Nostalgia thread, have you used selenium rectifiers? - Page 1
Forum section: electronics / general

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 11, 2018, 10:31:37 pm
content: My first electronic project that worked, a small audio amplifier, I used a scavenged selenium rectifier.I also repaired a couple of radios that used them.On one instance, one blew up and the smoke was nasty.I later learned that these rectifiers were highly poisonous.Did you ever came across one?

author: bd139
author_rank: Super Contributor
timestamp: October 11, 2018, 10:38:41 pm
content: Yes came across a few of these over the years. When I was a lot younger I used to buy old valve/tube radios from jumble sales and try and fix them. A lot of the time they had selnium stick and finned rectifiers and they would go woosh within a few seconds of power up, usually when the filter caps had gone short! I will NEVER forget that smell. Once was enough so further experiments were down outside. Still alive 35 years later after that oneRecently I came across them restoring some old Heathkit stuff. They were removed without power being applied. You can replace them with a 1n4004 usually and a series resistor. The selenium rectifiers have a large voltage drop compared to silicon diode so if you stick a resistor in there and see what happens to the output voltage on the filter cap. Usually around 220 ohms to 3.3k is required depending on current draw of the device.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: October 12, 2018, 01:17:18 am
content: I've found a few over the years. When I was young and poor I salvaged them from equipment I was scavenging, but I never got around to using any in projects. Might still have a couple buried in tubs somewhere. I have been lucky and haven't let the smoke out of one. Don't know anyone who has died from it, or even had directly related health problems, but the warnings about them are certainly dire.

author: lordvader88
author_rank: Frequent Contributor
timestamp: October 12, 2018, 04:19:13 am
content: They are on some tubes raido's I have. Once I figured out they were diodes I read about the danger? But I don't remember.I want to leave them there for the vintage look, but snip their leads and put a diode behind them. But iirc they dropped a big big voltage, like 20-30V in my radios. I haven't touched those since, that was last year. Another project to research and finish now that I have an isolation transformer.

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 12, 2018, 05:02:16 am
content: I know where I can get some NOS in Akihabara, but I certainly won't touch them.Silicon and a resistor is much safer and more reliable.

author: German_EE
author_rank: Super Contributor
timestamp: October 12, 2018, 06:38:51 am
content: I don't see the risk, selenium is in anti-dandruff shampoo so I rub some into my scalp every morning.

author: ivaylo
author_rank: Frequent Contributor
timestamp: October 12, 2018, 06:41:39 am
content: The first PSU I built had one of these as rectifier (the aluminum pack on top):It coul take abuse, I remember (over voltage, over current), but would also deteriorate performance with age relatively quick.

author: bd139
author_rank: Super Contributor
timestamp: October 12, 2018, 06:55:46 am
content: Quote from: German_EE on October 12, 2018, 06:38:51 amI think ingestion and inhalation are the main risk vectors.

author: G7PSK
author_rank: Super Contributor
timestamp: October 12, 2018, 07:29:58 am
content: I have used quite few over the years as well as copper oxide rectifiers. Many years ago I had a big three phase selenium rectifier that came out of a cinema when it was up graded, it was the size of a large suitcase and supplied power to the projector arc lamps. I used that in a large battery charger I built when I was 15 or so.

author: jancumps
author_rank: Unknown
timestamp: October 12, 2018, 08:11:41 am
content: the mains powered speed regulator of my Jouef model trains used a selenium rectifier. and the variable voltage was tapped of the transfo wires with a swiper. The enamel of the wire was removed in the swiper’s path.https://youtu.be/UlXyv5vL0Ic

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 12, 2018, 01:14:18 pm
content: Indeed, they had a large forward voltage drop.And their reverse leakage current, as one approached breakdown voltage, was also very large.I would love to have one just to see their V/I curve

author: GK
author_rank: Super Contributor
timestamp: October 12, 2018, 02:47:36 pm
content: https://www.eevblog.com/forum/repair/hv-psu-resto-metal-rectifiers/

author: Martin.M
author_rank: Frequent Contributor
timestamp: October 12, 2018, 03:02:48 pm
content: nice, with 575 : option 122 (400V) ?Martin

