# Weird voltages on a twin face Ge side



## kurtis1 (Apr 24, 2021)

I built this twin fuzz face from pedal pcb. The silicone side works fine but on the Ge side I can't get less than 8.2v on Q2.


The voltages are wierd all over the Ge side of the circuit. I've tried a different set of ac128 transistors and I get the same results. The voltages after R1 should be 10x what they are. What would cause this? Is C1 somehow dumping voltage to ground? Is that possible? I've attached my voltage readings, a gut shot and a diagram from electrosmash dictating the correct voltages.

Thanks


https://drive.google.com/file/d/11HeCZtQq7UNQSgBajusg15dBdL9xz1_A/view?usp=drivesdk


https://drive.google.com/file/d/11JzXTKd427Umf7C3R2YzHwNdkFP4bMte/view?usp=drivesdk


https://drive.google.com/file/d/11HwKKZ5r85hbMWDtrI2pKyV40K4kqqJr/view?usp=drivesdk


----------



## music6000 (Apr 24, 2021)

Are you switching the toggle to the GE Side to adjust  Voltage trimmer?


----------



## kurtis1 (Apr 24, 2021)

music6000 said:


> Are you switching the toggle to the GE Side to adjust  Voltage trimmer?


Yup for sure.


----------



## music6000 (Apr 24, 2021)

Switch up for Silicon, Switch down for Ge!
You should be getting Negative Volts on the PNP side!


----------



## kurtis1 (Apr 24, 2021)

music6000 said:


> Switch up for Silicon, Switch down for Ge!
> You should be getting Negative Volts on the PNP side!



Yeah, I definitely am getting negative volts. Sorry I thought that was implied, I should have been more descriptive. 
I just think it's so strange that my voltages are all 1/10th of what they should be.


----------



## music6000 (Apr 24, 2021)

kurtis1 said:


> Yeah, I definitely am getting negative volts. Sorry I thought that was implied, I should have been more descriptive.
> I just think it's so strange that my voltages are all 1/10th of what they should be.


Your Picture isn't Good for checking the resistors.
Here is the Resistor Calculator I use
Click on Bands for 5 :








						Resistor Calculator
					

Resistor Calculator is an App developed by CherryJourney to help the user find the value of a resistor.




					resistor.cherryjourney.pt
				




Has to be a Resistor value or a Bad solder joint!
I'm not a Fan of Transistor sockets!!!

Here's my Build with added Tone control
:https://forum.pedalpcb.com/threads/twin-face.2133/

You said '' GE side I can't get less than 8.2v on Q2''.
And here's my discussion with Crazy Voltages !!!! :


			https://forum.pedalpcb.com/threads/twin-face-correct-trimmer-adjustment.2130/


----------



## kurtis1 (Apr 24, 2021)

music6000 said:


> Your Picture isn't Good for checking the resistors.
> Here is the Resistor Calculator I use
> Click on Bands for 5 :
> 
> ...



I checked all my resistor values, they look good. 

Your build looks good, is yours a different version though? I have 2 caps above my ic yours only has one. 

I see your discussion. But just basically says "hit the switch" with no replies. my pedal works and plays fairly well and the GE side even sounds kinda alright, but I definitely need to get it biased correctly.


----------



## kurtis1 (Apr 24, 2021)

Running a jumper wire from lug 4 of the 4pdt switch to lug 3 on the fuzz causes my voltage to be correct. It seems to cause GE Q2 to read at the correct 4.5 - 5v

Wtf? Can someone help me wrap my head around this? What could be causing this?









						20210424_155350.jpg
					






					drive.google.com
				




Edit :I should add that all the other voltages are still nowhere near what they should be when I do this and the issue is not solved


----------



## music6000 (Apr 24, 2021)

Check for Continuity on the Toggle Switch to make sure only Centre & Bottom or Centre & Top.
If too much heat, you may lose connection!
Position 1 Up 
Position 2 Down :
You have to be careful when Soldering any Switch that you don't overheat Pads, 10 to 15 seconds between pads & always stagger, never next to each other !!!


