strange fuzz face biasing

[gutsofgold]

I just built a fuzz face on perf board using some old AC128's I bought from a guy on here a year or two ago. They are the ones with the built-on heat sink. For whatever reason I'm needing about 500k ohm on the resistor at collector of Q2 to get it to bias anywhere near 4.5v. Is there a reason for this? Is it normal and should I go ahead and box it up?

I checked my pinouts over and over again and I am damn near sure they are correct... these AC128s have a red dot on them and I am 99% sure that designates the collector.

Thanks!

[slim_blues_boy]

the one with heatsink is AC128K, and the red dot is the collector.
how about gain and leakage for those tranny? have you check them?

[jrod]

Hey man,
Double check your other resistor values and make sure they are correct. If they are off, they could affect the bias. 500K is way high to bias the collector of Q2.
Good luck!

[gutsofgold]

both have ~230 uA of leakage
gain of Q1 is 50 - 60
gain of Q2 is 90 - 100

The rest of the values are correct.

[jrod]

Man! That should sound kick ass!

I'm sorry I don't know the answer to this one.

Anyone else???

[gutsofgold]

Q1 C -.546 V
Q1 B -81.2 mV
Q1 E -0 V

Q2 C -5.15 V
Q2 B -.546 V
Q2 E -.522 V

This is with an 8.41 V battery and 512k Ohm resistor at the collector of Q2. I'm using the 100k feedback resistor, 33k at the power source, and the usual 2.2uF, 22uF, and 0.01uF caps.

Instead of the 470 ohm resistor, I am using a 370 ohm resistor.

[gutsofgold]

Just to be sure I ripped out all of the resistors and re-checked them on the DMM. They are all 10% within the original values, apart from my 370 ohm replacement of the original 470 ohm. The only thing I can think of is the AC128K's being dud's or maybe I ruined them with heat  ?

[gutsofgold]

this may be a very dumb oversight on my part, but do I need to have the input wired up and the pots as well to get a correct reading on all of this?

My Q1 collector along with the base of Q2 seem to be right on par. Q1's emitter is grounded which is correctly at 0 for me. My base is Q1 is low.

My emitter of Q2 is high.

[petemoore]

  512k Ohm resistor at the collector of Q2
  That's a bit high, there's probably a reason such a high value seems to bias Q2 collector, generally that resistance ranges between about 6k8 and 18k to bias Q2c around 1/2v.