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Old 25th November 2005, 01:00 PM   #1
peterr is offline peterr  Netherlands
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Default Aikido tube choice

I have seen several lists of possible tubes to use in the Aikido.
But can someone explain to me what to look for in a tube if it is to be suitable for first position and what parameters make it right for second position?
thanks,
Peter
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Old 26th November 2005, 05:15 PM   #2
peterr is offline peterr  Netherlands
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nobody?
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Old 26th November 2005, 05:33 PM   #3
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I am no expert on the circuit.. though i have built a few versions. BUT, it depends on what you are trying to achieve: eg. how uch gain, how low an impedance, etc. The first tube pretty much dictates the gain, and dominates the tonality and response over the second section, so linearity is good there, and low internal noise and low microphonics. Ti will also dictate the gain for the most part, so for high gin, pick hi mu tubes like 12ax7, or a pentode.. it is a totem amp, so you'll get roughly 1/2 the mu of the input tube as the overall gain.

For the second stage, which is a balanced totem pole, use SRPP logic to figure that one out. the top element is the cathode follower, and the bottom is the pseudo CCS, and the PSU noise input. Low noise and microphonics are important there too, but maybe not quite as critical as the input stage. This stage is the impedance buffer, so the tube will dictate the Zo of the total circuit. Also, the bottom triode sees half the PSU noise, so the gain has to be such t hat it amplifies that properly to get the desired noise-nulling effect.

hope that helps, maybe someone else could expound a bit.
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Old 28th November 2005, 03:36 PM   #4
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I've been watching some of the Aikido postings with interest too and was wondering what everyone's favorite tube-compliment choices were, that they felt gave them the best sound?


(I don't want to hijack anyone else's thread, but I've been wondering this similar question myself and it seems superfluous to start a speperate thread for something so close)
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Old 28th November 2005, 07:09 PM   #5
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I am currently running RCA clear top 6FQ7/6CG7 's as input tubes into cryo'd Tung Sol 5687's, very nice.

dr._sleep
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Old 28th November 2005, 10:44 PM   #6
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Hi,

dr._sleep wrote:
"I am currently running RCA clear top 6FQ7/6CG7 's as input tubes into
cryo'd Tung Sol 5687's, very nice."

I think that's a good choice (although I believe using the same type
for both positions can be quite satisfactory too). I'm running 7E6
(what?) into 6N30P (aka 6H30P), which is basically a pretty similar
lineup. The 7E6 is a close relative to 6J5 which is half a 6SN7 which
is an octal 6FQ7 (pretty much). And the 6N30P is much like a
higher-transconductance 5687.
I'd say using a valve with small paracitic capacitances for the first
spot is a good idea, as it will typically be preceded by a volume pot
or attenuator. Hence an increased source resistance facing the first
valve, so small miller effect is good (i.e. in practice medium-mu, low
current valve) for good bandwidth. And it doesn't hurt (if you want
a "neutral" tone) that this family of valves are very linear. (Another
obscure valve to try here would be the tiny 9002, which at least
looks good on paper.)
Using a more powerful valve for the CF/noise-reduction stage isn't
really necessary for normal cable runs, but if you want to plug a
high-impedance headphone directly into the output, this will work
with a 5687 or 6N30P running at 20+ milliamps - but not so well
with a "lesser" valve. I designed my Aikido with headphones in
mind, and it works a charm. Of course, if using an OPT good current
capability is somewhat less important, but I still think a chunky
output valve is a good idea for this too.

BTW, I did the opposite of cryogenics to my 6N30Ps: I put them in
the oven at 150 degrees C for 24 hours. Seems to have helped
with microphony, which can be bad with some exemplars. But
this could be coincidental. Oven baking can also reduce bad cases
of blue glow (gas) if you're lucky.

Morgan L
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Old 1st March 2007, 09:52 PM   #7
DougL is offline DougL  United States
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Rather than start another thread, I am also looking at the choices for a 9 pin Aikido. This is a present for my brother, who has been into tubes for the last 30 years. Simple line amp, moderately long cables @ 15 ft / 5 meters.

I have on hand:
8 6H23pi
8 6H6pi
16 6N1p
4 6H30 (for another project)
4 5687 (for another project)
16 12AX7
4 12AU7

The 6H23pi / 6DJ8 / 6922 seems at home in position 2.

Position 1, I was thinking of the 6H6pi, because of their Mu of 22.
The gain of ~ 11 would be OK.

My other choice would be to buy a couple of 6CG7/6FQ7.

My problems more ascetic. I would use a 6FQ7, but there isn't a cheep Russian equivalent I am aware of, and it seems wrong to use a lower RP tube such as the 6H6pi in slot 1.

Any comments welcome.

Doug
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Old 2nd March 2007, 02:45 AM   #8
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Hi,

Current thoughts have been towards John Broskie's circuit - but it seems strange that tubes providing dis-similar pairs have not been considered.

If one considers this type of tube, and looks at the circuit as "upstairs" and "down-stairs", then it is very easy to acknowledge the filament-cathode limitation and use Morgan Jones' "thingy" circuit for the top-tube. It just may be that separation between channels will improve...

I have been looking at the 6CM7 - got that that 6J5/6SN7 half for the input, then a lower impedance second-half if you are pursuing drive. 6GF7 is a starter also.....

Currently playing with HT regulators/snubbers. Previously I have built a clone of the SP10, but I doubled the regulators - each tube enjoying its own......channel-wise. Seems more correct somehow......

I am truly a fan of Audio Research - and that site that provides glimpses of circuitry. Pondering over the SP10 and SP11 circuitry where the series HT regulator went from tube to mosfet. Appears that there is a school of thought that the mosfet-circuit "rings" and results in a "steely" sound. Love to share comment in this regard......

Graeme
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Old 2nd March 2007, 02:57 AM   #9
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Quote:
Originally posted by Graeme
Current thoughts have been towards John Broskie's circuit - but it seems strange that tubes providing dis-similar pairs have not been considered.

If one considers this type of tube, and looks at the circuit as "upstairs" and "down-stairs", then it is very easy to acknowledge the filament-cathode limitation and use Morgan Jones' "thingy" circuit for the top-tube. It just may be that separation between channels will improve...
This may be stating the obvious, but you can also just use identical dual triodes for 1st and 2nd stage and make 1 tube the top half and the other the bottom half. This allows you to elevate the heater exactly where you want. But tube rolling seems to be a more popular activity
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Old 2nd March 2007, 03:36 AM   #10
DougL is offline DougL  United States
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Quote:
If one considers this type of tube, and looks at the circuit as "upstairs" and "down-stairs", then it is very easy to acknowledge the filament-cathode limitation and use Morgan Jones' "thingy" circuit for the top-tube. It just may be that separation between channels will improve...
For a gift, I am using the TCJ Circuit board. This allows my brother to tweak. If I point to point wire one, your recommendations would make much more sense.

Maybe next time.

Doug
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