The TrotskyDrive

[dano12]

As mentioned in the Russian transistor thread, I scored a box of 1984 soviet KT312 transistors. Eager to try them out, I installed one in a modification of the electra overdrive and am really thrilled with the results. A 2N3904 works fine, but the KT312 adds a bit of high-end that approaches treble-booster territory. Not sure why it sounds so good, but it does.

This is a very nice light overdrive. I tried various diode combinations and settled on a 1N914/1N34A pair that plays very nicely with my changed cap values. Finally, a simple SPST switch acts as a diode lift turning the TrotskyDrive into a very nice clean boost.

Here's the schemo--it is a super simple build and I highly recommend giving it a try.

[$uperpuma]

I will have to use the 3904 but breadboard here I come

[Meanderthal]

 Very cool! I may wanna try this with a GT311...

[KerryF]

Any other substitutes such as Germ transistors.  I dont know much about the KT312, like if its Germ or not.  Any sound clips?

Kerry

[Meanderthal]

 Yer gonna need a Russian Germanium. It absolutely must be Soviet made for best results. Otherwise you won't get that proletariate vibe. Heh...

[Dragonfly]

Interesting way to set up the gain pot.

[Meanderthal]

 Yeah, that's like a starve...

[markm]

Interesting way to set up the gain pot.

Yes....quite!

[DDD]

The Russian KT312 is a silicon transistor, not Ge at all ;-)
It is medium quality tranny with the relatively high leakage current and usual betta of about 30-40 (KT312A) and up to 60-100 (KT312B), if I remember properly.
So I wonder how could it function with the 2.2 MOhm resistor in the collector path. IMO there are couple mistakes in the chematic diagram.

[George Giblet]

Drawing error?  VR1 should go to the collector?

Gain is controlled by varying the collector resistor.

[stm]

The Russian KT312 is a silicon transistor, not Ge at all ;-)
It is medium quality tranny with the relatively high leakage current and usual betta of about 30-40 (KT312A) and up to 60-100 (KT312B), if I remember properly.
So I wonder how could it function with the 2.2 MOhm resistor in the collector path. IMO there are couple mistakes in the chematic diagram.

I agree, VR1 should go to Q1-C instead of Q1-B.
Also, if the KT312 is such a low gain device, a rather common alternative would be a 2N2369 (hfe around 60-70), or even a piggyback pair or 2N3904's.

[dano12]

Sorry about the schematic error--VR1 should indeed go to the collector, not the base. Drawing is updated.

The KT312 is silicon. I have some Russian germaniums which I haven't tried yet.

DDD: what other mistakes did you find, I'd be happy to look them over.

[Steben]

Just some ideas.
With a 680ohm resistor, you have input impedance of at least 680*30(20,4k) to 680*100 (68k), depending on the gain.
That is, if the current is theoretically 1mA. At lowest settings, you have a gain of 3300/680 ~= 5 but lower impedance (10k to 30k). At highest settings, the gain is around 70, yet higher input impedance (100k to 300k). that should work fine with guitar volume.

[Meanderthal]

 Damn, those are silicon? They come in the same flying saucer cans as the Germs...

And the gain is in the same neighborhood...

[dano12]

Damn, those are silicon? They come in the same flying saucer cans as the Germs...

And the gain is in the same neighborhood...

I ordered Kt312 silicons and Gt313a germaniums. Regarding your earlier question--yes I've saved all the cool zaftig packaging

I haven't figured out what the fourth leg on the 313's is.

[Meanderthal]

 It's attached to the outer casing. Seems to be for shielding- just connect them with ground. While testing the GT311 I noticed that touching the 4th leg(with fingers, or to ground) does reduce noise. Kinda cool, but kind of a PITA too...

[freddd]

dano : what do you create your cool looking schematics with? They look really good!

[markm]

dano : what do you create your cool looking schematics with? They look really good!

+1 

[Seljer]

I believe he's mentioned in the past that he uses Microsoft Visio (though he has had to most of the component symbols by himself)

[Meanderthal]

 Love those curves... I can do em in photoshop, but it's a pain. But, I almost never use photoshop anymore- takes too long to load, too many whistles and bells... so my few drawings are rather blocky looking...

And, all my graphics software is more than 10 years old anyway...