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Old 18th May 2006, 01:16 PM   #1
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Default Aikido pre tube for Minimum Gain

I have some of Basís Aikido PCBs, to feed a horn system Iím assembling that will have a max dB of about 117 dB.

(I was going to use an autotransformer volume control www.intactaudio.com/atten_FAQ.html, but they donít provide enough attenuation.
So Iíll use a stepped attenuator, for which attenuation is still less than an ordinary pot . . )

So: I want to build an Aikido pre, that other things being equal has the *minimum amount of gain. Gain = Half the first tube

What really good sounding tube has the *minimum amount of gain?

Thanks

Richard
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Old 18th May 2006, 01:40 PM   #2
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rick57,

Goto and look at the last page...

Aikido tubes: results and values

http://www.tubecad.com/2006/05/blog0064.htm

Alain.
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Old 18th May 2006, 01:58 PM   #3
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Default 6AS7 and 12B4

Thanks Alain!


Is there anything between the 6AS7 and 12B4 in sound quality/ price/ availability?

Cheers
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Old 18th May 2006, 02:11 PM   #4
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Hi Richard,

Unless you use wires from the 12b4 sockets to the board. The 12B4 cannot be accomodated. Also not in JB's boards because it is not a double triode.

The 6AS7 can be used in the octal boards.

Regards,
Bas
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Old 18th May 2006, 02:36 PM   #5
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Hi Bas,

Thanks for your info ~

How is the 6AS7 compared to similar Output Gain: 6BX7/ 6GM8/ 6H30?

Regards,

Richard
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Old 18th May 2006, 03:41 PM   #6
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6AS7 and 6BX7 are both octals
the
6GM8 and 6H30 are nine pin tubes


the "first tube" in the aikido really determines the gain. The second one is a cathode follower and all have slightly less than a gain of 1 (except for the 6AS7 which is bit lower).

So BALLPARK figures
6AS7=2
6BX7=5

6GM8=7
6H30=8

So the answer would be.
IF 9 pin THEN 6H30 OR 6GM8
END IF

I don't know how available the 6GM8 is though.

IF octal THEN 6BX7 OR 6AS7
END IF

Since the 6AS7 has a hefty filament current I would go for the 6BX7 but..YMMV

But if you really want MINIMAL gain..use the 6AS7 in first position and maybe something with less current hungry filamant as cathode follower...you would be using an insane amount of heater filament current for a preamp if you would use 4 6AS7's.
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Old 18th May 2006, 03:57 PM   #7
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Hi Bas

Can you remind us memory challenged -

Are the boards any more suited to octals or 9 pin tubes

Cheers
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Old 18th May 2006, 04:03 PM   #8
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Hi Rick

I gave a look at your link and found this question and answer

Q - what if I need more than 42db of attenuation.

A - Custom units can be wound to 54dB of attenuation. Note that that is a 500:1 stepdown and may compromise the performance slightly. If you require that much attenuation you might want to examine the gain structure of your system.

Isn't there a possibility in your system to reduce gain?

Erik
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Old 18th May 2006, 04:16 PM   #9
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Hi Erik

> Isn't there a possibility in your system to reduce gain?

Unfortunately no, the power amp is only 2 watts (a 45 SE).

My central question is:
Is there anything between the lowest mu tubes, eg 6BX7/ 6GM8/ 6H30?
in sound quality/ price/ availability?

Rick
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Old 18th May 2006, 05:57 PM   #10
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If one is trying this hard to limit the gain in an Aikido stage, why not just try a well-implemented cathode follower with current source loading? A 12B4A would be a good candidate.
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