Want a FuzzFace pcb layout for Russian GT311 transistors?

[Meanderthal]

 I've gotten them to work with stock Dallas values... but it took quite a bit of swapping, and the DMM hfe values weren't particularly helpful in finding 'working' ones (yes, I noticed!). The datasheet that came with them had no... 'schematic' showing an internal resistor, but for all I know it could have mentioned one 100 times. I can't read a word of Russian. But, an internal resistor might explain some of the wierdness... and bias pots are a good idea for these even if they are supposed to be consistant, because I've found them to be no more consistant than old pnp germs.   Or, maybe I had trouble because they ARE relatively consistant... and have a resistor...

[puretube]

radiated(?) shuntistors 

[hellwood]

Did anyone notice that the (strangely) low hFEs measured for these devices is what you'd expect if there's internal resistance(s).  A small emitter resistor (a couple of hundred ohms) might explain hFEs of 20 indicated on a DMM for a BJT with hFE of 100 or more.
cheers

     finally some hope for my russian tranny's that i thought were range piggers!!!! i measured 100 GT308V's and not one was leaky but all Hfe's measured 50% lower than i expected. please tell me the GT308V's have that same emitter resistor!

     also, has anyone had even more retarded readings on SFT353's?

[Skreddy]

Okay; here's teh FF schematic with both biases switched to trimmers



This parts layout should work now, yeah?


If so, then here's the transfer (print at 300dpi):

[ambulancevoice]

thanks alot for this

this is a happy coincidence for me, cause my gt311b's are coming soon (or maybe there already here???)
plus, i really like how you have layed out the pots, like
it allows me to use pcb mount pots on the copper side and so i dont have to use pcb standoffs

[Skreddy]

Hopefully the pots turn the right way, etc.  I still haven't built this.  Sorry, but I'm pretty busy.  Please do let me know if it works for you or if changes need to be made.

[brett]

Hi
looking at the data posted about the transistors with built-in resistance (on the emitter);
the base-emitter difference is about 0.1 V too high (0.39 V instead of 0.29 V), so there's about 0.1 V of drop across the resistor.
the collector current (= emitter current, close enough) was 2.5 mA

R=V/I, or 40 ohms.
This is enough to make the hFE look low when tested, but have only a small effect on the gain of q1 in a fuzzface (and no effect on q2).
cheers

[Rocket Roll]

All right, the layout's verified... in a sort of way.







I have used GT308 transistors, and therefore had to reverse the polarity of the PCB. I've reduced the values of the trimmers, as well - 47K for Q1, 22K for Q2 - in order to be able to bias the transistors more precisely. Everything else's stock.

I've expected a motherload of bass, because of the increased output capacitor, but it's not the case. Bass is just as expected, and the mids are nicely prominent.

I've biased it according to Joe Bonamassa's FF values (0,9V for Q1, 6,8V for Q2) and it sounds nice. The only problem is a slight fizz (gated decay) when the note ends, most prominent if I'm playing into a clean transistor amp. That could have something to do with the transistor gain (Q1 is showing cca 74 hFE, Q2 is showing cca 90 hFE), which is a lot in a GT308 world.