Just got a a couple of AC125 from eBay a few days ago, one bag of AC125 V and one bag of AC125 V1. Now, I want to stock up on some Russians, since they are in really good price right now. What Russian Germaniums to stock up on that that will work well in a fuzz face and tone bender? What Russian transistors are in the Dunlop Joe Bonamassa fuzz face?
GT308V for PNP and MP38A for NPN are both great. They both ranged from 50 to 90 hfe with either zero or extremely low leakage. For higher gain the GT402B are nice for PNP and ranged from 80 to 190 hfe. I haven't come across any higher gain NPN that are worth buying. All transistors that I measured were bought in boxes of 50.
I`ve tried GT404`s for NPN work as well, and I`m quite satisfied with them. Go for the GT404B or GT404G, which are higher gain range (60-250). The «B» and «G» will be in cyrillic letters, whereas the lower gain «A» and «B» (our V sound) look like english letters, so it can get confusing. Here is a cyrillic to english letter equivilant chart. Helps me sort out what`s what with Russian transistors sometimes.
(http://www.ancientscripts.com/images/cyrillic.gif)
Yes I got GT404B's as well, but they were very high leakage, with 21 essentially being unusable for anything other than buffers or as diodes. Out of the other 29 only 3 had less than 0.4mA leakage. The MP38As were much better with all of them being usable (0.11 to 0.23mA leakage), but I'd love some a bit higher gain.
Really? Wow, pretty high reject rate. I must have scored a nice lot then, I only had 6 bad ones out of 25.
Essentially, I passed on the MP38`s because of the low gain. Out of any of the other Russian NPN Ge`s that I bought, the 404`s were the only ones I liked. Used it in my Gemini III Dual Fuzz, along with a GT402, and an MP20. There`s a build thread here on the forum, complete with video.
That project really sold me on keeping a stock of the Russian Ge trannys.
I was unsure of the MP38's for the same reason but I figured that the GT308's sounded great in fuzz circuits despite not reaching the traditional expected "Q2" gain level and I'm similarly happy with the results. The GT404's I got were from gordelux04 and manufactured in 1982.
For PNP, I have a bunch of MP20B`s, which for some strange reason, I`ve had a hard time finding more. They range anywhere between 70 and 140. I tried them in a Burns Buzzaround circuit, and they sounded really good. They have a bit of a Muffish edge to them.
I know Jimi built a fuzz with lower gain MP16`s, and it sounded great.
MP25As (20-40hfe) are fine. I have fistfuls of them, and they distort softly or harshly, depending on how you tweak Rc.
Hello I'm awaiting some AC125z VI and wondering if they're dark or brighter and higher or lower gain sounding? Also would like to know the same characteristics about the Russian GT2 308 aka SFT308 clone? Thanks guys.
Nice thanks for your tips. I just placed another order on a 150 count bag of AC125 VI 75-150 hfe. So far, I've tested about two dozen AC125 and I've ranged from 49hfe to 144hfe. The leakage from 67uA all the way 398uA. I figure the high leakage ones, I would use for tone benders. I'm still looking at eBay for those russian trannies you all mentioned. i found that the Russians seem to be in the dark side, not as trebly as the AC125 and others in the tone frequencies....is this a fair statement?
Quick comparison of the AC125z vs GT108V:
Edit: i have spoken to orpheus, he has told me he has access to a milatary warehouse of electronics, i dont think the ac125's are going to run out any time soon. How cool would that be? Like a guitar pedal builders willy wonka factory...
Paul
It really depends on the circuit.
I can't speak for other designs, but I have a particular fuzz design in which I'm a big fan of the GT308A.
Really though, Russian germaniums are cheap enough that I'd just do a quick eBay run and make sort of a sample batch to see which ones you like the best and go from there. That's how I learned that I really like the 308A.
Quote from: chromesphere on April 04, 2013, 09:40:54 PM
Quick comparison of the AC125z vs GT108V:
Edit: i have spoken to orpheus, he has told me he has access to a milatary warehouse of electronics, i dont think the ac125's are going to run out any time soon. How cool would that be? Like a guitar pedal builders willy wonka factory...
Paul
Cool!! That's the seller I got my AC125s from. Great seller indeed, less than two weeks to the states, thats faster than some some venders I've ordered from :icon_mrgreen: BTW...your youtube channel is informative....thanks mate!!
Quote from: effection on April 04, 2013, 09:47:34 PM
It really depends on the circuit.
I can't speak for other designs, but I have a particular fuzz design in which I'm a big fan of the GT308A.
Really though, Russian germaniums are cheap enough that I'd just do a quick eBay run and make sort of a sample batch to see which ones you like the best and go from there. That's how I learned that I really like the 308A.
