 03:42 pm

How does it sound?

Well considering this is a build thread and no one posting in it has yet completed their amp, I'd say it'd be hard for anyone to answer that question.

DaveC113 · « **Reply #243 on:** 3 Jun 2008, 11:04 pm »

Coming Together...

I'm going to hope the elves put it together for me overnight.

The maple was all one thick board that I resawed on a bandsaw, the walnut will be used in the corners, and I have 4 Harbor Freight 16 Oz plumb bobs for feet. The top sheet is machined, and will be painted. I got the maple wet to get an idea of what it will look like finished. I used terminal strips except for the signal wire, which will be 3 strands of Jupiter silver/cotton wire. Most of the rest of the wiring will be 18 ga silver plated teflon. I made a custom powercord for the amp using 12g silver plated teflon wire. The PT and OPTs will be isolated from vibration using a 3/16" thick pure wool felt gasket. Also, its just a power amp using a JJ ecc99 driver tube, and Tung Sol 6550s.

JoshK · « **Reply #244 on:** 4 Jun 2008, 02:38 am »

Very niiice. Love the wood!

I played around in my shop today trying to figure out my dovetail jig and I just haven't seemed to see the way in which it is suppose to be set up.

I need to try a few more ideas.

DaveC113 · « **Reply #245 on:** 4 Jun 2008, 03:12 am »

Its been a few years since I've used my dovetail jig. I think you cut one board with the edge 90 degrees relative to the router, the other board parallel and shifted over some distance. Definitely practice on some scrap. I had to use someone else's bandsaw, and the thickness of my boards varies more than I'm happy with.

I'll probably just bang it together and keep the slop on the inside where you can't see it.

nodiak · « **Reply #246 on:** 4 Jun 2008, 04:21 am »

Dave, looks really good, keep the pics coming, helpful.
Question: Can I just use motor runs (have 50uF and 100uF) mounted off board instead of the Panasonic electrolytics for C1 and C2? I don't have to use the Pana's and then bypass with mr's right?
Don

DaveC113 · « **Reply #247 on:** 21 Jun 2008, 08:29 pm »

Finally got around to finishing the chassis:

Don, I'm probably not as qualified to answer those questions as others, this is my first DIY tube amp, and its based on a pcb I didn't design.

nodiak · « **Reply #248 on:** 21 Jun 2008, 10:06 pm »

Good to see your chassis together, looks mighty fine Dave, we have similar wood choices. Interested in your layout, motor runs on top right? Looks like you might be listening soon. No problem, I'll clear up my build questions at diyaudio where George hangs out.
Don

JoshK · « **Reply #249 on:** 21 Jun 2008, 10:11 pm »

Looks fantastic!

DaveC113 · « **Reply #250 on:** 21 Jun 2008, 10:38 pm »

Don, yep... the motor runs are on the right, opts on the left. I'm mounting the motor run caps with the clamps under the top plate for a little bit of a cleaner look. I'd be interested to see what the options are for replacing the electrolytic caps, and if its worth doing... maybe just adding smaller value film bypass caps would help in some places?

Josh, thanks, I hope to have it done soon.

jrebman · « **Reply #251 on:** 21 Jun 2008, 11:21 pm »

Don,

I will be using no electrolytics in my amp at all. I have two 100 uF motor run caps to replace the 120 uF electrolytic, 1 40 uF to replace the 47 uF electrolytic, and 4 film caps for cathode bypasses -- 75 uF 250 v for the driver tube and 39 uF for the output tubes. Amp will be hardwired in UL with no CFB, standby or Rectifier switches, and I may put in a dpdt switch for switching the gain stage cathode bypass caps in or out of the circuit.

I am also building a slightly different type of chassis starting with a steel hammond chassis and bolting that to a slab of maple butcher block countertop or some such thing.

Our other local guy got his amp working yesterday after a little issue with a bad rectifier tube shorteed out and took out the diodes (better that than the PT). I haven't heard it in person yet, but he's a happy camper.

