Author Topic: MP15A and GT308G germanium transistors any good?  (Read 983 times)

snow123

MP15A and GT308G germanium transistors any good?
« on: June 24, 2022, 09:10:05 PM »
I've been looking at buying some MP15As and GT308Gs, but i cant find anything about how they actually measure (like how the hFE measures and how leaky they are) or anything like that.

So Does anyone have any experience with these transistors?
« Last Edit: June 24, 2022, 09:11:43 PM by snow123 »

antonis

Re: MP15A and GT308G germanium transistors any good?
« Reply #1 on: June 25, 2022, 07:03:01 AM »
If you can't find anything about they actually measue WHY you're looking at buy them..??
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

digi2t

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Re: MP15A and GT308G germanium transistors any good?
« Reply #2 on: June 25, 2022, 08:35:00 AM »
I have to echo antonis' comment. "Why" is a valid question.

As for "actual vs datasheet" information, I've found that whatever the published gains are, 90% of low leakage (0.1mA or better) transistors will sit in the lower 25% of the specified range spec'd in the datasheet.

If you haven't already read it, this is a good primer;
https://www.diystompboxes.com/smfforum/index.php?topic=117061.msg1086042#msg1086042
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snow123

Re: MP15A and GT308G germanium transistors any good?
« Reply #3 on: June 25, 2022, 03:17:22 PM »
If you can't find anything about they actually measue WHY you're looking at buy them..??
because the MP15A is a super cheap lower gain transistor (theres 20 for $7 on ebay rn), and the GT308G is one of the only higher gain russian germaniums that i can find for a reasonable price.

antonis

Re: MP15A and GT308G germanium transistors any good?
« Reply #4 on: June 25, 2022, 03:43:12 PM »
Sorry but I still have to ask WHY..??
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

snow123

Re: MP15A and GT308G germanium transistors any good?
« Reply #5 on: June 25, 2022, 03:53:32 PM »
Sorry but I still have to ask WHY..??
'cause i want to have some germanium transistors of different gains on hand.

snow123

Re: MP15A and GT308G germanium transistors any good?
« Reply #6 on: June 25, 2022, 04:07:17 PM »
also, i want to build a catalinbread karma suture, which calls for a 1T308A, but theres only 1 lot of that on ebay, and the MP15A seems like it might be a good substitute while maybe being more usable for more projects (with the hFE being 50-100 instead of 25-75), and its also cheaper. so im just wondering if the MP15A is cheap for a reason (like actually being super leaky and super low gain), or if its actually worth using.

And for the GT308G, I'm just wondering if it's actually worth using for something like a tonebender.
« Last Edit: June 25, 2022, 04:09:54 PM by snow123 »

pacealot

Re: MP15A and GT308G germanium transistors any good?
« Reply #7 on: June 25, 2022, 04:09:12 PM »
Snow with germanium what could go wrong?  :icon_wink:
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snow123

Re: MP15A and GT308G germanium transistors any good?
« Reply #8 on: June 25, 2022, 04:11:36 PM »
Snow with germanium what could go wrong?  :icon_wink:
i mean, ive built a rangemaster and that worked fine.

antonis

Re: MP15A and GT308G germanium transistors any good?
« Reply #9 on: June 25, 2022, 04:22:06 PM »
also, i want to build a catalinbread karma suture, which calls for a 1T308A, but theres only 1 lot of that on ebay, and the MP15A seems like it might be a good substitute while maybe being more usable for more projects (with the hFE being 50-100 instead of 25-75), and its also cheaper. so im just wondering if the MP15A is cheap for a reason (like actually being super leaky and super low gain), or if its actually worth using.

My good old fellow.. :icon_smile:

We did agree in the past that any circuit based on BJTs particular hFE definitely is a BAD circuit, didn't we..??
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

snow123

Re: MP15A and GT308G germanium transistors any good?
« Reply #10 on: June 25, 2022, 05:11:41 PM »
also, i want to build a catalinbread karma suture, which calls for a 1T308A, but theres only 1 lot of that on ebay, and the MP15A seems like it might be a good substitute while maybe being more usable for more projects (with the hFE being 50-100 instead of 25-75), and its also cheaper. so im just wondering if the MP15A is cheap for a reason (like actually being super leaky and super low gain), or if its actually worth using.

