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Old 4th March 2002, 11:23 PM   #1
JoeBob is offline JoeBob  Canada
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Default I'd like to start with tubes.

Well recently I was at my local shop and it turns out I can buy tubes there, only the 6L6 and something like a "soltek", but I've heard of the 6L6 before so it's the only one I remembered. I know the 6L6 is usually used for poweramps, but could one build a pre-amp with it?

I'm looking for something like a SE, Class A tube pre-amp, balanced. Hopefully using the 6L6. If anyone knows of any good projects, let me know. I want to go with a top of the line, but still be at a resonable price... Afterwards I'll probably follow up with a tube power-amp, but I'd like to get the kinks out of my solid state one first...
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Old 5th March 2002, 12:34 AM   #2
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Default Re: I'd like to start with tubes.

Quote:
Originally posted by JoeBob
Well recently I was at my local shop and it turns out I can buy tubes there, only the 6L6 and something like a "soltek", but I've heard of the 6L6 before so it's the only one I remembered. I know the 6L6 is usually used for poweramps, but could one build a pre-amp with it?
Sovtek is a brand name, they make a large range of tubes -- perhps even the 6L6s. The 6L6 is not really all that suitable for a pre-amp.

Quote:
I'm looking for something like a SE, Class A tube pre-amp, balanced. Hopefully using the 6L6. If anyone knows of any good projects, let me know. I want to go with a top of the line, but still be at a resonable price...
An SE amp is Class A, but usually not balanced. If you want balanced a fully differential pre would be more appropriate, but perhaps not a good 1st tube project.

Do you need a phono-stage or just a line-stage?

dave
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Old 5th March 2002, 12:57 AM   #3
JoeBob is offline JoeBob  Canada
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I guess balanced isn't that important to me really. I only need a line-stage, not phono...

If you know of a design that uses a different tube (but that's still easy to get) let me know...
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Old 5th March 2002, 01:22 AM   #4
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Quote:
Originally posted by JoeBob
I guess balanced isn't that important to me really. I only need a line-stage, not phono...
A line-stage can be a pretty simple device -- and much of the quality resides in the power supply. Here is a simple linestage that uses a single 12AU7 per channel:

Click the image to open in full size.

This has to be very similar to the Bottlehead Foreplay. It could be made much better with a current source on the cathode of the cathode follower. The bit after the selector switch in the following shows this basic design taken to extremes:

Click the image to open in full size.

If you can get away without super-low output impedance, a single stage common cathode using a hi-current tube like the 6H30Pi get better.

Rosenblitz's grounded grid line-stage also gets good press... he will sell you a kit or you can buy his audio reality book with full details.

There are a ton of other ideas and designs out on the web...

dave
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Old 5th March 2002, 01:36 PM   #5
dice45 is offline dice45  Germany
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Joe,








if you want to go balanced, then it must be worth the hassle. Balanced input, SE->balanced converting input for SE sources, balanced preamp output, balanced power amp input, this makes sense, balanced all the way. Then you get black background, absence of hum and noise pickup.








And if the power amp is a differential PP amp, you even get gorgeous low end.

















But as long as you want to have some SE gear in between, i would not take the burden to have nearly any component twice in the circuit, and well-matched so.

















A real killer linestage is a 5687 driving a Simon Shilton / SJS pa102 line output transformer. Search the forum, i somewhere posted details about it. This linestage can drive 600Ohm inputs.





AFAIR, the 5687 is fed by a stepped attenuator (50k) and run at 25mA. Warning, these Shiltons are $$$. The linestage has been built by my friend Manfred Huber. He also built a cheapskate version of it, using a toroid power transformer as ouput transformer (believe me, he knows what he's doing), have a look on his homepage http://home.t-online.de/home/MHuber/ and look for the The cheapskate's transformer coupled line stage













A very good read to get into the basics (quite advanced basics):








Morgan Jones, Valve Amplifiers, 2nd ed., Newnes
http://www.amazon.com/exec/obidos/AS...954278-3976150

The book isn't cheap but it's worth every penny.
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Old 9th March 2002, 03:15 AM   #6
JoeBob is offline JoeBob  Canada
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Well, I decided I wouldn't be too picky for my first tube project, although I'd still like something good. So I've decided on a C22 with 12AT7 tubes (the 12AT7s can be drop in replacements for the 12AX7s, right?). I found the schematics for it but was wondering if anyone could show me a suitable power-suply schematic to run it off. Not the original C22 PSU, maybe something with the LM317 IC. The C22 needs 290V and 310V, but since I've never worked with tubes I'm not sure on what'd be good...

I like the idea of the C22, that is unless anyone thinks the SRPP is better, for they both look good...
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