-- JIm

nodiak · « **Reply #252 on:** 22 Jun 2008, 01:46 am »

Jim, So the values of C1 and C2 don't need to be 120uF and 47uF? Maybe I should make C1 more than 100uF? C2 at 50uF should be fine I'm guessing.
Cathode bypass caps - I had also planned on using much smaller than the spec'd 1500uF, and have a selection of Elna Silmic, Cerefine and Tonerex. Assorted values up to 470uF, but voltages no higher than 100v. Did you go 250v because for circuit purposes, or just availability?
Don

jrebman · « **Reply #253 on:** 22 Jun 2008, 02:10 am »

Don,

Nope, 200 uF for C1 would not be too much (as George describes an amp with a 120 uF electrolytic and an 80 uF motor run, which is in parallel with the 120 uF cap). You won't want to go over 50 uF on C2 as this is the load capacitor that the rectifier sees and 50 uF is getting near the top of it's range. The 50 uF will also probably give you a slightly higher B+, but probably not enough to worry about it.

The Axon film caps are available in 250 volt, which most film caps of this size are not -- they're usually at least 400 v and much larger physically. With this low-profile chassis (less than 2" to work with inside the amp) I might have to go with something like blackgate NXs for the output tubes., and 100 uF will give you a cutoff frequency of about 5 Hz. The 100 volt rating you have for the output tube cathode bypass caps is fine, and you only need 6.3 v rating for the gain/driver tube
So, in short, more capacitance for C1 is fine (within reason) but don't go over 50 uF for C2.

-- Jim

nodiak · « **Reply #254 on:** 22 Jun 2008, 02:25 am »

Thanks Jim. Got it.
One more. C3 - I got a Sonicap for it, but apparently not necessary for sq (been reading again...). Best to get the spec'd Mylar as it will fit the board?
Don

jrebman · « **Reply #255 on:** 22 Jun 2008, 02:32 am »

Don,

I'm not especially worried about that one myself and just plan to use the specified part. I think I have a couple extras so PM me a mailing addres and I'll look for them tomorrow, and if I have one I'll send it to you. No sense paying shipping charges for a 30 cent item. I'm signing off for the night now, but will be back online tomorrow.

-- Jim

JoshK · « **Reply #256 on:** 22 Jun 2008, 04:13 am »

I'd model the choices for C1 and C2 in PSUDII. You don't want ringing on a step change in current but you also want low ripple and no overshoot on power up. Quite often ideal capacitance is a bit less than many like to use. Small changes of +-5uf usually don't make much of any difference depending on which position the cap is in (after the first choke usually is less sensitive). You do have to be careful to not oversize the first cap because of your recitifer.

I have generally found that waveform of the ripple looks much nicer (in PSUD) with only a very small cap on the input (<1uf), then the choke, then the big cap after the choke. This also will produce less EMI generation and puts less stress on the rectifiers. I think that is why many tube amp builders swear by choke input.

Dave, where did you source your brass screws? I got a bunch online, but they were a bit spendy for nuts/bolts.

JoshK · « **Reply #257 on:** 23 Jun 2008, 03:04 pm »

This was always intended to be a build thread and a learning project for me. I wanted to experiment with a number of ideas, both circuit wise and chassis/aesthetics. So I have some comments on some things I've been toying with.

1) not completely related to this project, but I had tried a number of different primers for finishing aluminum. My Aikido preamp has also been a bit of an experimenting project on chassis building. The top plate is just a piece of aluminum cut from a sheet I got from onlinemetals.com. By the way, aluminum cuts really easily on your table saw, or in my case I use my miter saw for cutting it. Noisy, but cuts like butter and doesn't ruin your blades.

Aluminum, as anyone who has ever dealt with it, is near impossible to paint, or rather easy to paint, but it'll scratch off if you breathe on it. It turns out that it is due to the fact that aluminum instantly oxidizes and the oxide bonds with the paint but the oxide scratches off easily. What is needed to paint aluminum is an acid that will eat through the oxide and allow the paint to bond to the metal, but it oxidizes immediately as said, so it is very troublesome to do. However, auto part stores sell a "self-etching" primer that has an acidic additive that does the trick.