How are the hfe on those? I read the specs and it states "25-75" hfe, but are those the actual hfe less the leakage, if not then the hfe maybe much lower. The price is fantastic, $25 for 100 count, may just pull the trigger on it.
http://www.ebay.com/itm/Germanium-PNP-Transistors-GT308A-USSR-1980s-QTY-100-/160589077755?pt=LH_DefaultDomain_0&hash=item2563dadcfb
Cant speak of the GT308a, but i had bad luck with GT308v. they measure low as the test conditions had a higher collector current then what your likely to test yourself in the usual methods us diy'ers are using (including the DCA55 i believe). They are also ridiculously sensitive to ESD. Thats the GT308v though, not sure about the A variety.
Orpheus is good to deal with. Always helpful. Do a search on ebay for ac125 and you will see the bags he sells. If you buy a bag of the (V) variety 50-100 hfe and a (VI) variety 100-150 hfe you will have ALOT of sets on hand. I have the quoted hfe's to be very accurate! Some hfes are just way out of the ballpark, but i'd say...rough guess...70% in spec? 70% between 100-150. Thats pretty dam good from my experience.
The first ac125's i bought off him, i couldnt find any information on the net. I was worried about the (z) and the (v) (vi). I took a risk on a bag and they paid off! fyi the z stands for 'high voltage' they can take a higher voltage then the non z variety. Doesnt effect hfe either. Orpheus has since updated the listings to show what (v) and (vi) actually mean to make it easier for people new to the ac125.
I have done a few sound comparisons between ac128's and 125's and their difference is subtle to my ears. They arent a 'spectacular' sounding transistor, but i think they are a very good all rounder.
I have a bit of a history with the ac125 :D
Paul
As far as russians go the gt402 is a great sounding transistor, i wish i had of bought more though because they are now extinct. The gt108v and gt309g are my pick of the modern 'ufo' type of russian, with the gt309g sounding very slightly older and noiser to my ears (in a good way), and alas...extinct again! The GT308v is one to avoid imo for reasons stated. People have had good luck with them. I didnt. There was another russian i bought...gt422 something. Man they were useless. The hfe's were low, but the actual frequency response was terrible. Another one that sounded very good is the mp21D which is super cheap . The hfe's are not what is quoted. You'll get 40-70 probably. But i would sacrifice the slightly low hfe on q1 / q2 for the great sounding frequency response of these little puppies.
Anyway, thats a crash course in what i have learnt so far. Hope it helps.
Paul
Quote from: fuzzymuff on April 04, 2013, 09:57:34 PM
Quote from: effection on April 04, 2013, 09:47:34 PM
It really depends on the circuit.
I can't speak for other designs, but I have a particular fuzz design in which I'm a big fan of the GT308A.
Really though, Russian germaniums are cheap enough that I'd just do a quick eBay run and make sort of a sample batch to see which ones you like the best and go from there. That's how I learned that I really like the 308A.
How are the hfe on those? I read the specs and it states "25-75" hfe, but are those the actual hfe less the leakage, if not then the hfe maybe much lower. The price is fantastic, $25 for 100 count, may just pull the trigger on it.
http://www.ebay.com/itm/Germanium-PNP-Transistors-GT308A-USSR-1980s-QTY-100-/160589077755?pt=LH_DefaultDomain_0&hash=item2563dadcfb
Those Hfes are taken from the Mfg sheet on how they should perform. You can do a "Search Engine" on those doc sheets.
for example: http://alltransistors.com/pdfview.php?doc=gt308a-b-v_1t308a-b-v.pdf&dire=_russia
I've heard the 80's transistors of Ge aren't so good. Doping material or construction practice changed, changing their "sound. THis might be where "darker" or "trebly" comes from for the others.
One final 'tip' for anyone playing along at home.
Its really easy to buy ANY germanium thinking your getting a bargain when your not. 30 transistors for $7! Bargain! Wait...add the delivery. Another $6. So its $13 divided by 30 = 43c. Thats 'ok' in my books. But the method i just showed you is something i ALWAYS do before i hit the buy it now button. Its a good idea to see the unit cost before you decide. A 'good price' depends vastly on the transistor you are buying and how badly you want them i guess. Likewise theres no point paying 25c a transistor if they arent going to measure / sound very good. And conversely dont pay $1+ a transistor for run of the mill russians, when you can get another model cheaper.
Thats why i think the ac125's are currently the pick of the bunch. You have to order ALOT (1 x (v) and 1 x (vi) = 300 units). But you get then for around 30-35c each, they measure well and they sound good.
Confused? Me too.
Ok, i'm done 'rambling' :D
Paul
I still have packages of transistors from 80's Archer.
Jfets are 99c a piece, 15 2n3904's are 2$ a pack.
http://www.radioshack.com/product/index.jsp?productId=2062608
http://www.radioshack.com/product/index.jsp?productId=2062609
1.49 for a SINGLE 2n3904, and that isn't factoring in the shipping cost.
I think any transistors below 50c is a steal, especially if it is made of Ge.
http://www.radioshack.com/product/index.jsp?productId=12668957&numProdsPerPage=60
8 dollars for a single Ge transistor these day.
