1N4148 vs 1N914

Posted: 3/17/2021 2:02:58 PM

Joined: 3/16/2021

Hi, my Etherwave plus stopped working. Based on past threads I suspect a static shock may have toasted something I get full sound when I short C28. It's been suggested that very often the first thing to replace is D1, the 1N4148 diode. My DVM says it's good but I've read that can be inconclusive in-circuit. (At the limits of my electronics knowledge here.) Question is, I have a big pile of 1N914 diode and I've read they are functionally equivalent to the 1N4148. Any reason I shouldn't give it a try?

Posted: 3/17/2021 3:13:17 PM

From: Minnesota USA

Joined: 11/27/2015

There's no reason you shouldn't try it.  For most uses the two are interchangeable, to the point that I have received 1N914s as a substitution when the 1N4148s ordered were out of stock.

Posted: 3/17/2021 8:49:49 PM

From: Colmar, France

Joined: 12/31/2007

When the Diode D1 in the Etherwave stops working due to an electrostatic discharge, it’s often its so-called reverse breakdown voltage which has decreased, so that there is no more rectifier effect only for higher voltages which will finally mute the Etherwave. That can’t be diagnosed with the diode test function of a multimeter, an oscilloscope would be needed to check the (only partly) rectified waveform.

I don’t know by heart what a good 1N914 should have as a reverse voltage parameter, compared to a 1N41418. You can give it a try. Worst case scenario is that you can‘t get full volume because it would also do a partial reverse breakdown with the high rf voltage. Then, you can always buy a 1N4148.

Posted: 3/17/2021 9:28:32 PM

Joined: 3/16/2021

Thanks Thierry and pitts8rh.

I've been combing the archives on this, also verified => -4V DC at the node D1/R14/C12 and ~30ohms at the base of Q7. I don't have an oscilloscope so I don't know what else I can do. I'm waiting to hear back from Moog tech to see what their repair turnarounds are like these days. My soldering skill is maybe a little above amateur but I'd rather have them do it before I mess it up myself. 

Posted: 3/20/2021 8:38:45 PM

From: Montana, USA

Joined: 9/2/2019

1N914 and 1N4148 are the same diode in a different package (1N4148 is  smaller).   If you suspect D1 is bad, just change it.

If you blow it out regularly, you might try a beefier diode such as 1N4937... you will have to retune the volume oscillator though.

If you don't take your theremin on the road, you could even put in a couple of pin sockets for easy swapping.

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