----------



## kurtis1 (Apr 24, 2021)

music6000 said:


> Check for Continuity on the Toggle Switch to make sure only Centre & Bottom or Centre & Top.
> If too much heat, you may lose connection!
> Position 1 Up
> Position 2 Down :
> ...


I've checked that switch so many times already. I've bypassed each lug with a jumper wire and still no change in voltage. 

I also have checked every lug on the switch for continuity and the switch seems to work perfectly.


----------



## music6000 (Apr 24, 2021)

If you have the Toggle switch Down, what voltage do you have on NPN Q2 Collector.

When toggle is Up, what is the voltage on NPN Q2 Collector?


----------



## kurtis1 (Apr 24, 2021)

music6000 said:


> If you have the Toggle switch Down, what voltage do you have on NPN Q2 Collector.
> 
> When toggle is Up, what is the voltage on NPN Q2 Collector?


My 9v electro harmonix wall adapter I'm using is out outing 9.8v at the pedals DC jack.

With the toggle switch down (pnp selected) I have 9.63v on the Q2 NPN collector 
-8.7v on the PNP Q2 collector

Toggle switch up (NPN selected) I have 5.2v on the Q2 npn collector. 
-9.45v on the PNP Q2 collector 


Btw, thank you very much taking the time to think this over. I appreciate you helping me try to understand wtf is going on here.


----------



## Coda (Apr 24, 2021)

How does it sound?...


----------



## kurtis1 (Apr 24, 2021)

Coda said:


> How does it sound?...



PNP sounds louder than the NPN side. It sounds pretty heavy but lacks any sustain. Dialing back the guiter volume doesn't really clean it up much, just kinda kills the output 

NPN sounds exacly like a silicone fuzz face


----------



## music6000 (Apr 24, 2021)

kurtis1 said:


> My 9v electro harmonix wall adapter I'm using is out outing 9.8v at the pedals DC jack.
> 
> With the toggle switch down (pnp selected) I have 9.63v on the Q2 NPN collector
> -8.7v on the PNP Q2 collector
> ...


what happens if you rotate the PNP trimmer completely in the opposite direction with Toggle in PNP Down mode.
If you still have 9.4v to -8.7v, Your trimmer is shot


----------



## music6000 (Apr 24, 2021)

Can you test for Continuity on these matching Circles
If this is Good, Remove your Trimmer & use an offboard 25K TO 50K pot and attach 2 wires to the Pot outside leg & middle leg & attach the wires to the trimmer colours  marked Red ( either Red) & Blue
If this dials the Transistor to 4.5v, remove pot without moving pot setting & measure the resistance:


----------



## kurtis1 (Apr 24, 2021)

music6000 said:


> what happens if you rotate the PNP trimmer completely in the opposite direction with Toggle in PNP Down mode.
> If you still have 9.4v to -8.7v, Your trimmer is shot


With my pnp Trimmer a the way down I'm at 8.7v with it all the way up I'm at 9.5v.

Ill desolder this Trimmer and try a different one and report back.


----------



## kurtis1 (Apr 24, 2021)

music6000 said:


> Can you test for Continuity on these matching Circles
> If this is Good, Remove your Trimmer & use an offboard 25K TO 50K pot and attach 2 wires to the Pot outside leg & middle leg & attach the wires to the trimmer colours  marked Red ( either Red) & Blue
> If this dials the Transistor to 4.5v, remove pot without moving pot setting & measure the resistance:
> 
> View attachment 11277











						twinface-trimmer.jpg
					






					drive.google.com
				




I take it that this is good? I'm going to hook up another pot and report back 

Thanks for your help here!