The shipping could be an outrageous 20$, and those 30-50 bulk Ge transistors are still a huge deal compared to the major retailers. As long as you're buying ones which have very little negative feedback about them, or have a high reliability/aging rate, it should e fine. Tin whiskers can grow in the cans, shorting them and causing them to fail. Those whiskers can be removed through some methods to be found online, without destroying the Tx, if youre careful.
Lucky we arent paying 80's prices then i guess. Looking at the current market, i would agree that any (decent) ge's under 50c is a steal.
Edit: some people may like to pay more, some less, but i think that what im comfortable paying compared to the next person isnt really relevant. Keeping track of what your paying on a per unit cost is something i have personally found useful.
Paul
Well, I just placed placed an order on a MP39B and a GT308B PNP Russian transistors. I read these are the same transistors used for the Joe Bonamassa fuzz face. Damn great price....100 count per bag and about $60 total. Can't wait to try those out.
Quote from: fuzzymuff on April 04, 2013, 03:03:36 PM
What Russian Germaniums to stock up on that that will work well in a fuzz face and tone bender?
my experience is that they're not great for either. the tonebenders (except for MKIII/MKIV Q1/2 darlington pair) generally need more leakage than those super low leak Russian ones...Btw, can someone recommend some Russians ge's with gains 80 - 150 with 150-200+uA leakage?
those super low leak ones sound good in FF's but they have a harder sound...not as soft as ones with a little more leakage. Someone said in another thread that they sound somewhere between germanium & silicon
but, they're great for the TB MKIII/MKIV or Buzzaround darlington pair, Rangemasters, and Fuzzrites...and of course, any variants of those along with others that don't need leakage and/or aren't known for a softer, organic sound...
that high leakage you referenced sounds like a typical "bad" transistor.. :icon_eek:
Quote from: Thecomedian on April 05, 2013, 04:35:39 AM
that high leakage you referenced sounds like a typical "bad" transistor.. :icon_eek:
:icon_lol:
Quote from: LucifersTrip on April 05, 2013, 03:39:31 AM
...Btw, can someone recommend some Russians ge's with gains 80 - 150 with 150-200+uA leakage?
Im sure there are others, but so far only ones I have found with 100+ leakage are the GT402B's
Maybe I just got a REALLY good batch with my 308A's but I don't think I had a single one with bad specs. I don't remember the typical gain on them anymore, but I honestly don't trust my measurements when it comes to germanium transistors anymore. Just the temperature change from handling them to put them on my DCA-55 is enough to throw them out of whack. I just socket now and if I need to swap out the transistor when I'm done with a circuit, I do so.
I can tell you though that when I went on my sample buying, I liked Russians more than anything and have the tendency to only go that route. I even overpaid for some AC188s because of how much I read them being praised and absolutely hated them. The Russian stuff is a lot more consistent, in my experience. This is even good if you end up buying ones that you dislike, as you know that you dislike that transistor and probably didn't just get some bad ones.
EDIT: And to LucifersTrip... If you want high leakage, go American or European, I'd say.
Quote from: LucifersTrip on April 05, 2013, 03:39:31 AM
Quote from: fuzzymuff on April 04, 2013, 03:03:36 PM
What Russian Germaniums to stock up on that that will work well in a fuzz face and tone bender?
my experience is that they're not great for either. the tonebenders (except for MKIII/MKIV Q1/2 darlington pair) generally need more leakage than those super low leak Russian ones...Btw, can someone recommend some Russians ge's with gains 80 - 150 with 150-200+uA leakage?
those super low leak ones sound good in FF's but they have a harder sound...not as soft as ones with a little more leakage. Someone said in another thread that they sound somewhere between germanium & silicon
but, they're great for the TB MKIII/MKIV or Buzzaround darlington pair, Rangemasters, and Fuzzrites...and of course, any variants of those along with others that don't need leakage and/or aren't known for a softer, organic sound...
Those are the leakage I'm getting with the AC125 transistors I just got. About one out of 20 I tested was barely under 100uA. I'm currently putting together a Tone Bender MK1.5. Would that particular tone bender require a higher leakage like the MK1 or a lower leakage like the fuzz face since it's circuit is so identical to the fuzz face?
Quote from: chromesphere on April 05, 2013, 07:25:34 AM
Quote from: LucifersTrip on April 05, 2013, 03:39:31 AM
...Btw, can someone recommend some Russians ge's with gains 80 - 150 with 150-200+uA leakage?
Im sure there are others, but so far only ones I have found with 100+ leakage are the GT402B's
I have some GT320b that are in that range.
EDIT: Actually, I can't remember if they have the little "b" or a big "B" suffix, but they are GT320.
