I did some searching and I haven't found a complete answer.

So far my understanding is this, its taken and then expanded on from another post:

(Left Side)

v4: Phase Inverter
v3: Effects Loop Buffer, Cathode
v5: Gain Stage - Lead
v2: Gain Stage - Full Lead
v1: Gain Stage - Full Lead, Half Rhythm
V6: ??????????

(Right Side)

What is six responsible for? What are some suggestions for pre amp tubes for that spot?
Are you talking about the 120 or 60combo - as the 60 only has 5 preamp tubes (as does the 6505 standard head)
Im talking about the 120 watt 6505 plus head...

Also aside from just what the extra pre amp does what do each of them do specifically? I mean I see phase inverted but what does that mean? And I am curious about all of them...

I really like my Ruby tubes. I have heard that putting a JJ in the first 2 slots V1 and V2 (I am assuming, and not just the first two from the left or right, I guess...) since the numbers are not in a row. I heard starting the chain with JJ makes them sound better. Can anyone elaborate on this as well?
Okay, so here's the lowdown on the 6505+ preamp utilization...

Signal comes in to the amp from your guitar lead. From here it goes into V1a. This is what's known as your input stage. It's where it all starts. Every guitar amp has one. Even solid state.

From here, the signal has two options. Option one is the rhythm channel. This utilizes V6a and V6b. Clean and crunch are achieved by switching grid leak and bypass capacitor values to alter the signal magnitude from stage to stage, hence controlling overdrive. The amp is in fact, NOT altering the number of gain stages in this channel to achieve clean and crunch, which is likely a large reason why the clean tone is so lacking. instead of removing the extra gain stages that achieve the overdrive in crunch mode, Peavey chose to attenuate the signal instead, leaving all the gain stages in the signal path. V6b drives the rhythm channel tonestack. From the tonestack, the signal goes to V3b and V3a, which are together responsible for the FX loop. V3b is a cathode follower, which in this context is a preamp stage designed so that it is capable of high current drive. High current drive is essential for FX loops where signal can be lost due to heavy impedance. Impedance is the resistance of Alternating Current (AC) flow, which is what your guitar's signal is to a theoretically increasing magnitude from stage to stage, that is, until it runs into a load that impedes it too greatly and loss occurs. That's what the cathode follower seeks to avoid.

V3a is the FX loop return stage, which recovers the signal from V3b and any effects that were placed in the loop, and sends said signal to the Phase Inverter, also known as V4a and V4b. A phase inverter takes one input signal, and splits it into two (relatively) identical output signals of different magnitude. Why... because with the way the Peavey's power section works, if the signals were of identical magnitude, phase issues would cause the identical signals to cancel each other at the output... and in theory, you'd hear nothing. In practice, you'd likely hear faint, garbled crap.

Option two bypasses v6 altogether ,and here begins the signal's travel through the "lead" channel. From V1a it goes straight into the Pre control, which then passes signal to V1b, and then V2a, which is what is known as a "cold clipping" stage. This stage is largely responsible for the aggressive attack to the amp's tone.

from V2a it passes to V2b and V5b, both of which serve as standard gain stages. From V5b, the signal goes to V5a, which drives the lead channel tonestack, and feeds into V3b. That's right. The exact same V3b we discussed a minute ago that drives the FX loop, and from there - V3a to V4a/b, and then the power tubes.

So that, in a nutshell, is how and in what order the 6505+ head uses those 6 preamp tubes.
Tastes like chicken, if chicken was a candy.
Last edited by ConfederateAxe at Apr 11, 2012,