Do germanium transistors need to be "reformed"?I've re - Page 1
Forum section: electronics / projects

author: Peabody
author_rank: Super Contributor
timestamp: September 30, 2020, 05:37:18 am
content: I've received some new old stock 2SB324 germanium PNP transistors which I will use in trying to fix old Vivitar speedlight flashes.On testing, they seem pretty awful, with gain of around 7.5. But after installing two of them and restarting, I got no charging whine, and the transistors got quite hot. After removing them, they then tested much better, with high gain and low leakage current.So I just wondered if old germanium transistors need to be reformed in some way after not being used for decades.

author: bob91343
author_rank: Super Contributor
timestamp: September 30, 2020, 05:46:33 am
content: There is no cookbook answer to your question. Back in the day, manufacturing techniques were spotty. Competition was hot and everyone tried to upstage the others. There were so many types, and many were little more than garbage.So you just don't know. If a particular treatment works for a particular transistor, great. No idea if it will work for the next one. The company that made it, when they made it, how many they made, are all factors that can't be put into an equation.

author: srb1954
author_rank: Super Contributor
timestamp: September 30, 2020, 05:54:08 am
content: Quote from: Peabody on September 30, 2020, 05:37:18 amSome old transistors were known to develop tin whiskers internally which might partially short a junction lowering the gain or causing excessive leakage currents.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 30, 2020, 09:25:57 am
content: When emitter and collector are swapped the transistors also show a low gain and more leakage. A gain of 7.5 sound realistic for reverse operation. However the performance can also scatter a lot.In general there is the tendency of the GE transistor to age with increasing gain, but usually also more leakage. So heating the transistors for some time may actually increase the gain.An decreased leakage would more point to the tin wisker problem.

author: exe
author_rank: Unknown
timestamp: September 30, 2020, 10:10:23 am
content: Hm, I have a germanium transistor that my component tester cannot detect. I wonder if it's the same problem. I'll try to measure it's beta tonight...

author: Peabody
author_rank: Super Contributor
timestamp: September 30, 2020, 02:37:07 pm
content: Attached is the circuit I tested with, except I changed the base resistor to 47K. One transistor measured .56V at the collector when turned on. That was before the warmup. After, I get 3.2V at the collector. So the gain has changed a lot. But the leakage current has also increased - from about 115mV with the base open, to 225mV.I'd like to switch to silicon transistors, but don't know what else I'd have to change. This is one of those transformer-based multiplier circuits where the base is controlled by a tap on the primary I think. But I don't have a schematic. I think the problem with switching might be that the flash operates on two NIMH AAs, so the lower EB drop of GE may actually make a difference. The flash uses two ganged 2SB324s. I don't know what silicon PNP I would try.Of course the alternative is to toss these Vivitars as they fail, and replace them with Neewer manual flashes at $34 each. The Vivitars have worked well, but they are 35 years old, so maybe it's just time to retire them.

author: Cerebus
author_rank: Super Contributor
timestamp: September 30, 2020, 03:10:24 pm
content: Quote from: exe on September 30, 2020, 10:10:23 amOr the designer of the component tester didn't even take into consideration that someone might stuff a germanium transistor in there. I have to confess that if I was designing one I probably wouldn't, and my design would probably only detect germanium diodes by sheer chance because it would be set up to detect silicon schottky diodes.

author: magic
author_rank: Super Contributor
timestamp: September 30, 2020, 08:01:38 pm
content: It should detect a dual Schottky, though

author: floobydust
author_rank: Super Contributor
timestamp: September 30, 2020, 08:21:26 pm
content: I would just drop in a single modern silicon PNP part and bet it will work fine, compared to the two paralleled 2SB324's.From this thread here:https://www.eevblog.com/forum/repair/repair-vivitar-3500-speedlight/"I would use KSB1366G, KSA1010Y have higher gain 100-320 or D45H11 (80) and bend the B-C-E pinout to fit pcb holes. I'm not sure how a TIP32C would do, likely would work."The Neewer is surely cheap as borsch with a tiny flash capacitor and thus weak light output, compared to old Vivitars.The only danger or hassle is the shoe voltage might not be for modern cameras with low voltage drive. Some shoes are for old shutter-switches.Whisker shorts in germanium transistors to the case, people are zapping to clear them. Did you check the resistance to the case? I just find germanium transistors do not age well at all.

author: Circlotron
author_rank: Super Contributor
timestamp: September 30, 2020, 09:22:12 pm
content: That test circuit is going to draw a LOT of current from the 3.3V rail when the switch is closed...

author: Peabody
author_rank: Super Contributor
timestamp: September 30, 2020, 10:31:13 pm
content: Quote from: Circlotron on September 30, 2020, 09:22:12 pmLOL. Yes, I drew it wrong, didn't I. But fortunately, the fault is only in the drawing.

author: Peabody
author_rank: Super Contributor
timestamp: September 30, 2020, 10:47:21 pm
content: Quote from: floobydust on September 30, 2020, 08:21:26 pmIn reverse order:Can you tell me how to go about zapping the whiskers or otherwise reforming the germanium transistors? I don't have any leakage to any of the cases, but something is going on inside, and I'd like to try to bring them back to a normal state if I can.The Neewer flashes run on 4 AAs. My Vivitars run on two. And the flash capacitor on the Vivitars is 380uF. It's hard to believe the Neewers would put out less light than the Vivitars. And the only thing it would have to work with is a Cowboy Studios wireless receiver.That other thread is mine too. I'll probably post in that one about how to convert to silicon. I finally have a drawing of the charging circuit.

