Biasing NPN germanium transistors in Tone Bender Pro MKII

[mac]

I believe those values are from ElectricWarrior.  I just checked some easy to get notes and he had:
Vcc -9.67V, Q1.C -9.02V, Q2.C -0.17V, Q3.C -8.44V.

I remember those values very well from an old post. Actual values from a TB2, maybe his unit?
He slapped me in the neck when I posted I like to set Q1C at 7v and Q3C half way --> That's not Mr Page sound!      
In those days I had a clone with Toshiba 2SA52, very low leakage <25ua, so my problem was Q1 bias, not the FF stage 

BTW, there is a thread about transistors working close to Vcc with interesting simulations.

mac

[Rob Strand]

I remember those values very well from an old post. Actual values from a TB2, maybe his unit?
He slapped me in the neck when I posted I like to set Q1C at 7v and Q3C half way --> That's not Mr Page sound! 

  ElectricWarrior has posted "real values" for a few pedals.   He's done a great job documenting what things should be.   There's some scope to shift things say 0.5V for unit to unit variations but there's also a point where it becomes a different pedal - which might suit you better, nothing wrong with that.

[Big Monk]

I've always had success trimming the base resistor on Q1 and the Collector Resistor on Q3.

Q2 sort of goes with the flow but I've found success doing that. You can also trimmer the collector of Q2 to adjust Q3.

As Rob has pointed out, EW has always been a great resource on British Fuzz units and we've all sort of internalized the communications we have had with him.

[Electric Warrior]

I believe those values are from ElectricWarrior.  I just checked some easy to get notes and he had:
Vcc -9.67V, Q1.C -9.02V, Q2.C -0.17V, Q3.C -8.44V.

I remember those values very well from an old post. Actual values from a TB2, maybe his unit?

Yup, that would have been my SupaFuzz. I also got a Vox branded MKII a couple of years ago:

@21 °C
Battery: 9.7V
Q1 C -9.04V B -0.04V E 0V
Q2 C -0.26V B -0.08V E 0V
Q3 C -7.84V B -0.26V E -0.18V

Q2C is quite high in this one. Sounds quite similar to the Supa. A tad brighter.

[sirdavy]

Apologies to all of you. I am new to this but it turns out that I am also an idiot.

I have a new DMM and have been using the '9V Battery' range setting rather than 'V'.

In my wrong-headed troubleshooting I removed R2 and C3, and then through my attempts to clean the through-holes have managed to mangle the pads and generally singe the PCB. With newly installed R2 and C3, Q1, Q2, Q3 are all showing the correct collector ranges but alas the circuit is now not outputting any sound. So I have cut my losses and ordered a replacement PCB.

I hope me having to desolder the lugs of the pot is a fitting punishment for wasting your time.

[Rob Strand]

I hope me having to desolder the lugs of the pot is a fitting punishment for wasting your time.

No one is immune to human error.   It's all part of the processes.

[mac]

I hope me having to desolder the lugs of the pot is a fitting punishment for wasting your time.

I'm retired and on medical house arrest, winter, no beach nor bikinis... lots of time to waste!   

We are here to learn and help

mac

[sirdavy]

Thank you all!

I got a new PCB and replaced half the components and successfully recorded values (using correct meter range, and with 9.8V supply) of Q1 ~8.8V, Q2 - 1.75V, Q3 - 8.5V.

Then I put it in its housing and all was good. Then it went very quiet.

I retested the collectors and found Q1 ~3V. Moving the pcb around and this went back up to ~8V so I put the PCB back in place, and measured again - now it's ~6V.

One lead of R2 measures 9.8V the other ~6V.

One lead of C3 ~6V.

I'm confident it's not DMM user error this time. Maybe something mechanical is going on but I've given everything a good poke and retested - still Q1c ~6V. I've left the thing switched on and switched off and have not handled Q1 lots - ~6V.

Any pointers where to look?

[amptramp]

Did you cut excess lead length close to the board?  Are your input and output jacks insulated from the enclosure?  Are the aluminum pot bodies touching the leads?

Lots of reasons this can happen.

[Big Monk]

Did you cut excess lead length close to the board?  Are your input and output jacks insulated from the enclosure?  Are the aluminum pot bodies touching the leads?

Lots of reasons this can happen.

I agree. Pictures are worth a lot here.

99% of the time it's poor soldering that causes gremlins. We want to see it, not to pass judgement, but to quickly assess and diagnose the issue.

[pacealot]

Also, never underestimate the vagaries of even the highest quality sockets, particularly when paired with thin germanium transistor legs. Intermittence with movement is something of a hallmark...

[sirdavy]

Did you cut excess lead length close to the board?  Are your input and output jacks insulated from the enclosure?  Are the aluminum pot bodies touching the leads?

Lots of reasons this can happen.

Yes, I think I cut all the leads close enough. They are slightly lumpy Hershey Kisses.

I don't think the input / output jacks are insulated. The enclosure is steel (an old lamp base) and as far as I can see the metal part of each socket sleeve make contact with the enclosure. (see pics). But that's just grounding it, isn't it?

I don't think I have any pots touching long leads. Maybe they make contact with the enclosure?

