Help - Fender SS-1000 Super Showman Fuzz Circuit

[Pmelius]

1.What does it do, not do, and sound like? Every other channel and effect in this preamp works fine. The fuzz circuit works, but the bias seemed funny because the signal cuts off hard and sputtery on the decay of a note. I found that the 150k which ties the V+ to the Base of Q7, instead was a 68k from the factory. Changing this relieved the symptom, but now the effect has a "motorboating" sound occasionally, is noisy, and still has some bias issue (see Q6 voltages below). 
2.Name of the circuit = Fender SS-1000
3.Source of the circuit (URL of schematic or project) = https://www.dropbox.com/s/rh8lk75fs1sfbrf/SS-1000%20SCHEM.png?dl=0
4.Any modifications to the circuit? None, however I've recapped the power supply, as well as replaced the electrolytics in the fuzz circuit, as well as some out of spec resistors here and there.
5.Any parts substitutions? If yes, list them. None
6.Positive ground to negative ground conversion? N
7. PS voltage. - This is the one head scratcher.  The schematic says that 18v should be coming into the board, but I'm only getting 15.5. This was true both before and after the PS recap. R101 (33 ohms) between the rectifier and PS node C has drifted to 36 ohms, but I don't see this as significant enough? Please correct me if that's not the case.

Transistor voltages below
Q5
E-.94
B-1.6
C-4

Q6
E-0
B-.58
C-.39

Q7
E-0
B-.53
C-1.86 w 150k (.07 w 68k originally - this pointed me to this issue)

All the resistors around Q6 check out, except I havent gotten a good measurement on the 270k which ties v+ to the base because it can't be read in circuit. I haven't desoldered it to test it because this board is easy to roast. It's hard to remove a component without clipping the lead.

If you've made it this far, here's the reason I'm posting about this:
Should I be looking for something else causing my issue here other than an out of spec resistor?
Does the fuzz footswitch engaging that pot have any interaction with the circuit that may be contributing to my issue?
I really liked the way it sounded before finding that 150k issue, except for the sputtery disappearing decay.  After changing that, I notice it sounds kinda different.  Can I have the best of both worlds?

My biggest question: Is this circuit an exact replica of any other common fuzz circuits from the time period?

[Pmelius]

Also I'm at work and this is all I can think about but I don't know any humans who care hahahahaha

[Pmelius]

Tried popping that 270k to measure it, broke the resistor so had to replace it. Same voltages on Q6, but the motorboating sound is gone.  Still on the decay of the note, the signal gets weak.  I could button it up like this and it would be "a fuzz," and a pretty decent but those voltages on Q6 aren't right and I know it has more potential.

[Mark Hammer]

This does not help your situation one little bit, but that is definitely the most oddball Fender solid-state amp I've ever seen. 

Does it have an oilcan delay?

[Pmelius]

Yeah and the Oilcan delay sounds sweet!

[PRR]

Q6 C should be 2.9V(??), not 0.6V.

I suspect it also is a victim of part tolerance and aging. Try something larger than 270K base bias.

The whole thing reeks of non-robust design.

[teemuk]

Looks like Maestro Fuzz-tone clone with NPN transistors and saner biasing design. Particular characteristics of original Fuzz-tone is sputtery tone, which is due to transistors being biased to cutoff at idle and relying on collector leak biasing (that only works with ge transistors). Maybe they tried to intentionally copy that characteristic. ..base bias at least seems pretty low. Almost at cutoff at idle state.

[Pmelius]

Q6 C should be 2.9V(??), not 0.6V.

I suspect it also is a victim of part tolerance and aging. Try something larger than 270K base bias.

The whole thing reeks of non-robust design.

Cool, I'll try this when I get home! Just keep increasing until I get to a reasonable value?

[Pmelius]

Looks like Maestro Fuzz-tone clone with NPN transistors and saner biasing design. Particular characteristics of original Fuzz-tone is sputtery tone, which is due to transistors being biased to cutoff at idle and relying on collector leak biasing (that only works with ge transistors). Maybe they tried to intentionally copy that characteristic. ..base bias at least seems pretty low. Almost at cutoff at idle state.

I was digging through circuits and this was the closest one I came across.  This and a Sunn SB1. I'm into sputtery, but it's clear when playing this effect that something just isn't right about it yet. 

At the point I'm at now, it sounds great until the note starts to decay. Then the fuzz signal kind of "wears off" and almost has a weird tremolo, pulsating sound in the way that it disappears.

[Pmelius]

Can I use this to determine what value might solve my problem?

https://www.diystompboxes.com/analogalchemy/emh/emh.html

I'm trying to play around with it currently but I'm not sure if/how to find the beta of these transistors.