Quote from: Thecomedian on April 05, 2013, 04:35:39 AM
that high leakage you referenced sounds like a typical "bad" transistor.. :icon_eek:
actually not...100- 200uA leakage is common in vintage ge's and works great in a large variety of vintage fuzzes. here's a note from R.G. from his classic ge tester FF article:
http://www.geofex.com/Article_Folders/ffselect.htm
"How much leakage is too much? 100uA is common, 200 happens pretty often. More than 300uA means the device is suspicious, and more than 500uA I would say is bad."
edit:
Quote from: effection
EDIT: And to LucifersTrip... If you want high leakage, go American or European, I'd say.
The whole idea is that the Russian ones are cheap. I was asking for others who are not lucky enough to have a ton of American/Japanese/European ones for vintage circuits that need leakage.
Ive been using 300-500ua leakages for a while now with no issues. I live in Australia, so you know...it gets hot here...40+ degree summer days. Is ambient temperature the concern?
Over 500 perhaps. I had a few that started with ma's of leakage...1 or 2 ma from memory. They were stuffed. The leakage just keep going up in a self-perpetual sort of way.
Paul
I think the biggest problem with very high leakers is their higher temperature sensitivity...and the other thing fewer people mention...their tendency to fail quicker.
Quote from: LucifersTrip on April 05, 2013, 08:33:16 PM
I think the biggest problem with very high leakers is their higher temperature sensitivity...and the other thing fewer people mention...their tendency to fail quicker.
Ah! Just pm'ed someone that exact info!
So with a 500ua transistor, the <insert fuzz circuit name here> wont sound very good? Misbaised sort of sound or something else? I haven't witnessed this myself yet...
Paul
More leakage = higher Q point = uneven distortion pattern, perhaps.
With too much leakage, sometimes it's impossible to turn off a transistor. That means that it can't go into cutoff. If you build a circuit to account for the leakage, I'm sure it works fine.
Some good heat sinks or heat dissipation design within the chassis will help out.
its the same way transistors sound better/worse in cold/warm climate. The temp causes more leakage which changes the sound of it.
Hi
over the years I''ve bought a range of Russian devices. 308s 313s 311s.
I find it surprising that people have had low hFE and significant leakage with them.
Something that I agree with is the idea that some will sound 'dark'. In a fuzzface, there is a direct relationship between input impedance and the hFE of Q1.
If the hFE of Q1 is less than 50 to 60, it will drain more treble (even more so from high impedance pickups like humbuckers). A HFE of 35 will sound very dark and will need the fuzz control turned up more to get the same amount of fuzz.
I haven't tested all of my 308Bs, but the hundred or so that I've tested from about 20 different batches are very low leakge (~5uA), very quiet, and there's about a 50% chance that you'll get a really good device for a fuzzface or any other circuit that doesn't require a leaky device. Less than 1% are dead and less than 10% have very low hFE (less than 40).
Thank heavens somebody stockpiled these things. They're the future of vintage fuzz.
cheers
I also bought a bunch of these about 7-8 years ago.
The 308's I have A/B types and they mostly seemed low leakage and quite decent hfe's from 50 - 150 or so.
The little 309's are just superb = tiny flying saucer type, again I have two versions A&B IIRC.
Most of those tested out fine too and have made their way into a few very decent FF's etc.
I have some MPA 42??? that look like a Canadian mountie's hat and they were pretty useless as a Fuzz device.
I have a handful of VERY large battleship grey devices ( 404 ?? ) which sounded incredibly good, I don't have them
with me - they are in storage so hard to remember the exact numbers !
Best to get some while they are still available, Most of mine did come from Orpheus IIRC.
Marty.
Don't really want to necropost but I guess it's better than starting a new topic in this case.
I bought some Russian Germaniums from ebay seller elena8913. Reasonable prices, lots to choose. Below is a link to spreadsheet I made with the transistor measurements. Transistors are MP20B, MP42B an GT402V.
https://docs.google.com/spreadsheet/pub?hl=en&hl=en&key=0AmQTWdBVWu_DdGhTWHpQbXRKSGRGdXJQZVNQMGVQckE&output=html
MP20B are the most usable of the lot I guess and MP42B are bit dissapointing. Datasheet rated at 45-100 they all occupy the lower end of the scale. Guess I will try the leakiest one today in Q1 for Harmonic Percolator and see how it goes. GT402V behave just like the datasheet suggest, although I was expecting more hFE after chromesphere comments and video on youtube. Seems like it's GT402B or GT402E that are higher gain versions. Can't really find either of them on ebay though. The only place that seems to stock B version is this Chinese site http://www.module-igbt.com/electronic-components/transistor/gt402b-ex-ussr-germanium-pnp-transistor-qty-40/prod_38590.html Price seems reasonable so might give it a go sometime later. Also not Russian but close, I should have some Polish germanium transistors in my hands when I go back home for Christmas. They all look quite promising, with gains of 30-140.
Hope anyone finds the data useful when buying some Soviet Ge's!
Quote from: tjdracz on October 23, 2013, 09:45:16 AM
Don't really want to necropost but I guess it's better than starting a new topic in this case.
