LarMar - Grid connections

[angelodp]

Hi on a Lar Mar set-up on an AB165, when I make the Grid connections to the 6L6's, do I keep the grid leak resistors that are in place? I have 1.5k from pin 1 to pin 5 on each 6L6. Do I simply connect to pin1 at each grid or eliminate the 1.5k's.

Thanks A

[martin manning]

Keep the grid stoppers in place and connect the MV to pin 1.

[angelodp]

Copy thanks MM

[angelodp]

MM, I am transitioning my AB165 to AA864 for the power section only. Given the change in the NFB network (820r) would you exclude a variable pot on the NFB if I am moving to the PPIMV? Does Var NFB play well with a Lar Mar?

[martin manning]

Might be a nice asset if you can increase the FB at low MV settings. PPIMV reduces the FB voltage with respect to the PI input voltage.

[angelodp]

Hi, I am following this layout for the PPIMV in my AB 165. I have converted the Back end power section to AA864, with regard to the Bias supply.

1. Is the add-on of the 33uf 100v cap to the bias supply needed.

2. Should the grid caps be swapped from .022 to .1

3. Should I swap the 100k 100k V4 Plate R's to 100k 82k

4. Should I swap the coupling cap to V4 from .1 to 500pf like the AA864

Other wise this layout looks good. Its from Triode and modified by D-Lab

Thanks A

[angelodp]

Lar Mar installed and working. I have yet to change the various components mentioned above. Next up is the NFB change out to AA864. I went with MM's method of twisted wires and I did not use shielded runs, as the position of the pot was very close to the Power Tubes. I even left the original wires from the 220K's as the connection to the Lar Mar, I did twist them. I have from bedroom breakup to 50w of rock.

I am wondering about various ideas that I have read about, such as a tube loop in place of the bass channel, or a Marshallesque circuit in place of the bass channel components.

What about purposing the bass channel tubes and eyelets for a reverb circuit? Anyone tried that?