My good old fellow.. :icon_smile:

We did agree in the past that any circuit based on BJTs particular hFE definitely is a BAD circuit, didn't we..??
well, when I say "super low gain" I mean <50 hFE, which i don't think super usable in a lot of circuits.

antonis

Re: MP15A and GT308G germanium transistors any good?
« Reply #11 on: June 25, 2022, 05:33:12 PM »
well, when I say "super low gain" I mean <50 hFE, which i don't think super usable in a lot of circuits.

Circuits are designed by people..
People should be aware of MINIMUM hFE of particular devices implemented in respective circuits..

e.g. I should be a bad designer if I use a single 2N2222 of 5mA Base current to drive a 2N3055 Emitter follower for 15A load current..
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

mozz

Re: MP15A and GT308G germanium transistors any good?
« Reply #12 on: June 25, 2022, 07:54:40 PM »
There was a Russian website with a lot of info, it's down now. If MP15A is showing 50 hfe as the lowest, that's what you will get. Most all will read on the low end of the spec sheet. If your device needs leakage to work , the Russian trannys have very low leakage and might not work.
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snow123

Re: MP15A and GT308G germanium transistors any good?
« Reply #13 on: June 25, 2022, 09:44:21 PM »
There was a Russian website with a lot of info, it's down now. If MP15A is showing 50 hfe as the lowest, that's what you will get. Most all will read on the low end of the spec sheet. If your device needs leakage to work , the Russian trannys have very low leakage and might not work.
well according to this post: https://www.diystompboxes.com/smfforum/index.php?topic=108054.0
the actual hfe can get a bit lower than the published hfe.

and i actually want low leakage, 'cause one of the pedals i want to build (catalinbread karma suture) calls for a 1T308A, which has pretty low gain and super low leakage, and im wondering if the MP15As leakage is comparable to the 1T308A, and if the MP15As actual hfe is a bit higher than the 1T308A.

mozz

Re: MP15A and GT308G germanium transistors any good?
« Reply #14 on: June 26, 2022, 01:58:32 PM »
Measured some MP15A. First number is gain, second number is leakage in ua. Room temp is 75f. I have no GT308G only the A version.
65/83
62/165
65/155
61/93
64/77

Actually kind of hot here today, and i did use my fingers to hold them while putting in the socket on the DCA-55. I do expect the leakages would actually be lower.
« Last Edit: June 26, 2022, 08:08:22 PM by mozz »
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snow123

Re: MP15A and GT308G germanium transistors any good?
« Reply #15 on: June 26, 2022, 04:26:43 PM »
Measured some MP15A. First number is gain, second number is leakage in ua. Room temp is 75f. I have no GT308G only the A version.
65/83
62/165
65/155
61/93
64/77
and how does it compare to the GT308A?

mozz

Re: MP15A and GT308G germanium transistors any good?
« Reply #16 on: June 26, 2022, 08:06:28 PM »
GT308A

35/0
37/0
37/10
27/0
24/0

Here is something else. MP15A
 Transition Frequency (ft): 2 MHz
Collector Capacitance (Cc): 50 pF

GT308A
 Transition Frequency (ft): 90 MHz
Collector Capacitance (Cc): 8 pF

GT308G
 Transition Frequency (ft): 120 MHz
Collector Capacitance (Cc): 8 pF

You can see the GT are more of a RF transistor. higher freq and a lot lower capacitance. You may have to put a 47pf cap across C-B when used in a fuzz. Making good RF transistors with higher gain/less leakage was always a problem back then.

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antonis

Re: MP15A and GT308G germanium transistors any good?
« Reply #17 on: June 27, 2022, 08:22:44 AM »
MP15A
Collector Capacitance (Cc): 50 pF

@snow123: Don't consider the above mentioned capacitance as a constant value.. It can (and will) increase by more than an order of magnitude as the collector current is increased from a low value into the quasi-saturation regime at a fixed collector-emitter voltage of 1 V.  :icon_wink:
(you can look for transition & diffusion capacitance and "base-widening"/Kirk effect, also..) :icon_wink:
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

duck_arse

Re: MP15A and GT308G germanium transistors any good?
« Reply #18 on: June 28, 2022, 11:22:27 AM »

snow123

Re: MP15A and GT308G germanium transistors any good?
« Reply #19 on: June 28, 2022, 07:23:11 PM »
Also, how do GT313V transistors actually measure? Asking 'cause the GT313 series as a whole has a super wide hFE range, and I'm wondering where within that range, they actually measure.