I had tried all the big box stores and they don't carry it, but my local auto parts store had it. It works a treat and it mildly pits the aluminum yield a slightly textured finish, which has a nice look. I tested the results and it isn't easy to scratch off with your fingernail like all the other primer types I tried. Aluminum is a bit soft, so you can scratch it off, but it basically takes something sharp that gouges the aluminum to take the paint off. This would be enough force to scratch any finish, including anodine or painted steel, etc. So if you ever wanted to paint aluminum, look for self-etching primer at an auto parts store.

2) I've conclude the Craftsman Industrial Dovetail Jig is a POS!! I bought it used off ebay, and didn't receive the manual/instructions, which I thought was the reason for my frustration. I scoured the internet but didn't turn up any manuals, not even the sears parts store make it available. So I read a bunch of online tutorials and some of my woodworking mags that I acquired. When I felt I had the jist of the idea I went to try it out with some offered up test pieces.

The jig comes with a 9/16" template guide for making a finer box joint, what I needed for my 2.5" wide wood. The jig comes with some guide bushings, none of which fit any of my three routers, two of which are extremely popular routers. Nevermind that the bushings don't fit my router, but the required 0.40" (2/5") bushing's barrel is 2 times too deep for the template! This is what comes with the jig and it doesn't even come close to working. Try finding another 3rd party 0.40" bushing and you'll quickly find noone makes them. Sears doesn't carry such an animal, they offer one other 0.40" bushing in their bushing kit, but it is too long as well (I know I bought, tried and returned it). So this template guide is worthless and there went my Sunday.

3) Benchdog products rock! Every product I've bought from them has been worth the asking and then some. I had previously bought a cast iron router table insert for my tablesaw. I really liked it and the attention to details make it very useful. Even my wife used it a couple times when building trim and commented that it was worth the money and very handy.

My shop is slowly coming into order. Half our basement got refloored and we laid granite tiles after releveling (it had about 3" of variation before in the concrete). All my tools are on casters, and with the exception of my tablesaw, all the tools will be stored against the wall and be pulled out into a work area when in use and hooked up to a drop down attachment to my dust collector. So I decided to pick up the benchdog's stand for the insert and use it as a independent router table.

I looked around and the cheapest stand that wasn't made of plastic or particle board was about $40, but benchdog's purpose made one was $60 with free shipping. I decided to spend the $20, but was a little skeptical that the birch ply stand wouldn't be that nice and sturdy. I was wrong, it is very nice and very sturdy. The instructions (for putting the stand together; its shipped as flatpack) were actually clear and intelligible, imagine that! Benchdog has reassured my faith that there are still companies that make quality products.

PS) My craftsman skill saw died after 3 years of light use. Died as in won't even budge when trigger is pulled. My grizzly economy priced hammer drill died after a year's use. Its reinforced the saying to me, "buy nice or buy twice," when it comes to tools.

PS2) I still plan to finish up my experiments in patinization. I think I might have figured out the formula that gets me the closest to what I want. I just need to try a couple variations before I call it. This is the hold up on making progress on my UBM chassis, that and the dovetail fiasco.

DaveC113 · « **Reply #258 on:** 23 Jun 2008, 03:41 pm »

Quote from: JoshK on 22 Jun 2008, 04:13 am

Dave, where did you source your brass screws? I got a bunch online, but they were a bit spendy for nuts/bolts.

Local hardware store... they are pretty expensive, the #8 x 3/4" wood screws were $0.15 ea, the total bill for all the hardware was around $10.

jrebman · « **Reply #259 on:** 23 Jun 2008, 04:13 pm »

Josh,

Yes, that SEM self-etching epoxy primer is good stuff. Two coats is also a good idea. I'll be using that on my steel chassis, and may even use it on the transformer bells and motor run caps.

As for brass screws, I just bought a few packs of 10 8-32 x 1/2" buttonhead machine screws for about $3.80, which is also approximately the price of a set of 8 threaded brass inserts for wood.

Hopefully I'll be able to report on that project sometime soon, but it's going to be good.

-- Jim