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Old 12th March 2011, 03:48 AM   #1
ksporry is offline ksporry  China
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Default How to best drive an 845?

Different power amps have different driver tubes, and I was wondering how an 845 is best driven, for optimal sonic performance.
For example, I have seen amps that use E88CC tubes and 5687 tubes to drive the 845, delivering 28Wpc. But I have also seen amps that use a 6NS7 and 12AU7 tubes.
So which combination would perform better sonically?
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Old 12th March 2011, 04:00 AM   #2
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Quote:
Originally Posted by ksporry View Post
Different power amps have different driver tubes, and I was wondering how an 845 is best driven, for optimal sonic performance.
MOSFET source follower.
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Old 12th March 2011, 04:10 AM   #3
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Quote:
Originally Posted by Miles Prower View Post
MOSFET source follower.
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Old 12th March 2011, 05:41 AM   #4
Serge66 is offline Serge66  Switzerland
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HI,
Push-pull KT66 and interstage transformer. This is going to be 2012-2013 project.
Cheers,
Serge
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Old 12th March 2011, 06:51 AM   #5
ksporry is offline ksporry  China
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actually, I was hoping some more advice on the use of tubes when driving an 845. Considering that several tube amp manufacturers use tubes to drive the output tube, I'd like to focus on that approach.
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Old 12th March 2011, 07:08 AM   #6
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Hi!

here is my opinion:

The 845 needs close to 400Vpp drive voltage for this kind of output power. This is quite a challenge. I prefer to have a lot of headroom in the driver, which makes it even more challenging.

The best driver I have used for the 845 was a 211. You could use a second 845 like Sakuma does, but a 211 has more voltage gain. Coupling was with interstage transformer.

If you want to stick to a more 'sane' approach, I'd recommend the 6AH4 transformer coupled. This is a strong indirectly heated triode which can provide large voltage swing.

I'm about to finish a 211 amp whih uses a 6HS5 as driver. I will introduce this project with schematics on my blog in a few days, just need some more time to finish the article.

Best regards ... Thomas
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Old 12th March 2011, 08:01 AM   #7
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Russian tube 6E5P /6Е5П/ or similar octal 6P9/6П9/ with current 30-40 ma and You will have two stages ampl. with minimum passive elements for very good sounding. It gain is enough to drive 845. If You will use it in triod mode, You will need interstage transf. 1:3
with power about 5 watts. /I prefer 2 stages ampl./.
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Old 24th March 2011, 11:07 AM   #8
multi is offline multi  Australia
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I have built 845 single ended using all types of driver tubes; they are very hard to drive and you end up with a dull sound.
i run mine at 800 volts with 3.4k sowter Output transformer about 15 watts; i use horns so no need for more watts. I got the best results using a High Gm pentode and screen driven 5881. all the other circuits sounded very dull no Dynamics. The sound is excellent with powerful bass and fast and dynamic sound. Mush cheaper than using interstage transformers. An advantage of this circiut is that the 5881 runs with 800 volts supply; 400 volts on the plate.
Phil
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Old 24th March 2011, 12:34 PM   #9
Alkis is offline Alkis  Greece
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In my opinion,you have to use interstage transformers. This tube is hard to drive as mentioned before.
In my project, I use 211 as a driver.
Vinylsavor has gave you allready some facts.
In any case, this will be an expensive realisation.
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Old 24th March 2011, 01:04 PM   #10
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I haven't built a 845 amp, but I've fidgeted around with some designs on screen (for a ESL direct drive amp). When I someday build it, my first choise for driver tube is a 45, with an input stage of maybe the 27.

6E5P is a very good tube, especially at good currents (35mA+). However I find it a bit cold and uninvolving as a spud. Very detailed and clean however. Definitely worth a try.
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