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space-cake 4th June 2007 10:38 PM

what monoblocks to build?
so i'm moving next month and i'll finally have a proper listening room... so i made up my mind about building my entire setup on my own (preamp, monoblocks, speakers). i also found a good local supplier for aluminium so i can finally make my own cases and save mucho $$$

the problem is that i'm stuck because i don't know what design to start with. i'm basically looking for something that will push 30 - 50W using tubes that are still in production. that most important thing for me is freq. response (i have a thing with that), as far as topologies go i'm open for suggestions.

also, this is not my first project. i already build a jtm45 guitar amp with kt66 tubes, a pair of full-range speakers and a tripath based amplifier with switching power supply.

the_manta 4th June 2007 11:30 PM

Hi !
Ha...have fun while building the monoblocks. I won't do it ever again. It is a real mess. No feeling of success when I finished my first case. When I remeber the effort....I'm really not looking forward for the second case.

There are many designs out there which match your conceivabilities.
There is the usual EL34 35W design. It won't cost you as much as KT88 or 6550 designs.
I would go another way. recently JJ launched the new KT66. A really nice tube....
Another more unique design is to use four EL84 per channel. YOu will get about 30W out.
regards, Manta

space-cake 5th June 2007 12:04 AM

thank you very much for your answer, your amp seems nice and yes i know how much work it takes to build one of these amps.

i have sovtek kt66 (got a few at home actually), how are the JJ better? also, do you have a link or two to share with amp designs like you suggested?

kevinkr 5th June 2007 04:12 PM

Actually I have built many monoblocks, and with one exception (the dreaded 6C33 OTL on my pages) they have all been successful. They were fun to build and I have no regrets. I mostly build stereo amplifiers now because of space. (I like outboard supplies)

You can't go wrong with a design based on current production 6550 driven by say a 6SN7 LTP driver stage and 6SL7 LTP input stage. Variations of the Mullard 5-20 are also a pretty good place to start. I'd replace the 12AX7 in that design with a 6SN7 and the EF86 with half a 6SL7.

I think you would be hard pressed to get more than 25W out of a pair of KT66 and achieve reasonable service life with current tubes, so I recommend the 6550/KT88 instead. They aren't really that much more expensive. For 50W you'd need a quartet of KT66 per channel, and obviously that is going to cost somewhat more than a pair of 6550/KT88.

Current JJ stuff seems to have serious quality control issues, based on comments I've read on other threads here at diyaudio. You might want to look into this before investing in tube purchases.

Linear Tech LTspice is a great tool for simulating your design. Tube models are readily available, it's free and very robust. No limit on nodes simulated either.

Output transformers are the heart of the project, and in your neck of the woods perhaps an imported pair of Bartoluccis from Italy would be a good bet. Power transformers can be wound locally, just make sure they understand the voltages are nominals at a specified line voltage and load current and not minimums as much misery will otherwise result.

Summers are hot enough in Israel to make me recommend these be used in airconditioned space or in the winter time only.

the_manta 5th June 2007 06:05 PM

Hi !
I didn't have any problems with JJ Tubes so far. I only heard about problems with their EL34 with higher screen grid voltages. I had much more problems with EH and Sovtek.
The JJ KT66 is a real KT66, and not a 6L6 derivate like the Sovtek or EH. As the text on Jogi's page tells, he sent some to the JJ factory and they broke the bulb and made an exakt replica.

I picked a few amps out of jogis page. Directly translated in english via google.
Regards, Simon

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