author: floobydust
author_rank: Super Contributor
timestamp: October 12, 2018, 07:18:44 pm
content: Selenium rectifiers are very hard to replace because their Vf is high with soft slope. Every car battery charger, power supply etc. I've swapped out to silicon gives way too much voltage afterwards.Any Spice model would be nice, maybe we could make one from the Tek 575 curves and # stacks...As a kid I bought $0.50 US military surplus selenium rectifier bridge, it was in a soup can filled with PCB oil. It worked but kept getting hotter and hotter until the can leaked. That was 25VAC and maybe 1A on my bench PSU.There was a huge report 1957 on the USAF using selenium rectifiers on aircraft, if poisonous smoke etc. in B-52's.Selenium is in dandruff shampoos to kill scalp fungus, probably not great stuff if smoking...

author: Astrodev
author_rank: Regular Contributor
timestamp: October 12, 2018, 08:38:33 pm
content: Yes I have also still got some of these in a box and I remember the smoke on one occasion, fortunately it was in a well ventilated area but it still took about a week for the smell to die down.

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 14, 2018, 12:15:59 am
content: Quote from: GK on October 12, 2018, 02:47:36 pmJeeezI am green with envy!

author: @rt
author_rank: Super Contributor
timestamp: October 14, 2018, 02:30:43 am
content: I’ve still got a few that were taken out of radio gear where they were replaced.I guess I kept them just for collection.My radio club has massive ones that are part of their first repeater.I guess they kept the old 6m repeater just for collection

author: SeanB
author_rank: Super Contributor
timestamp: October 14, 2018, 10:06:59 am
content: I still have some NOS ones around somewhere, and kept the one in the 1950's battery charger I got from dad till I decided to upgrade it to include charge termination. Then replaced with a near similar size silicon bridge rectifier dating from the 1970's, and kept the current limiting resistor inside it as well. GE made unit, and could do 2V, 6v and 12V battery packs at up to 6A. Just modified to 12V only ( still can do lower, but no charge termination then on 6V) and added as well reverse voltage protection, with a SCR charge limiter. Also added a light for the meter, using a 12V festoon lamp behind the meter, run on the 8VAC winding off the transformer.

author: Martin.M
author_rank: Frequent Contributor
timestamp: October 14, 2018, 10:14:29 am
content: Pikoskop used that, the little scope from eastern germany.

author: Cubdriver
author_rank: Unknown
timestamp: October 15, 2018, 06:46:54 am
content: The ancient Electro Instruments DVM in my repair queue has some:I also grabbed some little NOS bright orange ones at a surplus place a while back to use as techie-geek Christmas tree ornaments.-Pat

author: coppercone2
author_rank: Super Contributor
timestamp: October 16, 2018, 01:10:45 pm
content: are there small signal possibilities with selenium diode or rectifier in use with analog circuits in modern engineering?

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 16, 2018, 01:21:12 pm
content: I don't think so.As others have mentioned, the forward voltage drop is several times that of a plain silicon diode, and the reverse leakage current also is not comparable to modern devices.My guess is that they would also exhibit a ton of stray capacitance.

author: coppercone2
author_rank: Super Contributor
timestamp: October 16, 2018, 01:25:48 pm
content: I wonder if that can all be exploited to make some kind of do-dad though. Not necessarily precise or fast, but maybe low power or minimum parts count. Like a JFET current sink (I don't actually mean a current sink but the same spirit of circuit).

author: calexanian
author_rank: Super Contributor
timestamp: October 16, 2018, 06:12:51 pm
content: There are a number of big ole ones in my friends storage pulled from old power supplies. You know when they blow! also as i recall my Honda CT70 had one off the coil for charging the 6 volt battery. I pulled it out and replaced it with a 6A4 diode and never looked back.

author: floobydust
author_rank: Super Contributor
timestamp: October 17, 2018, 06:51:24 pm
content: They had one advantage over silicon diodes, the reverse surge-withstand.I think selenium-rectifier diode construction resembles MOV's, so exceeding their PIV was not harmful. It's not avalanche conduction.I remember this from old cathodic protection power supplies. (ground) lighting strikes did not generally blow them up but silicon diodes would die and needed added transient protection. Cathodic protection is low voltage high current, 2-70V 5-50A and the industry was a large user of selenium rectifiers.