Tube Amp Archive

Didn't see any responses. See attached schematic.

I noticed there was some interest in switching between multiple amps. I've built a relay-activated 5-way switcher that can switch between amps via a common input jack either while playing through the selected amp's speaker, or it can direct the speaker output of the selected amp to a common speaker ...

I just built a 5-way amp switcher that works like a charm. Uses 15 cheap little 5v relays! Will switch between 5 different amp inputs. Since I route my amps through an OX box, I can also feed each of the speaker outputs from each amp to a single output jack to the OX. Was a real challenge since one ...

Rule of thumb for wiring - avoid soldering when 5 hours jet-lagged. (Scotland is amazing).

I miswired several connections - I have no idea how the amp even worked at all. After correcting the tone variation is much more pronounced as the Bode plots show. Still a lower output but very usable.

Paul

Maybe it's my old ears but Its hard to tell. I still have ch 1 which can be pushed to get some breakup. Ch 2 is just on the edge with my Texas Specials pickups. I wouldn't call it a deal breaker - nice to have the option on ch 2. I think the mod is more balanced with the curves swiveling around the ...

So I finally got around to modding using the "Big Muff" single tone control suggested. Aside from some slight deviations in capacitance - 1nf instead of 1.5nf due to availability and wiring the tone pot backwards, the circuit seems to be behave. The over cut in max volume compared to the original do...

Yes. I was just deciding where to make the connection. Without the 270k coupling resistor one would have to run the modded channel at full volume in order to use the un-modded channel - would add some hum. Will try it both ways. The 6db may be too much - its not a high gain amp even with the feedbac...

I notice that the circuit provided by Martin Manning might have an issue since the volume pot at minimum will set the output to ground. This output on the original circuit goes through a 270k resistor before going to the phase inverter stage as does the output from other channel tone stack. This iso...

Thanks for the tips. You've inspired me to learn a little LTspice. At the point where I should be able to replicate bode plots. There's a bug in the Mac version in selecting the resistance step curves - doesn't look like Analog Devices is too interested. Yes, that is glue. All the long jumper wires ...

That's the baby. They don't show the pot and jack side of the chassis - I have to zoom in with my iPhone or use ohmmeter to trace the circuit. I made the mistake of removing a flickering pilot light (can be seen on right side of image) to Deoxit. Bulb faces down into the chasis. Had to be Houdini to...

Thanks. The tone is nicely isolated from the volume. Thanks for the link you sent on the M-15 rehab - good to hear someone else's experience. He had a blown PT. In my case it was the OT. Surprised me since the fragile speaker seems alive and well - would have thought that would go before or with the...

For the original circuit I see how much the full volume compresses the curves, almost no variation - just what I hear. Out of curiosity, can you run the curves at half volume. Are both pots linear or is the volume an audio taper? Just need to determine the layout for the mod. Lots of long wires cris...

Thanks. Looks like a nice transition from base to treble. Do you think the -25 db is more attenuation than the original circuit?

I think you are correct. The tone certainly changes with different OX UA cab models. The original 15" speaker also inhibits the highs. As you point out, some of the caps are there for a reason besides tone ( hum control). The Ampeg manual actually warns that the 15" speaker can easily be blown. Prob...

In the process of tweaking an old amp with single volume and tone control, I realized the volume control setting has a big impact on the tone control and can actually make it almost ineffective at full volume. Why not use the guitar volume instead to control preamp distortion and, instead have an in...