Testing Ge diodes

[croquet hoop]

I know the subject of Ge diodes has been beaten to death, but I'd like to be sure of one or two things. First of all, I bought 1n34a and 1n270 diodes from Tayda on two separate orders (one month apart), 5 of each each time, and I've just taken the time to test them with the diode setting of my DMM, with varying results:

- 1st batch of 1n34a: nothing, continuity test fails, the things seem to be dead, not even useful as jumpers
- 2nd batch of 1n34a: the DMM indicates values around 330, so I guess it's in line with the expected .3v drop.

- 1st batch of 1n270: same here, values are between 300-350
- 2nd batch of 1n270: the values are around 700 this time; silicon diode in a glass package?

Now I'm wondering if the diodes that seem to be proper Ge are really what they look like, or if there's something fishy with them as well. I know that the fv is supposed to rise under the heat of a finger, can anyone tell me more about this test (how long do I have to heat the diode before I see the fv rise, and in which proportions is it supposed to increase?)

Additionally, can anyone recommend reliable sellers for Ge diodes? (I've just received 1n34as from Banzai as well, the readings are all over the place, between .35 and .56... is this to be expected?) Preferably European sellers, I'd rather not wait three more weeks before I get usable 1n34as.

[Gledison]

jiiiiz mate! I thought that the voodoo was only with Ge transistors....
good luck!

[midwayfair]

0.33v is fine for a 1n34A. It's actually a bit low. They should be closer to 0.35-0.38v. 1N270 should be closer to 0.27-0.3v.

New production Ge diodes are inconsistent as all get-out. I test them before each use. I've had more than a few bad ones from multiple sources including US sources with impecable e-bay feedback. It's not limited to Tayda and they're about par for the course (I usually get 10% are out of spec). You seem to have gotten incredibly unlucky, I would even say ... too unlucky.

But here are some things to think about:

1) Germanium is leaky. Yes, even in diode form.

2) Heat will raise the Fv. It won't take long. If you measured batch one in a colder environment, you'd get a higher reading on batch 2. But it shouldn't be that big of a difference.

3) Some multimeters tend to just be horrible at measuring germanium diodes. The Peak Atlas is known to double the expected reading, making all germanium diodes look like they're silicon. You can test this a different way by setting up the diodes on a breadboard between 9V and ground inseries with a 100R resistor:
9v > diode anode > 100R > ground
The difference in voltage between the anode and cathode is your Fv drop.

If the 1n270s you got really are measuring consistently at 0.7v and don't pass the heat test, I'd notify Tayda that they may have been supplied fakes. It's happened before.

If they DO pass the finger heat test but still measure .7v, then use those suckers in some overdrives and fuzzes, they'll sound bangin'. Or I'll take them.

EDIT: Best way to get GOOD germanium diodes is get vintage ones and Russian ones.

[croquet hoop]

Thanks for your feedback. I'll double check them using the setup you recommended and keep your remark on the .7v 1n270s in mind! I'll get in touch with Tayda too (and I know their customer support won't nitpick on those dead 1n34as) and try to find a supplier for those Russian diodes.

[Gledison]

Which are the most common Russian diodes used in pedals? I have a friend going to Ukraine that can bring some..

[midwayfair]

Which are the most common Russian diodes used in pedals? I have a friend going to Ukraine that can bring some..

None are specifically used. And a lot of them are similar or identical. I have a thread somewhere.

[croquet hoop]

Quick update. I double checked the faulty diodes to be sure but the results were the same. I informed Tayda and they offered store credits in compensation, and told me that they will see to sort out the problem with their Ge diodes. I ordered a bunch of 1n34a's from PPP along with a few enclosures so my needs are covered for now, but it's nice to see a seller give a quick and satisfying answer.

[pickdropper]

FWIW,  I ordered a dozen of these on my last build.  11 were open and 1 was WAAY put of spec.

The quality of their parts seems to be getting worse.  I suspect they just buy from other Chinese vendors without screening them first.  I know firsthand that doesn't always work out well.