Tube Amp Archive

dbharris wrote: ↑Sat Aug 23, 2025 11:27 pm ... or add the driver from the SSS to the power amp.

-Dan

Do you mean the gain stage that comes between the PI and Power Tubes? I've been looking at trying something like that but haven't broken ground yet.
What kind of effect does that have (ie, more crunch? more PT compression?)

It occurred to me to DC Couple the V2 stage straight into the Effects Send - I've tried a few arrangements and this is working well now. - At the moment I have two unused triodes and I will either rebuild the circuit and just remove a tube, or think of something to do with the available triodes... -...

With the current transformer, which most likely came out of one of the 1200 series Univoxs, you can expect to see a voltage in the high 600s. I have seen a few 1200s just over 700V. I attached a U1221 for reference (which eccentrically is what this modified U320 is now). To hit a target of 450V, yo...

Thank you for your replies RG, Martin, and others. this is the closest I could find (there are some small differences between this schem and my unit) https://el34world.com/charts/Schematics/Files/Univox/Univox_Lafayette_U320.pdf I've second guessed myself a bit on this because it's been modded by so...

martin manning wrote: ↑Sun Jul 27, 2025 3:20 am Yes, but how much voltage are you looking to drop?

Somewhere beween 60-80v ?

... Use a 10W resistor, and it will dissipate about 5W, same as the MOSFET would have to do. Simple, reliable, and cheap. I thought the reason folks were recommending the Mosfet/zener was because a dropping resistor will react badly to fluctuating current and sag and suck tone and inevitably melt?

thanks Martin!

Is this the whole picture then?

thanks for the replies! I'm not going to spend much money on this amp, so if we're not happy with the power zener approach, I may just lobby the owner to stick with 6L6's You're almost half-right. I am half-smith lol, the other half is dyslexic and dim. you would also likely need another filter cap ...

Where to place a Mosfet B+ reducer in a Voltage Doubler circuit? Japanese Univox (Lafayette) U-320 - designed with a voltage doubler and meant to run 7591's Someone earlier changed the transformer and rewired it for 6L6GC's Owner wants it returned to 7591's The new transformer is putting out 268vac...

I decided to put it in place of the BASS Ch (as pictured in first post) after all, for a proof of concept.
Now that I know how it works I wish it was swapped, my sense of feng shui is a little thrown having the signal path wrap around itself, but I'll leave it for now.

Hi Martin, here's the schematic. I've only made a few changes from the posted Dumbleator schematic. * 4k7 Grid resistor on input (was unstable, I'm not sure if this was the ticket, but the problem went away after I installed it so I left it) * 50K DRIVE pot and bigger resistor (ala Martin) * Send ja...

guys, it's incredible. It gives you so many options. It makes the standard Bassman into a big broad raging monster or gentle chimey whispering angel And the effects loop is so much better for reverb etc. * I had to add another .1uf 600v AFTER the MV, I think it was interacting with the next stage (i...

thanks Glenn, that makes sense.

Olomert Brever wrote: ↑Thu Jul 10, 2025 5:36 pm ... If this is more about building a circuit for the sake of building and learning, then that is a great motivation.

Yes this is my project amp and I've been using it to experiment and learn.

*deleted (to declutter the thread)