I bought some Russian Germaniums from ebay seller elena8913. Reasonable prices, lots to choose. Below is a link to spreadsheet I made with the transistor measurements. Transistors are MP20B, MP42B an GT402V.
https://docs.google.com/spreadsheet/pub?hl=en&hl=en&key=0AmQTWdBVWu_DdGhTWHpQbXRKSGRGdXJQZVNQMGVQckE&output=html
MP20B are the most usable of the lot I guess and MP42B are bit dissapointing. Datasheet rated at 45-100 they all occupy the lower end of the scale. Guess I will try the leakiest one today in Q1 for Harmonic Percolator and see how it goes. GT402V behave just like the datasheet suggest, although I was expecting more hFE after chromesphere comments and video on youtube. Seems like it's GT402B or GT402E that are higher gain versions. Can't really find either of them on ebay though. The only place that seems to stock B version is this Chinese site http://www.module-igbt.com/electronic-components/transistor/gt402b-ex-ussr-germanium-pnp-transistor-qty-40/prod_38590.html Price seems reasonable so might give it a go sometime later. Also not Russian but close, I should have some Polish germanium transistors in my hands when I go back home for Christmas. They all look quite promising, with gains of 30-140.
Hope anyone finds the data useful when buying some Soviet Ge's!
Great info! Thanks for posting!
Mind you they were all tested yesterday evening with the heating on and the room temperature around 20 degrees. Now it's about 16 egrees in my room (cold!) and leakages are definitely smaller, more in line with the low-leakage reputation of russians
Quote from: tjdracz on October 23, 2013, 09:45:16 AM
Don't really want to necropost but I guess it's better than starting a new topic in this case.
I bought some Russian Germaniums from ebay seller elena8913. Reasonable prices, lots to choose. Below is a link to spreadsheet I made with the transistor measurements. Transistors are MP20B, MP42B an GT402V.
https://docs.google.com/spreadsheet/pub?hl=en&hl=en&key=0AmQTWdBVWu_DdGhTWHpQbXRKSGRGdXJQZVNQMGVQckE&output=html
MP20B are the most usable of the lot I guess and MP42B are bit dissapointing. Datasheet rated at 45-100 they all occupy the lower end of the scale. Guess I will try the leakiest one today in Q1 for Harmonic Percolator and see how it goes. GT402V behave just like the datasheet suggest, although I was expecting more hFE after chromesphere comments and video on youtube. Seems like it's GT402B or GT402E that are higher gain versions. Can't really find either of them on ebay though. The only place that seems to stock B version is this Chinese site http://www.module-igbt.com/electronic-components/transistor/gt402b-ex-ussr-germanium-pnp-transistor-qty-40/prod_38590.html Price seems reasonable so might give it a go sometime later. Also not Russian but close, I should have some Polish germanium transistors in my hands when I go back home for Christmas. They all look quite promising, with gains of 30-140.
Hope anyone finds the data useful when buying some Soviet Ge's!
honestly, I prefer necroposting, it's a lot more sensible than making topic after topic on the same issue, to me at least. A lot of rehashed and reposted stuff gets the reply "do a search function", it seems like that advice would go hand in hand with "bump an original thread instead of making a new one on the exact same topic".
It's a bit surprising to hear the leakage is so high and the gains are so low. They usually measure for me around 20-40uA. As far as gains go, mp20b is a 25mA bias and mp42b is a 10mA bias. That's a lot of current.
Quote from: Thecomedian on October 23, 2013, 12:42:40 PM
Honestly, I prefer necroposting, it's a lot more sensible than making topic after topic on the same issue, to me at least. A lot of rehashed and reposted stuff gets the reply "do a search function", it seems like that advice would go hand in hand with "bump an original thread instead of making a new one on the exact same topic".
It's a bit surprising to hear the leakage is so high and the gains are so low. They usually measure for me around 20-40uA. As far as gains go, mp20b is a 25mA bias and mp42b is a 10mA bias. That's a lot of current.
Thought so! Checked some of them again today and leakages are much lower, gains still low too. I guess they must have been bumped up by the radiator in the room and heat from the laptop. Can't see any other explanation.
Also what is meant here by transistor being xy mA bias? I'm clueless with theory here and I'm keen to learn and try to understand our properly so any explanation would be great!
