Dukane 1F460 project

[martin manning]

Here's how I'd do a one-or-the-other 6G4-A "Lite."

[Phil_S]

Martin, you've outdone yourself! Thanks very much. This looks very do-able. What's the fun of eliminating the f/s, especially since I have one (will have to share with the Tremolux.) I've also got a decent round DPDT that will fit in one of the holes on the rear panel where the mic inputs used to be (removed this morning.)

[Phil_S]

So, just to stir the pot over my bone pile, I've been thinking (not always a good thing.) I have many, many 12AU7's harvested from an organ...close to 4 dozen. I've got 8 noval sockets. Let's assume keeping the 12AX7 LTP design. How about the others? Can I use a few extra 12AU7's to make up for the gain I'm losing? You wet my appetite when you showed me about bootstrapping a c/f, but we don't have one in the 6G4A. That leaves us with the cascode, parallel triodes, or simply adding a gain stage or two to ramp up the input to the PI. I've got 8 noval sockets of which the 6G4A would take 5 without the normal channel. Thoughts (about design, not my mental state)?

[martin manning]

12AU7's don't show up in guitar amp circuits much... too clean and not enough gain I guess. I think I'd get the thing working and then consider more stages. You could do like I was thinking above and add a stage to the normal, then it would mix with the vib at the PI. I'm wondering what the harmonic vib would sound like as a parallel effect. I don't think you have any more knobs available though, and that might become a limiting factor.

[Phil_S]

I've got room on the back. I removed 5 mic XLR plugs. I'll be closing the holes with a metal plate that can be drilled out for a pot or switch. Look back at the original post for a picture -- 4.5 of them are in the rear view.

I think the "get it working first" view of construction is the right one. I'll try to focus.

Thanks.

[Phil_S]

I can't read it. Can you help?

On the 6G4-A schematic, I think I see an 8.2M resistor in the tremolo circuit.Working back from the Intensity Pot, the bottom lug couples to a .02u cap and then the 8.2M. Or is that 2.2M? It is clear as mud on the schematic. The layout drawing isn't much better.

The thing is, I actually need to buy one of these if it is 8.2M because what amateur would be lucky enough to find one in the parts bin?

The next question is, how critical is the value? Would 8M do just as well? How about 9.4M (which is 2x 4.7M)?

Thanks. And happy new year everyone!

[martin manning]

I see 8.2M. Here are some pretty good .pdf's. Anything within 10% should be good.

[Phil_S]

Thanks, Martin. I have those same muddy PDF's. I think it is the same one all over the 'net. Short of actually finding an original drawing, I suppose someone might actually own the original amp and verify the component. I wasn't actually thinking either would happen. Let's go with 8.2M as the consensus.