GT308B / GT308V information

Started by brett, November 27, 2007, 07:13:11 AM

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brett

Hi
GT308s are PNP germanium transistors made in the former Soviet block countries.  Mine are from Bulgaria.
Here are some leakage and hFE results. 

In RG Keen's tester (see geofex.com for details), five devices all leaked less than 25uA. That's ridiculously low.  In order of hFE, five randomly-selected devices tested 44, 54, 60, 62 and 67.  The former (44) will probably be too low for a fuzzface, but would still be good for a rangemaster.  The others appear to be prime specimens for all uses.

Indeed, MartyMart has already built a fuzzface with these, and indicated the results were good.  A PCB layout is available (search GT311 ?) to suit the unusual B-C-E pinout (emitter indicated by a dot). 

Unfortunately, these devices only seem to come in large batches (50).  But maybe The Small Bear or Aron will procure some and start selling them?
cheers
Brett Robinson
Let a hundred flowers bloom, let a hundred schools of thought contend. (Mao Zedong)

MartyMart

Brett, I did alert Steve to these but he had other commitments and so declined to get some in.
I got similar results after testing a few dozen, plenty in the 80-120 hfe range also, leakage seemed
negligable on almost every example, so I was quite impressed with the quality overall.
50 pieces was only around 15 Euro's so they are not at all expensive, even in those numbers !!
Look out for the much smaller "UFO" looking GT309's also, they have "a" and "b" suffix to denote
gain range.
MM.
"Success is the ability to go from one failure to another with no loss of enthusiasm"
My Website www.martinlister.com

RedHouse

Quote from: MartyMart on November 27, 2007, 08:23:28 AM
...Look out for the much smaller "UFO" looking GT309's also, they have "a" and "b" suffix to denote
gain range...

Look out for them as good, or as in bad? do you know what the A and B gain ranges are?

snoof

I'm still waiting for mine to arrive, been a few weeks  :-\

MartyMart

Quote from: RedHouse on November 27, 2007, 08:55:03 AM

Look out for them as good, or as in bad? do you know what the A and B gain ranges are?

As good , "a" is lower range than "b" so one of each should be FuzzFace setup
I have a pair built with these and they give a nice "rubber band" kind of English old fuzz tone.
MM
"Success is the ability to go from one failure to another with no loss of enthusiasm"
My Website www.martinlister.com

brett

QuoteI'm still waiting for mine to arrive, been a few weeks 

If it's the same fellow (in Sofia, Bulgaria), my first order was here in 10 days, which is good for Europe->Australia, but this order took about 3 weeks.  Maybe he's getting more business now.

Brett Robinson
Let a hundred flowers bloom, let a hundred schools of thought contend. (Mao Zedong)

hellwood

i got a bunch of the gt308v's from sofia and these are the hfe's...pretty sad if you ask me although none were leaky.
67,34,52,48,52,38,52,52,43,52,45,54,52,51,61,37,46,51,46,49,49,42,43,51,49,55,48,48,49,57,49,58,41,49,42,55,37,53,56,47,63,37,58,51,44,57

smnm

Quote from: hellwood on November 28, 2007, 02:58:43 AM
...
67,34,52,48,52,38,52,52,43,52,45,54,52,51,61,37,46,51,46,49,49,42,43,51,49,55,48,48,49,57,49,58,41,49,42,55,37,53,56,47,63,37,58,51,44,57

This is pretty much the range in my batch too - maybe someone already skimmed off the higher gains?
I like them though.
I might try some from another supplier.

jakenold

Didn't we discuss this earlier, about the internal resistor making the HFE readings different from AC128's, etc.?

I've made some KILLER fuzz faces with mine, just get two trimmers inside the effect to tune the bias.

mfg Jake

hellwood

Quote from: jakenold on November 28, 2007, 09:04:35 AM
Didn't we discuss this earlier, about the internal resistor making the HFE readings different from AC128's, etc.?
mfg Jake

yeah, we did, but the thread was referring to gt311's or gt313's and nobody replied when i asked if the 308's had the internal resistor.

Quote from: MartyMart on November 27, 2007, 08:23:28 AM
I got similar results after testing a few dozen, plenty in the 80-120 hfe range.
MM.

how were these measured for gain?

vanessa

#10
They make for some good fuzz (cranked) but they are very noisy, even with low leakage. I've tried other ge's in the same circuit to compare with and the GT308's sound pretty good for the price but in terms of noise are on par with very leaky western made ge transistors with similar hfe's.

For me the beauty of a ge based fuzz is the way it cleans up to an almost crystal clear clean tone. When the 308's clean up it's like the sound of an old dusty record before the music kicks in.
Out of all the Russian ge's I've tested the 308's were about the best offered, which to my ears is not saying a lot. In an old Russian DIY pedal book from the early 80's they seem to have thought the same about the 308's for fuzz circuits, but then again that was all they had.

The best I've found are old western and Japanese ge's. There is still an abundance you just have to look a little harder these days. I've found that you can get a nice handful of some pretty hard to find model numbers (OC's, NKT's) out of old transistor radios. Go out to some garage sales or swap meets. On a lot of vintage (early 60's) hand held transistor models you can lift the whole back panel off without a screwdriver and it will reveal the circuit board's bounty of germanium goodness. @ $1 - $5 This has yielded me a very inexpensive source of transistors for use on projects. Even on ebay you can get like 3-5 of these units in a one off auction for under $20 depending on how uncollectible they are. Depending on the model number that can yield 35-50+ ge transistors.


brett

It's a pity about the noise issue.  I was hoping that low leakage meant few "noisey" flaws in the semiconductor materials. 

