1N34a equivalent replacement - Page 1
Forum section: electronics / projects

author: 460voltclub
author_rank: Contributor
timestamp: November 02, 2020, 08:07:04 pm
content: 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.

author: Benta
author_rank: Super Contributor
timestamp: November 02, 2020, 08:32:03 pm
content: 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.

author: 460voltclub
author_rank: Contributor
timestamp: November 02, 2020, 08:47:59 pm
content: 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.

author: TimFox
author_rank: Super Contributor
timestamp: November 02, 2020, 09:19:35 pm
content: Probably the more important spec (which is consistent with the one you quote) is Vf< 1 V at If= 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:Vf< 1 V at 15 mA, < 0.41 V at 1 mA.

author: bdunham7
author_rank: Super Contributor
timestamp: November 02, 2020, 09:32:27 pm
content: https://www.allelectronics.com/item/1n34a/1n34a-germanium-diode/1.html

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: November 02, 2020, 09:40:49 pm
content: 1N60, 1N290, 1N295, 1S188https://www.ebay.com/itm/20pcs-1N34A-Germanium-Diode-DO-35-1x-1N34-US-SELLER-FREE-SHIPPING/133530100291?hash=item1f1703a243:g:zx8AAOSwdjZfb185https://www.tubesandmore.com/products/diode-1n34a-germanium-low-leakage

author: tggzzz
author_rank: Super Contributor
timestamp: November 02, 2020, 11:17:20 pm
content: Why do you want an eqivalent? Won't a 1n34A be OK for your purposes?https://octopart.com/search?q=1n34a

author: David Hess
author_rank: Super Contributor
timestamp: November 03, 2020, 01:17:08 am
content: Quote from: Quarlo Klobrigney on November 02, 2020, 09:40:49 pmAnd 1N270s if you can find them.But a small signal schottky diode is what I would try first.

author: 460voltclub
author_rank: Contributor
timestamp: November 03, 2020, 02:43:51 am
content: 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.

author: TimFox
author_rank: Super Contributor
timestamp: November 03, 2020, 03:48:28 am
content: Quote from: 460voltclub on November 03, 2020, 02:43:51 amSo, try the 1N5711 or its SMD equivalent.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 03, 2020, 12:41:27 pm
content: 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

author: Vovk_Z
author_rank: Super Contributor
timestamp: November 03, 2020, 01:01:59 pm
content: How about BAT54, BAT41 (small signal Shottky diodes)? Or BAV99?

author: CaptDon
author_rank: Super Contributor
timestamp: November 04, 2020, 07:16:49 pm
content: 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 havea different transfer function which will effect the performance. The schottky stuffdoesn't work well in military and marine radar units designed for the old germanium1N23A/E/R or 1N21A devices.

author: rsjsouza
author_rank: Super Contributor
timestamp: November 04, 2020, 07:25:01 pm
content: Quote from: akimpowerscr on November 03, 2020, 12:41:27 pmOne of my solder techniques was to havethis heat sink clamptied to the device's leads while soldering. It practically eliminates the thermal stress on the junction.

author: TimFox
author_rank: Super Contributor
timestamp: November 04, 2020, 07:40:21 pm
content: Quote from: CaptDon on November 04, 2020, 07:16:49 pmThe 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.

author: CaptDon
author_rank: Super Contributor
timestamp: November 04, 2020, 09:54:21 pm
content: Don't think I ever realized the 1N23A/E/R versions were silicon?They aged so poorly, were easily destroyed by reverse leakagemeasurements using ohm meters with 9vdc open circuit voltageand required a different I.F. impedance than the schottky stuff.Their noise figure was poor although a really old radar wouldperk up with careful adjustments of L.O. injection using the newer1N23E version or I forget 1N216 or something like that wasa newer 'direct replacement' although you really did have to tweakto get the best performance!!

author: TimFox
author_rank: Super Contributor
timestamp: November 04, 2020, 10:24:19 pm
content: 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.

author: David Hess
author_rank: Super Contributor
timestamp: November 04, 2020, 10:50:30 pm
content: Quote from: CaptDon on November 04, 2020, 07:16:49 pmIf 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.

author: mag_therm
author_rank: Frequent Contributor
timestamp: November 05, 2020, 12:10:26 am
content: 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.

author: Haenk
author_rank: Super Contributor
timestamp: November 05, 2020, 02:01:25 pm
content: 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)

author: TimFox
author_rank: Super Contributor
timestamp: November 05, 2020, 02:38:23 pm
content: 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.

author: tkamiya
author_rank: Super Contributor
timestamp: November 06, 2020, 02:20:54 am
content: I have some comments but they are stupid so I will withhold it, because OP said so.