how typical .. to need change (adjust) bias resistors in Vint.Fuzz? (Fuzzrite)

[analog kid]

 Hey guys, I have searched for others experience with having to mess w/ stock components on  a vintage fuzz for the same purpose but eveything that comes up concerning "bias drift" is to do with Germanium heat stability. Maybe there's a more proper term for age related bias drift which I don't know.. but anyway.
I recently picked up an original very early Mosrite Fuzzrite (still has alot of lettering ) in exchange for some pedal repairs at a local music shop. Germanium not silicon
after getting power to the circuit it works , both controls work but the fuz is harsh..misbiased?... I noticed that the 2N2613 tranny though listed as Q1 in the schem reads only 3.8v on the collector. the 2N408 may not be working at all?  75mv C   58mv B  0 E
but the low bias voltage on the 3.8v made me think maybe the bias had drifted and one of the bias R's is in need of changing value?  how possible is this?
needed a new Battery ON/OFF switch and a couple broken leads on the switch , which is the wierdest wired DPDT bypass switch I 've seen!  AND MAYBE I did get something wrong reconnecting.. I will explaint the dpdt wiring here
1     -    3  -   5 -
2    -     4 -    6 -
lug 1 INPUT....Lug 2 Output
lugs 3 and 4 are tied to crkt  ground
lug  5  in jack ground
lug 6  bat +v
does this sound right? As I said it's working now just sounds as if slightly misbiased when effect on. Typical need to hit strings hard for good fuzzing ie; lightly strumming = gated
that's it

[markm]

I read an article online, I can't remember where the heck it was located on the net,
But I seem to remember it stated that most of the Fuzzrites were biased quite poorly and
had the tendency to be quite hars sounding.
I know this doesn't help you but, maybe what your hearing from it is quite......well...."normal"
I experimented with this circuit a bit and did "tame" it slightly to rid it of the harshness but,
I was using silicon trannys.
Good luck with it
    MarkM

[analog kid]

No, I appreciate your input. this is a good bit of misbias I'm getting here. I can however tell that , especially at the higher "depth" thinner sounding settings , that this fuzz will be quite harsh indeed.. this is a little different I think , this is Splatty sounding GATING when the strings are lightly plucked and strong fuzz if strings are hit hard enough.
So long as I know that there is nothing else wrong in the circuit causing it, i would most definitely say that that 3.7v Q1 collector vltg being brought up closer to 4.5-5v would do away with the gating
It's jst something that intimidates me greatly desloldering stuff from vintage old circuits which AREN'T PCB!! This is one of those old Eyelet boards where three or more components share an eyelet so you ONLY want to desolder something only when you KNOW it's needed
IF Q1 is the tranny that sits at 1/2V in this circuit then I guess it's sort of viceversa of a typical face?  If this is all the case than I assume that it'll be the 22k R between Q1 Collector and -9v  is all that'll need adjusting to bias it .
     by the way  NOT saying what you said isn't true at all! I'm sure the fuzzrites WERE biased badly stock. Whether or not that attributed to the harshness I don't know , but I can't imagine they were blatty Gating monsters out of the box!
thanks anyone who is familiar with or has one of these old beasts.  Maybe they're NOT really that rare at all ??and I shoudln't hesitate desloldering around the trannies?

[MartyMart]

Depends on how "precious" you are about the circuit/board ? and what it's worth too !

I would be tempted to "carefully" make a couple of new holes and wire up a trimpot, or
two from the supply connection to the tranny's collectors, perhaps just cutting away the
original resistors so as to not overheat the "eyelet nodes" where transistors pins connect.

Twist the trimpot wiper over to one other side leg and solder it, then you have two legs
to push through the new "holes" and quickly solder to power ( - or + which ever the circuit is? )
.......... and collector node.

That should let you bias it in much better 

MM.

[Gus]

The collector voltages do not have to be 1/2 the power supply.

Sometimes you want collector voltages  at a different place look at the rangemaster.

The fuzzrite is a simple harsh fuzz.

Cool if you adjust the "mix" you can get an octave up in the sound.

I need to check but a Si type version I built I have the collectors at 2.5V or so.

3.something V should have nothing to do with gating, this is a different circuit than the FF.

The 2n408 Collector  at 75mv is the hint.

disconnect the cap to the base of the 2n408 check if the collector voltage changes to 3 or so volts.



The gating might be something else, what transistor is the 2n404 in the schematic.  Say if it is the second maybe a leaky  bad cap to the base or check the collector to base resistor value.  The transistor reading don't look to be a shorted transistor but one that is in saturation

Two different transistor numbers?  Maybe someone was inside the fuzz before you bought it.

[R.G.]

I don't think that there's any question that someone was in it before you got it.

The originals did not have 2N404's in them. The 2613 might be stock, though. 2N408 was used primarily in logic circuits in the day, and I do have one schemo of this with the 2N2613 numbers in it.

The problem with old germaniums is that they drift with time and can get leakier and leakier. Also, the pedal is probably built with those vintage carbon comp resistors. And those drift too.

Can you compare your schematic to the one available on the net for us? If you can, I can suggest what to change to change the biases.

[Gus]

R.G.   I just noted I used 2n404 and 2n408 in my post and AK has 2n408 in the first post.

I think they could drop a PNP Si like a 2n2907 2n3906 etc in as a fast test of the parts around the transistor if disconnecting the signal to the stage by lifting the cap does not help. 

[analog kid]

The fuzzrite is a simple harsh fuzz.


I need to check but a Si type version I built I have the collectors at 2.5V or so.

this may be true that  its a very harsh fuzz by nature but this is really gating. but the fact you built a silicon version with a tran.collector vltge of 2-3vlts gives me more faith that the gating probably ISN'T due to Q1's bias vltge of 3.8v and makes it more likely that vltg on the 2n408 Q2 would have to be the problem .   C 70mv  B 60mv E 0   I mean, that tranny can't even be ON can it?
I AM nervous especially of 'clipping' leads of components however , looking at Q2's B/C there's a 1Meg between them and a .05 ceramic before Q2 to base. I may try disconnecting this cap to look for a collector vltge jump. meaning a bad/leaky cap right??
   also thanks also RG and Gus for responding, I got on some other jobs and forgot to check back on this thread ! 
NO WAY doubting  your guys opinion and assesment of this circuit, but based on visual appearance and by direct comparison with the most accurate (or said to be the most) schem I've found   SEE ABOUT BELOW . . . This Fuzzrite appears to be comletely stock.
   The schems I've seen seem to show two versions.  One with both tranny's labeled "TZ82  " which was noted as possibly Silicon...AND the one I have which I think is the original one,  first tranny labeled 2N2613 And the second 2N408.   These match exactly the trannies in mine.  Of which both look identical and are stamped RCA.   I also did go over the entie crkt comparing to the afformentioned schem  and found and all matched up right  down to the 350k depth pot, transistors, cap values, all carbon comp R values , even the "all Caps are ceramic except the C6 "ducati" (maganese dioxide) note was on the money. 
So i think were dealing with stock here.  
  I wish I knew if I could post or link to that schem here but  since I won't do that ... at the bottom it says "Mosrite Fuzzrite", " fffworks" , " Rev. 1.01"   if that helps.
thanks again  guys

[analog kid]

BUMP
Noone has more advise here on things to check causing the gating BEFORE I start hacking into a vintage, eyelet circuit board? OR on whether those two different tranny types are THE original version?