http://www.learnabout-electronics.org/bipolar_junction_transistors_06.php
http://www.fairchildsemi.com/ds/PN/PN2222A.pdf
Let's take this example. at Ic = 150mA and Vce (voltage difference from collector to emitter) of 10V, gain is 100-300. At Ic = 500mA, gain is 40 minimum. That's a huge difference. Conversely, gain at 1.0mA is only around 50 minimum, which could mean that it's actually in the right gain pockets for the fuzz face circuit, provided the biasing keeps the gains around 70-120 or whatever the "good" numbers are, through amp "starving". When using most Ge parts for the fuzz face, such as NKT175, they bias best at 1mA, which is approximately where Q2 lands anyway in the original circuit. AC128, on the other hand, is a 50mA bias http://html.alldatasheet.com/html-pdf/131441/ETC1/AC128/94/1/AC128.html so its a lot starved, and the highest gain versions of AC128 will probably be within the pocket when putting it in, if all transistors have as sharp a drop off in gain for "undervolt/undercurrent" biasing, but some graph help will prove or disprove that. http://alltransistors.com/pdfview.php?doc=ac128.pdf&dire=_valvo
This is what all those graphs on data charts help visualize: The way it's gain will react to different voltages and currents. That's why there are so many different types of transistor out there, they all have different reactions. Then again, different datasheets and different mfg and internet help will give you different answers. Some say hFE bias means the current going into the base as a function of how much to apply to get the right gain, some say its Ie, and some say its Ic, as per the AC128 and PN2222 datasheets. I'd probably assume Ie unless it specifically states Ic or Ib as the function, since that'd be almost what Ic would want anyway if it turned out Ic was the intended function to bias around by the mfg.
Quote from: Thecomedian on October 23, 2013, 02:04:17 PM
http://www.learnabout-electronics.org/bipolar_junction_transistors_06.php
http://www.fairchildsemi.com/ds/PN/PN2222A.pdf
Let's take this example. at Ic = 150mA and Vce (voltage difference from collector to emitter) of 10V, gain is 100-300. At Ic = 500mA, gain is 40 minimum. That's a huge difference. Conversely, gain at 1.0mA is only around 50 minimum, which could mean that it's actually in the right gain pockets for the fuzz face circuit, provided the biasing keeps the gains around 70-120 or whatever the "good" numbers are, through amp "starving". When using most Ge parts for the fuzz face, such as NKT175, they bias best at 1mA, which is approximately where Q2 lands anyway in the original circuit. AC128, on the other hand, is a 50mA bias http://html.alldatasheet.com/html-pdf/131441/ETC1/AC128/94/1/AC128.html so its a lot starved, and the highest gain versions of AC128 will probably be within the pocket when putting it in, if all transistors have as sharp a drop off in gain for "undervolt/undercurrent" biasing, but some graph help will prove or disprove that. http://alltransistors.com/pdfview.php?doc=ac128.pdf&dire=_valvo
This is what all those graphs on data charts help visualize: The way it's gain will react to different voltages and currents. That's why there are so many different types of transistor out there, they all have different reactions. Then again, different datasheets and different mfg and internet help will give you different answers. Some say hFE bias means the current going into the base as a function of how much to apply to get the right gain, some say its Ie, and some say its Ic, as per the AC128 and PN2222 datasheets. I'd probably assume Ie unless it specifically states Ic or Ib as the function, since that'd be almost what Ic would want anyway if it turned out Ic was the intended function to bias around by the mfg.
Thank you very much! Definitely sheds some light on the subject. Much associated :)
no problem. Throw into that the monkey wrench of different B-C junction capacitances, and different transistors for different fuzzes may sound very different.
Here's some bits from http://www.amazon.com/Designing-Audio-Power-Amplifiers-Cordell/dp/007164024X
QuoteJunction Capacitance
All BJTs have base-emitter capacitance (Cbe) and collector-base capacitance (Ccb). This
limits the high-frequency response, but also can introduce distortion because these
junction capacitances are a function of voltage.
The base, emitter, and collector regions of a transistor can be thought of as plates of
a capacitor separated by nonconducting regions. The base is separated from the emitter
by the base-emitter junction, and it is separated from the collector by the base-collector
junction. Each of these junctions has capacitance, whether it is forward biased or reverse
biased. Indeed, these junctions store charge, and that is a characteristic of capacitance.
A reverse-biased junction has a so-called depletion region. The depletion region can
be thought of roughly as the spacing of the plates of the capacitor. With greater reverse
bias of the junction, the depletion region becomes larger. The spacing of the capacitor
plates is then larger, and the capacitance decreases. The junction capacitance is thus a
function of the voltage across the junction, decreasing as the reverse bias increases.
This behavior is mainly of interest for the collector-base capacitance Ccb, since in
normal operation the collector-base junction is reverse biased while the base-emitter
junction is forward biased. It will be shown that the effective capacitance of the forwardbiased
base-emitter junction is quite high.
This may be another key to FF "mojo", or it may be a red herring. It will suffice to say that a FF goes into some form of cutoff when the Vbc junction voltage difference drops below the value required, 0.2v for Ge and 0.7v for Si, which means that as the signal plays around this, the junction capacitance will be at it's largest, and so transistors with naturally larger capacitances will color tone a bit more. This is just my theory based on what I've read, however.
QuoteCurrent Gain
If a small current is sourced into the base of an NPN transistor, a much larger current
flows in the collector. The ratio of these two currents is the current gain, commonly
called beta (β) or hfe. Similarly, if one sinks a small current from the base of a PNP transistor,
a much larger current flows in its collector.
The current gain for a typical small-signal transistor often lies between 50 and 200.
