I'm am looking into building another amp. This time around it will be a single channel 50w push-pull amp. I intend to be able to use it for bass as well as guitar. I found the site below that has a guy's simplified version of a 60s Ampeg Portaflex. I like the design, but there is no mid control and no Master Volume. I can put a different tonestack in there no problem, but my amp experience is with Single-Ended Class A amps.

My question: To add a master volume to http://thejaffes.org/rory/bassamp/bassamp.pdf, do I put the pot after the tonestack and before the phase inverter, or would I need a dual-gang pot attached to both the wires leading to Pin 5 on the 6L6? Or am I way off?

Your second pic isn't showing.

EDIT: Sorry, forgot to thank you. I'm glad hear both would work.

1 more question. This amp uses 4 diodes in the rectifier section. Is there a specific reason to use 4 rather than 2? I will use four, I mean it's $.18 difference. This is just more curiosity.
Last edited by end_citizen at Dec 17, 2008,
Just increase the reverse bias breakdown voltage.

If you have one diode reverse biased then the reverse bias voltage is that of that one diode. If you have two diodes in series the voltage adds. Basically having two diodes in series in your PS just makes sure the diodes don't fry.
Chris on your diagram, there wires just going off out of the picture, where do they all go, where are the outputs, inputs etc etc?
Does it use a transformer? I can't see one but i though all Valve amps had one...

the pic is just a small part of the overall schematic from marstran.8k.com