[teemuk]

The exact beta value will vary from device to device. Without actually measuring it case-by-case you will have to satisfy to working only within a certain range of expected beta. Is datasheet any help?

Problem with these "distortion" thingies is that you can start by throwing all "schoolbook" circuit design rules into the trashcan. Yes, the circuit will have very non-linear frequency response, it will distort greatly, bias voltages will likely be something very unothodox. Without actually talking to the designers there's really no way to know how the circuit was planned to operate and sound. Just because it sounds "wrong" to you is no indication that it isn't already working as intented.

Which is one big issue as well... Consider the original Fuzz-Tone: At least two stages idling without any other bias except that provided by collector leak current (in original Fuzz-Tone ALL OF THEM). Plus highly temperature sensitive germanium transistors. According to patent the circuit was also designed to produce almost 100% THD. Some sputtery decay.... heck, it's supposed to sound like "crap" compared to linear HiFi circuits. Some sputtering and chaos is just a feature for a device that is supposed to sound like something is seriously broken.
And these circuits could never be built in a consistent manner without serious handpicking of transistors, and any variation in ambient temperature would still effect their performance. Greatly. So, good luck finding a "reference" unit because all of them were different. There's a good reason why transistor circuits are not built like that any more, terrible inconsistency in performance being one of them. This silicon version with somewhat saner biasing setup is only slightly better. Still, can't really talk about consistency...
...And, the whole design concept is basically an antithesis to any "sane" circuit design so you can't approach it by using any logical thought process of how the circuit is ideally supposed to work.

Luckily, in this case the schematic lists some working voltages for reference... how close to them is your circuit? I'd start from that point.

[Pmelius]

The exact beta value will vary from device to device. Without actually measuring it case-by-case you will have to satisfy to working only within a certain range of expected beta. Is datasheet any help?

Problem with these "distortion" thingies is that you can start by throwing all "schoolbook" circuit design rules into the trashcan. Yes, the circuit will have very non-linear frequency response, it will distort greatly, bias voltages will likely be something very unothodox. Without actually talking to the designers there's really no way to know how the circuit was planned to operate and sound. Just because it sounds "wrong" to you is no indication that it isn't already working as intented.

Which is one big issue as well... Consider the original Fuzz-Tone: At least two stages idling without any other bias except that provided by collector leak current (in original Fuzz-Tone ALL OF THEM). Plus highly temperature sensitive germanium transistors. According to patent the circuit was also designed to produce almost 100% THD. Some sputtery decay.... heck, it's supposed to sound like "crap" compared to linear HiFi circuits. Some sputtering and chaos is just a feature for a device that is supposed to sound like something is seriously broken.
And these circuits could never be built in a consistent manner without serious handpicking of transistors, and any variation in ambient temperature would still effect their performance. Greatly. So, good luck finding a "reference" unit because all of them were different. There's a good reason why transistor circuits are not built like that any more, terrible inconsistency in performance being one of them. This silicon version with somewhat saner biasing setup is only slightly better. Still, can't really talk about consistency...
...And, the whole design concept is basically an antithesis to any "sane" circuit design so you can't approach it by using any logical thought process of how the circuit is ideally supposed to work.

Luckily, in this case the schematic lists some working voltages for reference... how close to them is your circuit? I'd start from that point.

Thank you for this thorough response!  This really puts things into perspective.

In response:
I was looking at the data-sheet for the current production of these resistors (2n3391 and 2n3391a) and still couldn't piece together "beta." I'm not wrapping my head around the concept and what information is needed from where 

I can barely read these voltage measurements on the schematic to a degree where I feel comfortable guessing that I'm right about what was written.  It's so small and blown out that I didn't really trust my best guess on them.

I do have some good news though.  After fighting this thing basically every evening for a week, I jumpered in some 500k pots instead of the 150k and 270k resistors, found good working values for each and soldered in some resistors in series to make the circuit work as desired.  It still is a little light on the very end of the decay of a note, but I'm very much content with the overall results. I'll post some voltages in here after a bit and maybe you guys can tell me if I'm looking good.  Pretty sure I am.  Maybe I'll post a video too, it's pretty wild. The other effects kind of need to be driven with a boost to really be effective, but they're pretty cool.

I'm considering modifying this so that the EQ section of each channel drives the effect section of each channel.  Currently, the effect just blends with the clean EQ section at the end and it's not really effective (pun). This thing would be so much more useable if it worked this way. I also need to find a way to get the Dim IV motor to be less noisy, and the tremolo too. There is some pulsating going on in the background when not playing.  Super annoying.