Tone stack effect on volume

[E biddy]

Yes, but checking the amp schematic I found input stage is built out of a single triode.

So **in this particular case** you might replace that single triode with a 12AX7 and have a "real" extra triode gain stage with little investment.

I bet transformer can feed extra 150mA filament, and you might enlarge the current 7 pin socket hole to accomodate a 9 pin one.

In fact, they might *already* have a noval compatible hole there (since chassis are often built for various models) ; the FET suggestion was to avoid punching a new hole and taxing the transformer, but it looks like "here" itīs not the case.

I made the chassis, so enlarging it wouldn't be any problem and the transformer is oversized for this application, so that wouldn't be any problem. Thanks.

[J M Fahey]

Cool.
Fets (or Op Amps) are used to substitute tubes where space or filament power is a premium but here , not that a big deal.

[Chuck H]

Adding a front end boost via a FET behind a BF tone stack sounds like a fun idea (at least Dumble thought so ). So absolutely do that if you're interested and like the idea. You'll get no argument from me against experimenting. But...

You could skip it and just add a tone stack bypass switch for getting dirty. Since the amp will get to the edge of breakup now you do have full clean power/watts. With the addition of the second stage cathode bypass cap you'll have a little more gain for the basic, clean tone. That, and a tone stack bypass option would have a good bit more gain than a stock 5f10 for getting dirty. Of course this means no tone stack when the switch is flipped. But once you're clipping much the tone stack is really only used for mitigating LF to avoid flatulence. This could be built in to the switched circuit. And no extra "shtuff" in the amp.

[E biddy]

Adding a front end boost via a FET behind a BF tone stack sounds like a fun idea (at least Dumble thought so ). So absolutely do that if you're interested and like the idea. You'll get no argument from me against experimenting. But...

What would this look like? Something like this?



Or would that be a buffer? I don't really know these circuits.

[Chuck H]

I've seen it demonstrated a couple of ways. But the circuit is typically indicated as an "input" switched system. So I'm going to guess it's an input boost/buffer. That is, the first stage the guitar sees and before the first tube stage of the amp. Sorry, I'm not a Dumble enthusiast or expert. I just know they included a FET circuit near the input of their BF-ish styled amps. And Dumble never did anything that didn't sound good. Circuit references on line are EXTREAMLY ambiguous.

[Helmholtz]

That's what I collected from the internet:

dods100.pdf

dprefet.pdf

[E biddy]

Would something like this work?

Fet stage in harvard.pdf

[eschertron]

Notice the two designs Helmholtz offered both have the fet right at the input. Anywhere later in the signal path and you run out of the fet's input headroom.