author: floobydust
author_rank: Super Contributor
timestamp: September 30, 2020, 11:26:47 pm
content: Vintage germanium transistors are very popular for guitar effects pedals. Just use a low voltage applied only between the case and all the three leads tied together. Even a 9V battery works. Some people apply it between junctions (with correct polarity to keep junction off) if they test shorted, because you have nothing to lose anyway.NASA x-rays and good failure investigation of Ge transistor tin whiskers:https://nepp.nasa.gov/whisker/anecdote/af114-transistor/2005-Brusse-tin-whiskers-AF114-transistors.pdfIt looks a bit hairy inside.

author: Peabody
author_rank: Super Contributor
timestamp: September 30, 2020, 11:39:14 pm
content: Quote from: floobydust on September 30, 2020, 11:26:47 pmI don't understand. I don't detect any conductivity between the case and any of the leads. So how would this method do anything?

author: floobydust
author_rank: Super Contributor
timestamp: October 01, 2020, 12:01:20 am
content: The only "reforming" I know of is just clearing tin whiskers (blowing it as a fuse) which show up as short-circuits to the case or between junctions or both, in old Ge transistors.Six ohmmeter readings. If your transistor has no shorts and just really low hFE=8 then I would say it's faded due to old age, and not whiskers- or your tester might never have seen germanium before. My 328 component tester gives the wrong VF around 600mV (instead of 180-200mV) for a bunch of 2SB56's I have lying around, reporting hFE from 130-530. Another 328 tester is convinced the Ge transistors are diodes.

author: Peabody
author_rank: Super Contributor
timestamp: October 03, 2020, 05:12:25 pm
content: I went back to test the 2SB324 transistors again. I think I was doing it wrong, or had the transistors backwards, or something. Anyway, I actually measured the current. With a 5V supply, a 10K base resistor, and 20R collector resistor, a typical reading is base current of 0.48mA and collector current of 115mA, which appears to be a gain of 235. But of the new transistors, only one had no EC leakage current with the base either NC or tied high. All the others were in the tens of millamps. But I still have no conduction from any lead to the case.Is there any way to reverse the leakage deterioration, or is this just inevitable with Ge transistors?Attached is all I can find about the 2SB324 (also marked "ST" after that, which I think is the gain class). What would be a good single TO220 PNP transistor to replace the two ganged 2SB324s? The KSB1366G and KSA1010Y previously recommended are not stocked by Digikey. Also attached is the oscillator circuit.

author: mag_therm
author_rank: Frequent Contributor
timestamp: October 03, 2020, 05:33:41 pm
content: The two old parallel transistors are each rated Ic = 1000mA.Could you shoe horn a TO220 case in there?I have some old Pentax flashes, very difficult to work on.A TIP32C is rated Ic cont = 3 Amp,hfe is about 80 at 1 Amp

author: Peabody
author_rank: Super Contributor
timestamp: October 03, 2020, 07:11:02 pm
content: Yes, I think I can make a TO220 fit, but without any additional heatsink. What about this one:https://www.digikey.com/en/products/detail/on-semiconductor/KSB1366GTU/1052866]https://www.digikey.com/en/products/detail/on-semiconductor/KSB1366GTU/1052866The gain would be more like the original transistors, so maybe the base bias resistor would still work.

author: mag_therm
author_rank: Frequent Contributor
timestamp: October 03, 2020, 10:09:09 pm
content: Yes, 1366 looks OK to try.The Vce sat is around 200mV at 1.5 AmpThe hfe is about 50 at 1.5 AmpThe design would have had a forced gain low enough to start with a cold battery near end of life.(meaning feed back tap gives high enough current to the base.)The Ge transistor has a lower vbe which gives a bit more base current than the Si replacements will have.When you test it you could start with new alkaline batteries as they have higher terminal voltage.

author: Peabody
author_rank: Super Contributor
timestamp: October 04, 2020, 04:19:27 am
content: On measuring again, I don't think a TO220 will fit. It's too tall, and there's no room to lay it down. What about this one:https://www.digikey.com/en/products/detail/on-semiconductor/2SA1593T-E/3536037This is the high-gain version of this transistor. It's only 2A continuous, and 1W versus 2W for the TO220, but once the big cap is charged, this circuit doesn't do much.

author: mag_therm
author_rank: Frequent Contributor
timestamp: October 04, 2020, 04:05:53 pm
content: Yes, Maybe the higher gain will make up a bit for the increased Vbe(sat)Hopefully you will find one that works without changing any other components.One time I re- did an old '63 Sansui early transistor stereo amp that had aged to awful hiss in both channnels.I changed all the Ge to Si pnp, and bias came up good without changing any bias resistors.Cured the hiss too!

author: Labrat101
author_rank: Unknown
timestamp: October 04, 2020, 06:16:54 pm
content: Hi,Only way I know to check the old tin germanium transistors is with a Transistor Tracer .I know that the old AF116 transistors would just die . They use say it was due tobreakdown of the chemical structure . True or false would not know .(more probably bad tech)But the jelly stuff inside was either white or yellowish like Vaseline,The white stuff dried out and became hard giving poor heat transfer.I have a few old transistors in a box somewhere, new from the early 50s .If I could remember were . I could check in my tracer.They are still making germanium transistors in To-92 cases . Maybe a better option.I think like any electronic component will have a shelf life . Germanium may well decay over40yrs or drift from its original specsQuoteBut in those days they were state of art . If we needed a computer it was a Slide ruler & fingers .