----------



## kurtis1 (Apr 25, 2021)

Okay, I hooked up wires to pad 1 and 3 for the trimmer. I then ran those wires to a 100k potentiometer lugs 2 and 3. It took 74.3k of resistance to get that collector on Q2 to read 5v

The voltage on q1 still read the same low numbers as indicated in that first diagram I posted with my voltage readings


----------



## music6000 (Apr 25, 2021)

kurtis1 said:


> Okay, I hooked up wires to pad 1 and 3 for the trimmer. I then ran those wires to a 100k potentiometer lugs 2 and 3. It took 74.3k of resistance to get that collector on Q2 to read 5v
> 
> The voltage on q1 still read the same low numbers as indicated in that first diagram I posted with my voltage readings


After everything said & done, I think you have counterfeit AC128 Transistors, where were they purchased from?
If they ae genuine, you have an issue in the soldering of components on the PNP side.


----------



## kurtis1 (Apr 24, 2021)

I built this twin fuzz face from pedal pcb. The silicone side works fine but on the Ge side I can't get less than 8.2v on Q2.


The voltages are wierd all over the Ge side of the circuit. I've tried a different set of ac128 transistors and I get the same results. The voltages after R1 should be 10x what they are. What would cause this? Is C1 somehow dumping voltage to ground? Is that possible? I've attached my voltage readings, a gut shot and a diagram from electrosmash dictating the correct voltages.

Thanks


https://drive.google.com/file/d/11HeCZtQq7UNQSgBajusg15dBdL9xz1_A/view?usp=drivesdk


https://drive.google.com/file/d/11JzXTKd427Umf7C3R2YzHwNdkFP4bMte/view?usp=drivesdk


https://drive.google.com/file/d/11HwKKZ5r85hbMWDtrI2pKyV40K4kqqJr/view?usp=drivesdk


----------



## kurtis1 (Apr 25, 2021)

music6000 said:


> After everything said & done, I think you have counterfeit AC128 Transistors, where were they purchased from?
> If they ae genuine, you have an issue in the soldering of components on the PNP side.







__





						Fuzz Face high gain transistor set :: Transistors (matched, selected) :: Semiconductors :: Electronic Parts :: Banzai Music GmbH
					





					www.banzaimusic.com
				




These are the transistors I purchased, I also purchased their medium gain and their low gain sets, all give me this same issue... Is it possible that they audited and packaged counterfeit ones without knowing?

Ive also attached a picture of the readings from my cheap tester I tried them in.

Ive also tested every connection by bypassing the pcb/solder joints and using a jumper wire as I followed the connections through the schematic.

Ive also tested most of the components that are next to each other for shorts and everything looks good but I'll continue the audit.









						20210421_085246.jpg
					






					drive.google.com
				












						20210421_085152.jpg
					






					drive.google.com
				




Do the readings indicate counterfeit or do you not know until you actually try them in a pedal?

Thank you again for your help, this is my 6th build, I've always been able to figure any issues out. This twin fuzz face build was suppose to be the most simple build I've done. It's now proving to be the most difficult.


----------



## music6000 (Apr 25, 2021)

I believe they are the real deal, Can you confirm that 1 - E , 2 - B , 3 - C  matches the pinouts on the PCB
I can't make out the DOT on the Transistors ,Is it aligned with the Collector?


----------



## kurtis1 (Apr 25, 2021)

music6000 said:


> I believe they are the real deal, Can you confirm that 1 - E , 2 - B , 3 - C  matches the pinouts on the PCB
> I can't make out the DOT on the Transistors ,Is it aligned with the Collector?
> 
> View attachment 11279



It looks like collector is opposite to the little tab on the transistor. I've attached a better picture depicting it. 









						20210425_065032.jpg
					






					drive.google.com


----------



## music6000 (Apr 25, 2021)

These type of Motorola ? AC128  TO-5 have been the topic of discussion since around 2014, Your Tester is showing them as PNP & quite a few members swear by them as  being a good tool!
The tab is pointing to the Emmitter so that also appears to be correct.

