Leaky Russian Germanium PNP - GT403

[bmsiddall]

Hi all.

Can be a bit difficult to find leaky Russian Ge for fuzz pedals so thought I'd give a heads up.

In the middle of a buzzaround build for a customer and and was working with ASY/23 transistors for Q3 (I like low leakage Russian for Q1 and Q2).  These tend to be quite leaky (up to 500 µA) and work well in vintage circuits.  Had more or less settled on one around 115HFe/320uA for Q3 but on a whim tried one of the GT403G I have.  Sounded every bit as good, possibly a little richer with good cleanup.  It was around 88 HFe/350 µA.

Random measurements of the box I have ranged from 40 HFe > 140 Hfe.  Leakages from about 280 µA- 700 µA.  An older batch of GT 403A ranged from 30-80 with high leakages from about 400 µA up to 1.3 mA.

Have tried to use GT403 previously in harmonic percolator circuits without much success (spatty/farty).  With hindsight should have tried biasing them properly!

Cheers,
Brett

[Reg18]

That's good to know, I have some GT402 pnp on the way and the npn version which from
Memory is a GT404? I'm keen to try a few to see what they are like in an npn tone Bender etc.

[bmsiddall]

You should get some good (Ie: medium) leakages out of the 404 (100-400uA). 

The 402 PNP I've got are pretty low leakage, but would work well for an OC81D TB MK2.  Or Q3 in a MK1.

[Reg18]

You should get some good (Ie: medium) leakages out of the 404 (100-400uA). 

The 402 PNP I've got are pretty low leakage, but would work well for an OC81D TB MK2.  Or Q3 in a MK1.

I've got a few OC81 transistors which are somewhere between 70-110hfe and most are 0.08-0.30 mA leakage. I've used a couple in mk1 and Zonk machine builds but found I had to try a lot to get a good combination, I ended up reversing Q2 so the emitter and collector were opposite which cost me some gain but came with the benefit of being virtually silent and no issues biasing or with artifacts, weird noises etc.
Are these oc81 in the right range for TB mk1?

[Invertiguy]

You should get some good (Ie: medium) leakages out of the 404 (100-400uA). 

The 402 PNP I've got are pretty low leakage, but would work well for an OC81D TB MK2.  Or Q3 in a MK1.

Can confirm that 404s are good in a Buzzaround/Dizzy Tone/MkIII build. I made a hybrid PNP/NPN version to make use of my stash and used MP20s for Q1 and Q2 and a GT404 for Q3 since very few of my PNPs were leaky enough and it sounds great!

[bmsiddall]

Are these oc81 in the right range for TB mk1?

Well, I'd use them! Try lowest leakage at q3- I've built several mk1s recently and <100uA gets you >8v at the collector, lovely crackly gate and dead quiet when not strumming.

[percyhornickel]

My MKII has a leak (300 / 400 uA) in all the transistors and sounds amazing. I just follow the tips from electric warrior and many others guys in the forum to set the bias correctly or close to the original one.





P.H.