oscillation - Page 3

Merlinb · 7th May 2006, 11:47 AM

Also, long tailed pair phase inverters are liably to oscillate if you feed them with too low frequencies. C12 is there as a quick fix to stop this, but for a proper design I would reduce the value of C11 to 4n7 for a roll-off of 17Hz.

merkur · 7th May 2006, 04:30 PM

For the grid stop of the output, I had try bigger resistor like 10 K with no result justifing them.

I will try with lower capacitor in C11 and I 'll get back with the result

Thank's

SY · 7th May 2006, 04:41 PM

One more thought- you might be having a negative resistance condition in the screens as you push it hard and the supplies sag. That could cause an oscillation burst. I haven't experienced this myself, but I've sure heard about it.

Merlinb · 7th May 2006, 05:04 PM

Quote:

Originally posted by SY
One more thought- you might be having a negative resistance condition in the screens

Doesn't that only apply to tetrodes?

SY · 7th May 2006, 05:25 PM

You can see those kinks in some pentode/beam power curves.

merkur · 7th May 2006, 10:39 PM

How much in (%) ripple is acceptable on the plate and on the screen voltage supply when the amplifier is driving at maximum?

I'm not sure about the voltage doubler. Does it need more capacitor?

The oscillation seem to have stop but now i'm hearing like a gost note
especially when i'm playing up the neck on the guitar only when i'm driving the amp at maximum.

Any hint?

SY · 7th May 2006, 10:51 PM

I'm ignorant of what guitar guys do in that respect. It might be worth poking through the tech notes at Aiken Amplification to get a better feel for it.

merkur · 7th May 2006, 10:58 PM

By sure that I already whent trought all aiken have put on his web site.

merkur · 10th May 2006, 01:19 AM

Thank you guy's for all the information but my problem was that the driver was clipping before the maximum preamp signal. Now I have change that and the oscillation disapear. But now I see 120hz in my signal and I know that it come from my supply so any advice on my voltage doubler, publish earlier, will be welcome.

7th May 2006, 04:41 PM	#23
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	One more thought- you might be having a negative resistance condition in the screens as you push it hard and the supplies sag. That could cause an oscillation burst. I haven't experienced this myself, but I've sure heard about it. __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

7th May 2006, 05:25 PM	#25
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	You can see those kinks in some pentode/beam power curves. __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

7th May 2006, 10:51 PM	#27
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	I'm ignorant of what guitar guys do in that respect. It might be worth poking through the tech notes at Aiken Amplification to get a better feel for it. __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

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7th May 2006, 11:47 AM	#21
Merlinb diyAudio Member Join Date: May 2006 Location: York	Also, long tailed pair phase inverters are liably to oscillate if you feed them with too low frequencies. C12 is there as a quick fix to stop this, but for a proper design I would reduce the value of C11 to 4n7 for a roll-off of 17Hz.

7th May 2006, 04:30 PM	#22
merkur diyAudio Member Join Date: May 2006	For the grid stop of the output, I had try bigger resistor like 10 K with no result justifing them. I will try with lower capacitor in C11 and I 'll get back with the result Thank's

7th May 2006, 10:39 PM	#26
merkur diyAudio Member Join Date: May 2006	How much in (%) ripple is acceptable on the plate and on the screen voltage supply when the amplifier is driving at maximum? I'm not sure about the voltage doubler. Does it need more capacitor? The oscillation seem to have stop but now i'm hearing like a gost note especially when i'm playing up the neck on the guitar only when i'm driving the amp at maximum. Any hint?

7th May 2006, 10:58 PM	#28
merkur diyAudio Member Join Date: May 2006	By sure that I already whent trought all aiken have put on his web site.

10th May 2006, 01:19 AM	#29
merkur diyAudio Member Join Date: May 2006	Thank you guy's for all the information but my problem was that the driver was clipping before the maximum preamp signal. Now I have change that and the oscillation disapear. But now I see 120hz in my signal and I know that it come from my supply so any advice on my voltage doubler, publish earlier, will be welcome.

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