Did Leo Fender use math?

[Chuck H]

Why it's universal use?
You don't mess with what works fine..

That was always my take on it too. The gain block is just that. The connected circuits were adjusted accordingly. In todays genre of high gain preamps it's more common to see different values for gain or symmetry control. But if your making amps that overdrive the power tubes before the preamp clips there's no need to get fancy with the vanilla gain block circuit.

[Helmholtz]

Some ECC83 datasheets contain design tables for different B+ and plate resistance:
https://frank.pocnet.net/sheets/190/e/E83CC.pdf

[Dave H]

If you want to know "How" use the formulas in the literature but if you want to know "Why" sooner or later you're going to need advanced math. For example we all know Vrms for a sine wave is 0.707 x Vp but why? To answer that you need advanced math (calculus).

[Helmholtz]

To be clear I do think that the Fender circuit has good signal performance. It's just noisy....

I see, thanks for sharing your design. Like it.
The virtual earth stage makes a perfect mixer.
Also the extra PS node makes a lot of sense.

This said, having played Fender Reverb amps (BF and SF) since the 80s, I've never been bothered by excessive amp hum or hiss.
Most of the noise typically comes from the PUs.
BTW, the thermal noise of the 3.3M or 4.7M dry signal mixing resistor is significantly lowered by the output resistance of the reverb recovery circuit (around 150k).

[Chuck H]

If I'm honest I've never had a Fender reverb amp on my bench. I've only played a few as they came up for stage gear as a musician. So I can't speak to their condition. I do know the 6G16 circuit was quieter than the 3.3M/10p circuit in an amp I built where I tried both circuits. But only just noticeable.

EDIT: I'm glad you asked about my pervieved problem with the Fender circuit. Interesting about the thermal noise due to resistance being less of an issue because of the output circuit resistance. There's plenty I don't know. All I really know in this case is that I have an aversion to really high resistance values in the signal path for the obvious reasons. I came into this game when high gain preamps were becoming popular and high resistances with parallel capacitors were used all through the signal chain. These amps hissed like a snake. So I've made it part of my design ideology to avoid high resistances in the signal path from the beginning.

[Chuck H]

thanks for sharing your design. Like it.

I'm actually fortunate to have that amp back in my possession. It's a 2x12 combo and the owner only used it for stage work. He retired from playing out and was selling all his gear. I built it for him for cost about ten years ago and he was good enough to sell it back to me for what he paid. Now I just need to get the trem dialed in.

[Helmholtz]

Now I just need to get the trem dialed in.

Never liked tremolo. Not even sure if the tremolo in any of my amps still works.
In my shop days in the 80s I often modded the tremolo circuit to an extra gain stage on customers' request.

[Justin Thomas]

Full Disclosure:

Chuck, I downloaded that one too. I'm not gonna clone it but I'll look at the reverb, because yes, the hum is annoying.

I'll have to see if "Spitfire With Cheese" is on my computer; otherwise I only have guts of the particular amp I built. It's PTP so now it has "Extra" cheese.

Jusrin

[g1]

It has only one set of tone controls on the panel but two tone stacks wired on dual gang pots.

Can you clarify? Do you mean single shaft dual 'ganged' pots, or split shaft dual pots? From the drawing it looks like the latter which would make more sense to me. Sorry if I'm being pedantic.

[Chuck H]

Can you clarify? Do you mean single shaft dual 'ganged' pots, or split shaft dual pots? From the drawing it looks like the latter which would make more sense to me. Sorry if I'm being pedantic.

The former. Just plain dual gang pots. Not concentric. Since it's not a channel switching amp I didn't see the need for independent adjustment. And I was careful to voice it so that it would feel intuitive at similar eq settings. What I wanted was just a basic vintage amp with reverb and tremolo. And then a different amp with the same features just by flipping a switch

That said... It was a little dissapointing how similar the two circuits sound with the same guitar running through the same power amp, cabinet and speakers. The only difference being the preamp topology and the NFB circuit. The difference is real and good, just not as profound as I'd hoped for.