6550/KT88 SET amp aka "Uber Beam Machine"

Dmason · « **Reply #20 on:** 2 Dec 2007, 07:57 pm »

One person I have spoken with, Mr Robert Simpson of Port Colborne, Ontario, a friend of my brother, who is a professional custom guitar amplifier builder with clients like Gordon Lightfoot, Alex Lifeson, Jim Cuddy, Leon Redbone and others, is completely smitten with the new production TungSol big pentodes and tetrodes, as well as the octal dual-triodes. He feels the new production 6550, and 6SL7 are at least as good as the much sought after NOS ones, and has his best effort SE triode-strapped 6550 at home and feels it leaves nothing to be desired, to shi shi DHT triode tubes. He thinks this reason alone is a good one to pursue this angle, and feels George Anderson's PCB would be a very good test bed for this, and if it worked to satisfaction, so much the better. He is getting around 12 watts SE with the 6550, and with good outputs as he uses, turns the whole affair into a muscle amp with SET sonics.

jrebman · « **Reply #21 on:** 2 Dec 2007, 07:58 pm »

The other option with the octal board is the 12sn7 and 12sl7 -- cheaper than their far more popular 6 volt brothers, and lots and lots to choose from -- for those who have to stick to a tight budget and still want top-notch NOS octal tubes. Dr. Lloyd uses these quite regularly in his designs.

I totally agree with the 1 volt input sensitivity -- as that easily covers modded SBs, which will be my most likely primary source in this system.

So, are we looking at something around 7-9 watts triode and maybe 12-15 UL?

Looking good,

Jim

jrebman · « **Reply #22 on:** 2 Dec 2007, 08:40 pm »

I'm starting to consider the idea of using an Aikido and a tubelab SimpleSE together -- perhaps bypassing the 12AT7 on the SimpleSE board and configuring the output stage of the Aikido to meet the requirements of the SE amp board. Not sure it will work, but I'll give it some thught.

-- Jim

JoshK · « **Reply #23 on:** 3 Dec 2007, 02:49 am »

That could work, but I am not sure it'd buy you anything other than ease of some of the build, but then you'll have to mod the board to cut out the front end of George's and accept the Aikido.

As far as output power, that is probably about right. About the same as a 300B I'd guess but a bit more on A2 if you can provide the current. UL gives you more but at the expense of lower dampening factor (higher output Z) without added feedback. If you used cathode feedback, it'd probably offset the UL setting.

Added: George says about 8 watts for 6550/KT88 in triode and ~14w for UL. About what I expected. EL34 in triode is about 5w.

JoshK · « **Reply #24 on:** 3 Dec 2007, 03:27 pm »

Here is a model of the aesthetics that I am going for. I have some copper plates to use and enough wood types around to choose whichever looks best. I am showing it here though because the layout is pretty much ideal. It isn't symmetric and some may not like that aesthetically but the power supply is away from the signal stage and this makes routing wiring easier to avoid hum pickup and such problems.

jrebman · « **Reply #25 on:** 3 Dec 2007, 04:39 pm »

Josh,

By your description, it sounds like pretty much what I had in mind, except that I'd like a brass or bronze top plate. I'm thinking walnut or Brazillian Rosewood with a slight convex profile (it's nice to have a friend with a CNC

. )

Thinking it over last night, I think the SimpleSE is a good way to go (at least for myself), and I can build an Aikido linestage later if desired. Size, cost, and complexity all figured in, and I'd rather put the money towards the iron, caps, etc. that are going to have the biggest impact on sonics.

BTW, I was pointed to these 100 uF 650 volt Sprague motor run caps yesterday
(and bought a couple of them):

http://cgi.ebay.com/New-100UF-100-UF-RUN-OIL-CAPACITORS-CAPACITOR-370V_W0QQitemZ180187455916QQihZ008QQcategoryZ4662QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

-- Jim

JoshK · « **Reply #26 on:** 3 Dec 2007, 05:00 pm »

Yep, I have those linked in my list for sources of caps. I just didn't point to them yet because I haven't completed the PSU yet and I am not 100% sure I'll use that value. Most likely though I will. I also have a few other sources for caps, as well as dual section motor run caps at reasonable prices. The dual sections have essentially the tuning cap and the filter cap in one.

nodiak · « **Reply #27 on:** 3 Dec 2007, 05:57 pm »

Hi guys,

I pm'ed Bill (on another site we visit) who built the SimpleSE below about this thread. He may not see my pm for awhile so I thought I'd go ahead and post the pic of his amp - the one at the bottom of the page in the link. I like the use of the upside down roasting pan, have seen this elsewhere too. The amp did well at burningamp, using Hemp 8's in a metronone cab. I would likely go with a similar layout for my SSE.

http://www.tubelab.com/UsersAmps.htm

Yours is very nice looking and well thought out Josh! I've also planned on wood, but will go with chunky corners/feet that extend below wood sides a little (.5 - 1" ). I've seen and like that look.
BTW, is it best to use non magnetic metal for top plate?

Don

JoshK · « **Reply #28 on:** 3 Dec 2007, 06:20 pm »

That isn't my amp, it is someone else's for whom I can't remember. It is just the one I was going to use as a model of aesthetics.