For an output transistor, β typically lies between 20 and 100. Beta can vary quite a bit
from transistor to transistor and is also a mild function of the transistor current and collector
voltage.
Because transistor β can vary quite a bit, circuits are usually designed so that their
operation does not depend heavily on the particular value of β for its transistors. Rather,
the circuit is designed so that it operates well for a minimum value of β and better for
very high β. Because β can sometimes be very high, it is usually bad practice to design
a circuit that would misbehave if β became very high. The transconductance (gm) of the
transistor is actually the more predictable and important design parameter (as long as
β is high enough not to matter much). For those unfamiliar with the term, transconductance
of a transistor is the change in collector current in response to a given change in
base-emitter voltage, in units of siemens (S; amps per volt).
gm = ΔIc/ΔVbe
I added some bold emphasis to one of the important "design principles" that is more common practice, and you'll note that the Fuzz Face does actually follow this, as the circuit "works" with any of the transistors that were in the originals, however, as lots of "mojo" claims led to people hand picking out of large quantities of FF, and as we have later learned what values of gain and voltage on the collector sound "like the best/original used by hendrix/people like the most", we're trying to pick transistors with the right gain, even the right material. eBay has a huge industry of people trying to sell germanium transistors because of the Fuzz Face alone. Anyway, I was kindly enough told about this design practice by R.G. so I've kept it in mind when trying to redesign the Fuzz Face for specific transistors. It's not something one would normally do, but with NOS and non-renewable transistor sources for "the mojo semiconductor", I think it might be something FF builders have to bite the bullet and design around. Joe Bonamassa did a Fuzz Face based on MP39B and some other transistor, low gain devices, so I feel a little more confident that I can push something out of some transistors that people don't usually think of when they consider what kind for Fuzz. Mostly, the backup stock for Ge transistors not associated with fuzz face are far, far cheaper.
True. It seems that you only need to mention fuzz face in the eBay auction title to automatically bump up the price to £5+ per transistor, even if they're Japanese 2SB's, not normally associated with this pedal. Obviously AC128 and such are the worst. I've actually seen TWO AC transistors on eBay with NOS/fuzz face claim going for £60! Madness!
I've actually talked about it with my dad the other day and he couldn't get his electronics engineer head around the idea that people go crazy about germanium mojo. In his mind, germanium is this less than ideal device, rightly replaced by silicons.
And Russians seem to be last cheap readily available types, but this cannot last. If people start redesigning effects around them, then they would get more popular, then more expensive. Supply and demand. That's why I'm researching the virgin land of polish transistors.
Anyway, I will experiment with this Russians in fuzz face, see how it goes and sounds after some trimmer based bias fun!
Quote from: tjdracz on October 24, 2013, 09:54:54 AM
True. It seems that you only need to mention fuzz face in the eBay auction title to automatically bump up the price to £5+ per transistor, even if they're Japanese 2SB's, not normally associated with this pedal. Obviously AC128 and such are the worst. I've actually seen TWO AC transistors on eBay with NOS/fuzz face claim going for £60! Madness!
I've actually talked about it with my dad the other day and he couldn't get his electronics engineer head around the idea that people go crazy about germanium mojo. In his mind, germanium is this less than ideal device, rightly replaced by silicons.
And Russians seem to be last cheap readily available types, but this cannot last. If people start redesigning effects around them, then they would get more popular, then more expensive. Supply and demand. That's why I'm researching the virgin land of polish transistors.
Anyway, I will experiment with this Russians in fuzz face, see how it goes and sounds after some trimmer based bias fun!
The vintage type larger-case AC125, AC128, and NKT275 trannies are the expensive ones, the ones in the skinny case with the bottom flange and tab indicator are the more modern ones, which are more abundant. The vintage type large case type are in short supply these days, as guys like Fuller and Analog Man (and other boutique makers) have scoured Europe for supplies of those, and subsequently the ones that are left are expensive. The Tungsram AC125/128 are the more modern ones, which are fine but supposedly the best ones are the older large-case versions. Here's a good article on AC128's and similar trannies:
http://www.jacquesstompboxes.com/ac128.htm (http://www.jacquesstompboxes.com/ac128.htm)
The first version, which he calls "the real ones" are the now-expensive ones, and the type that were used in vintage Fuzz Faces and other vintage fuzzes. I have a few of the AC128's in the "heat-sink" package, they are pretty good too. I have one in a modded Dunlop Fuzz Face along with a Toshiba AC176 in the other position, and get a good sound with the pair.
Al
Im waiting for one of those tube making factories to start producing old-style Ge transistors again. ;)
Quote from: zombiwoof on October 24, 2013, 11:29:45 AM
The first version, which he calls "the real ones" are the now-expensive ones, and the type that were used in vintage Fuzz Faces and other vintage fuzzes.
I've never seen AC128s used in any vintage fuzzes.
I think they were used in the Crest Fuzz Face re-issues from the 90s, but that's about it.
