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Old 3rd June 2007, 11:40 AM   #1
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Default 6688/E180F line stage?

I got a pair of 6688/E180Fs, a transformer with 190-0-190, 50V tap, and 3.15-0-3.15, 2 120H 36mA plate chokes and a used Hammond aluminium chassis. Can I put together a nice sounding line stage out of this without much extra cost?

If so, suggestions on operating conditions please? I can't seem to find its triode curves anywhere... that is if triode connection are the way to go if I read correctly... Also is this a lot of gain for a line stage?

cheers!
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Old 3rd June 2007, 01:03 PM   #2
Zen Mod is offline Zen Mod  Serbia
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Default Re: 6688/E180F line stage?

Quote:
Originally posted by pengboon
I got a pair of 6688/E180Fs, a transformer with 190-0-190, 50V tap, and 3.15-0-3.15, 2 120H 36mA plate chokes and a used Hammond aluminium chassis. Can I put together a nice sounding line stage out of this without much extra cost?

If so, suggestions on operating conditions please? I can't seem to find its triode curves anywhere... that is if triode connection are the way to go if I read correctly... Also is this a lot of gain for a line stage?

cheers!

it will be too much gain,even in triode- if I remember correctly- in range of 40 to 60;
you have two ways to do this- anode follower with choke load or-even better- WOT stage,parafeed or not.

btw -awesome toob.......

no!!

dreky toob,send that to me for proper disposal !
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Old 3rd June 2007, 02:56 PM   #3
alexg is offline alexg  Philippines
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I have a 6688 grounded grid line stage for my DAC. The DAC I got from diyparadise.com and the 6688 circuit was also featured on that website.

I think my voltages are close to the power transformer that you have.

These linestage sounds very, very good.
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Old 3rd June 2007, 04:56 PM   #4
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I have my headphone amp running 6688's right now. They are quite nice -- more detailed than 5842's, but less full sounding perhaps. I have some 7788's on the way to try too.

Search is failing me, but here are some curves that were posted when I asked the same question a while back.
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Old 3rd June 2007, 05:29 PM   #5
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The problems with the 6688 is the bias: grid current begins at -1,3 Volts, so the max. input signal is limited.

Andreas
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Old 4th June 2007, 04:40 AM   #6
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Zen Mod,

I'm probably going to do it anode follower with choke loading. Don;t think I want to spend on OPT at this point of time. Any nice operating points to recommend?

Alexg,
I know you are using it for DAC, but have you compared GG vs anode follower for line-stage?

AndreasS,
Thanks for the reminder, should be sufficient for regular 2V output from CDP, phono right?
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Old 4th June 2007, 05:49 AM   #7
alexg is offline alexg  Philippines
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Quote:
Originally posted by pengboon

Alexg,
I know you are using it for DAC, but have you compared GG vs anode follower for line-stage?
Unfortunately I have not compared GG vs anode follower for line-stage.

But I would be very interested on the result of what you will be doing, for I have some 6688 tubes and would like to experiment with them.
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Old 4th June 2007, 05:55 AM   #8
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How about a mu-follower, using the pentode as CCS??
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Old 4th June 2007, 06:42 PM   #9
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Quote:
Originally posted by soundbrigade
How about a mu-follower, using the pentode as CCS??
Why a high-transconductance pentode for the upper tube? It is difficult to stabilisize the operation point, because you can use only a small cathode resitor.

Andreas
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Old 4th June 2007, 06:58 PM   #10
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If you don`t need gain,,, a choke loaded cathodefollower?
http://www.tubecad.com/2007/04/blog0104.htm
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