I can't adjust my bias pot any further than 19ma? I have a set of JJ6v6 in fact a hole set or JJs. What I understand the JJs sound really sweet around 24ma. I can't get it passed 19ma the adjustment pot just can't be turned any further? Is there away to adjust the pot adjustment ? Has anyone ever come across this?
What's your plate voltage at 19mA?
There's a lot more to bias than just the cathode voltage/current.
"...pray do not imagine that those who make the noise are the only inhabitants of the field;
that, of course, they are many in number; or that, after all, they are other than the little,
shriveled, meagre, hopping, though loud and troublesome, insects of the hour."
-Edmund Burke
You will have to change the resistor connected to the bias pot. Like NT is saying, they will sound good at 24 mA if your plate voltage isn't to high. If it is, 19 mA might be just fine.
I'm useing the Weber Bias Rite BR-AH it does the proper scaleing for you. The reading I'm getting is about 350-370@19ma. How does sound to you? Thanks
I have used JJs in my DRRI (now have Tung Sol RI 6V6s in it). I have similar plate readings and can set the bias to up around 25+ if I wanted.....
Just being stupid though - the amp is switched on and not in standby, or?
"Sorry" - John Belushi as he smashed a guitar in Animal House
You are looking for less -bias voltage, so you have two way to get that happing.
1) increase the value of the resistor before the bias diode( most times a 470 ohm 1 watt) or
2) lower the value of the resistor off of the bias pot that goes to ground.
Getting 1.5 to 2 volts less negitive bias voltage should let you swing those 6V6s up to near 26 ma if you care to see how they play like that!
The amp is on and not in standby,thanks for asking.
So the only soulution is to change the value of the resistor?
What I'm wondering now is the DRRI is mass produced,shouldn't all of the bias pot adjustments on the DRRIs be very similar in the adjustment range?
Is it possible I'm missing something? or a easier soulution than changing a resistor and voiding my 5yr warranty.
If I am not mistaken if you get work done by a factor authorized tech the warranty isn't kaput. At least that is what the guy said who worked on my DRRI last summer. He is a Fender authorized service tech and he said no problems if I need warranty work.
The tubes that Fender uses in their amps are color coded by how they bias. The idea is that if you get Fender tubes with the same color code they should fall within the bias range of your amp. I believe that Bob at Eurotubes rates his JJ tubes as well and if you tell him what the color code was on your Groove Tubes he should be able to sell you a set that will bias correctly without changing the bias circuit.Originally Posted by mach3
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