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Old 28th January 2005, 01:51 PM   #1
zxx123 is offline zxx123  United States
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Default 6V6 Single and 12AT7 SRPP

I can find nothing wrong, when I listen to music.
No hum is heard without heater floating.

Only thing concerned is that the gain is little bit low.

Any comment?
If you have 6v6 single with 12AT7 SRPP, plz show me.
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Old 28th January 2005, 07:22 PM   #2
Yvesm is offline Yvesm  France
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I've a 6A5 single with 12AT7 SRPP

Look at

http://geek.scorpiorising.ca/yves-0.html

Yves
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Old 29th January 2005, 12:44 AM   #3
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Hi,

Quote:
Only thing concerned is that the gain is little bit low.
Using a mu-follower instead of the SRPP as Yves did should give you a little more gain.

Also 10 F across 1K seems rather small. Didn't do the math though.

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Old 29th January 2005, 02:41 AM   #4
zxx123 is offline zxx123  United States
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Thanks for your comment, fdegrove & Yvesm.

In fact, it is the first time for me to try SRPP.
I am not good at math things....

fdegrove!, how about 820ohm with 100mf
in cathode (3)?
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Old 29th January 2005, 03:01 AM   #5
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Hi,

Quote:
fdegrove!, how about 820ohm with 100mf
That's more like it.
What happens with too small a bypass cap is that the cathode resistor isn't bypassed for the lower frequencies.

That in turn creates some degenerative feedback reducing the gain in that band giving an impression of too little bass, or too much of a mid/high frequency boost depending on your POV.

You may have noticed that Yves left the bypass cap out altogether.
In his case it only has a minor effect on output impedance, given the already low enough Zout of the mu-follower/12AT7 combo to drive his triode I assume he didn't want to live with the drawbacks of the (usually) electrolytic bypass cap.

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Old 29th January 2005, 08:28 AM   #6
Yvesm is offline Yvesm  France
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Quote:
I assume he didn't want to live with the drawbacks of the (usually) electrolytic bypass cap.
(John Ford voiced) :
Yeah man, the best bypass cap is a short'd one, yeah

Yves
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Old 29th January 2005, 02:04 PM   #7
zxx123 is offline zxx123  United States
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thanks, guys.

1.
I`ve changed 1K to 820 ohm and 10mf to 100mf of the cathode (3).

It does not sounds bumpy bass, however, smoother
and more powerful than before. Wow, is this really 6V6 SE?

2.
But I have not tried to change location of output from 12AT7.
From the plate (1) or cathode (8)? Which one is more ideal?
Can you explain its difference? (What I know is that there is impedence difference.)
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Old 29th January 2005, 06:15 PM   #8
Yvesm is offline Yvesm  France
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Hi,

Quote:
Can you explain its difference? (What I know is that there is impedence difference.)
That is !
Using the cathode as output does not add the 6V6 grid leak resistor as a load for the lower triode, more gain, more linearity, more bandwith ... better !

Yves.
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Old 29th January 2005, 06:18 PM   #9
zxx123 is offline zxx123  United States
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Default 2nd thought....

..hmm....
sparkling hi seems to be decreased little bit.
ya, it is thicker sound than before..
...next time i will try to add lower value of bypass cap. (50mf?)
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Old 30th January 2005, 01:18 AM   #10
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Hi,

Quote:
...next time i will try to add lower value of bypass cap. (50mf?)
That won't change the tonal balance much.

For as long as the cap is big enough so that the resistor is bypassed for the audio frequencies (say 10 hz for the lowest frequency -3dB point) then a bigger cap would only lower that corner frequency a little.

However, using too small a cap would have a filter effect subjectively boosting the mid/high frequencies.
Which is probably what you were getting used to.

If you want to find out what the amp sounds like, just remove the cap on the SRPP leaving the one on the output tube in place.
Chances are you'll like it best this way.....

If the amp still sounds too dark after that then I suspect you're listening to the the sound of the PS caps.

Having some way to measure the amp would of course settle the issue.

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