The Amp Garage

The purpose of twisting wires together in signal wires is to present equal exposure to outside interference, which will cancel due to phase. The purpose of twisting heater wires is to keep the wires close to each other and parallel, so any AC hum emanating from them is cancelled out due to phase. If...

Nope. Marshall employed many women, so I'm guessing that's Joyce H. not Joyce, H.

You're in phase with the signal being injected as negative feedback. Negative feedback reduces noise, and gain. Because you're in phase, it's no longer negative feedback. It doesn't have to squeal to be wrong, more gain and noise are also symptoms.

Here is an update. I replaced the .047 capacitor feeding the grid on the suspect tube socket. The amp is working great now! My grid and plate voltages are perfect giving me very near 70% plate dissipation. One clarification is that I do have the 2000 pf caps on the grid to ground. They were mounted...

1. I can hear no difference between the old and new PT. 2. Voltages appear identical everywhere. Any differences are insignificant enough to be attributed to how the measurement is taken and possible voltage changes from the electric company. I did take the amp out this weekend, and it is loud, clea...

If anybody is interested, the new Hammond transformer came today. I looks identical to the Schumacher, at least as much iron, and perfect drop in. Installed it, brought up the voltage gradually on a Variac and current limiter while measuring B+ and bias voltages -- all ok, no smoke. Plugged directly...

Note that if it’s the coil winding pack that is loose on the core ( which does happen at times ) then isolating washers will not improving things one bit and your only hope will be filling it up with the sealer / gasket maker I posted about. A few years ago I got a BF 1967 Bassman that needed a PT ...

A possible cause may be old solder joints on the B+ connections that are going cold. I had this very same thing on a new Marshall build. The chassis was vibrating, very low, along with hum. After reflowing the connections to all the B+ connections this vibration/hum went away. All solder joints hav...

Stevem wrote: ↑Sun Feb 28, 2021 12:18 am Compact as in one speaker?

2x10. Smaller than a Deluxe Reverb or Vibrolux Reverb (speakers are angled).

Yet another AB165 Bassman. It had mods, which I undid, and I put it into a combo cab with the intention of having a clean but compact gigging amplifier.

It is indeed an old amp. When I bought it someone had bumped up the reservoir filtering from 35uf to 110uf. It's solid state rectifier but I'm thinking that could have put some strain on the PT. There is a bit of goo that leaked and hardened again on the outside bottom. Again, it's faint until you t...

I have an amp that hums (what else is new?). After checking everything I noticed the power transformer is actually vibrating. I pulled the transformer away from the chassis and checked that all the bolts holding it together were tight (they were). If I hold the transformer in my hand and run the amp...

I did this mod to a Bassman. I'm primarily a clean player, so the cold clipper did nothing for me and I put the third stage back to stock. I did, however leave the tonestack alone, it is a nice contrast to the Normal channel, giving more variations, and, really gives some nice tone when the channels...

Nope. It's all there, and looks pretty well stock. bm100.jpg Odd schematic and nowhere near correct for a Bassman 100. pdf64 referenced the correct schematic above. I don't remember where I got that schematic, but even the one you're showing has two 12AX7s in the preamp, one 12AT7 for the PI -- exa...

Stevem wrote: ↑Mon Nov 30, 2020 11:13 am That amp is no where near stock!!

You're missing preamp tubes and only the normal channel is wired up to work.

Far better pictures are needed and all the number stamping info off of the PT or OT would be a great help!

Nope. It's all there, and looks pretty well stock.