MiniBlues 2 watt Express?

[ODwan]

Hi all,



I've already built a Torres Tinytone marshall
Allan

Hi, Allan!

How is that above amp? Could you please share the schemo?
Thanks,

Timo

[galtjunk]

I could not read the values in the Layout for the TinyTube so I have attempted to create my own.
This is my first effort so I need some one to check my work.

I could not find R20 on the schhematic. Is is it necessary?

The 820 ohm resistor from the volume pot to v1-7 isn't used on some of the Express schematics.
Is it necessary and what does it do?

Are the powersupply resistors (R21,22,23 and Rsag) 1 watt or larger?

How do you read the pots on the schematic?
Do you rotate the drawing 90 degrees right or left to wire the pots?

Attachment has been deleted because it isn't workable.

Thanks

[ODwan]

[quote="galtjunk"]I could not read the values in the Layout for the TinyTube so I have attempted to create my own.
This is my first effort so I need some one to check my work.

I could not find R20 on the schhematic. Is is it necessary?
I think I renamed it Rsag.

The 820 ohm resistor from the volume pot to v1-7 isn't used on some of the Express schematics.
Is it necessary and what does it do?
No, it's not really necessary. It creates a low pass filter with the Miller Capitance of the tube, thus helps prevent ultrasonic oscillation. If you make it larger, say 50k+ you will start to hear the effect.

Are the powersupply resistors (R21,22,23 and Rsag) 1 watt or larger?
I used 2W metalloxyd, but 1W will surely suffice as this amp doesn't draw much current.

How do you read the pots on the schematic?
Do you rotate the drawing 90 degrees right or left to wire the pots?
Hu, that's a tough question! I recommend to use the layout of the Express tonestack. That's what I did. Have fun!
Timo



Thanks

[MarkB]

I built a similar amp - same tubes - with a LTP phase inverter. The clean is nice, but the distortion is kind of ratty. I'll have to try the power section from that schematic and see how it sounds. It's nice to have a practice amp that actually gives you practice volumes.

[Doug H]

I experimented with a wreck pre and 12au7 p/p output stg idea a year or so ago. It sounded good and worked well for low volume use. But for better bass response I tried a pair of 6em7's for the PI and output stage and it sounded great. The 6em7 is an octal dual dissimilar triode that was used for TV circuits. The higher mu stage makes a good PI while the lower mu stage can be used for the output stage, given that you use a low Zpri OT. I used the 1500 ohm setting on the 125E I was using, IIRC. It was a little louder than the 12au7 amp but was very smooth sounding.

YMMV...

Doug

[2thick4uni]

I tried a pair of 6em7's for the PI and output stage and it sounded great. The 6em7 is an octal dual dissimilar triode that was used for TV circuits. The higher mu stage makes a good PI while the lower mu stage can be used for the output stage, given that you use a low Zpri OT. I used the 1500 ohm setting on the 125E I was using, IIRC. It was a little louder than the 12au7 amp but was very smooth sounding.

Sounds very interesting, do you have a schematic of the PI and output stage you could share for those of us not capable of working it out for ourselves? Also, you may be able to offer an informed opinion on differences between this amp and Firefly with hi-gain stage switched in

Allan