Tube Amp Archive

I'm doing a tune up on a red bear mk60, and at some point someone put a 100ohm resistor across the heaters (Pin 7/2) then to ground on one of the power tube sockets.. Any idea what this was trying to achieve? It was strange enough for me to believe it was some sort of mod that I'm not aware of.

If it's not a open plate load resistor on V1-1 then I would have thought that replacing the low Jack would have done it! OK, so after testing everything up to the PI, re flowing anything that looked suspect.. and replacing everything around V1.1, this response made me want to double check the jacks...

ok, new update. The EQ is indeed not doing anything on the low channal as well. I'm going to start working my way to the tone stack..

Is this your amp? If so, the way the hi/lo is setup, it could only be a handful of components that have failed. This is assuming your lo channel is indeed 100% OK. My first guess would be plate load resistor, then coupling cap, but only because you said you replaced the tube and the input jack. The...

So the high channel on my Mig60 lost volume, tone knobs don't really do anything, and there is little to no distortion. "Low" channel remains fine. I replaced both input jacks, tubes, replaced C22, R3, R2, and reflowed any suspect areas in the high input signal path. (I know I shotgun-ed it) I chops...

A winding has two ENDS, you understand. You apply AC to two ends of the same piece of wire, which is wrapped around the core, to get the magic happening. If you are presented with two primary wires and you're unsure, use your ohmmeter. You should read very low resistance (a couple of ohms or so), i...

Also, what brought this up is trying to figure out what I connect to the North on the incoming AC from the wall.

I'm not real clear on exactly what you have so I will assume that the primary has two separate 115V primaries, unlike the modern version which has a 0 start, 115V tap and 125V end primary winding. If it truly has two separate primary windings then you would simply parallel the two windings, the sta...

I'm doing a 2204 build with a Hammond 272jx, one of the older ones that only runs 115v. My question is what do I do if there is no 0v or common tap on the primary? I have little understanding of trannys and this is my first build, but I have done a lot of repairs and mods before this. The primary ha...

If you want to learn for yourself. Use the continuity setting on your dmm if you have one and see what is connected with what when you flip the switch. 3 pin switch switches between center and outside. 4 pin switch switches between the bottom lugs and the top. I'm assuming from this that the power ...

I'm having trouble with the wiring for a 3 prong standby switch and a 4 prong mains switch.
Its for a JCM 800 style build.

As for background, I am basically erector setting a jcm 800. I was given the amp in pieces, and I'm learning as I build. Standby and power switches are still a mystery to me.

But to your original question, I seriously think it would take less time if you just modded the existing board(s). It's already so close in topology, even w/ the plate driven stack and cathodyne PI. I remember it being a fun project, too, and the boards are relatively easy to work on. There are sit...

2 boards were given to me, one is a complete 2203, and the other is a mystery, pretty close to some sort of marshall... with zoso caps, the works. I Want to throw it in a PV windsor I've had at the shop for a while. What would be the most painless way to achieve this? I'm thinking I strip all the bo...

Put in the resonance knob. I can't really tell the difference. I dunno, maybe the shelving is too low. Time to play with some cap values

thanks by the way