[97] Effect of Heat on Ge transistors

Date: May 15th, 2008 | Comments : [7] | Categories: Uncategorized.

AC188 germanium transistors
I was reading some posts on HCFX and a discussion about germanium transistors and temperature caught my attention. I decided to go into the lab to do a couple of quick experiments.

Results are after the break…

Room temperature was 72°F and my fingers were warm and dry.

I picked up a germanium AC188 with a pair of needlenose pliers and managed to place it into my test rig without touching the body of the transistor with my fingers.

Using my Peak transistor tester, I checked the gain and leakage, then pressed my fingers against the transistor case for 10 seconds and tested again. Then another 10 second heating with the fingers followed by a final test.

1st Transistor
HFE, Leakage
84, 150uA
95, 380uA (after 10s)
100, 500uA (after second 10s)

2nd Transistor
HFE, Leakage
84, 150uA
96, 400uA (after 10s)
100, 520uA (after second 10s)

As you can see, handling the transistors for just a few seconds caused a substantial shift in the gain and leakage measurements. I may do some more exact tests when I get the time.


7 Responses to “Effect of Heat on Ge transistors”

[434] phill Says: 12:16 pm, May 16th, 2008

That’s incredible! Now stick ’em in the freezer to test the curve.

It’ll be hard to find a valid use for this information though, considering most of us keep our transistors in little metal boxes that we throw around and jump on. 😉

[439] one leg Says: 9:50 am, May 21st, 2008

How much for one?

[440] admin Says: 2:24 pm, May 25th, 2008

Do you want to buy one of the AC188 transistors? I’ll sell you one for $8 which includes shipping. Write an email to me and I’ll reply with a Paypal invoice.

[447] Noel Grassy Says: 10:58 pm, June 15th, 2008

Howdy, I’ve been wanting one of those Peak analyzers. Where did you buy yours?
Thanks for posting this data. I get outdoor gigs in the Summer and I’ve wondered why my Ge fuzz can’t be tamed for use. I usually omit it from the FX chain. Can these figures be brought back to usable with a bias control added?

[452] Matthew Miller Says: 3:21 pm, June 21st, 2008

Good thing my Germanium transistors are inside an enclosure where I can’t touch them. The real test to do is to find a wireless humidity and temperature tester to put inside of the Fuzz or whatever enclosure and keep track of changes in temp and humidity over a period of time. Keeping track of differences between changes while idle and changes that happen while playing.

[2193] pinkjimiphoton Says: 6:13 pm, April 29th, 2011

interesting…it’s weird, i keep having the opposite problem with ge transistors…they sound great at room temp, but let ’em get cold, boy, and they sound like poo!!! i’m in new england, so no idea how they’ll react in the heat, but they sure don’t like cold concrete floors!!! gotta hit ’em with a bic lighter to get ’em to work…

[2197] admin Says: 8:37 am, May 2nd, 2011

It is all to do with bias… it changes up or down depending on the temp, and will only sound good at the temperature that the bias is optimized for. So, hotter or colder than room temp can make the circuit sound less than perfect.

regards, Jack


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