Can you give me what Voltages are at the 3 Red Circles hilighted? :


----------



## kurtis1 (Apr 25, 2021)

music6000 said:


> These type of Motorola ? AC128  TO-5 have been the topic of discussion since around 2014, Your Tester is showing them as PNP & quite a few members swear by them as  being a good tool!
> The tab is pointing to the Emmitter so that also appears to be correct.
> 
> Can you give me what Voltages are at the 3 Red Circles hilighted? :
> ...











						Screenshot_20210425-082523_Chrome.jpg
					






					drive.google.com
				




All the voltages are negative volts (for got to indicate that)

The trimmer is still off the board but I used a jumper wire to connect the 2 top leads.

Input voltage from my DC brick is 9.8v

Edit :
I'm not sure I'd they're Motorola. They do have an "M" logo on the top though.


----------



## music6000 (Apr 25, 2021)

kurtis1 said:


> Screenshot_20210425-082523_Chrome.jpg
> 
> 
> 
> ...





kurtis1 said:


> Screenshot_20210425-082523_Chrome.jpg
> 
> 
> 
> ...


The Voltages should all be around - 0.92 Volts with your Power Supply.
They are all connected by one trace!
Are you sure it wasn't 7.5k on your external Trimmer pot to achieve 4.5v on PNP 2  Collector.

Is your DMM a Good one ?


----------



## kurtis1 (Apr 25, 2021)

music6000 said:


> The Voltages should all be around - 0.92 Volts with your Power Supply.
> They are all connected by one trace!
> Are you sure it wasn't 7.5k on your external Trimmer pot to achieve 4.5v on PNP 2  Collector.
> 
> Is your DMM a Good one ?



Yeah, I noticed that on the wiring diagram that they're all connected. It looks like I'm getting the proper voltage to them with no trimmer pot and the trimmer pegs 1 and 3 shorted to each other... But the voltage at Q2 collector is way too high like this... If I install and dial back a 100k pot at the trimmer to +5v I don't get the -0.92v on those points you told me to test... They're super low, like -0.03v

I'm positive I was using a b100k pot... I tried a 25k pot at first and it couldn't get the Collector voltage down enough.

I'm almost positive that I read my meter right, it's a decent fluke 115 I believe. I also checked the trimmer I removed and it definitely had 10k accross it.


----------



## music6000 (Apr 25, 2021)

Confirm  that these Resistors have these matching Colours,
I don't know what else is causing your issue!

R1 - 33K = Orange, Orange, Black, Red, Brown

R2 -1K = Brown, Black, Black Brown, Brown

R3 - 470Rr = Yellow, Purple, Black Black, Brown

R4 - 100K = Brown, Black, Black, Orange, Brown


----------



## kurtis1 (Apr 25, 2021)

music6000 said:


> Confirm  that these Resistors have these matching Colours,
> I don't know what else is causing your issue!
> 
> R1 - 33K = Orange, Orange, Black, Red, Brown
> ...



Yeah, just checked again. They're all the correct values. Here's some close photos. 









						20210425_200902.jpg
					






					drive.google.com
				












						20210425_201100.jpg
					






					drive.google.com


----------



## kurtis1 (Apr 26, 2021)

Okay, I pulled the Transistors out and traced board by following the wiring diagram. Everything has continuity to what it's supposed to. I checked every single solder joint against every single solder joint and have no shorts. The voltages are still all funky. It takes 22k at the trimmer to get the Collector down to - 5v after being on for 5 minutes it settles out to the trimmer needing about 72k to get - 5v at the Collector and holds at needing that.

Could my IC be bad? I've tried another one but I bought them in the same batch? They all put out the -9.5v

Would a safe, valuable test be to pull the IC, put +9v to the PNP circuit and try to see if NPN transistors work? Or will I burn something up here?

Man, I'm losing my mind here haha!


----------



## music6000 (Apr 26, 2021)

No, The IC converts it to Negative 9v which is what PNP Transistors need to operate.
That's why you can't daisy chain Germanium PNP Fuzz Pedals.


