OA1160 diodes. Faulty?

[HF1600ie]

Hi,
I bought 3 of these and put 2 in my tube screamer in the very same place and orientation that the factory ones were.
But I got no distortion. If any, a very very tiny volume increase as I turn the gain up.

I tested with a multimeter. Put it in "diode testing" mode and got absolutey no reading even when swapping the leads.
Then, I tested for the basic "continuity testing" mode and it beeped on all 3.

At last, I measured the resistance with leads in normal place and again by swapping the leads:
First one : It reads 45K and 49k.
Second one and i read 68K and 77K
Third one : 53K and 40K

Are they faulty? Sorry, first time having an issue with diodes and needing to test them. Don´t know if I am missing something.

Thanks!

[duck_arse]

may not be helpful but we always like to look at photos of diodes. where did the diodes come from?

[HF1600ie]

I got these from Hungary !

They look exactly like these (bought from this vendor) :

https://qrpparts.com/diodes/germanium/oa1160.html

[Rob Strand]

It is possible your DMM diode test range is testing the diodes at high currents.

Using the resistance range to test diodes on a DMM is unreliable.


Try wiring up your own test circuit:



Use:
- 9V battery
- 10k resistor
- DMM set to 20V.

Test current in the forward direction is just under 1mA.
With the diode pointing downward (forward), as shown in the diagram you should get something like 0.3V or 0.4V; typical for ge more like 0.3V.
With the diode pointing upward (reverse) it should read a little under 9V.


I found this VI curve for the OA1160,



Seems to pass through 0.35V @ 1mA.

More germanium curves here,
https://www.diystompboxes.com/smfforum/index.php?topic=117550.0

[HF1600ie]

Well, the reality is put them in my tubescreamer and I get no sound from the distortion/clipping part of the pedal. It just mutes it.
I even tried reversing them. Makes weird tones.

Put the factory ones back in and everything is normal.

[Rob Strand]

Well, the reality is put them in my tubescreamer and I get no sound from the distortion/clipping part of the pedal. It just mutes it.
I even tried reversing them. Makes weird tones.

Put the factory ones back in and everything is normal.

The fact your DMM diode tester doesn't work means the diodes have a higher voltage drop than normal.

If you look at the 1N55/1N55A curve at the top right it also has a high drop for a given current.    The curve is almost like a resistor, so it will act very much like you are putting a resistor there, which will reduce the gain.

https://postimg.cc/MXshTbyV

[HF1600ie]

So, you mean it is normal for the diode to "kill" all the distortion effect from the pedal?

All I get is a very slight volume increase when I turn the distortion knob. No distortion audible. As if the sound doesn´t compress/crush at all.

Put the stock back into their place and all looks fine.

[iainpunk]

the thing is, the leakage is high enough that it overpowers the function of the potentiometer. not all diodes are suitable for distortion circuits, and evidently, these are among those which aren't. i have a few Ge diodes that don't work nicely with clipping circuits, but they do work well in series with other diodes, especially schottky diodes.

cheers

[HF1600ie]

So perhaps I could put one in series with one of the factory ones? Like "factory diode+OA1160" against the other factory one alone?

I´d like to reach something different and have never experimented with diodes.

[anotherjim]

So perhaps I could put one in series with one of the factory ones? Like "factory diode+OA1160" against the other factory one alone?

This is worth trying.