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Old 22nd March 2004, 03:16 AM   #1
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Default How low 6922/ECC88 can go?

Hi all,

Wanted to ask the tube expert about this schematic. I have problem with PS, so I wanted the tube section works in lower voltage.
How much lower the tube can go? I wanted the tube to be able to work in +/-2V p-p sinusoidal without defect or clipping. Will it go to +/-15V for the tube?
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Old 22nd March 2004, 03:28 AM   #2
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Hi,

Quote:
I wanted the tube to be able to work in +/-2V p-p sinusoidal without defect or clipping. Will it go to +/-15V for the tube?
The tube will probably still handle the +/- 2V p2p but what you'll probably be feeding it is quite likely 2V RMS or put differently 6 V p2p.

With an effective B+ of 30V I'd expect some distortion with the 6DJ8/ECC88.

What you can try is use a 6GM8/ECC86 instead or otherwise explain us what the problem is you're experiencing with the GC.

Cheers,
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Old 22nd March 2004, 03:42 AM   #3
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Hi, fdgrove,
Quote:
The tube will probably still handle the +/- 2V p2p but what you'll probably be feeding it is quite likely 2V RMS or put differently 6 V p2p.
Yes, I wanted to take all kind of input without problem. Maybe there are CD player / preamp that have much output.
Quote:
With an effective B+ of 30V I'd expect some distortion with the 6DJ8/ECC88.
The datasheet of ECC88 have max voltage included, but not min voltage. I read somewhere that tubes cannot work in order with too low voltage. Just how much low voltage can the ECC88 works properly in this design? Is +/-35V is minimum, or it can go lower?
Quote:
What you can try is use a 6GM8/ECC86 instead or otherwise explain us what the problem is you're experiencing with the GC.
All I can get here is ECC88/6922. Also, I read somewhere that ECC86 does not sound so good.

Why I ask the question? I wanted to built this design into 2 possibilities. First the tubed gainclone. It is ok with the supply, since it is the same value.
Second to built a tubed preamp (replacing the gainclone with opamp). In this tubed preamp, the opamp needs only +/-15V, so to make things simple, could the tube take the same +/-15V also (or I will need other supply just for the tubes)
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Old 22nd March 2004, 03:55 AM   #4
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Hi,

Quote:
Just how much low voltage can the ECC88 works properly in this design? Is +/-35V is minimum, or it can go lower?
If it were me I'd go higher but not lower.

Have you considered using a voltage doubler as a powersupply?
It's not the best there is but short of adding another xformer it might save you a lot of hassle if your current xformer can handle it.

Also, have you put your question to mr Rasmussen himself?

Cheers,
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Old 22nd March 2004, 04:13 AM   #5
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Hi, fdegrove,

I will ask a question. But I take your answer is Higher, instead of Lower.

I'm not familiar with tubes. In this cathode follower, is the input signal have the same height as the output signal (as buffer) or it will have somekind of magnification?
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Old 22nd March 2004, 04:19 AM   #6
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Hi,

Quote:
But I take your answer is Higher, instead of Lower.
Higher than the +/- 15 VDC rail you suggest, yes.
I noticed you put the question to mr Rasmussen already.

What you need to work with tubes is an understanding of loadlines.
It's a little beyond the needs of what you're doing now but if you plan to work with tubes in the future you'll find it quite interesting.

Hope it was of help,
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Old 22nd March 2004, 09:19 AM   #7
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Hi,

my last experiments with ecc88 show good behavior with power supply of +/-19V, FET cs with 2mA and Va ca 30V. (grid is about -10V). Maximum AC voltage thru buffer was ca 5Vpp.

Standard ECC88 buffer circuit (grid on 0VDC) can't work good on +/-15V PS, IMHO.

Regards
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Old 22nd March 2004, 11:19 AM   #8
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HI
Quote:
Also, I read somewhere that ECC86 does not sound so good.
At low voltage ECC86 sounds very good. In my op. better than
ecc88, e88cc,6922, pcc88 , 6dj8 etc.

Quote:
Standard ECC88 buffer circuit (grid on 0VDC) can't work good on +/-15V PS, IMHO.
I do not agree, these tubes work and sound rather good at low
voltage. The following cir, for instance, shows high dist.
at 2Vrms ( 0.5% about) but , irrespective to this, it sounds good.

Bye Federico
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Old 23rd March 2004, 02:49 AM   #9
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Hi, Moamps,
Quote:
my last experiments with ecc88 show good behavior with power supply of +/-19V, FET cs with 2mA and Va ca 30V. (grid is about -10V). Maximum AC voltage thru buffer was ca 5Vpp.
Do you have drawings on your schematic? I'm not quite understand it. The supply is +30V and -10V?

Hi, Federico,
I'm also confused with your drawing. The supply is floating and where is the output is taken.
What does the THD of 0.5% behave, if we use big rating power amp? Will it produce hiss, or distorted sound, or something else, or nothing?
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Old 23rd March 2004, 07:39 AM   #10
moamps is offline moamps  Croatia
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Quote:
Originally posted by lumanauw
[B]
Do you have drawings on your schematic? I'm not quite understand it. The supply is +30V and -10V?

Hi,

schematic looks similar to second schematic on this site:
http://www.diyzone.net/diy/referenc...dj8buffer_2.htm.

Cathode is on ca -10V potential. Supply is +/-19V.

Regards
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