----------



## kurtis1 (Apr 26, 2021)

music6000 said:


> No, The IC converts it to Negative 9v which is what PNP Transistors need to operate.
> That's why you can't daisy chain Germanium PNP Fuzz Pedals.


I understand that, but I'm saying "convert" the PNP circuit to +9v so that I can then test NPN transistors in it. Or is there another reason why it wouldn't work? Like maybe the electrolytic caps won't work.


----------



## music6000 (Apr 26, 2021)

Under Investigation, Hang Five, could be 5 Hours!


----------



## kurtis1 (Apr 26, 2021)

music6000 said:


> Under Investigation, Hang Five, could be 5 Hours!


Haha, no rush. I gotta get to work here.


----------



## Chuck D. Bones (Apr 26, 2021)

Those two transistors are extremely leaky.  1st one has Iceo = 830μA and the 2nd one has Iceo = 1.2mA.  I usually draw the line at 300μA.  Personally, I would not install either one of those in a Fuzz Face.  Can you measure the voltage across R4?  Black meter lead on the end closest to the edge of the board, red meter lead on the end closest to the transistors.

You would have been better off buying Germanium transistors from Small Bear.


----------



## music6000 (Apr 26, 2021)

music6000 said:


> Under Investigation, Hang Five, could be 5 Hours!


Well, there you have it.
Chuck, Your familiar with this Tester, Does it have seperate screen showing leakage?
I use a Peak DCA55 that tells you what leakage is as you Scroll through the menu.
Banzai should be banned for selling this Crap!


----------



## Chuck D. Bones (Apr 26, 2021)

It's all on one screen, you're seeing it in Kurtis1's pix.
HFE = DC gain, corrected for leakage
VBE = base-emitter voltage
IC = collector current for the HFE & VBE measurements
ICEO = collector current with the base lead open ("O" signifies open)
ICES = collector current with the base lead shorted to the emitter ("S" signifies shorted)

In a real circuit, the effective leakage will be somewhere between Iceo and Ices because some of the leakage current at the base is drained off by other parts of the circuit.


----------



## music6000 (Apr 26, 2021)

kurtis1 said:


> Haha, no rush. I gotta get to work here.


Can you test the Transistors you just pulled to give us those readings?


----------



## Coda (Apr 26, 2021)

Chuck D. Bones said:


> You would have been better off buying Germanium transistors from Small Bear.


I would also add PedalHacker. Hive him the numbers you need, and he’ll test for leakage and hfe for $3 each.


----------



## kurtis1 (Apr 26, 2021)

Chuck D. Bones said:


> Those two transistors are extremely leaky.  1st one has Iceo = 830μA and the 2nd one has Iceo = 2,200μA.  I usually draw the line at 300μA.  Personally, I would not install either one of those in a Fuzz Face.  Can you measure the voltage across R4?  Black meter lead on the end closest to the edge of the board, red meter lead on the end closest to the transistors.
> 
> You would have been better off buying Germanium transistors from Small Bear.


Sorry for the late reply, it's my wife's birthday today so I've been occupied. 

On R4 measured how you describe, I have -0.028v. 

I gotta be honest and say that I never really understood what "leaky" is. All I know is that I've always heard it's bad. 

I originally tried to order some pnp transistors from Small Bear but they've all been sold out. That's why I ordered from banzai music. 

But if the transistors being bad is the issue then I'm incredibly relieved. I've been going insane here trying to figure this out! Thanks for your insight.


----------



## kurtis1 (Apr 24, 2021)

I built this twin fuzz face from pedal pcb. The silicone side works fine but on the Ge side I can't get less than 8.2v on Q2.


The voltages are wierd all over the Ge side of the circuit. I've tried a different set of ac128 transistors and I get the same results. The voltages after R1 should be 10x what they are. What would cause this? Is C1 somehow dumping voltage to ground? Is that possible? I've attached my voltage readings, a gut shot and a diagram from electrosmash dictating the correct voltages.

