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Old 27th March 2008, 04:24 PM   #11
Cappy is offline Cappy  United States
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I meant to say 5687 "D" Getter in my post above.

Later Tung Sols had a round getter.

There are 5687 Raytheon Square Getters of the same general period, 1955-59 or thereabouts, that also sound very good.
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Old 27th March 2008, 07:19 PM   #12
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I had a simple RC coupled 5687 linestage that I converted to use 6N6Ps. The 6N6Ps stayed - I liked the sound even more than the Tungsol 5687s (bronze or BP).

As usual, my speakers, my system ,etc
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Old 27th March 2008, 08:36 PM   #13
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Well that is good to hear.

What are your operating points?
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Old 27th March 2008, 10:27 PM   #14
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Default Choice of 6CG7's

I built the Aikidio several months ago now, and truely love it! When I first got it up and running I used electro-harmonix 6CG7's in both positions. Since I've tried RCA 6CG7s greyplates with the side getters much nicer and now I'm running RCAs black plates with the horseshoe getters. I don't think it gets much better than these tubes. WOW they are nice! They can easily bought on ebay fairly cheap. I'd really would be happy with either of the RCAs but the black plates are a little smoother sounding, tiny bit. Good luck with your build! You're going to love this preamp.

Steve
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Old 27th March 2008, 10:34 PM   #15
Cappy is offline Cappy  United States
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Steve,

Thanks for the useful info. Just what I was looking for.

What B+ are you running at and what are the values of your cathode resistors?
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Old 28th March 2008, 12:30 AM   #16
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Hi Cappy

Great to hear about your Aikido. I am going to build an Aikido myself but it will take som time before it is finished.

Regarding tubes, please bear in mind that the EH 6CG7 actually is a 6FQ7 (a 6CG7 without shield between plates). I know that EH writes "6CG7" on the tube and the tube box, but it is a 6FQ7!

John Broskie recommends that you go for the "real" 6CG7 tubes. These are, however, only availabe as NOS tubes (at least to my knowledge).

I know that tubes are a matter of taste but according to Broskie you should go for the 6CG7 tubes from before 1965. And stay away from GE´s after 1970. Please note that I have no experience myself regarding these tubes - the words are from John Broskie.

I have read a lot of different opinions on the Internet about different types of 6CG7´s. It seems as the RCA clear tops and the RCA black plates are the best sounding tubes (and often, of course, the most expensive).

If you search on eBay for 6CG7 tubes please note that some sellers don´t know the difference between 6CG7 and 6FQ7 so please remember to ask them about this. According to Mr. Broskie this is rather "important" because the 6CG7 tube has the "shield between plates".

This shield i aka a screen between the two plates which minimizes cross-talk. Furthermore, it gives the tube a better mechanical stability. Both topics should be the reason for the superior sound compared to a 6FQ7.

Electrically the two mentioned tubes are the same so you will get no problems if you would like some tube rolling between these two types of tubes.

Good luck with your Aikido.

Karsten
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Old 28th March 2008, 05:21 PM   #17
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Hi Cappy,

I went looking for my build folder and can't find it, but I can tell you, I used the values out of the manual that comes with the boards from John Broskie. I know it gives two valus one for the input tubr and one for the output tube.

My B+ voltage is 297V which is very close to the 300V I was shooting for.

One lucky find I came arcoss was a remote controlled attenuator from Bent audio, (John Chapman at www.bentaudio.com call him that's the best) it not the one he displays on he site, which is a Gold Point attenuator with a motor on the rear of the unit and a remote to operate it, which is nice also, but this is the one he uses in the preamps he builds. Way nice! It's a little pricey but it's beautiful, controls attenuation, selects up to 6 inputs and has its own power supply and a diplay that mounts on the front of your preamp unit. He had it all setup and ready for installation , including the ribbon cables.

I wish I could find that folder! I think John calls it a PRM unit. He partnered with Gold Point to make the unit.

Give him a call if your interested.

Steve
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Old 28th March 2008, 05:39 PM   #18
Cappy is offline Cappy  United States
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Steve,

Thanks. It was your B+ I was most interested in since I will be "resistor rolling" to hear the sound changes myself.

I agree, the Bent products are great. I have a TVC Kit I built from John using S&B Mk. III TX-102s.

My Aikido will be used as a DAC output stage feeding into my Bent Preamp. The output caps will be larger at 2.2 uF to accommodate the TVC.

I'll be using a Lundahl LL1683 Power Transformer which will give about 260vac out, given that my voltage is 120vac. With a choke loaded LCLC or LCRC (if the LCLC doesn't sound good) I can get a 210-215 vdc B+. With a CLC or CLCRC I can get 300 vdc B+. I'll probably try both. Does anyone have opinions on the sweet spot B+ for 6CG7 and 5687/6n6p? Steve, it sounds like you found success at 300vdc for 6CG7/6CG7.

Soon I will post my PSUD generated LCLC power supply ideas for a "design review" in this thread.
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Old 28th March 2008, 07:36 PM   #19
Cappy is offline Cappy  United States
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Karsten,

Thanks, I'll look for 6CG7s with grounded screen.
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Old 28th March 2008, 09:29 PM   #20
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Heres how my 24V aikido turned out:

This is the more recent board with the headphone output.

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Fran
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