AC128 - looking - me too

[ethrbunny]

Im wanting to experiment with some fuzz clones. Most call for AC128s. The only place I see them en masse is at banzaieffects.com.

Question: what hfe should I be looking for? This is C->E gain right? Im not sophisticated enough with my EE knowledge to know how much I should be looking for.

Question: is the a reliable US supplier? How about a substitute transistor?

[96ecss]

Hi, here is a trany substitution chart from Dragonfly. http://www.aronnelson.com/gallery/v/DRAGONFLY-LAYOUTS_0/The-Mod-Zone-_/TRANSISTOR_SUBSTITUTION_CHART.gif.html There are a few subs for the AC128: OC76, AC188, NKT275, OC44 and NTE158.

Smallbear has a nice selection of matched GE's too. No AC128's though. http://www.smallbearelec.com/Categories.bok?category=Germanium+Transistors

Dave

[ethrbunny]

Thanks for that - Im a bit more hopeful now.

I was reading about NOS Ge transistors. Lots of people spoke of 'leakage' in the devices and the need to pick through some quantities to find units that were useable. Is this still the case if I order a 'replacement' (according to Mouser) like the NTE 158?

[soulsonic]

I've used the NTE158 and had very good results.

I wouldn't necessarily consider an OC44 as a replacement for an AC128 - they have very different characteristics.

[Nasse]

I´m not expert at this but I think yes. Last time (years ago) I mail ordered 10 pieces of AC128´s, two were good for Fuzz Face, and other two so and so. I was lucky I believe, new 128s are in bad reputation.

My granddad said our house is made of selected tiles. Good tiles have been selected off. Does not matter if tiles are twisted or ugly (they take the below freezing point and around weather better I know) because they are covered with plaster.

[ethrbunny]

I guess that socketing the transistors will be in order.

[Nasse]

I think it is best to check the leakage, I found good info at Geofex, it was easy. And germaniums are such by nature that it is best buy more than parts list say and hand pick working ones.

[Baktown]

On the topic of transistors, can anyone recommend a good DMM with a transistor tester?

Axl Bundy

[JHS]

AC151 are a good subs, they sound like NKT275.

I select all my Ge-trannies by ear,  stuck them in a RM-type circuit  (10k for the gainpot) and listen how the sound. You can hear if they are noisy, if the hFE is 70, 100 or more and you can hear if they are trebly, middy, muddy or whatever....

JHS.   

[Paul Perry (Frostwave)]

On the topic of transistors, can anyone recommend a good DMM with a transistor tester?

I suspect that the average DMM assumes that there is no significant leakage - fair enough for a silicon transistor - but doesn't correct for the (sometimes enormous) leakage on a Ge transistor. Which would make a DMM unreliable for testing Ge's.

[Meanderthal]

 2N404a are great subs also. 

[Dragonfly]

I've used the NTE158 and had very good results.

I wouldn't necessarily consider an OC44 as a replacement for an AC128 - they have very different characteristics.

The chart states that "results may vary" depending on the circuit it's being used in. For instance, OC44's wouldn't really be a great replacement in a FF (though theyd work), but you could certainly use a AC128 in a Rangemaster.

Not always interchangeable...but often.

[Branimir]

I've tried AC122 in fuzz face, it works as a replacement for AC128 but it just doesn't sound that good, much harsher and brighter - I didn't like it much, used for Q1 trannie with hfe around 80 and the second one is around 100.

Later on, I've ordered AC128 "medium gain" pair from banzai, put them instead of AC122 and it sounds GREAT!

I also had MJM London Fuzz in my possesion and I think it had transistors matched different than in my unit - it sounded very very similiar, but less fuzz going on.
Overall, I have a trimmer next to the input - I tamed the fuzz with it a bit, the mjm doesn't have the trimer.

I say go ahead with the pair from banzai, sounds great and my pedal suits me better than the mjm unit. The nuances make the difference, so someone could say different, but both great sounding pedals.

[foxfire]

it looks like amz has them, http://www.muzique.com/.

[ethrbunny]

from "Muzique.com"

Transistors have been tested for leakage (<500uA) but not tested for gain.

Gain = hfe?

Whats a good value to shoot for? Is this totally subjective?

[amz-fx]

it looks like amz has them, http://www.muzique.com/pcb.htm.

I actually have very few of them left...   when sorting I was getting acceptable leakage on about 1 out of 6, which has made it a losing proposition.

The 2N404a transistors that I have are much much better.  They are mil-surplus and have already been sorted. Leakage is quite low with good gain. Not many of them left either and unlikely that I could get more from my source.

Best regards, Jack

[petemoore]

  Best of luck, try SB matched sets, pick 'em wisely.
  I'm real picky because I've tried lots of transistors, there ARE differences, finding the exact right set for FF is tricky enough same except add 1 for the tonebender.
  just re-tweeked the tonebender, finished about 5 minutes ago.
  the only 'type or brand' suggested is the russuan ones are tending to replace my others.
  I've yet to make a transistor tester that wasn't didn't have a Fuzz Face, Tonebender or RM 'in' it...ie I just build the circuit...if I find a noisy transistor I put it in the 'other' bag [storage], other than that lower gain [like 65-110hfe] for Q1 of the fuzz face [which is Q2 in a tonebender], and whatever sounds good and cleans up at the guitar volume.
  Of course I trimpot the collector output of the FF amp stage for biasing.
  I think it's the 250k pots in my new LP which don't allow cleanup like the 500k ones did in my old LP, I also can't find a bypass cap value which treble 'boosts' [allows the pot to cut overall volume while increase treble proportion of signal].
  I found testing by ear to be the way...matched sets tried...and numbers disregarded except for 'in the ballpark/out of usable range', testing for 'actual performance' [in circuit]  got the greatest 'winnings' count in the long run of FF tweeks anyway.
  Don't forget to diddle with bias after each Q swap, also gain settings, volume controls, etc.

[ethrbunny]

..hmm so AC128 - hard to find, hard to find 'working' units, require 'matching'... this sounds like a losing proposition.

Would I have the same issues if I went with an NTE158 from Mouser?

[smallbearelec]

..hmm so AC128 - hard to find, hard to find 'working' units, require 'matching'... this sounds like a losing proposition.
Would I have the same issues if I went with an NTE158 from Mouser?

Please read my FAQ:

http://www.smallbearelec.com/HowTos/FuzzFaceFAQ/FFFAQ.htm

This article reflects most of what I have learned over the past seven or eight years of supplying NOS germanium. About the only thing I don't discuss is my wholesale sources for these items, because that's part SBE's intellectual capital.

NB: For not much more than the price of unmatched NTE devices, you can have a matched and audited pair from my stock. My guarantee is that the sound must curl your short hairs, or you can return the devices unsoldered for refund or exchange. Or if you are willing to give some time to learning how to test and audit, check out my rough-sorted U.S.-made lot, SKU 0115A.

Two things can't be emphasized enough: Part numbers don't mean much when it comes to qualifying devices for Fuzz Faces and such, because the variation in gain even within a group of a "good" number is so great. And, once you have sorted for leakage and gain, everything comes down to small variations in internal electrical characteristics that can't be measured on instruments, but whose effect Can be heard...you gotta listen to them.

Happy Distortion!
SD

[MetalGod]

If you just want to build a great sounding fuzz and take out the guesswork, buy direct from Smallbear - it's THAT simple.

All the Ge's I've bought from Steve have been very low leakage and gain as advertised/marked - price isn't too bad either considering you could pay the same for a few unsorted ones elsewhere and have them all be unusable.

btw Steve, you can send me that $5 directly through Paypal