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Old 10th January 2008, 06:00 AM   #21
OzMikeH is offline OzMikeH  Australia
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thanks for so many replies in such a short time.

ArnoldC, 26? Is that how many times people have asked the same question?

I can see a lot of parts in the bottlehead kit I don't need. If sound quality is slightly less then that effectively crosses it off the list.

The Aikido looks interesting, I'll need to see what matched sets of tubes are available around here. It's tolerance of poor power supples is a big plus, power supplies can get expensive.

12B4 looks good too, nice and simple, though the added complexity of power supply is a big minus.

Poindexter's looks interesting too, the power transformer arrangement is very clever but may not be entirely safe. Generally isolation between primary windings is not of the same standard as primary-secondary.
In which ways do you think it is better than the Aikido?
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Old 10th January 2008, 06:35 AM   #22
arnoldc is offline arnoldc  Philippines
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OzMikeH, the 26 is a DHT tube. I have 12AU7 (Foreplay I), 12B4, 407A, 6SN7, 5687-based preamps and the 26 is better for me.

Kevin Kennedy, Jim de Kort and others have ready circuits you can find in the web as well as in this forum.

However, based on what you posted, I don't think the 26 is for your project this time.
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Old 10th January 2008, 06:45 AM   #23
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Quote:
Originally posted by OzMikeH In which ways do you think it is better than the Aikido?
I heard both good & bad about the Aikido... personally i think it is too complex. The 12B4 is really appealing, i'll probably build that. Poinz was one of the guys that seemed a god to me when i was 1st picking up tube lore on the JoeList, so anything he does (& likes) is worth a serious look. The music machine is a very good example of elegant simplicity. I'd probably look at doing his too, but i don't have any of those tubes in my "junk box"

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Old 10th January 2008, 06:52 AM   #24
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Quote:
Originally posted by OzMikeH
12B4 looks good too, nice and simple, though the added complexity of power supply is a big minus.
What complexity? PSU implementation is no different to any other common cathode triode stage. Unless you want to make it more complex to improve performance.
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Old 10th January 2008, 07:38 AM   #25
OzMikeH is offline OzMikeH  Australia
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Power supply complexity: It needs to be very, very clean because of poor PSRR. Lots of filtering at a couple of hundred volts can't be cheap.

Perhaps the people who wrote about their build of it went overboard with the power supply.

Performance is important, Particularly low noise and high detail.
If performance isn't excellent then I may as well spend a few hundred bucks on super-duper op-amps. I'd rather not go down that path though.
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Old 10th January 2008, 11:20 AM   #26
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Performance is important, Particularly low noise and high detail>>>>

If you want the ultimate tube for a preamp, I have no doubt that it's the 10Y. It's just that bit better than the 26 and the 01A. We've done multiple shootouts over several years at the London Audiocircle and this is the current favourite. It can be run at low voltage and low current, even. Sounded wonderful at 107v and 5mA into a Lundahl LL1660/5mA. An amorphous core would be the icing on the cake. It likes an OPT.

Yes, you will need a good filament supply. I suggest a 0-12, 0-12 60VA transformer into schottky bridge into 15,000uf cap into a LM1084 voltage reg to bring voltage down to 12v, then another LM1084 as current source. This is simply a LM1084 with adj connected to output via a 1 ohm resistor, 12W, and output taken from adj pin. Needs a nice big heatsink. You should get 7.25vDC out of this - perfect.

What you will get with the above is pure magic. In fact it's almost psychodelic.

6SN7 and 12b4 preamps went out the window years ago for most of us in the London Audiocircle, though clearly they still have fans.
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Old 10th January 2008, 12:03 PM   #27
56oval is offline 56oval  Australia
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My pre use's a 6H30pi into line output transformer .Trannies wound buy a guy in Melbourne .Very simple my first project
Might have to much gain .

Cheers.
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Old 10th January 2008, 12:11 PM   #28
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I suggest a 0-12, 0-12 60VA transformer into schottky bridge into 15,000uf cap into a LM1084 voltage reg to bring voltage down to 12v, then another LM1084 as current source. >>

I should point out that the above is ONE filament supply per TUBE - schottky bridge into 15,000uf cap into a LM1084 voltage reg to bring voltage down to 12v, then another LM1084 as current source. Two tube supplies can therefore be run off one 60VA toroid with double 12-0 secondaries.
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Old 10th January 2008, 12:56 PM   #29
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Quote:
26!!!
Arnold,

Most people don't have the ability to build a really quiet good performing 26 line stage without the extensive use of high dollar transformers or complex battery charging circuits.

I've been working on one for a long time and still cannot get the hum out of it.

Quote:
6SN7 and 12b4 preamps went out the window years ago for most of us in the London Audiocircle, though clearly they still have fans.
What is wrong with a 6SN7 preamp? its very neutral and most can built it without a hum problem.

Quote:
If you want the ultimate tube for a preamp, I have no
doubt that it's the 10Y
Got a schematic of the 10Y?
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Old 10th January 2008, 01:11 PM   #30
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Most people don't have the ability to build a really quiet good performing 26 line stage without the extensive use of high dollar transformers or complex battery charging circuits.>>

I don't think it's difficult at all - people seem to be put off by mythology about DHTs, i.e. that they need battery supplies, are all microphonic etc. A DHT will work perfectly well off a bench supply - I've used bench supplies to develop circuits for a while.

<<<I've been working on one for a long time and still cannot get the hum out of it.>>

Ah - you're not wrong here!!!! Once you put the filament supplies inside the preamp you can get all sorts of interactions, and I've also been plagued by hum in some one box units. But I don't get a problem when you use outboard supplies. I'm learning all the time here, like also you bypass cathode resistors with large polypropylene caps.

quote:
6SN7 and 12b4 preamps went out the window years ago for most of us in the London Audiocircle, though clearly they still have fans.

<<What is wrong with a 6SN7 preamp? its very neutral and most can built it without a hum problem.>>

What's wrong only stands out when you directly compare a 6SN7 pre against a DHT like 26, 01A or 10Y. We did this in a repeated A-B test and while the 6SN7 was smooth and pleasant it wasn't so detailed, delicate or magical in terms of the tone of intruments. Sounded a bit "thicker" while the DHTs were more quicksilver and mercurial. Aren't you hearing this extra dimension with your 26 pre?
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