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Fizzy distortion in a 6n1p amp


 
11/12/2004 9:20 AM
Bob
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Fizzy distortion in a 6n1p amp
I built a Gilmore Jr. from a kit http://www.guytronix.com . The overall tone and quality is good until it's cranked into overdrive, then there's some bad sound on the sustained notes especally on the bottom end, kinda fizzy.  
 
I'm thinking that the power tube is the cause, possibly bias or the amount of signal driving it. It's got one 12AX7 in the preamp, a single tone control and the self split 6n1p running at just about 300VDC. Here's the schematic without the values, Guytronix doesn't publish these. http://www.gerhartamps.com/gilmorejr/Gilmore_Jr.pdf  
 
The 6n1p cathode resistor is 330ohms.  
 
Here's a clip of the tone, listen at 0:15 when I crank up the guitar volume. I used a 5751 in the preamp to lower the amount of gain and it cleaned up a little, still I'm not happy with the distortion.  
 
http://www.patmedia.net/bob-ingram/Gilmore/Clip1.mp3  
 
Any suggestions on what to look at?  
 
Thx in advance.  
 
Bob
 
11/12/2004 4:12 PM
Chris @ CMW amps
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Hi Bob  
 
If you can post or email me ( at adsl255744@tiscali.nl ) the values I can help you, I also need to know the measured voltages on the plates and cathodes.  
 
Kindest regards,  
 
Chris
 
 
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11/12/2004 6:43 PM
Bob Ingram
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Thx Chris,  
 
I'll e-mail you the schematic.  
 
Measurements.  
 
Plate voltage 310  
Cathode 5.3  
Grid 0 as expected.  
 
Bob
 
11/13/2004 9:11 AM
Bruce /Mission Amps
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I'm with Chris.  
A schematic with no component values is worthless when asking questions like this.  
 
It sounds like severe overdrive or over coupling clipping above 2Khz to 3KHz to me.  
What causes that?  
One or more of all those unnamed values are to blame I'm sure.  
 
Bruce
 
11/13/2004 9:20 AM
Chris @ CMW amps
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off topic
Hi Bruce  
 
Have a nice weekend!!!  
Just preparing a gig with some Texans in Amsterdam... one of the guys is really enjoying a tweedy ( "the overdriven tones are so easy to play" , "how many watts, 50?" :) )  
 
Chris
 
11/13/2004 5:45 PM
Bob Ingram
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Re: Fizzy distortion in a 6n1p amp
Bruce,  
I sent the schematic to Chris and he made some suggestions. The vendor asked me to not share the schematic so of course I'll respect that and not post it on this forum. If you don't mind I'll e-mail you the schematic and please respect the vendors wishes and keep it to yourself.  
 
I agree with your assessment.  
Bob
 
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