Bios Mod my Peavey 6505+

rcanpolat · 22-01-2009 11:46PM #1

someone pass me on some contact details to get my Peavey 6505+ head bios'ed. the plates etc are all set cold as f*** but i wana crank em up more.

dont wana have to send it of to FJA mods in the states to get it done, shipping will cost an arm and a leg because the head is so dam heavy

Eoin Madsen · 23-01-2009 02:58AM

Hmm. Are you talking about increasing the bias voltage to the grids?

I'm curious as to why you would assume it's biased cold. If you don't even know how to adjust it yourself, there's no way you could tell how the bias is currently set.

Anyway, you definitely don't need to be getting it shipped off for something as relatively simple as adjusting the bias, or even modding the bias circuit. I'm sure someone around will be able to recommend somewhere. Where are you based?

Paolo_M · 23-01-2009 08:39AM

Eoin Madsen wrote: »

Hmm. Are you talking about increasing the bias voltage to the grids?

I'm curious as to why you would assume it's biased cold. If you don't even know how to adjust it yourself, there's no way you could tell how the bias is currently set.

Anyway, you definitely don't need to be getting it shipped off for something as relatively simple as adjusting the bias, or even modding the bias circuit. I'm sure someone around will be able to recommend somewhere. Where are you based?

The 6505+ like the 5150 before it has true fixed bias, like Boogie, and it's not adjustable. It has a fixed bias of about -47Vdc on the 5150s (485/490Vdc plate) I've seen and gives about 60% PD for a typical 6L6GC (36/37mA), which isn't cross over notch territory but is a little cold.
The guy in FJA does a mod on the bias circuitry which basically provides a trimmer pot on the PCB to allow bias adjustment just like you'd find in a Marshall etc.

rcanpolat · 23-01-2009 09:22AM

what paolo said!

Eoin Madsen · 23-01-2009 12:15PM

The 6505 has a pot, albeit somewhat limited in range.

Paolo_M · 23-01-2009 12:45PM

Eoin Madsen wrote: »

The 6505 has a pot, albeit somewhat limited in range.

My bad, didn't realise the 6505+ had a pot. :mad: It's the 5150s I've worked on and I understood that they were pratically the same circuitry.
From what I've read the 6505+ pot almost no range, as you say, and is still "cold" even maxed out. The bias circuit could easily be modded to bring it more "in range" in the traditional sense.

Eoin Madsen · 23-01-2009 03:10PM

Definitely. Though I think turning up the pot and seeing how it sounds a little hotter would be indicated here before anyone pulls out the soldering iron.

Bios Mod my Peavey 6505+

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