Ultraphonix adventure

[Reeltarded]

Happy New Year!

Yeah, I use 470k mixer. It sounds as expected. Great!

[fred.violleau]

A quick update on the build, slowly getting there, as I am missing a few resistors and caps.
That feeling when you realize you're missing one diode, the day after placing your order at mouser!

The boards are almost populated, planning on testing a few different coupling caps in the overdrive section.

PXL_20240104_210535041.jpg

I have a few holes left to drill on the back panel, should be done by tomorrow.

Fred.

[bepone]

100k below the tail in PI?

[martin manning]

Mods - This thread belongs in the D Discussion section.

[fred.violleau]

100k below the tail in PI?

Oups, mistake indeed, corrected, thanks Bepone.

Fred.

[fred.violleau]

After tweaking like crazy all morning, adding RC elements, separating decoupling the tube halves, changng pot, raising the wires in the air.. all what should stop osc - nothing. V1a stopping with LF osc only when i disconnect V1b!

Now im quitting , mazbe i ll rebuild all, but at the end i was changing amplitude in freq. gene and i saw miracle! And tragedy in the same time

Hey Bepone, have you fixed the motorboating issue on V1?
Did you try to add a 100pf cap between plate and cathode of V1?
looks like it adds stability on JCM800, maybe that could help ?

Fred.

[Mark]

The standard board material can become conductive, have you ruled that out as a possibility?

I rebuilt a Bassman 100 and I replaced the fibre board with a Garolite board as the original board was conductive.

[bepone]

After tweaking like crazy all morning, adding RC elements, separating decoupling the tube halves, changng pot, raising the wires in the air.. all what should stop osc - nothing. V1a stopping with LF osc only when i disconnect V1b!

Now im quitting , mazbe i ll rebuild all, but at the end i was changing amplitude in freq. gene and i saw miracle! And tragedy in the same time

Hey Bepone, have you fixed the motorboating issue on V1?
Did you try to add a 100pf cap between plate and cathode of V1?
looks like it adds stability on JCM800, maybe that could help ?

Fred.

my problem is very strange, i tried all what i can think off, remove pot, input, ground input v1a, still is oscillating. but only at no, or low signal, when i increase input to 200mVpp then it acts normally..
So it us motivating me to work more, some kind of low level creepage??
Conductive board?? Can be..
I will rebuild this part of circuit on another board and connect in the air when i have time and we will see ..

[bepone]

The standard board material can become conductive, have you ruled that out as a possibility?

I rebuilt a Bassman 100 and I replaced the fibre board with a Garolite board as the original board was conductive.

Can be.. i have cleaned totally and varnished this board but never checked conductivity between the eyeletts

[Mark]

I don’t have an insulation tester so is open an amp and solder an earth wire from the amp and a HT wire across the board and start measuring the eyelets.

https://ampgarage.com/forum/viewtopic.php?f=8&t=36597

[rayrayman]

Thanks for this thread and fun schematic!

I am curious, what are you doing for the negative feedback circuit?

And is the second volume control is 1meg?

I built a similar version as close as I could get with parts on hand, and it sounds great so far... Gonna keep tweaking and see what I can come up with.

[fred.violleau]

It's alive and kicking!

I have some oscillation going on in the background, could be because of crapy tubes, used whatever was around to test the amp.

OD feels like a Marshall, and EQ responds quite well.
Clean has not much headroom with humbuckers. Past 9o clock and the preamp starts to overdrive. Need to try with single coils.

Put a lar mar type 2 MV and quite happy with it.

I have put different choice of mixer resistors on a relay, so far it does not seem to make much difference. I am playing a celestion rocket, so will report back after playing on my 2x 12.

In terms of NFB where did you end up?
I thinks my Bassman has a 4 ohms output, so will check what I should put in.

17076707557694419899326563812384.jpg

Need to touch up a few things here and there, but so far it's a promising start!

Thanks guys for all the info shared!

[bepone]

interesting, very nice, one more is alive!

[Reeltarded]

Yay, Fred!!

I think 100k on the 4R.. nope, I think I moved it to the 8.

[fred.violleau]

I tried the preamp out into another amp cause the clean was bugging me. It is outstanding, very close to the john Mayer amp feel and no issue with the overdrive, channel, so something is happening down the line. Will check voltages again, but nothing seemed of.

Fred.