Scratch build Orange Tiny Terror mod Question

[EKDENTON]

I am working on a layout for an Orange Tiny Terror with the Mercury Magnetics mods. The question I have is about the voltage divider mod. If I do the layout as the schematic is showing RV1(B) may be changed so that it works like a tone pot rather than a gain pot. This would cause the amp to change tone whenever you increase or decrease the gain. Could someone verify this part of the mod? I called MM people and they said that in order for the rest of the mods to work correct (except the optional mods)the voltage divider had to be there.  Attached is a photo with the mods. I think Doug has the original layout here on his schematic pages.

[sluckey]

Sure looks like RV1(B) will operate as a treble bleed tone control in that schematic. That should be fun since RV1 is a dual gang pot with a single shaft/knob, one section operating as a gain control, the other section operating as a tone control. Sounds crazy to me.

If the mods are shown in red I don't think the voltage divider mod has anything to do with the operation of any of the other mods.

If I was gonna build this I think I'd build it according to the original schematic. I don't see anything interesting with those mods other than the expensive MM iron.

[EKDENTON]

Today I will email the guys at MM and ask them if the voltage divider was intended to change the tone as the volume is increased.  For whatever reason maybe that is the purpose of that mod.  I have seen several posts of people that have done the mod on the pcb versions and no one dislikes it they all seem to think it improves the amps sound at all volume levels. If no one else here chimes in with any ideas, and I don’t get a good answer from MM then I think I will go with your advise and not do the mods except for adding a choke.

What  do you think of the Bias resistor/capacitor  120ohm5watt/220uF?  Would it be better to change that to a 150 ohm 10watt and a 50uF cap?

[sluckey]

Depending on the plate voltage, 120Ω may cause the tubes to run very hot. Using the 150Ω will cool it just a bit. I don't know if you'll be able to tell a difference. I doubt I could tell the difference between a 50µF and 220µF cap. I'd probably start with a 120Ω and 220µF just to keep it the same as the original. You can always change later.

[candletears7]

I've just finished modding my Tiny Terror to the schematic above. Got a Hammond 18w OT coming in next week for it too.
My question is, what exactly is the purpose of the voltage divider mod in this circuit?
Having done it, the Tone control's sweep now happens in the first 1/10 of it's rotation - the rest of the way it's pretty much a Mid control, increasing clockwise.
This is very cool and useable - is this it's purpose?
What would happen if I was to increase or decrease the value of the Silver Mica cap in this setup (currently I'm using a ceramic cap).

Thanks,
Jesse

[turtle441]

Just out of curiosity, what PT are you using?

[candletears7]

Just out of curiosity, what PT are you using?

I ordered this one and it arrived a couple days ago.
Hopefully I've got time to put it in this weekend and hear the difference.

https://www.evatco.com.au/1750pa-marshall-18-watt-combo-output-transformer

[jojokeo]

Hi Ed!
I don't get the "mods" as being anything special and it all seems pretty basic, just "normal" design sensible stuff? The filament ground reference resistors look like they're drawn/implemented incorrectly and the placement of the standby switch allows the reservoir cap to charge before flipping it on. This is usually desired when running a tube rectifier but doesn't do anything to protect when the amp is without one.