Thanks


https://drive.google.com/file/d/11HeCZtQq7UNQSgBajusg15dBdL9xz1_A/view?usp=drivesdk


https://drive.google.com/file/d/11JzXTKd427Umf7C3R2YzHwNdkFP4bMte/view?usp=drivesdk


https://drive.google.com/file/d/11HwKKZ5r85hbMWDtrI2pKyV40K4kqqJr/view?usp=drivesdk


----------



## kurtis1 (Apr 26, 2021)

music6000 said:


> Banzai should be banned for selling this Crap!



They're that bad eh? I'll have to get in contact with them and maybe see about getting a refund or sent some transistors that will work.


----------



## Chuck D. Bones (Apr 26, 2021)

The R4 measurement confirms that PNP1 is way too leaky for this circuit.

Leakage is not "good" or "bad."  Some circuits rely on a certain amount of leakage to function.


----------



## kurtis1 (Apr 26, 2021)

music6000 said:


> Can you test the Transistors you just pulled to give us those readings?


Just tested these 2 









						20210426_210927.jpg
					






					drive.google.com
				




https://drive.google.com/file/d/11yzMbZLuy32Drm9aY7x96STigBjtUq-7/view?usp=drivesdk 

I've also tried and tested they other "medium gain" set and the "low gain" set I purchased from them. Both sets read like :
Medium2
Iceo=0.55m
Ices=0.16

Medium 1
Iceo=0.36m
Ices=0.12m

Low 2
Iceo=0.58m
Ices=0.16 m

Low 1
Iceo=0.39m
Ices=0.11m

Even the low set takes 16k resistance on a trim pot to bias to -5v


----------



## kurtis1 (Apr 26, 2021)

Chuck D. Bones said:


> The R4 measurement confirms that PNP1 is way too leaky for this circuit.
> 
> Leakage is not "good" or "bad."  Some circuits rely on a certain amount of leakage to function.


I tried to get some readings with my low gain ac128. I still only get - 0.25v on pnp2 emitter. Electrosmash dictated it should be -0.5v

When I test R4 with the method you mentioned earlier I get -0.2v

And it still takes 16k to bias it... But I guess it's better than the 72k it takes to bias the high gain transistors I've been dealing with.


----------



## Chuck D. Bones (Apr 27, 2021)

Did you use the transistor you call "Low 1" as PNP1?


----------



## music6000 (Apr 27, 2021)

kurtis1 said:


> They're that bad eh? I'll have to get in contact with them and maybe see about getting a refund or sent some transistors that will work.


Yes, There that bad!


----------



## kurtis1 (Apr 27, 2021)

Chuck D. Bones said:


> Did you use the transistor you call "Low 1" as PNP1?


Yes, in all cases #1 was always used and tested in PNP1. 

The "low" matched set seems to give me the voltages closest to what electro smash dictates. But they're still only half the voltage that they should be and can't even be biased unless I use a much larger trim pot than the pedal pcb build doc specifies.


----------



## Chuck D. Bones (Apr 27, 2021)

Electrosmash is a good website, but you should treat their biasing recommendations as suggestions, not hard and fast rules.  Fuzz Face biasing is a matter of personal preference.

I'm betting that once you get some decent transistors, your Twin Face will work as it should.  In most Germanium-based pedals, leakage is much more important than HFE.  In a Fuzz Face, the lower the leakage, the better.

Here's a typical Russian P28. These would work great.


----------



## kurtis1 (Apr 27, 2021)

Chuck D. Bones said:


> Electrosmash is a good website, but you should treat their biasing recommendations as suggestions, not hard and fast rules.  Fuzz Face biasing is a matter of personal preference.
> 
> I'm betting that once you get some decent transistors, your Twin Face will work as it should.  In most Germanium-based pedals, leakage is much more important than HFE.  In a Fuzz Face, the lower the leakage, the better.
> 
> ...


Awesome, thanks for the help. I'm checking with banzai music to see if they can send out some AC128's that arn't so leaky and if not maybe ship out some "work alike" transistors. If they cant then I'll try to source some from pedal hacker if small bear doesn't get any in soon.


