So I took a shot on a lot of 50 Russian MP38A NPN germanium transistors because I found them for cheap, but I really know nothing about them. They are being shipped form Russia so I'm guessing I'll have to wait a week or 2 for them to get here. I have been searching all over, but I can't find any info about them anywhere. If you have any insight on these I'd love to hear it.
I'm hoping to use them in some fuzz projects after testing them via the RG method. I'll gladly share whatever I learn from this since there doesn't seem to be any info around on these.
the RG method.
In this case I recall correctly, he mentions Hfe and Gain as the two most important factors for Ge in effects.
All the other categories are dwarfed in importance, including what is stamped on the side of any individual Ge transistor, if it doesn't meet the above criteria, there are some work arounds but if it does it'll bias and work.
Some slight differences in tone may be true, and huge differences in tone may be percieved, IME also, Hfe and Gain [leaky is basically no good, medium/lowish gain may be preferrable.
Pc: 150mW; Ucb: 15V; Uce: 15V; Ueb: -; Ic: 20mA; Tj: 75°C; Ft: 2MHz; Cc: -; Hfe: 45/100
Quote from: kupervaser on July 21, 2010, 03:12:55 AM
Pc: 150mW; Ucb: 15V; Uce: 15V; Ueb: -; Ic: 20mA; Tj: 75°C; Ft: 2MHz; Cc: -; Hfe: 45/100
Thanks! Where did you find this?
You can find a lot of info in Russian if you google: МП38A
I can read Russian.
Quote from: kupervaser on July 21, 2010, 08:17:10 AM
You can find a lot of info in Russian if you google: МП38A
I can read Russian.
I can see how that can be helpful. lol
Here's a bit of an update. I still haven't taken the time to measure the gain/leakage of this transistors. However, yesterday I got curious a plugged a random pair into a silicon fuzz face, and they sound fantastic! I had some time to play through it this morning and I definitely like it a lot more than the silicon transistors in that same fuzz pedal. The silicons I took out were BC107a in Q1 and 2n2222A in Q2.
Without the gain/leakage #'s this isn't very scientific, but i think it says good things that a random pair of these sound great. A couple of things to be aware of for anybody who might try these:
1 the metal can casing of these is 2-3 times larger than that of your common T05 types
2 the base is connected to the casing
Somehow i forgot that my silicon fuzz had transistor sockets in it or I would have tried this a long time ago.
Quote from: Exactopposite on October 17, 2010, 01:17:20 PM
...A couple of things to be aware of for anybody who might try these:
1 the metal can casing of these is 2-3 times larger than that of your common T05 types
That's some extra mojo factor, there! If you can, would you mind posting a pic of one next to a "normal" sized transistor?
Quote from: Earthscum on October 17, 2010, 01:25:10 PM
Quote from: Exactopposite on October 17, 2010, 01:17:20 PM
...A couple of things to be aware of for anybody who might try these:
1 the metal can casing of these is 2-3 times larger than that of your common T05 types
That's some extra mojo factor, there! If you can, would you mind posting a pic of one next to a "normal" sized transistor?
Here you go:
(http://i55.tinypic.com/24ymkbp.jpg)
Oh, heck yeah! Those are like little flying saucers! It's a shame they spend most of their life inside a case.
I have a couple in a FF from a few years ago and they do sound great.
IIRC I found a pair that were hfe's of 65 and 100.
GT308/309 are also crackers.
MM
So I just finished testing all of them and the results are good. According to the specs the Hfe range is 45-100. The vast majority of them are in the 50's and 60's. There was one that measured 92, none in the 80s, and a probably about 5 in the 70's.
Most of them had very low leakage. Only 2 of them had leakage around 500uA and one had a leakage of 1000uA. There were a few that were right around 300uA. Everything else was really low. I didn't make note of the exact figures for leakage because they were (almost) all so low. 2 of the 3 leaky ones had gains down in the 30's, which I thought was odd, because everything I read would indicate higher gain transistors are more prone to leakage.
The 2 that I tried in the fuzz mentioned earlier in this post were 62 in Q1 and 74 in Q2. Those are lower than the "sweet spot" that people usually mention for the fuzzface, but they sound great to me.
I wanted to share the results, because I have learned a lot from what other people have shared here.
I've very pleased with the results. I'd like to see some higher gains, but with only 3 duds in the bunch, I can't complain. I can find plenty things to do with 47 good germanium transistors. ;D