Author Topic: MP15A and GT308G germanium transistors any good?  (Read 963 times)

snow123

Re: MP15A and GT308G germanium transistors any good?
« Reply #20 on: June 28, 2022, 07:29:13 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.
the karma suture already has that 47pf cap across the C-B, and im assuming i would remove said capacitor when using the MP15A, correct?

andy-h-h

Re: MP15A and GT308G germanium transistors any good?
« Reply #21 on: June 29, 2022, 04:07:01 AM »
Hello - given the low price, just buy some and give it a try on a breadboard.  You might be overthinking this.   :icon_wink:

antonis

Re: MP15A and GT308G germanium transistors any good?
« Reply #22 on: July 01, 2022, 03:48:38 PM »
Snow with germanium what could go wrong?  :icon_wink:

I suppose we should be getting worried by now.. :icon_cool:
"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..

DrAlx

Re: MP15A and GT308G germanium transistors any good?
« Reply #23 on: July 01, 2022, 05:48:41 PM »
Not come across the GT308G before. 
I did try some 1T308B (the military spec version of the GT308B) in a fuzz before.
Capital B is "V" in Russian, so really should have called this "1T308V".

Note datasheet (link below) has info for "a","b","v" versions of the 308, with "v" (i.e. capital "B") version being the highest gain.
Leakage was very low, but hFE was not as high as I expected.
When I got hold of the datasheet I saw why.

Graph shows hFE close to 200 but that is for 60mA of collector current.
At the much lower currents of a typical fuzz design, hFE is way lower.

https://alltransistors.com/adv/pdfview.php?doc=gt308a-b-v_1t308a-b-v.pdf&dire=_russia

There were also lots of short bursts of "fizz" noise that would randomly flare up out of nowhere and then die away.
I never got to the bottom of that.  I ended up using AC128s.
« Last Edit: July 01, 2022, 05:54:09 PM by DrAlx »

snow123

Re: MP15A and GT308G germanium transistors any good?
« Reply #24 on: July 04, 2022, 07:08:28 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.

antonis

Re: MP15A and GT308G germanium transistors any good?
« Reply #25 on: July 05, 2022, 07:23:02 AM »
@snow123: Jeanne d'Arc is considered the 1st person burned at the stake due to repeatedly quoting herself.. :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..