----------



## Chuck D. Bones (Apr 27, 2021)

After Banzai screwed you once, you're going back for more?  

I don't usually recommend buying transistors on eBay, but that's where I got the one in the pic.  Paid less than $2 ea including shipping for 60 transistors, a mix of P28 and MP38A.  They came from Ukraine, so shipping took a few weeks.


----------



## kurtis1 (Apr 28, 2021)

Chuck D. Bones said:


> After Banzai screwed you once, you're going back for more?
> 
> I don't usually recommend buying transistors on eBay, but that's where I got the one in the pic.  Paid less than $2 ea including shipping for 60 transistors, a mix of P28 and MP38A.  They came from Ukraine, so shipping took a few weeks.


Yeah, good point about banzai... Maybe I'll try doing some research on ebay then. I'll Look for someone with some good feedback, at 2$ a piece I don't really care if I have to throw-away 3/4 of them.


----------



## Chuck D. Bones (Apr 28, 2021)

I checked on eBay to see if the guy I bought from in 2019 is still selling Germanium, but he has disappeared.  There are plenty of other sellers in Russia selling the same or similar devices.  The MP38As were all leaky (<500uA) and medium gain (55 to 75) and are all usable in one pedal circuit or another.  The P28s were all slightly lower gain (50 to 70) and very low leakage (<50uA).  It's always a crapshoot on eBay, but they do protect the buyer if the product turns out to be crap.


----------



## giovanni (Apr 28, 2021)

I got some really good vintage germanium PNP ones on eBay a few years ago. I never tested them but I used them in 4 fuzz factories and worked great.


----------



## Coda (Apr 28, 2021)

These are already tested, though a tad expensive because of it. Just let him know the numbers you need when you order. Good service, and genuine...









						NOS TUNGSRAM AC128 Tested PNP Germanium Transistor Fuzz
					

NOS TUNGSRAM AC128 Tested PNP Germanium Transistor Fuzz



					www.pedalhackerelectronics.com


----------



## kurtis1 (Apr 28, 2021)

Chuck D. Bones said:


> I checked on eBay to see if the guy I bought from in 2019 is still selling Germanium, but he has disappeared.  There are plenty of other sellers in Russia selling the same or similar devices.  The MP38As were all leaky (<500uA) and medium gain (55 to 75) and are all usable in one pedal circuit or another.  The P28s were all slightly lower gain (50 to 70) and very low leakage (<50uA).  It's always a crapshoot on eBay, but they do protect the buyer if the product turns out to be crap.


Thanks chuck, I took your advice and ordered 20 p28's from ebay. They where like 18$ with shipping. I'm still going to try to get ahold of some AC128. Looks like pedal hacker is the only reliable source currently.


----------



## kurtis1 (Apr 28, 2021)

giovanni said:


> I got some really good vintage germanium PNP ones on eBay a few years ago. I never tested them but I used them in 4 fuzz factories and worked great.



I ordered 20 p28's from ebay. At this point, as long as 2 of them work, I'll be a happy man.


----------



## music6000 (May 15, 2021)

kurtis1 said:


> I ordered 20 p28's from ebay. At this point, as long as 2 of them work, I'll be a happy man.


Did you end up getting this sorted ?


----------



## kurtis1 (May 15, 2021)

music6000 said:


> Did you end up getting this sorted ?



I'm still waiting for the p28's to arrive in the mail but tracking says they've been in Canada for 5 days (just not where in Canada) so I should have them fairly soon. 

Also I ordered some real ac128's from pedal hacker but they still haven't arrived yet. 

I tested all My leaky Motorola ac128's from banzai and used the least leaky ones (still in the 300-600 range) and they arn't exactly "matched" and the pedal does sound pretty good. But I'm using a 17k resister to bias it down to 5.2v. 
This setup actualy sounds usable, it's just a little quiet and I don't end up with a ton of fuzz. So I'm 99% sure that my issue was bad transistors.

