Peavey 6505 bias and grounding issue

[metalangst]

The Peavey 6505 is close to the 5150, but I don't see the bias adjust. How is the bias set on the 6505? I have an amp that's running at 15mA a tube. That seems cold. Is this typical of the 6505, or should it be closer to 30mA a tube? The pre-amp tubes/pcb is shock mounted with rubber bushings using two metal brackets. The brackets are isolated from ground and produce a nasty buzz when touched. I don't know how this effects the operation, but they seem like two antennas right next to the pre-amp tubes. I ran a wire from the two brackets to ground. There was even a nut and bolt in the chassis that looked like that's what it was for, it wasn't doing anything.

[defaced]

5150s don't have adjustable bias, and yep, they're cold. I don't have a schematic of their power supply so I can't say how to make them adjustable, but this is a pretty popular modification to the amp. Here's the first hit from Googoe "5150 bias mod". http://www.blueguitar.org/new/schem/...0_bias_mod.pdf

I don't know if the 5150 and 6505 boards are the same, so you may have to do some reverse engineering to make this work.

[metalangst]

The bias circuit was easy enough to sketch out by looking through the pcb, it's exactly the same as that link. And my schematic of the 5150 does not include the power supply so it may be exactly the same. So if "they're cold" does that mean I should bias it cold after re-tube? Or if I turn up the juice will the shredder give me grief because his tone is off?

[Enzo]

The 5150 and 6505 are EXACTLY the same amp. When Eddie Van Halen's contract with PV expired, they could no longer use the name 5150, since it is a trademark that Eddie owns. So they renamed it the 6505 in honor of their 40th anniversary - company started in 1965 and it was then 2005. 5150-2 became the 6505+.


You can get complete schematics for any Peavey product by asking customer service at PV.

The 5150/6505 is not adjustable and would have to be modified to make it so.

Your current may be cool by conventional wisdom, but most of the tone in that amp comes from the preamp anyway. The bottom line is how it sounds. Does the stock amp SOUND good? The only reason to modify the thing would be if the sound was suffering.


The method in the link should work just fine. I find most ideas on Steve's Blue Guitar site to be good ones.