JoshK · « **Reply #29 on:** 4 Dec 2007, 06:00 pm »

Does anyone know how to calculate critical inductance for a power supply such as this?

JoshK · « **Reply #30 on:** 5 Dec 2007, 12:26 am »

Got the tubes today and the transformers too! aa Lots of fun in store!

Does anyone know of a very simple drawing program (2D) that would be good for drawing layout. I want to put in a scale so I put in real measurements and have it scaled accordingly and preserve dimensions.

jrebman · « **Reply #31 on:** 5 Dec 2007, 12:29 am »

Josh,

I think there is something called google sketchpad or something similar that you can get on google. I obviously don't use it, but one guy I sold some parts to used it to sketch up his amp.

Are those the tung-sol 6550s you're talking about?

-- Jim

JoshK · « **Reply #32 on:** 5 Dec 2007, 01:08 am »

Yeah and I got some TS 6SL7gt's to try too.

SET Man · « **Reply #33 on:** 5 Dec 2007, 01:20 am »

Hey!

Josh, look like you have one more project in your hands. Hope you have room in your lab for this.

Anyway, seriously... I do have a bit of fascination with the SE KT88/6550 also. I did considered this type of amp before I found my current amp.

I have read somewhere back than that KT88 dose measure much like 300B in SE mode... if I remembered correctly

There are some SE KT88/6550 amps out there like Audio Note and recently Quick Silver just released SE KT88 also. Very interesting.

Anyway, I will be very interested to see and hear you amp once is done. Maybe you could bring it over to my place someday, hook it up to my 94dB Single Diver speaker. And I will put on a record of a girl singing with a guitar for you

Have fun Josh.

Take care,
Buddy

JoshK · « **Reply #34 on:** 5 Dec 2007, 01:22 am »

A cheap and simple chassis would be to use a pro bake pan, like these

https://www.surfasonline.com/products/15122.cfm

$23 and pretty thick aluminum and then just add wood trim around the edges and/or paint as is. You can also purchase raw aluminum sheets from onlinemetals.com and just make a top plot and the frame from wood. Options that don't cost an arm and a leg and still turn out nice.

JoshK · « **Reply #35 on:** 5 Dec 2007, 01:45 am »

poseidonsvoice · « **Reply #36 on:** 5 Dec 2007, 02:12 pm »

Quote from: JoshK on 4 Dec 2007, 06:00 pm

Does anyone know how to calculate critical inductance for a power supply such as this?

Josh,

I don't know if you mean 'calculating the critical inductance for a choke input power supply' but its pretty straightforward.

Critical inductance can be roughly calculated as Evolts divided by Ima, where Evolts is the desired PS output voltage and Ima is the current draw in milliamps.

I then take that value and multiply by 2 so I have a some leeway. In my own headphone/linestage tube preamplifier, the B+ is about 375V and the current draw is 40mA so my critical inductance is (375/40) or 9.375H. Thus, my input choke is a 20H Lundahl

Pictures are in my gallery.

Best,
Anand.

JoshK · « **Reply #37 on:** 5 Dec 2007, 03:35 pm »

Thanks.

That is what I want. (my google searches didn't turn anything up).

So for our case it is roughly 400/175 = 2.3, 5H would be a good choice.

poseidonsvoice · « **Reply #38 on:** 5 Dec 2007, 03:50 pm »

Quote from: JoshK on 5 Dec 2007, 03:35 pm

Thanks. That is what I want. (my google searches didn't turn anything up).

So for our case it is roughly 400/175 = 2.3, 5H would be a good choice.

Excellent, you got it

Make sure the choke can handle at least 200 mA though for good measure. You will probably have a few bleeder resistors in the power supply which would increase the current requirements just a little.

This info is also available in Allen Wright's preamp cookbook.

I actually use a 'pseudo' choke input power supply. I have a small input capacitor (anything less than 1 uf but able to handle large peak voltage surges like 2 times B+) and it should be a nice oil cap. Mundorf's SIO would be ideal as they are rated for 1200V but expensive. I then model the whole thing on Duncan amps PSUD II and tweak around until I get the low ripple I want but with a smooth ramp up to B+. I hate having a very spiky B+ for the first couple hundred milliseconds before it settles. Very easy to model with Duncan amps PSUD II though.

Best,
Anand.

JoshK · « **Reply #39 on:** 5 Dec 2007, 05:06 pm »

Anand, your sentiment and approach looks like mine. This is also how I am going about designing this PSU. It will be a choke input PSU most likely. A "tuning" cap may be used, for reasons you mentioned, but I think this is still a choke input supply when viewed from the perspective of frequency (i.e. 60hz). At high freq it becomes cap input.

I like enough capacitance to damp ripple but not so much that is makes rise time quite long. I am not sure rise time is the appropriate verbage but I think you get my drift.

With regards to tuning cap, motor-run caps have quite high voltage tolerances, at least in DC terms and for short term periods. So small motor-run caps will work and are very inexpensive. Also I have some ERO MKP caps that are rated at 1000V that are reasonably priced. Then there are Russian military caps, both PIO and Teflon with 1000V ratings (apparently conservative at that). These are quite nice and not expensive. I see no reason to choose Mundorf in this case.