1N34a equivalent replacement

[460voltclub]

I have searched for days so keep stupid comments to yourself. I need a germanium that has an If of 2 to 4 mA. I have two old theremins that I built new cabinets for and I want to change some obsolete parts because the rf coils are not tuning properly.

[Benta]

What do you mean by "an If of 2 to 4 mA"?
The 1N34A is rated at 50 mA.

A replacement candidate could be the AA143.

[460voltclub]

On the data sheet I have it shows "Forward voltage"  "Vf = 1V" (test condition) "Min 4mA  Typ 2 mA. When it comes to finding replacement parts for obsolete parts I get a case of dain bramage and drive myself nuts looking through data sheets. From what I have found out is the 1N34 starts to conduct at .2 to .3 volts instead of the basic .7 volts.
I'm old so have pity on my ignorance.

[TimFox]

Probably the more important spec (which is consistent with the one you quote) is  V_f < 1 V at I_f = 5mA.
The 0.2 to 0.3 V typical voltage is the obvious difference between Ge and Si.  A lot of guys would use a signal-level Schottky diode, such as the 1N5711:
V_f < 1 V at 15 mA, < 0.41 V at 1 mA.

[bdunham7]

https://www.allelectronics.com/item/1n34a/1n34a-germanium-diode/1.html

[Quarlo Klobrigney]

1N60, 1N290, 1N295, 1S188
https://www.ebay.com/itm/20pcs-1N34A-Germanium-Diode-DO-35-1x-1N34-US-SELLER-FREE-SHIPPING/133530100291?hash=item1f1703a243:g:zx8AAOSwdjZfb185
https://www.tubesandmore.com/products/diode-1n34a-germanium-low-leakage

[tggzzz]

Why do you want an eqivalent? Won't a 1n34A be OK for your purposes?

https://octopart.com/search?q=1n34a

[David Hess]

1N60, 1N290, 1N295, 1S188

And 1N270s if you can find them.

But a small signal schottky diode is what I would try first.

[460voltclub]

I could most likely buy obsolete diodes but I question why. If a part is obsolete I make it a point to upgrade to a part that can be purchased fast and easy plus having a shelf life before it becomes obsolete.
I think all through hole parts are going to become obsolete in the near future but I am all set up for SMD.

[TimFox]

I could most likely buy obsolete diodes but I question why. If a part is obsolete I make it a point to upgrade to a part that can be purchased fast and easy plus having a shelf life before it becomes obsolete.
I think all through hole parts are going to become obsolete in the near future but I am all set up for SMD.

So, try the 1N5711 or its SMD equivalent.

[akimpowerscr]

If I may give you a tip:

Do not solder or unsolder germanium diodes or transistors unless it is absolutely necessary (you are sure they need to be replaced because they are faulty) and that you are fully aware of all the precautions that must be taken for this.

The germanium junction melts at low temperature (90 ° C) and is easily destroyed by the heat of the soldering iron.

Other germanium diodes which could replace diode 1N34a: AA119, OA85

[Vovk_Z]

How about BAT54, BAT41 (small signal Shottky diodes)? Or BAV99?

[CaptDon]

1N34A diodes should be readily available as would any similar germanium diode.
In the Theremin they can be in a detector circuit and the schottky diodes may have
a different transfer function which will effect the performance. The schottky stuff
doesn't work well in military and marine radar units designed for the old germanium
1N23A/E/R or 1N21A devices.
 

[rsjsouza]

Do not solder or unsolder germanium diodes or transistors unless it is absolutely necessary (you are sure they need to be replaced because they are faulty) and that you are fully aware of all the precautions that must be taken for this.

The germanium junction melts at low temperature (90 ° C) and is easily destroyed by the heat of the soldering iron.

One of my solder techniques was to have this heat sink clamp tied to the device's leads while soldering. It practically eliminates the thermal stress on the junction.

[TimFox]

1N34A diodes should be readily available as would any similar germanium diode.
In the Theremin they can be in a detector circuit and the schottky diodes may have
a different transfer function which will effect the performance. The schottky stuff
doesn't work well in military and marine radar units designed for the old germanium
1N23A/E/R or 1N21A devices.

The 1N21 and 1N23 series are point-contact silicon diodes (WWII vintage).
Typical forward voltage for the 1N23 is 500 mV at 10 mA.
It's not clear that a theremin is critical for this diode application;  the 1N34 series was a default detector diode back in the day.

[CaptDon]

Don't think I ever realized the 1N23A/E/R versions were silicon?
They aged so poorly, were easily destroyed by reverse leakage
measurements using ohm meters with 9vdc open circuit voltage
and required a different I.F. impedance than the schottky stuff.
Their noise figure was poor although a really old radar would
perk up with careful adjustments of L.O. injection using the newer
1N23E version or I forget 1N216 or something like that was
a newer 'direct replacement' although you really did have to tweak
to get the best performance!!

[TimFox]

If the 1N21/23 silicon diodes weren’t well sealed, I assume the point contact junction would age ungracefully, or be easy to disturb mechanically.  The 1N34 germanium diodes are also point contact, but sealed in glass.

[David Hess]

In the Theremin they can be in a detector circuit and the schottky diodes may have
a different transfer function which will effect the performance.

If the transfer function is so critical, then it should have been temperature compensated, typically using a second diode, in which case changing the diode type would make no difference.

[mag_therm]

According to wiki, some of the original Thermin modulated the filament current (!) of a diode to control its transconductance and hence volume.
It is interesting to compare the thermionic diode with the semiconductor diode.
The thermionic diode starts to conduct at +0 volt, but in the high current end is suffering from plate resistance.
I converted the am detector of a shortwave radio to full-wave, and it is using 1n4148 s in parallel with 6AV6.

I doubt that it changes the original 6AV6 much, but on the 'scope, the recovered audio has a bit higher level due to the clamping of the 1n4148.

[Haenk]

Completely Off Topic, but Theremin is quite a name in that business that shall not be named:

https://en.wikipedia.org/wiki/The_Thing_(listening_device)

[TimFox]

So, to summarize:
1.  The OP has reason to suspect one or more 1N34A diodes in his theremin.
2.  Several posters have found 1N34As for sale.
3.  The OP is reluctant to replace his 1N34As with "obsolete parts", such as 1N34As.
4.  Several posters have suggested Schottky diodes with similar I-V curves.
5.  The OP seems uninterested, but suggested he is interested in SMT devices.
6.  There are no germanium diodes in SMT, but Schottky diodes are available in SMT.

[tkamiya]

I have some comments but they are stupid so I will withhold it, because OP said so.