The Amp Garage

It looks like the diameter is 20.3; the notch adds ~2 mm.

Does anyone have a bit or punch for 20.3 mm?

I prefer the 5k too. I just don't like the sweep of the 25kB (with || 4k7 R) pot.

I recently started using a wet tile saw to cut G10. It cuts well and keeps the hazardous dust down.

FourT6and2 wrote: ↑Sat Jul 29, 2017 1:14 am I really love having a power transformer with solder tags. Makes wiring it up much cleaner. Wish more companies would do it this way.

What gauge wire are you using on the primary side?

I think a lot of old amps have both. You have to hunt for them. Some have the fuse tucked away inside the chassis somewhere. I don't think I've seen a Marshall with just a Mains fuse and no other fuse. The JTM45 has another fuse tucked away inside the chassis. I think the fuse is on the PT center t...

I've never seen an amp without them. Yeah and I've only seen may 15-20% as a rough guess that actually fuse both, most only fuse mains. But then I mostly look at old amps, not newer stuff. ~Phil I think a lot of old amps have both. You have to hunt for them. Some have the fuse tucked away inside th...

A couple additional points to keep in mind: - different tube types have different limiting values for the grid leak resistance. - the limiting value is typically lower for fixed bias than for cathode bias. So, for example, a JJ 6V6S in fixed bias has a limiting value of 100k, whereas the limiting va...

Are you going to do anything special to ventilate the tubes. I'm kinda surprised the tubes were placed up front rather than along the rear edge of the chassis.

It's that way to stop the scratchie pot on the guitar...or when you go too low of a voltage on that first preamp tube ...it will build up a small voltage on the grid ..this is because of the 330k or higher plate resistor... also the guys that use VVR circuits have to do this also for the input and ...

In both positions, C17 ties grid to ground. As drawn in the circuit above, you'd think its purpose was to bypass the grid leak resistor, but that is not the case. Its purpose is to add to the input capacitance of the tube. And the best place to do that is right at the tube. R16 should come before C1...

So if you had a choice for high-gain amp design, would you stick with what Ceriatone has done, or go with something more like this (a friend suggested it a few years ago with regard to the standard 68K input grid stoppers you see in many Marshall style builds (like this one): "You can also try this...

I don't know how Merlin derived his mu-based formula. I guess that is the missing piece of the puzzle. The aim, according to Merlin, is to pick Rseries and Rshunt values that will give you a maximum negative bias equal to HT / mu, where HT (i.e., B+) depends on the Vac of the HT secondaries. Rseries...

yep. Make sure you have -46Vdc (or less; -50 would be fine too) on pin 5 of each octal when your bias pot is rotated for maximum resistance. Season to taste. On another note: whenever possible (e.g., designing a new amp), try to keep the resistor values small (with a separate bias tap). The output i...

Thanks for the explanation! So how does one determine what value is needed for that dropping resistor (or resistors, in the case of dual bias)? Is it possible to know what value to use before the amp is turned on for the first time? Merlin Blencowe has a forumula on his bias supply page (check out ...

And also think about what the bias circuit must do. On one end of the spectrum, it needs to basically 'turn off' the tube by supplying its grid with a "large" negative voltage (large in the absolute-value sense). At the other end of the spectrum, it must deliver at least some negative voltage to the...