Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 66merc on February 03, 2011, 09:08:19 pm

Title: Master volume on jukebox amp
Post by: 66merc on February 03, 2011, 09:08:19 pm

Howdy folks,

Been a couple of years since I touched an amp.  I'm pretty sure I didn't know what I was doing then and now I'm even more rusty than that.

I'm tearing into the stack of stereo Rowe-AMI jukebox chassis again that I have stacked in the garage.  The last one I gutted and made a self-split stereo ipod player using russian surplus 6v6-type tubes.  Plays great but I guess I'm feeling guilty about tearing them up, so this time I'm just starting with adding a master volume.  It appears that each channel uses a single 12ax7 for one gain stage and a PI.  Simple question--should I put a pre-PI MV like this?

Plate of 12ax7----pot---blocking cap----PI

or this?

Plate of 12ax7---blocking cap---pot---PI

or this?

Plate of 12ax7---blocking cap---pot---blocking cap---PI

Keep in mind that there was no volume control on these amps.  The volume was controlled by a remote by the bartender, probably behind the bar next to the baseball bat and double barreled shotgun.

Any help appreciated

66merc

Title: Re: Master volume on jukebox amp
Post by: DummyLoad on February 03, 2011, 09:20:28 pm

Plate of 12ax7---blocking cap---pot---blocking cap---PI  that should work. blocking cap from pot <> PI can be smallish - 1-2nF.

Title: Re: Master volume on jukebox amp
Post by: sluckey on February 03, 2011, 09:23:10 pm

Quote

Plate of 12ax7---blocking cap---pot---blocking cap---PI

Without seeing a schematic I'd recommend this one.

Quote

The volume was controlled by a remote by the bartender

You mean a remote located volume control right? Not a wireless remote like for the TV? If so, there should be a plug on the chassis for that remote vol pot. I'd just put a pot on the chassis and wire it like the remote, only with shorter wires. Probably need a dual pot if this is a stereo amp.

Title: Re: Master volume on jukebox amp
Post by: 66merc on February 03, 2011, 10:19:42 pm

Thanks for the replies.  Seems like cap on each side of pot is the answer.

Hmmmm, Sluckey, I hadn't thought of that.  There is a plug on this thing with about 12 wires leading to it.  I gotta tell you, the underside of this thing is complicated.  I have never been able to find a schematic and doubt I could draw a good one. Anyway, each rca input sends a wire to this plug prior to the input cap and grid to ground resister.  I will clip a pot here to bleed signal to ground and see what happens.  I do have a concentric stereo pot for the final placement.

Thanks again

66merc