I gave up on sockets as they did not look trustworthy - all the transistors are soldered in.

I've just measured Q1c in situ and it's around 6.8V. The pedal sounds good too - just what I has expecting.

[amptramp]

You are correct to give up on sockets.  No piece of military equipment uses sockets because they will always go intermittent.  All semiconductors are soldered to the board or terminal strip.  Sockets can go intermittent because of movement of the leads or corrosion due to dissimilar metals where the most anodic material becomes a sacrificial anode and corrodes away, which is not very good for electrical continuity.

Stompboxes are often subjected to the kind of treatment military equipment gets such as mechanical shock, vibration, temperature extremes, humidity and any other kind of torture including user stupidity.

On one spacecraft program I was on, we had a problem with 2N2222A transistors with gold-plated leads.  It seems the kovar leads were rusting away under the gold plating because the kovar (a type of steel with the correct proportion of nickel to have the same coefficient of expansion as the glass seals on the transistor case) is anodic with respect to the gold and gold plating is usually very porous, allowing humidity in.  We couldn't solder them because they had already rusted before we started to assemble the boards.

[GibsonGM]

Cardboard is a good insulator to protect a board from touching the enclosure. So is non-conductive foam. I use both of those rather than standoffs in my builds, and have never had a problem with a short happening later.
 
As for 'going silent'...well, ya, could be mechanical.  I've had it happen when a stranded wire flexed so much it actually broke (solid wire does this too, I just didn't expect it from the stranded).   A bad patch cord can do it (!).  The above-mentioned bad solder joint. 

Dirty pot, dirty jack,bad switch contact, something moves and touches where it shouldn't are the usuals.

Yes, the sleeves of the jacks should be in contact w/ground, AND wired up to ground to prevent horrid noise when they loosen. The input jack is my 'main gnd' when I build, and connects to the enclosure for shielding.  Stomp voltages are almost always so low that ground loops aren't a concern.  Keeping them insulated from the enclosure is good on amps, higher voltage things, where you need ONE positive ground point.

How does the back of the lamp go on? Is that metal too (for shielding...)?

[amptramp]

Cardboard is a good insulator to protect a board from touching the enclosure. So is non-conductive foam. I use both of those rather than standoffs in my builds, and have never had a problem with a short happening later.

There used to be a common material known as "fish paper" which was a bluish-grey cardboard material that was used to separate contacts from each other and insulate circuit boards from chassis.  I have never seen it get punctured or fail in any way.  It will look like a throwback to the tube radio days, but it works.

[mac]

There used to be a common material known as "fish paper"

I googled "fish paper" out of curiosity, roll ‎5" x 50' x 0.010 usd 35 @ AMZN
Because of english to spanish translation I'm not sure if this is the insulating paper in some of my 60s radios and recorders.

mac

[PRR]

material known as "fish paper"

You can get scraps of electrical fishpaper where truckers and factories get their burnt generators and motors re-wound. Every town has a rewinding shop.

You can get the same stuff in thicker gauge at the car-parts shop, they call it "gasket stock". Get one sheet of their thinnest gasket-sheet- it will do several pedals and is sure tougher than you need.

https://www.mcmaster.com/products/fishpaper-sheets/
https://oliner.com/vulcanex-vulcanized-fibre/
https://www.napaonline.com/en/search?text=gasket%20stock&referer=v2

[Rob Strand]

There used to be a common material known as "fish paper" which was a bluish-grey cardboard material that was used to separate contacts from each other and insulate circuit boards from chassis. 

I googled "fish paper" out of curiosity, roll ‎5" x 50' x 0.010 usd 35 @ AMZN
Because of english to spanish translation I'm not sure if this is the insulating paper in some of my 60s radios and recorders.

The electrician's lingo in Australia refers to it as "elephant's hide".  For some year's it's been dark red but I'm pretty sure a few colors have been used over the years.

Not sure if there is a distinction between "fish paper" and "elephant's hide".   Some of the "fish paper" seems to have adhesive on one side but the "elephant's hide" never had adhesive.

[amptramp]

There used to be a common material known as "fish paper" which was a bluish-grey cardboard material that was used to separate contacts from each other and insulate circuit boards from chassis. 

I googled "fish paper" out of curiosity, roll ‎5" x 50' x 0.010 usd 35 @ AMZN
Because of english to spanish translation I'm not sure if this is the insulating paper in some of my 60s radios and recorders.

The electrician's lingo in Australia refers to it as "elephant's hide".  For some year's it's been dark red but I'm pretty sure a few colors have been used over the years.

Not sure if there is a distinction between "fish paper" and "elephant's hide".   Some of the "fish paper" seems to have adhesive on one side but the "elephant's hide" never had adhesive.

I have never seen fish paper with adhesive on it.  It sounds like we are talking about the same stuff other than the colour.

[duck_arse]

Our fish paper, vulcanized fiber, dielectric papers, boards and films are all available with or without adhesive backing.

https://emipapers.com/specialty-paper-products/electrical-insulation-fish-paper/

was the second link I saw.

Elephant's Hide I understand because I've seen and handled it, but why the fish in fishpaper?


also - biasing germanium.