Dr. Z MAZ reverb circuit

[52 Bill]

Had to fix one of these and was surprised to see a single triode stage used as the reverb driver (with a transformer) and two paralleled triodes for the return circuit. This is the exact opposite of what we have all seen for years in the usual Fender circuit.

Searching on-line shows this same design for other Dr. Z amps.

Any opinions or knowledge as to why this was done?

[Enzo]

Because it works for them. There is not ONE WAY to do circuits. For example Fender runs their tone stacks right from a plate, while Marshall takes the same tone stack (with some different values) and drives it from a cathode follower. Neither is wrong. It doesn't take a lot of power to drive a reverb input, There are other single triode 12AX7 drives with transformer. I was just looking at a Seymour Duncan Convertible 100, which has that circuit.


As to the dual triode recovery, perhaps they paralleled triodes for noise. Or maybe they had a half tube left over and figured why not use it thus.

[g1]

If they had half a tube left over it's probably because they forgot to use it on the driver side.
I think reverb sounds much better driven pretty hard, like Fender style with both halves of higher current 12AT.

[Steve A.]

Because it works for them. There is not ONE WAY to do circuits. For example Fender runs their tone stacks right from a plate, while Marshall takes the same tone stack (with some different values) and drives it from a cathode follower.

Are you feeling okay today??? Do I really need to remind the amp tech with 30,000+ posts here that the Marshall CF-driven tone stack was borrowed from the Fender 5F6A tweed bassman?
You better take your temperature!

Steve A.

[Enzo]

And all those guys took their circuits from the 1930s. Just pointing out that in two different very high profile brands, the same circuit is implemented in two ways, and neither is wrong. Just as the different reverb circuits are not wrong.

[minim]

Are you feeling okay today??? Do I really need to remind the amp tech with 30,000+ posts here that the Marshall CF-driven tone stack was borrowed from the Fender 5F6A tweed bassman?
You better take your temperature!

Steve A.

It seemed to me his example was based on Blackface vs Tweed.

[tubeswell]

A lot of guys have built amps with 1-tube reverb, and there's a whole heap of boutiquey amps out there with them. I had a Morgan SW22R in the other day and took some gutshots and reverse engineered the schematic. The 12AX7-based reverb isn't 'surfy' intense like BF Fender, but it is still quite a good amount for what it is. And its economical on tubes

[pdf64]

A lot of guys have built amps with 1-tube reverb, and there's a whole heap of boutiquey amps out there with them. I had a Morgan SW22R in the other day and took some gutshots and reverse engineered the schematic. The 12AX7-based reverb isn't 'surfy' intense like BF Fender, but it is still quite a good amount for what it is. And its economical on tubes

Yes, Mesa Boogie seem to get good results with a single 12AT7 section tx coupled reverb driver in most of the later mk series amps, eg https://el34world.com/charts/Schemat...oogie_mkiv.pdf
What is the value of the 'level' master vol control on that Morgan?

[tubeswell]

1MA IRRC

[Randall]

That's an odd tone section on that Morgan.

[tubeswell]

That's an odd tone section on that Morgan.

It’s a Dumble-ish contrivance. Not really as confusing as it looks at first glance - I did a circuit analysis of the 'bass emphasis' switch in order to simplify it a bit. The 1M in parallel with the 0.01uF is so large it doesn't do anything in the context of the RC network, except act as a switching noise suppressor YMMV. (Die-hard Dumble fans would probably insist on its' mojo factor).

[tubeswell]

Some gut shots of the Morgan TS controls (for Randall)