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Old 25th June 2007, 11:41 AM   #1
jarthel is offline jarthel  Australia
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Default KT88 PP suggestion

Since this morning, I've been looking at various Kt88 designs.

I've seen the ones from Pete Millett, those in simpletube database, Andrea Ciuffuli, diyparadiso and various others sites.

2 main criteria:

1. can be used without an active preamp (i.e. I can use a log pot at the input and that would be enough for my CD player)

2. no interstage. I've seen the design by Andrea but it requires an interstage.

I can live with without no.1 I suppose if you know of a pre-amp schematic that is a good match

Thank you for the help
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Old 25th June 2007, 12:59 PM   #2
Sherman is offline Sherman  United States
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I've been looking at the possibility of using these being sold by Uncle Ned at Tube Zone.

http://store01.prostores.com/servlet...-Mark-3/Detail

(If the link doesn't work go to www.tubezone.net and click on the 'Online Store' link and check out the printed circuit boards.)

They are small enough that you could put both in a single chassis with the KT88 tubes and iron and build a stereo amp. The Hammond 278CX or 378CX PTX that should be able to power the beast.
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Old 25th June 2007, 01:26 PM   #3
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Quote:
Originally posted by Sherman
I've been looking at the possibility of using these being sold by Uncle Ned at Tube Zone.

http://store01.prostores.com/servlet...-Mark-3/Detail
I rebuilt a pair of (almost completely) gutted Mark IIIs using those boards. With a good set of tubes, they sound pretty dang good to my ears. They have a certain ease to the sound and I also like the current sinked LTP. My only gripe is the use of 1/2 of the 5751 for the input circuit. I guess I don't like having a section 'wasted'.
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Old 25th June 2007, 01:46 PM   #4
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Jarthel,

You seem to be very undecided about what you want to do. You need to decide the output power you're seeking and make a decision, also, on the topolopgy that you think will meet your needs.

You expressed interest recently in the H-K Cit II, which uses KT88s in UL mode but also uses video pentodes in the front end/splitter/driver stages and seems to me to be a very demanding project. If I were you, I would stick to something where the chances of success are high.

I would guess that you could probably meet many of your requirements with a PP amp using KT88 (or 6550) in triode mode. This would greatly simplify the design, requiring very little in the way of negative feedback to attain good damping and low distortion, thus avoiding complicated phase compensation networks and the risk of instability. PS design should also be very straightforward.

The simpler the design, the better, consistent with gain being sufficient to give full power from your CD player input. If I were you, I would avoid a Williamson-type design because of the number of stages involved. I suggest either:

* a 'Mullard' style design using a high-mu triode front-end, a medium-mu LTP phase splitter/driver, with CCS in the tail and KT88s in triode-strapped push-pull, using a small amount of global NFB; or

* a fully differential design, with a high-mu LTP phase splitter with CCS in the tail, a differential medium-mu driver and, again, KT88s in triode-strapped push-pull, including cross-coupled balanced negative feedback, which I have found to be particularly effective since it was suggested by Thorsten Loesch on this forum some months ago.

In either case, I would recommend a 6SL7 as the high-mu triode and 6SN7 as the medium mu splitter/driver.

I'm sure you will receive many other suggestions from members here (including those who will assure you that a Williamson will do the job). Try not to get too confused, and good luck!
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Old 26th June 2007, 01:19 AM   #5
arnoldc is offline arnoldc  Philippines
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Yeah, it seems to me that Jarthel is in a state of confusion right now, and I can understand that.

If you really wanted flea powered SET amps, you have to work on your speakers. If you're not willing to do that, then might as well shift to more powerful amplifiers.

In my experience, the success of a SET system is mainly based on what speakers it will drive. I made a journey from commercial speakers to what I have now- a DIY. I'm not going back.
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Old 26th June 2007, 11:53 AM   #6
jarthel is offline jarthel  Australia
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the WAF (I've seen it several times but never understood what it meant until today) will be thrown out the window if I decide to go for highly efficient horns!
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Old 26th June 2007, 12:04 PM   #7
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http://www.triodedick.com/pdf_files_td/Bill_En.pdf
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Old 26th June 2007, 12:15 PM   #8
jarthel is offline jarthel  Australia
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Quote:
Originally posted by LaMa
http://www.triodedick.com/pdf_files_td/Bill_En.pdf
I have seen that and I believe it does not come with a log pot. I can't read dutch so I do not know if the amp has enough gain to eliminate a preamp.

unless you have a suggestion for a preamp schematic to match the MonoBill?
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Old 26th June 2007, 12:41 PM   #9
tinitus is offline tinitus  Europe
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This New Boully 66 with KT66 might be interesting

http://www.diyparadiso.com/ppdesign1.htm

But PeteMillets "UNI" should do KT66 too
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Old 26th June 2007, 05:32 PM   #10
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Quote:
Originally posted by jarthel


I have seen that and I believe it does not come with a log pot. I can't read dutch so I do not know if the amp has enough gain to eliminate a preamp.

unless you have a suggestion for a preamp schematic to match the MonoBill?
This is the integrated version. The dutch version of the article also shows some foto's with the extra switches (not yet translated I think). It has enough gain (extra 6sn7 tube, the mono bill doesn't have that).

http://www.triodedick.com/Bill_deel10.htm

You can mail him for additional questions.

ps there are two amplifiers with KT88, the one chasis Bill (also usable as integrated) and MonoBill (without the 6sn7) this one needs a preamplifier. His new 6h30 (or 6n30 for us europeans) Cleo 6 should be a nice option.
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