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Vacuum Tube OTL power amp!!
Vacuum Tube OTL power amp!!
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Old 3rd December 2011, 07:59 PM   #481
M Gregg is offline M Gregg  England
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Tried to do 10khz square wave and 25k..

however the True RTA makes a right mess of it looks like triangular..

So I will have a look at it with a sig gen..


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M. Gregg
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Old 3rd December 2011, 08:17 PM   #482
M Gregg is offline M Gregg  England
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10khz..square wave.
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Old 3rd December 2011, 08:25 PM   #483
M Gregg is offline M Gregg  England
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20khz square wave..

Could do with a tweek to sharpen the edges..
Could be the coupling caps to the 6c33c's..looking to change them,,




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M. Gregg
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Old 3rd December 2011, 08:47 PM   #484
M Gregg is offline M Gregg  England
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Half 6c33c 10khz square wave..

The scope leads arn't the best my others got squashed in the loft...
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Old 3rd December 2011, 08:56 PM   #485
M Gregg is offline M Gregg  England
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Half 6c33c at 20hz

just for fun..
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Old 3rd December 2011, 08:58 PM   #486
M Gregg is offline M Gregg  England
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Here it is..
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Old 3rd December 2011, 09:33 PM   #487
Alastair E is offline Alastair E  Wales
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Well, Thats all pretty interesting!

I really should get my scope out and do some tests too. It would be interesting to see where the onset of distortion is actually happening above 8W, whether in the driver or the O/P stage...
--Have to open the FB loop to do that though, and alter I/P level accordingly...

To sharpen up the square-waves, it may be worth dropping the value of the PI grid-coupling resistor to 100K, (or just link it out) in view of what a previous poster mentioned concerning the Miller capacitance of that stage....

Worth trying anyway, see if it makes a difference...
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Old 3rd December 2011, 10:03 PM   #488
Dimitris AR is offline Dimitris AR  Greece
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Quote:
Originally Posted by Alastair E View Post
Well, Thats all pretty interesting!

I really should get my scope out and do some tests too. It would be interesting to see where the onset of distortion is actually happening above 8W, whether in the driver or the O/P stage...
--Have to open the FB loop to do that though, and alter I/P level accordingly...

To sharpen up the square-waves, it may be worth dropping the value of the PI grid-coupling resistor to 100K, (or just link it out) in view of what a previous poster mentioned concerning the Miller capacitance of that stage....

Worth trying anyway, see if it makes a difference...
Hi Alastair , in previous post I talked about input capacitance only , because the phase spliter didn't make any amplification , its a unity gain and therefore it haven't any Miller capacitances .
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Old 3rd December 2011, 10:26 PM   #489
M Gregg is offline M Gregg  England
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Dimitris AR,

Just asking because of your previous post...

Looking at the square wave do you think the 470K on the phase splitter/driver is responsible for the slight slope?

Or coupling capacitor issue?

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M. Gregg
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Old 3rd December 2011, 10:30 PM   #490
M Gregg is offline M Gregg  England
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Quote:
Originally Posted by Alastair E View Post
Well, Thats all pretty interesting!

I really should get my scope out and do some tests too. It would be interesting to see where the onset of distortion is actually happening above 8W, whether in the driver or the O/P stage...
--Have to open the FB loop to do that though, and alter I/P level accordingly...

To sharpen up the square-waves, it may be worth dropping the value of the PI grid-coupling resistor to 100K, (or just link it out) in view of what a previous poster mentioned concerning the Miller capacitance of that stage....

Worth trying anyway, see if it makes a difference...
Yep drop the scope on the pl519..see what the O/P is...

It's quite interesting this is the first test I have done on this amp...i've just been listening to it...

Regards
M. Gregg
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