Cascade Mod

[LennX]

Hi all I found this diagram for the cascade mod. it looks correct but I would like a 2nd opinion.

[Bieworm]

I wouldn't bother trying this layout. It looks like they put the normal channel in series with the TMB channel, without voltage dividers or anything. It will sound harsh and overpowered...

[LennX]

Thanks so much for the reply. I think I will stick with the tube screamer pushing the front. I was looking for a little more gain on the TMB channel. The amp I built is from the downloads here and I love it. Thanks again.

[Psychodog]

Since you’re already experienced working with tubes, and you’re looking for more gain, you might do a search at DIY Stompboxes for “Pentadrive” or “Valvecaster.”

They’re basically Tube Screamer pedals but they use actual tubes for gain stages. Either subminiature tubes or something like a 12AU7. People were experimenting with a lot of different types and getting varying results.

Then it’ll feel more like adding additional tube gain stages, rather than just throwing some diodes in your signal chain, which it sounds like you’re not completely satisfied with.

[LennX]

Thanks for your reply. I am already using a tube screamer in front and it works great but when I don't like say just for rhythm and single notes it just sounds fizzy. started to recheck the voltages and found the PI voltage is low. any idea how to boost it up a little?

[Bieworm]

Please post the voltages

[LennX]

JMPGuitars_18_Watt_TMB_Voltage_Test_Chart.pdf

[JMPGuitars]

JMPGuitars_18_Watt_TMB_Voltage_Test_Chart.pdf

You also need to check and share the bottom row voltages.

[LennX]

I don't know where to check A B C on the amp.

[JMPGuitars]

I don't know where to check A B C on the amp.

Those are the first 3 B+ nodes.

A= 1st filter cap
B= 2nd filter cap
(those are usually a cap can, but not always)
C= the point after the resistor that follows node B before it connects to the circuit board.

Thanks,
Josh

[LennX]

ok a=323 b=302 c=270

[JMPGuitars]

Those are all low. What's your power transformer?

Post some photos of your build.

[LennX]

The power transformer is a Hammond from a Brownnote 18 watt lite.

[JMPGuitars]

That power transformer wiring is a mess. Your B+ voltages should probably be high, not low. Are there some Zener diodes hiding in there? Something is dropping your voltages coming from the PT. Or the PT is wired incorrectly.

Thanks,
Josh

[LennX]

Well I checked and double checked the wiring on PT. Could it be the PT lying directly on the chassis? Or could it be the EZ 81 tube?

[JMPGuitars]

It certainly could be the EZ81 tube. If it's a JJ, throw it right in the trash. A bad rectifier could drop the voltage too low.

[LennX]

I was also leaning to that tube. I was also thinking of taking out the tube recto and replacing it with SS recto. any thoughts on that. Oh by the way i really appreciate your input very much.

[JMPGuitars]

I only use solid state rectifiers unless somebody requests a tube rectifier. I don't see the point in them, unless you need a tiny bit of extra sag, that you may or may not be capable of perceiving.

There's a couple videos on my youtube of a couple amps I made with switchable SS vs. Tube rectifiers. The B+ voltages are different by (IIRC) 15V. Can you tell the difference in sound at all?



Thanks,
Josh

[LennX]

Well I really don't hear any difference in tone between the two. Well looks like SS Recto hit is. Thanks Josh.