AC germanium transistors for Tonebender MKII

[LaserMan5000]

Hi. Which germanium transistors from AC series most usable in Tonebender MKII for authentic tone?

List of available transistors:

АС 128 18
АС 125К 52
АС 125F 12
АС 125? 3

As well available that transistors:

Р 15 Т 10 -
2SA518 20 Toshiba
2SA58 4 Toshiba
2SB200 1 Toshiba
2SA41 10 Hitachi
2SA358 1 Hitachi

P.S. Sorry for bad English.

Thanks.

[tubelectron]

Hi LaserMan5000,

It is said that the TBMK2P used OC75 and/or OC81D.
In mine (DIY) I used OC72...
A friend (DIY) used AC128...
I made a TBMK3-3K with AC180...
So your array of transistors would probably do, if these are in good condition.

Much more than the reference number, what I found important on the TBMK2P is :
1/ the Hfe - choose around 50,
2/ The Ice0 leak - check around 150µA,
Since that it was probably the OC81D average "good" parameters.
Nonetheless, these values are not compulsory, but a low leakage (under 200µA) is preferable.

See on the web R.G. Keen's interesting article "The Technology Of The FuzzFace" for more info about Ge transistors.

A+!

[Electric Warrior]

OC81Ds often had much higher hfes than that. It's the modern replacements that are all low gain.

The MKII Tone Bender mostly came with OC75s. These usually leak quite a bit. No need to worry, though. The circuit was designed with that in mind. Especially Q1 needs a fair amount of leakage to work correctly.
AC125s might be a great replacement for the 75s. They were used in some D*A*M MK2s and they seem to work well for Graemey, too: http://www.youtube.com/watch?v=Immtik9JqSs

[MikeH]

OC81Ds often had much higher hfes than that. It's the modern replacements that are all low gain.

The MKII Tone Bender mostly came with OC75s. These usually leak quite a bit. No need to worry, though. The circuit was designed with that in mind. Especially Q1 needs a fair amount of leakage to work correctly.
AC125s might be a great replacement for the 75s. They were used in some D*A*M MK2s and they seem to work well for Graemey, too: http://www.youtube.com/watch?v=Immtik9JqSs

Seriously, did you go to Germanium transistor fuzz college or something?

[Electric Warrior]

Sure, Class of '66 
But seriously, I just collected some gut shots, tried some things and asked the right questions to the right people - like that OC81D thing: some people on the other board got some and naturally I had to ask them about the hfes because there was contradicting information and I was curious. One said in his experience they average from 60 to 100, somebody else provided measurements and his were mostly around 100 and up. Gain and leakage wise they're very similar to most OC75s that are available today. However Sola Sound decided to bias the OC81D units a bit differently.  Several people who have experience with NOS OC81Ds and OC75s reported to me, that the 100k resistors at Q1's base an Q2's collector work better for the OC81Ds while the 10k and 47k are better for OC75s and most replacements, indeed. Go figure..

BTW, correct schematics for both versions can be found here: http://www.diystompboxes.com/smfforum/index.php?topic=91000.0

[LaserMan5000]

Thanks for answers and information. OC75 needs in testing and selection? Or I may just buy that and forget about testing and selection?

[Electric Warrior]

Every transistor will need testing and selection in this circuit. I suggest you use sockets, so you can swap transistors until you find a combination that you like.

[yeeshkul]

Also Matsushitas 2SB175 sound brilliant. And they don't leak too much (they leak enough to make the first stage work though). I purchased JMI TBMkII with OC75, and it sounds identical to my clone equipped with 2SB175.

[tubelectron]

Especially Q1 needs a fair amount of leakage to work correctly.

How much ? Have you measured it ? And what was the protocol and instruments used for the measurement ?

A+!

