Tube Amp Archive

What are the ramifications of using a standard Marshall tone stack without running it after a cathode follower? I'd like to skip the follower and just use a ax7 gain stage prior, but am wondering if that would impact compoenent selection? thanks!

Say I'm looking at a standard cathode follower gain stage with too much gain: what is the best way to reduce the gain? Between throwing a voltage divider on the output side and changing the value of the grid/cathode resistors, it would seem that the voltage follower route would decrease the S/N rati...

I bought an organ from a thrift store several years ago for 15 bucks. This was long before I became interested in tube amps. It sort of worked at the time but I had no use for it so I gave it to a friend, whose garage its been sitting in ever since. Tonight I realized it might have some potential a...

The biasing on the second stage 12AX7 is suspect. You would like the plate voltage to be about 2/3 of the B+. With two 100K's for a plate load something around 2.2K would be right for a cathode resistor. . Exactly what I was going to say at least 1.5K for better bias I hate that style of schematic,...

Working on a '65 Kalamazoo Bass 30 that has the funky flip out control panel. Love the amp, hate the hum: This thing sounds like a bee hive when you turn the volume above 12 oclock. Nice tone, but ugh! What I'm wondering is if anyone has experience with this amp and reducing the hum and if so, what ...

You could reduce bass (with no tone controls) by: Reducing the value of the cathode cap on stage 1. It's 100u? Try 1u or 0.1u. Reducing the value of the .02 coupling cap(s.) Stage 1's should have the most affect. Maybe try .005 or .01. Removing the treble reducing resistor/cap on the plate of the 3...

The biasing on the second stage 12AX7 is suspect. You would like the plate voltage to be about 2/3 of the B+. With two 100K's for a plate load something around 2.2K would be right for a cathode resistor. The 68K in series with the .5uF cap could be replaced with a short to brighten the amp a little...

All those 100uF bypass caps have a lot to do with the bass, especially with HBs. Yet they are fighting against very small interstage coupling caps. Why? Are you trying to minimize phase distortion? The cathodyne inverter could be simplified a bit. The gain stages are unusual, what is the intended r...

Here is a schematic for a modified amp I'm working on. The amp is a bodge of a power amp section [to the right of the second volume control] and two separate preamp stages cascaded together to form the circuit to the left of the second volume control. 1] anything obviously wrong with this circuit? 2...