Adding a master volume to an old Masco amp

[dearborndave]

I've been working on an old (1953) Masco ME-36 P.A. amp and I was thinking about ditching the phono channel and using the pot space on the front panel for a master volume. I am totally new to this modifying an old amp thing. I've built amp kits before, but this is the first time I've tried my hand and breathing new life into an old amp. I've already went through the amp and replaced all the capacitors, and a bunch of resistors that had drifted off their original values. I've replaced the old screw type mic inputs with 1/4" jacks and the old 6 pin speaker connections with 1/4" jacks. The phono channel will never be used so I was thinking about adding a pre-phase inverter master volume in its place. I was going with the pre-phase inverter master volume because it seems to be the easiest way to do it. Anyways, I just wanted to make sure I was going to add it to the right place in the circuit. I've attached a schematic of the amp, and I figured I was going to add the 1 Meg pot for the master volume in between C13 (the .05uF coupling cap) and R24 (the 470K grid leak resistor). Is this where it should go? Any help would be greatly appreciated and would move me along on my learning curve! Thanks in advance!

[sluckey]

That's a good place for it. I would actually replace the 470K resistor with a 500K-A pot.

[dearborndave]

Thanks Sluckey, that's exactly why I asked the question here, I would have never thought to just replace the 470K resistor with the master volume pot. But after you mentioned it, I remember reading about a lot of amps using a potentiometer in place of a grid leak resistor. Thanks again for the help, you are advancing my education in tube amp knowledge!

[dearborndave]

And it just so happens that the phono volume pot is a 500K-A pot. It don't get any easier then that!