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Old 20th January 2010, 07:33 PM   #101
taj is offline taj
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Hey guys,

I've become interested in this project, and hope to one day build one (after my never-ending home renovation is complete and my construction workshop is converted back to an amplifier/speaker "lab".) In the meantime I'd like to contribute by doing what I enjoy second-most. I'm an ex-technical writer and technical illustrator, so I see an opportunity here to help out with some documentation.

Something I've been looking for is a well documented project, and there doesn't seem to be too many of those here in tube world. This project looks like a great candidate to become one of those. I'm new to tubes and I've discovered a great way to gain a better understanding of new subjects is to draw and write about them (at least until said reno is just a distant memory and I can resume burning myself and buying parts.)

If you guys are game, send me all your latest schematics, BOMs, specs and plans and I'll compile them and turn it into a project that others can follow (eventually). Once the amp design is finalized and a couple amps are built and debugged, a "constructor's thread" can be started for others to get help building this.

Oh, I also think this amp needs a catchy name. Got one in mind?

... Todd

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Old 20th January 2010, 08:17 PM   #102
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Originally Posted by TubeMack View Post
Thanks Guy's

Eli, I may shoot you a PM a little latter on to get your thoughts on the 6GK5 vs the EF86.....
Is the 6GK5 an option here in the first hole?
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Old 20th January 2010, 09:28 PM   #103
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Originally Posted by taj View Post
Hey guys,

I've become interested in this project, and hope to one day build one (after my never-ending home renovation is complete and my construction workshop is converted back to an amplifier/speaker "lab".) In the meantime I'd like to contribute by doing what I enjoy second-most. I'm an ex-technical writer and technical illustrator, so I see an opportunity here to help out with some documentation.

Something I've been looking for is a well documented project, and there doesn't seem to be too many of those here in tube world. This project looks like a great candidate to become one of those. I'm new to tubes and I've discovered a great way to gain a better understanding of new subjects is to draw and write about them (at least until said reno is just a distant memory and I can resume burning myself and buying parts.)

If you guys are game, send me all your latest schematics, BOMs, specs and plans and I'll compile them and turn it into a project that others can follow (eventually). Once the amp design is finalized and a couple amps are built and debugged, a "constructor's thread" can be started for others to get help building this.

Oh, I also think this amp needs a catchy name. Got one in mind?

... Todd

PM me for my email address.
That sounds like an awesome contribution and I hope everyone will take you up on it. I think this will probably be my next build as well and it would be great to have everything in one spot and easy to access.
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Old 21st January 2010, 01:44 AM   #104
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Glad to see more come on board! I'm afraid I don't have much yet. The last posted Main, and PS schematic by me is it. The PS appears to be about done with most parts listed above by wonderboy. The main amp is also about done, but no parts have been decided on. I may need more help with this. I'm also unsure about the OT specs. I'm thinking about 100W rating, 40% UL tap, but I have not yet learned how to spec the Impeadance. I'm still unsure about the CCS, as there hasn't been any strong comfirmation on it yet. There is also the question of a possible sub of the EF86 with a 6GK5? I've been resorting to rereading my books!

Taj, document away! I see many many new guy's comming to the forum looking to built KT88 monos. Currently there is no FULL documentation to do this. Like me, many have to resort to building some variation of a ST70 due to the lack of comlpete documentation. I'd love to have a part in a change here. The great thing about this amp is that it first saw light a few years ago by another forum member, and many members here helped with it's current form. It has had a long birth, first by Mullard, then redone by Claus Byrith with yet another redesign here on this forum buy several experts. My main contribution has been the decision to break it up into monoblocks. I can send you bigger files for the schematics.

Hmmm. A name.........? I think something classy from classical music I reckon.....

Last edited by TubeMack; 21st January 2010 at 02:03 AM.
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Old 21st January 2010, 01:59 AM   #105
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Originally Posted by TubeMack View Post
Glad to see more come on board! I'm afraid I don't have much yet. The last posted Main, and PS schematic by me is it. The PS appears to be about done with most parts listed above by wonderboy. The main amp is also about done, but no parts have been decided on. I may need more help with this. I'm also unsure about the OT specs. I'm thinking about 100W rating, 40% UL tap, but I have not yet learned how to spec the Impeadance. I'm still unsure about the CCS, as there hasn't been any strong comfirmation on it yet. The is also the question of apossible of the EF86 with a 6GK5? I've been resorting to rereading my books!

