DR504 what's up w/ V3?

[lowell]

What yall think V3 does in this preamp? Only "guess" I can make is that it modulates V1's power supply with the signal on the PI grid.

[Enzo]

It is a cathode follower with its grid tied to B+. If I had to offer a guess, it looks to me like they used it to establish a bias supply for the grids of the PI tube. I'd have to think about why they would bother with that added complexity.

[lowell]

FWIW the amp seemed to soften in attack a bit and sound warmer when I modded a different hiwatt to have the V3 circuit.

[octal]

It is a cathode follower with its grid tied to B+. If I had to offer a guess, it looks to me like they used it to establish a bias supply for the grids of the PI tube. I'd have to think about why they would bother with that added complexity.

I agree...the 1meg to B+ and the 220K form a voltage divider to hold the output of the cathode follower at a fixed fraction of B+ I'm not 100% sure why they couldn't just bias the PI directly from a pair of resistors.

If I had to guess, the fixed biasing of the PI would increase the headroom of the PI, or at a minimum change its clipping behavior.

Nathan