Tube Amp Archive

After dinking around with the presence control as designed, and trying to get a Marshall style presence to work without changing too much near the phase inverter' I went nuts.... No matter what I tried there was no effect! I finally tore it all out and replaced the presence control with a Vox style ...

Well I managed to get everything working 100% except the presence control. The treble and presence squealing was solved by rerouting, using shielded on the PPIMV AND reversing the OT secondary. Everyone here told me to check it, but I had convinced myself that it was either a full power honk or noth...

Well I managed to get everything working 100% except the presence control. The treble and presence squealing was solved by rerouting AND 1reversing the OT secondary. Everyone here told me to check it, but I had convinced myself that it was either a full power honk or nothing and I only had subtle fe...

Glad you're making progress :) I reached a point where I had all sorts of leads looping through the air like McDonalds arches Just a comment: You can reduce cross-talk and feedback between wiring by running it tight against the (grounded) chassis, rather than up in the air - a bit like a half shiel...

Anyway, disconnecting the presence still doesn't fix the treble. Weird huh? Maybe. Keep the lead from the wiper of the treble pot *well* away from the MV connections on the board and the connection to pin 6 of the PI - the layout shows these right next to each other which is a bit poor, IMHO. Bette...

The treble control workers normally when full up or down. +1 on possibly bad or dirty pot. I have disco necked the treble pot and it tests fine, at about 241k on both sides with no weirdness in the taper. I even checked for intermittent shorting to the pot case. Nada. I hoped like hell that it WAS ...

I completely disconnected the presence and thus the negative feedback. It did not fix the treble problem at all. But did it solve your oscillation problem? Yes. Rerouting or disconnecting the presence wires fixed the feedback problem. I still have the treble problem. The treble control workers norm...

I may be completely off the mark here, and I'm certainly no expert, but after looking at the schematic I can't tell how in the heck the presence knob does anything other than vary the overall level of negative feedback coming into the phase inverter. Maybe someone else could chime in on this, seems...

Moving the leads around suggests the issue with howling might be due to the long red lead coming off the presence knob. I would suggest running it under the filter cap board and shortening it so its no longer than it needs to be. Keeping the leads short helps prevent feedback loops from occurring b...

Thanks for the welcome. I don't think I have a reversed OT issue. I can play cranked with no issues. It's not until I both crank the master AND THE PRESENCE that I have problems. I have spent several days triple checking the tone stack. I can't find anything that's not like the layout. However, I ha...

Hello everyone. I'm new to the forum, I've read a lot here and I finally decided to jump in. I'm a player, small time collector and electronics hobbyist. (Im a radio amateur, Extra Class. My nerdiness knows no limits) I built my first ever guitar amp. I started on April fools day and lit her up four...