Quote67,34,52,48,52,38,52,52,43,52,45,54,52,51,61,37,46,51,46,49,49,42,43,51,49,55,48,48,49,57,49,58,41,49,42,55,37,53,56,47,63,37,58,51,44,57

90 % of those numbers are good for Q1 in a fuzzface or for a rangemaster.  Because it's *much* more important to use Ge in Q1 than for Q2, GT308B can be used to make hybrid Fuzzfaces. 

I see that the GT308B has a really high transition frequency (Ft = 120 MHz, whereas it's something like 1 MHz for the AC128s).  So GT308Bs can handle frequencies those annoying upper harmonics that older devices can't, and this might make for a "cold/sharp" tone.  It might be worthwhile putting a small cap (33pF) between the collector and the base, so that high frequencies get absorbed.
cheers

Brett Robinson
Let a hundred flowers bloom, let a hundred schools of thought contend. (Mao Zedong)

moro

Quote from: vanessa on November 28, 2007, 05:28:48 PM
Out of all the Russian ge's I've tested the 308's were about the best offered, which to my ears is not saying a lot. In an old Russian DIY pedal book from the early 80's they seem to have thought the same about the 308's for fuzz circuits, but then again that was all they had.

D'oh. I just put a bid on some of those on eBay. I guess we'll see. I'm not a big fuzz fan anyway and I'm more interested in them for the sake of the build.

vanessa

Quote from: brett on November 28, 2007, 07:46:38 PM
It's a pity about the noise issue.  I was hoping that low leakage meant few "noisey" flaws in the semiconductor materials. 

Quote67,34,52,48,52,38,52,52,43,52,45,54,52,51,61,37,46,51,46,49,49,42,43,51,49,55,48,48,49,57,49,58,41,49,42,55,37,53,56,47,63,37,58,51,44,57

90 % of those numbers are good for Q1 in a fuzzface or for a rangemaster.  Because it's *much* more important to use Ge in Q1 than for Q2, GT308B can be used to make hybrid Fuzzfaces. 

I see that the GT308B has a really high transition frequency (Ft = 120 MHz, whereas it's something like 1 MHz for the AC128s).  So GT308Bs can handle frequencies those annoying upper harmonics that older devices can't, and this might make for a "cold/sharp" tone.  It might be worthwhile putting a small cap (33pF) between the collector and the base, so that high frequencies get absorbed.
cheers



The low leakage is a deception with these little buggers. They seem to have a very consistent low leakage and great hfe ranges for fuzz type projects particularly fuzz face's (I really did not like the tone at all with Rangemaster's or Tonebender's).
Honestly they are not really that bad (cough, cough), but they are not really that good either.
I've noticed that some of Russian ge transistors that have a 4th ground leg that seem to help with cutting down this noise factor for audio applications, but the four legs that I've found don't sound that good for fuzz's. Maybe they made a 4 leg version that is like a 308 with out the noise?

MartyMart

Vanessa, well I must have gott'n lucky with a batch, they perform very well and are streets ahead of any
Ac128's etc that I have.
I don't seem to have a noise issue, though I am a fan of "the trimpot" and of small pf caps rolling off high crap
here and there !
Some of the HUGE GT402's are very good too, though several more had "duff" leakage/hfe readings than the 308's
Marty.
"Success is the ability to go from one failure to another with no loss of enthusiasm"
My Website www.martinlister.com

brett

QuoteWhen the 308's clean up it's like the sound of an old dusty record before the music kicks in.
The randomness (rather than a consistent "hiss") makes me think it's radio interference. 

2 options for eliminating this are the old-fashioned 0.001uF cap to ground from the base of Q1 (as seen in many older pedals), or using a 33pF cap (experiment from 10 to 100pF) between the base and collector of Q1 (and Q2 if you want to be sure!).

I might get time to build and test a couple of pairs on Sunday.  I'll throw them on the scope +/- caps.
cheers
Brett Robinson
Let a hundred flowers bloom, let a hundred schools of thought contend. (Mao Zedong)

vanessa

Quote from: brett on November 29, 2007, 05:36:15 AM
QuoteWhen the 308's clean up it's like the sound of an old dusty record before the music kicks in.
The randomness (rather than a consistent "hiss") makes me think it's radio interference. 

Maybe, I've built a lot of germanium based projects over the years and I've just about always put some of these in "just to see". Where others are dead quite (unless they are junk) these always have that "off in the background sound of an old dusty record before the music kicks in".

vanessa

Quote from: MartyMart on November 29, 2007, 03:51:55 AM
I don't seem to have a noise issue, though I am a fan of "the trimpot" and of small pf caps rolling off high crap
here and there !

Hey Marty! I think the issue I'm describing would definitely be resolved by using those small caps filtering off the high frequencies where this stuff seems to reside. Personally it's not worth the effort,  I've other transistors a ton of which I found from old transistor radios when I was working on that Brian May "Deacy" amp a while ago.