I'm restoring a Stromberg Carlson TV from 1954 and it has a 1N64 crystal diode as a video detector.
What is the best modern replacement for this part ?

Thanks.

I'm also interested in what people are finding best for this. So far, I have best luck using glass germanium diodes recovered from 1960s and 70s radios. But my supply of those is pretty limited. Would very much like to find a modern replacement that really works well. NTE may sell some actual germanium diodes.

It's a germanium diode, not silicon like the all so popular 1N914 diodes of late. I believe you can likely get a germanium diode at a RA..R.RRR..RA Radio Shack. There, I said it. Most likely will be a 1N34 but it should work. I've seen either listed in old schematics.

You can also find 1N34A germanium diodes at http://www.tubesandmore.com/ .

Phil Nelson

I wonder if those are NOS ancient things (which might not be the best choice) or some "relatively" modern glass-cased diodes? Only 13 in stock suggests maybe NOS.

I have a bunch of NOS ceramic-cased ones, but I don't really trust them to hold up.

I usually just use modern 1N34A germanium diodes. They are widely available and seem to work fine, at least I have not had trouble.

http://www.mouser.com/Search/Refine.aspx?Keyword=1n34a

-Matthew

Those are NTE. NTE seems to sell quite a bit of actual NOS stuff they have had stashed in warehouses for decades. Good to see they are easily available. Will also check Radio Shack.

I read last year a suggestion-- To parallel a newer replacement diode with a resistor, as the germanium diodes were "lossy". Newer diodes perform too well.

i packed up most of the library, but I will try to find it again. Sorry, but i can't reopen all the packed boxes. Many aren't even here with me in the apartment, but stacked in storage. But I will try to find it, so I can give you the source. I am sure it wasn't in the Coyne Applied Practical Radio Television books. But to now try to remember where I DID see it. Arg!

In the "New Shortcuts to TV Servicing" books, which were part of the RTTA course sponsored by Sylvania {1958}, Leonard Lane stated that good Germanium diodes have a 1 to 1000 ratio minimum, front to back. So for example, 50 ohms forward resistance, 50k or better backwards. A "good" diode had a forward resistance of 50 to 100 ohms.

Lane even states that rather than spend the time checking a diode, to just replace it, as a poor diode can cause so many issues. Like good sound + no video. Or AGC problems up the whazoo. Many more. He suggested that there could be so many symptoms, all different, that it wasn't worth the downtime looking and probing to see if it was bad. I got the feeling that even in the same model set, different sets could give different symptoms. He also went on to say that many diodes degrade over time. I wonder if he was inferring that if you just swap in a new one, that it will prevent a service call in the future, even if it isn't the immediate fault.

I don't have a set to try this in, the idea of parallel diode and resistor. And new diodes wouldn't have a forward resistance of 50 ohms, either. But it would be interesting to see. Food for thought.

John S.

I have never seen a detector circuit where leakage would improve the operation of the circuit. Perhaps someone could do some tests, but I really do not believe that a parallel resistor could ever help anything.

There is one very large difference between germanium and silicon diodes. A point contact germanium diode will start conducting when the forward voltage reaches about 0.2 volts. A silicon diode will not start to conduct until the forward voltage is around 0.6 to 0.7 volts. Depending on how much signal there is coming out of the IF strip, that 0.6 volt loss could be significant. Also, a point contact diode is able to turn on and off very fast. Silicon diodes are almost always junction diodes, some of which can be quite slow.

Might be a good idea to try a modern schottky diode.

DigiKey and West Florida Components carry the 1N6263 at 50 cents and 18 cents each.
DigiKey also stocks the 1N5711 at 50 cents.

about 350mv forward drop.

Corby

1n60p Schottky works very well. Should last forever unlike all the ge diodes that are going bad from age.

Cool
I did not know about the 1N60P!
Are they as easy to find as the ones at DigiKey?

Corby

Interesting! Searching on the web, you can find places that claim a 1N60/1N60P is a point contact Ge diode (for example here: http://www.taitroncomponents.com/catalo ... t/1N60.pdf ) and other places that call it a Schottky diode.

I would be interested in hearing peoples' opinions of how well they work, and whether to purchase the ones claiming to be Ge vs. Schottky? Maybe they're really all the same and it doesn't matter.

Hmm... A Schottky diode is a diode that uses a metal to semiconductor junction instead of a semiconductor to semiconductor junction. And a point contact diode is a metal to semiconductor junction. As I understand it, a Schottky diode does not use a cats-whisker for the contact but instead has the metal plated on. I suppose that it is possible to make a point contact diode with a plated on contact instead of a cats-whisker contact. Perhaps both descriptions are correct.

I got them off ebay. I could drop one in the mail to you if you like.

Thanks for all the advice and information. I had been away from this hobby for about 10 years as I concentrated all my spare time on my son and the Boy Scouts. I just found a stash of 1N34A's in a parts drawer that I must have bought a long time ago. Back in 1997, I had restored a GE locomotive tv and had to replace some diodes. I just couldn't remember what I had used then.
Thanks again for all the advice.

By the way, I finished restoring the Stromberg Carlson and it works great with the 1N34A.