|Author:||automap68 (registered user: 127 posts )|
|Date:||Sun, Feb 05th, 2012 @ 15:36 ( . )|
On 02/05/2012 @ 15:20, MadDog wrote :
My guitar playing is somewhere in between piss-poor and unbelievable, so you probably got me beat.
Although it seems very loud it is only 4 watts.Welcome to the world of tube amplifiers, where the hardest thing we do is convince people they don't need 400 Watts. : )
I also happen to have an HP distortion analzyers at my disposal which yeilded 13% distortionWhat kind of distortion? Distortion in guitar amps is intentional; if you don't have distortion, you don't have 'tone'.
: Which is way higer then it should be even for a high gain amp
No its not tube distortion. that not what i ment
That is actually the least of my issues.
Right now there are several main concerns
One, the bias is incorrect, with the 430 ohm resistor.
It is reading about 27 volts where are 60ma the kt88 should be closer to 35
The other thing is 4 watt output is on a kt88 at that plate voltage and current should be more like 10 to 12 watts more like 10
Basically if you put an osscilator on the amp and look at the signal, the tube is clipping way to earlier. Hence the 4 watts.
There is def a major issue here somewhere in the circuit. So far i have retraced my steps. Checked all applicable values and ive also fooled with the bias a bit
with a 390 resistor the cathode dropped to 25 instead of 27
with a 550 and a 620 the result was about the same @ 31.8 volts or so.
which is odd, with that much reistance we should of seen far different cathode voltages.
Also, there is a voltage drop of about 35 volts or so from the anode to cathode.
The plate is really only getting about 319 volts
the main concern is bascially, the tube is maxing out and clipping at 4 watts
These are brand new 50$ gold lion tubes.
My mentor happens to own Vaccuum tube supplies here in denver and ive been at his shop all morning on the big boys bench. Even he is semi stumped.
Does anyone have any idea why the tube would be clipping at 4 watts?
--* SEL DONE layout check and pics please
2/05/2012 @ 15:39--automap68
2/05/2012 @ 16:13--MadDog
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