When I get my new transistors, I'll post back here and let you know how it goes. 
Thanks again for all your help!


----------



## fig (May 15, 2021)

Coda said:


> These are already tested, though a tad expensive because of it. Just let him know the numbers you need when you order. Good service, and genuine...
> 
> 
> 
> ...


They are part of a lot I had gotten (that's why they are already tested).


----------



## Coda (May 15, 2021)

fig said:


> They are part of a lot I had gotten (that's why they are already tested).


Are you pedalhacker?


----------



## kurtis1 (Apr 24, 2021)

I built this twin fuzz face from pedal pcb. The silicone side works fine but on the Ge side I can't get less than 8.2v on Q2.


The voltages are wierd all over the Ge side of the circuit. I've tried a different set of ac128 transistors and I get the same results. The voltages after R1 should be 10x what they are. What would cause this? Is C1 somehow dumping voltage to ground? Is that possible? I've attached my voltage readings, a gut shot and a diagram from electrosmash dictating the correct voltages.

Thanks


https://drive.google.com/file/d/11HeCZtQq7UNQSgBajusg15dBdL9xz1_A/view?usp=drivesdk


https://drive.google.com/file/d/11JzXTKd427Umf7C3R2YzHwNdkFP4bMte/view?usp=drivesdk


https://drive.google.com/file/d/11HwKKZ5r85hbMWDtrI2pKyV40K4kqqJr/view?usp=drivesdk


----------



## fig (May 15, 2021)

Coda said:


> Are you pedalhacker?


No, just another customer.


----------



## Coda (May 15, 2021)

fig said:


> No, just another customer.


Sorry, I mis-read your post.


----------



## fig (May 15, 2021)

Coda said:


> Sorry, I mis-read your post.


I wish I had his inventory  and contacts!


----------



## Coda (May 15, 2021)

fig said:


> I wish I had his inventory  and contacts!


I agree. I ordered some diodes and the ones he sent look straight out of the 60s...


----------



## fig (May 15, 2021)

Coda said:


> I ordered some diodes and the ones he sent look straight out of the 60s...


Be sure to lick the inside of the pouch.....just sayin


----------



## JE53303 (Jun 6, 2021)

Any luck with the Russian versions? I actually bought Pedalhacker AC 128s and have the same problems with the Ge Biasing from the beginning of the post. I'm not as proficient to fully understand the earlier readouts of the transistors, but I'm suspecting the batch I bought might be 'leaky' as well. At this point, I just hope there's a 'verified' source for Ge transistors that work with this kit.


----------



## kurtis1 (Jun 6, 2021)

JE53303 said:


> Any luck with the Russian versions? I actually bought Pedalhacker AC 128s and have the same problems with the Ge Biasing from the beginning of the post. I'm not as proficient to fully understand the earlier readouts of the transistors, but I'm suspecting the batch I bought might be 'leaky' as well. At this point, I just hope there's a 'verified' source for Ge transistors that work with this kit.


Sorry I haven't kept this thread up to date. I'm a golf course superintendent and I also manage a small water treatment plant so I've been incredibly busy lately. But I did get to try my pedal hacker ac128's and I have the same problem with biasing them. I'm currently using like 21k of resistance to get them biased down to 4.5v 

I've just received my Russian p28's on Thursday. I'll maybe find some time later today to audit them and test them out in the pedal. 

If they don't work. I'm going to switch that side of the pedal to +9v and try some bc108's to double check wtf is going on... Maybe PNP and NPN transistors just hate being in the same circuit, I don't know...


----------



## kurtis1 (Jun 6, 2021)

Okay, I pulled out those ac128's from pedal hacker and installed the p28's. And they work awesome!!! They bias with only 7k resistance and they sound amazing. They cleanup very easily with the guitar volume. I don't know why the ac128's from pedal hacker where so shity. So I guess I'll stick with these p28's. I'm finally happy with this pedal. 

Thanks chuck for suggesting these p28's


----------