Quote from: skrunk on October 24, 2013, 11:04:04 PM
Quote from: zombiwoof on October 24, 2013, 11:29:45 AM
The first version, which he calls "the real ones" are the now-expensive ones, and the type that were used in vintage Fuzz Faces and other vintage fuzzes.
I've never seen AC128s used in any vintage fuzzes.
I think they were used in the Crest Fuzz Face re-issues from the 90s, but that's about it.
If only we had a time machine :P, but honestly what matters is how the waveform clips and the frequency response, if the requirement is "vintage sound".
I wonder how the simulation of leakage on the silicon fuzz face via BFH resistor between C and B could improve traditionally "not leaky enough" Ge transistors..
Quote from: Thecomedian on October 24, 2013, 02:10:06 PM
Im waiting for one of those tube making factories to start producing old-style Ge transistors again. ;)
Actually, in the last few years, a couple of companies were making the old-style AC128's, NKT275's, OC81's, and other similar types in the large case versions, and I saw some in some catalogs for electronics companies (one of the manufacturers was Magnetec, the other I can't remember). Small Bear tried out some samples, and found they were all in extremely low hfe ranges, and when he asked about gain ranges that would be more applicable for pedal builders, he was quoted some outrageous price for pre-selected gain ranges, so he gave up on them. So there have been attempts to replicate those old transistors, but the results have not been too good.
As for the comment about AC128's never being in vintage fuzzes, the point about the article about AC128's that I posted was that the vintage transistors that were used in old Fuzz Faces (I think NKT275's were the most frequently used in the germanium versions), were not the modern skinny, bottom flange type that are around now, and the larger case versions (whether they are AC128, NKT275, or whatever) are the ones that are harder to find now, and thus more expensive, especially in preselected gains for Fuzz Faces or Tone Benders or whatever. Analog Mike talks of scouring Europe for usable vintage NKT's for his pedals, and he would score large batches at a time, then have to sort through them for ones that would be usable in his pedals. He had to pay a lot in the first case for the transistors, then there were many rejects, so the usable ones ended up being quite costly. Mike Fuller of Fulltone used to use the vintage large case transistors in his '69 Pedal, I've seen NKT's and various Japanese large-can types in the older '69 pedals, but at some point he just stopped making that pedal, due the problem of finding those types of transistors in enough quantity to make the pedals. I would assume (although I haven't seen inside them), that the newer '69 pedals he is making are using the modern type of germanium transistors, in order to be able to mass produce the pedal. I would be interested in hearing how the change in transistors has impacted the sound of those pedals, if that is the case, I really haven't heard any side-by-side comparisons of his older '69 pedals to the newer versions.
Al
I think Jacques' opinions on the AC128 are a bit eccentric. As I understand it, the AC128 is a European standard transistor type made by a wide range of manufacturers, as opposed to a branded tranny like the NKT series (although other people besides Newmarket have made the NKT275, especially since Newmarket's passing). Therefore what he's identifying as the original and best is probably just one manufacturer's output. Some manufactures are going to have better quality control than others. The hfe range for an AC128 that complies with the standard is 45 to 165, which gives you an idea how all over the place they are.
The case he identifies is a TO1 as opposed to a TO1H - the difference is a millimetre in height. Not sure what makes a tophat "modern". It might be cheaper to package things in something flanged that way which would explain the different reputations.
I have a bag of the Tungsram AC128s and another bag of Tungsram AC125s. From the general state of decay of the packaging etc I'm not sure if they count as modern. Possibly 80s, considering they were made in the Eastern bloc, but I'd plump for early 70s. Anyone know if there's a way to date these things?
The AC128s are pretty uniformly rubbish, by the way. The AC125s on the other hand have a sprinkling of mojo, especially if you pair them up with something genuinely magic.
One other historical note. The ACxxx sequence is part of the Pro Electron standard which was established in 1966. AC anything has to be '66 or later. NKT and OCs were available earlier - Mullard started making OC71s in 1954, just 7 years after the Bell invention. The fact that they were available and familiar to UK electrical engineers probably explains appearance of the UK branded types in the iconic effects of the period.
Quote from: zombiwoof on October 25, 2013, 11:05:14 AM
Quote from: Thecomedian on October 24, 2013, 02:10:06 PM
Im waiting for one of those tube making factories to start producing old-style Ge transistors again. ;)
Small Bear tried out some samples, and found they were all in extremely low hfe ranges, and when he asked about gain ranges that would be more applicable for pedal builders, he was quoted some outrageous price for pre-selected gain ranges, so he gave up on them. So there have been attempts to replicate those old transistors, but the results have not been too good.
lol isnt that life. When we try to replicate old technology, it often fails miserably because we don't have the same frame of reference. I wonder, though, what exactly is wrong with their fab process, why they cant go through expired patent documents to get the proper recipe? All the same, if they have some dirt cheap low hFEs, I'd support their agenda with my dollar-votes.
bah, their products are all discontinued.