[yeeshkul]

As you may have noticed there should be no DC voltage at the base of Q1 the way the schematics go. However if the tranny Q1 is leaky, there is enough leakage current through c-e that creates enough voltage at the Q1 base (the base resistor) for the Q1 to open. Silicon transistor, that have no leakage would not work. Low gain Ge transistors usually have low leakage and need 100k resistor at the base. Hi leakage trannies are fine with just 10k. Go for 100k and any Ge tranny will do the Q1 job just fine. Even low leakage Q1 and 10k will work, but there will be noticeably less fuzz as a result as the Q1 won't open enough.

[Electric Warrior]

Also Matsush*tas 2SB175 sound brilliant. And they don't leak too much (they leak enough to make the first stage work though). I purchased JMI TBMkII with OC75, and it sounds identical to my clone equipped with 2SB175.

Weird, I found it hard to make 'em sound anything like OC75s. They're less fuzzy, lack the thick midrange  and it ain't easy to make the circuit gate a little, to get rid of the noise - and if I do get some gating it sounds like crap. Maybe they would work better with the OC81D resistor setup?

It's easy to make an MKII that cleans up well with them, though... and I like them a lot in a Fuzz Face circuit.

As you may have noticed there should be no DC voltage at the base of Q1 the way the schematics go. However if the tranny Q1 is leaky, there is enough leakage current through c-e that creates enough voltage at the Q1 base (the base resistor) for the Q1 to open. Silicon transistor, that have no leakage would not work. Low gain Ge transistors usually have low leakage and need 100k resistor at the base. Hi leakage trannies are fine with just 10k. Go for 100k and any Ge tranny will do the Q1 job just fine. Even low leakage Q1 and 10k will work, but there will be noticeably less fuzz as a result as the Q1 won't open enough.

guess that answers my question

I have some low leakage/low gain OC45s. they were unuseable for Q1, but ok for Q2 and Q3.

[yeeshkul]

Weird, I found it hard to make 'em sound anything like OC75s. They're less fuzzy, lack the thick midrange  and it ain't easy to make the circuit gate a little, to get rid of the noise - and if I do get some gating it sounds like crap. Maybe they would work better with the OC81D resistor setup?

It's easy to make an MKII that cleans up well with them, though... and I like them a lot in a Fuzz Face circuit.

I just may haven't tested enough types of Ge trannies to really judge. I like 2SB175 and i have enough of them to pick the really good ones. Yes, FF works great with them. By the way what you mean by " it ain't easy to make the circuit gate a little"?

[Electric Warrior]

You can set it up so that it works like a noise gate, gating away the hiss the circuit produces itself. But the more it gates, the worse the clean up will be. It can give this circuit a very distinctive attack, too. This vintage unit would be an extreme example: http://www.youtube.com/watch?v=YMIbuXjnUlw Very wild sounding 

[yeeshkul]

The Little Games riff sounds absolutely amazing (i'm not that impressed with the stuff before that). Can you gimme a bit more technical data on the gating setup please?. I still don't know what exactly you mean. Thanks  

[Electric Warrior]

Try transistors with higher hfe for Q2. Leakage may play a role as well, I'm not quite sure. I just swap transistors until I get that sound 

[mac]

Also Matsush*tas 2SB175 sound brilliant. And they don't leak too much (they leak enough to make the first stage work though). I purchased JMI TBMkII with OC75, and it sounds identical to my clone equipped with 2SB175.

I have tons of 175s, very good sounding and reliable.

I have also lots of Toshiba germs, they dont leak as much as Matsushitas so they are better for q2. Or q1 in a Fuzz Face.

mac

[mordechai]

I want to make sure I understand correctly that an Ge transistor in Q1 will be suitable provided I used a 100K resistor to ground on the emitter...is that right?  Also, just to be clear -- since the Q2 and Q3 of the TBMkII are very similar in function to a Fuzz Face circuit, would the standard gain ranges work...i.e., having Q1 be around, say, 70, and Q2/Q3 be around 85/120 or so?  If Q1 is a little lower in gain, would that darken the overall tone as would be the case in a Fuzz Face circuit, or is this just a different beast that way?