Taj, document away! I see many many new guy's comming to the forum looking to built KT88 monos. Currently there is no FULL documentation to do this. Like me, many have to resort to building some variation of a ST70 due completely to the lack of comlete documentation. I'd love to have a part in a change here. The great thing about this amp is that it first saw light a few years ago by another forum member, and may member here helped with it's creation. It has had a long birth, first by Mullard, then redone by Claus Byrith with yet another redesign here on this forum buy several experts. I can sent you bigger files for the schematics.

A 100 W. rating is correct. You need to allow magnetic headroom for a low freq. NFB error correction signal.

I not expert on the primary impedance subject, but 8 K for "12" W. tubes, 6.6 K for 6L6s and 7591s, 4 K for EL34s, and a bit less still for KT88s seems to do quite well. The Edcor model CXPP100-MS-3.3K will get the job done, at something resembling reasonable cost.
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Old 21st January 2010, 02:07 AM   #106
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Eli, While your at it, what are your thoughts on the EF86 compared to thr 6GK5 you have reccomended in the past for voltage drivers on LTP amps
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Old 21st January 2010, 02:30 AM   #107
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Eli, While your at it, what are your thoughts on the EF86 compared to thr 6GK5 you have reccomended in the past for voltage drivers on LTP amps

I strongly favor high gm types in the small signal circuitry of amps, which employ loop NFB. High gm provides protection against HF error correction signal induced slew limiting.

The EF86 is a VERY nice small signal pentode, perhaps the best ever, but it's hardly high gm. OTOH, the 6GK5 is a very slick combination of high μ, high gm, and low RP. Yes, the curves are bunched up, when large negative voltages are applied to the grid, but the curves look pretty darn good in the area of a 2 VRMS I/P signal. Poindexter has taken to using 6GK5s in the small signal circuitry of his "Musical Machine". That (IMO) is a positive endorsement.
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Old 21st January 2010, 08:57 AM   #108
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Originally Posted by Eli Duttman View Post
I not expert on the primary impedance subject, but 8 K for "12" W. tubes, 6.6 K for 6L6s and 7591s, 4 K for EL34s, and a bit less still for KT88s seems to do quite well.
Most projects I've seen specify something between 4,5k and 5,5k. If understood correctly, within the viable range, the less impedance you use, the more power you get but the more quality you loose, too. Correct me if I'm wrong.

Quote:
Originally Posted by TubeMack View Post
Taj, document away! I see many many new guy's comming to the forum looking to built KT88 monos. Currently there is no FULL documentation to do this.
I'm on that. Have to finish the amps first, have them working, complete the documentation, translate it and THEN ....
...we can all state together that my ugly build doesnt work as a model.

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Originally Posted by TubeMack View Post
Hmmm. A name.........? I think something classy from classical music I reckon.....
Stradivirus?
I'd call it "KTulu Amp" or "KT Lord". It's not easy to make up a word play with "KT"... The KT = good thing is the only thing i can think of.
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Old 21st January 2010, 04:29 PM   #109
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I'm also unsure about the OT specs. I'm thinking about 100W rating, 40% UL tap, but I have not yet learned how to spec the Impeadance.
TubeMack: see the KT88 tube data from Duncan amps TDSL here:

TDSL Tube data [KT88]

Look at the application data, it gives power out, distortion, etc, for various topologies, B+ voltages and anode loads. Focus on the UL data, since this design is UL.

Ia is the anode current (which=bias current in triode, and is close to the bias current in the other topologies, except g2 current needs to be factored in), Rk is the cathode R for cathode bias; in this case we are using fixed bias, so we don't need to worry about Rk......except that since there is no (actually negligable) voltage drop across the cathode R we can lower the B+ a little to compensate.

As mentioned above, increasing the OT primary impedance lowers power out and distortion, and reducing the OT primary impedance increases power out and distortion.

Eli: I have built two iterations of Poinz' 6GK5/EL34 MM, but I am too green to have any idea about dropping in the 6GK5 in this design...any input would be greatly appreciated. I suppose that I should draw a couple of load lines, one for the EF86 and one for the 6GK5 operating in it's happy place.....

Last edited by boywonder; 21st January 2010 at 04:51 PM.
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Old 22nd January 2010, 12:31 AM   #110
taj is offline taj
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Classy classical names huh? I won't be of much help there, I'm a jazz/blues guy who finds most classical music annoying (not that there's anything wrong with it).

The only name I can think of in that genre is "Nocturne" which does actually have a nice evening glow to it.

..Todd
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