germanium diode sub - Page 1
Forum section: electronics / projects

author: m3vuv
author_rank: Super Contributor
timestamp: November 11, 2021, 01:50:51 am
content: Hi all i have an old bradley ct471c multimeter that i am trying to fix,i found a pa47 germanium dione cracked,will a 1n5711 work as a sub,its a shottky

author: CaptDon
author_rank: Super Contributor
timestamp: November 11, 2021, 02:02:28 am
content: I think the scaling may be a bit weird, such as reading a bit low at the low end of the scale while at the same time perhaps reading a bit higher than expected at the high end. Can you tell by the markings/schematics/color bands what the original diode number was? 1N34A (orange stripe / yellow stripe perhaps)? You can still find germaniums with all of their built in hateful characteristics (leakage, aging, easy to destroy with to much PRV, etc). I still service radars with 1N23E and 1N23ER diodes and they are still made. Radars of that vintage went to Hot Carrier and Shottky and the next generation went to an all inclusive MMIC Fet preamp, local oscillator, balanced mixer and I.F. amplifier in one die cast aluminum housing ready to bolt on.

author: m3vuv
author_rank: Super Contributor
timestamp: November 11, 2021, 02:29:48 am
content: sorry i had a typo,it was a mallard 0a 47 not pa.it was a white glass tube with black lettering.

author: m3vuv
author_rank: Super Contributor
timestamp: November 11, 2021, 03:03:30 am
content: coz i am a tight ass and i want to use what i have in my junkbox,at least to prove it is repairable,if i manage to get it halfway working then i will but one.!

author: Kleinstein
author_rank: Super Contributor
timestamp: November 11, 2021, 08:02:47 am
content: It depends a bit where the diode is used. The 1N5711 looks like a reasonable replacement at the rectifier. However the maximum current is a bit lower. A slightly larger schottky diode (e.g. BAT47, BAT54 or similar) may be betters.If used in the rectifier, the AC ranges may be a bit off. There is also a chance that another diode is bad too - in rectifiers they tend to fail together.

author: silverback
author_rank: Contributor
timestamp: November 11, 2021, 09:39:16 am
content: There are 10 to 12 OA47's used in CT471. It all depends on where it's used.

author: m3vuv
author_rank: Super Contributor
timestamp: November 11, 2021, 11:04:18 am
content: its mr 6 on the psu pcb if that helps?

author: Renate
author_rank: Super Contributor
timestamp: November 11, 2021, 04:18:55 pm
content: Quote from: edavid on November 11, 2021, 03:40:29 pmHow about a 5U4GB?

author: TimFox
author_rank: Super Contributor
timestamp: November 11, 2021, 04:47:48 pm
content: Quote from: Renate on November 11, 2021, 04:18:55 pmNope--that's a dual diode.

author: Gyro
author_rank: Super Contributor
timestamp: November 11, 2021, 05:34:54 pm
content: Quote from: TimFox on November 11, 2021, 04:47:48 pmTry an EY87.

author: TimFox
author_rank: Super Contributor
timestamp: November 11, 2021, 05:52:23 pm
content: Quote from: Gyro on November 11, 2021, 05:34:54 pmFor those who abhor vacuum, try a 3B28.

author: Renate
author_rank: Super Contributor
timestamp: November 12, 2021, 03:03:10 am
content: I actually started out working on amplifiers with 5U4GB's. Something that I never really took note of before, the filament takes 3 Amperes. That's 15 Watts down the drain just for the filament of the rectifier!My latest project has been Bluetooth modules that can run for a few years on a 2032 coin cell. That's quite a difference!

author: james_s
author_rank: Super Contributor
timestamp: November 12, 2021, 03:17:42 am
content: Nobody ever claimed vacuum tubes were power efficient, they sure are neat though, and electricity was cheap back then. It's easy to forget that back in the days of incandescent lighting you could easily have 1kW or more just lighting a single medium sized room.

author: floobydust
author_rank: Super Contributor
timestamp: November 12, 2021, 03:55:11 am
content: OP, MR6,7 are the voltage-doubler for the 20V regulator, so1N5711would not work with only a 15mA rating, I think.1N5819would be better.http://www.vmarsmanuals.co.uk/archive/1248_CT-471_Multimeter.pdfhttps://vintage-radio.net/forum/attachment.php?s=ebf9c2a7a22b300a29e860d057ada1f7&attachmentid=62872&d=1329819727I used866Arectifiers a long time ago because they were on sale for $0.50 each at the Army Surplus store. Only 12.5W filament. But so much RFI with sloowwww recovery time of mercury vapor. Once I saw a drive-in movie power amp use them in a bridge rectifier, I saw the guy replacing one middle of the movie.

author: gbaddeley
author_rank: Regular Contributor
timestamp: November 14, 2021, 12:11:32 pm
content: MR = Metal RectifierDoes anyone remember stacked Copper Oxide diodes and Selenium diodes? Still in use in 1960’s in the likes of multimeters (little ones) and high power battery chargers (really big ones). I still have some.

author: Gyro
author_rank: Super Contributor
timestamp: November 14, 2021, 01:13:52 pm
content: Oh yes. I still have some little ones around. The reliable method of telling them apart (apart from reverse rating and forward voltage) was the stink when they blew. Curiously, the MR designation on schematics outlasted their actual use by many years (decades?) in some companies.