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DIY Stompboxes => Building your own stompbox => Topic started by: Yazoo on November 23, 2020, 11:43:33 AM

Title: 2n3906 transistors from Tayda
Post by: Yazoo on November 23, 2020, 11:43:33 AM
I've just received an order from Tayda, including 2n3906 transistors. Before I soldered them to the pcb, I tested them with one of those little multi-function testers. They all tested as PNP with a fairly consistent hfe of 420-430. I already had some other 2N3906s in stock and they tested in the low to mid 100s, which is what I have seen in the past. I am suspicious of the Tayda 2n3906s. What do you think?
Title: Re: 2n3906 transistors from Tayda
Post by: iainpunk on November 23, 2020, 12:00:36 PM
on the trannies themselves, are they labeled 2n3906 A, B or C?, because that is a gain-indicator, the A ones are the low gain ones and the C are the high gain ones, and B is the middle of the road.

cheers, Iain
Title: Re: 2n3906 transistors from Tayda
Post by: GGBB on November 23, 2020, 12:02:14 PM
Depending on which manufacturer, the 2n3906's upper limit for hFE is 400, so 420-430 measured on a DMM might be within spec. Check the manufacturer-specific data sheet and compare to your results and to your DMM manual's specification for voltage and current used when measuring hFE.
Title: Re: 2n3906 transistors from Tayda
Post by: Yazoo on November 23, 2020, 05:39:16 PM
Thanks for the replies. I checked and they are the B version. The reason for querying them is, while Tayda is generally good, I have had bad transistors from them before, 2N5457s which were out of spec.
Title: Re: 2n3906 transistors from Tayda
Post by: iainpunk on November 23, 2020, 05:44:49 PM
what kind of DMM did you use? some can be pretty inaccurate.

in my experience, Hfe doesn't matter to much if its not a fuzz or power amp.

cheers, Iain
Title: Re: 2n3906 transistors from Tayda
Post by: Yazoo on November 23, 2020, 06:19:30 PM
I used one of these little multi-testers. It is very useful and generally pretty accurate.
(https://i.postimg.cc/w7LP9NJc/D17009-D8-7-D25-4913-9-E11-0129-ED4-E4-DF6.jpg) (https://postimg.cc/w7LP9NJc)

It was more about if the hfe is wrong, then maybe itís a fake. Iíve ordered some more and I will check these out when they arrive.
Title: Re: 2n3906 transistors from Tayda
Post by: GGBB on November 23, 2020, 06:23:40 PM
I used one of these little multi-testers. It is very useful and generally pretty accurate.
(https://i.postimg.cc/w7LP9NJc/D17009-D8-7-D25-4913-9-E11-0129-ED4-E4-DF6.jpg) (https://postimg.cc/w7LP9NJc)

It was more about if the hfe is wrong, then maybe itís a fake. Iíve ordered some more and I will check these out when they arrive.

Meter accuracy isn't the issue. The question is whether or not the meter measures the hFE using the same current and voltage as specified in the device datasheet.
Title: Re: 2n3906 transistors from Tayda
Post by: PRR on November 23, 2020, 07:03:59 PM
...meter measures the hFE using the same current and voltage as specified in the device datasheet.

Yeahbut... 2N3906 datasheet shows remarkable hFE flatness vs current. hFE is usually not very voltage sensitive, especially on today's devices.

I have a suspicion he has been sold 2N3906-like devices. Which will work well in 97% of 2N3906 applications (high hFE "should" not be a problem). Of course funky pedals may be the exception. But if you NEED beefsteak, don't be buying mystery-meat.
Title: Re: 2n3906 transistors from Tayda
Post by: Ben N on November 24, 2020, 06:11:09 AM
Not from Tayda, but I've gotten 2N3904/2N3906 in the past that were all over the map hfe-wise.
Title: Re: 2n3906 transistors from Tayda
Post by: dennism on November 24, 2020, 08:11:16 AM
I certainly don't have any scientific answers to the question, but out of curiousity I just checked some 2N3906 from Mouser that I got probably 15 years ago.   They measured 300 or so hfe using the same quick and dirty approach as the OP.   No A, B, or C suffix.

I know there is a lot of justified concern about faked transistors, particularly super rare and valuable things like germanium NKT213.   But, since Tayda sells 2N3906 for 2 cents each, how would there be any incentive to make or sell fake ones?
Title: Re: 2n3906 transistors from Tayda
Post by: duck_arse on November 24, 2020, 08:44:11 AM
can anyone here show me a photo of a 2N3906B, please? failing that, can anyone find me a 2N3906 datasheet that shows A, B and/or C suffixed parts?

I am curious, as I thort the 2Nxxxx suffix only indicated an improved device, whereas the Pro-Electron series parts can/are/do have [none]/A/B/C gradings.
Title: Re: 2n3906 transistors from Tayda
Post by: antonis on November 24, 2020, 10:13:00 AM
can anyone here show me a photo of a 2N3906B, please?

(https://i.imgur.com/ocEkY1d.jpg)

Of course, B (or Q or H) has nonthing to do with hFE classification.. :icon_wink:

Title: Re: 2n3906 transistors from Tayda
Post by: iainpunk on November 24, 2020, 02:57:27 PM
Quote
I am curious, as I thort the 2Nxxxx suffix only indicated an improved device, whereas the Pro-Electron series parts can/are/do have [none]/A/B/C gradings.
i thought the 2Nxxxx means 2 junctions, just like diodes having only one junction being labeled 1Nxxxx. and some mosfets, having 3 junctions, being labeled 3Nxx

Quote
Of course, B (or Q or H) has nonthing to do with hFE classification.. :icon_wink:
doesn't it? i was taught that the A/B/C suffix was a gain indicator with any transistor!?!

cheers
Title: Re: 2n3906 transistors from Tayda
Post by: antonis on November 24, 2020, 03:17:04 PM
Quote
Of course, B (or Q or H) has nonthing to do with hFE classification.. :icon_wink:
doesn't it? i was taught that the A/B/C suffix was a gain indicator with any transistor!?!

If so, what about H/Q suffix, like in my photo posted..??  :icon_biggrin:

I mean, one clould get misled from a batch of only B suffix..

As Stephen said, there are no A/B/C hFE gain classification suffixes for 2NXXX series BJTs..
Title: Re: 2n3906 transistors from Tayda
Post by: Marcos - Munky on November 24, 2020, 03:42:24 PM
Quote
Of course, B (or Q or H) has nonthing to do with hFE classification.. :icon_wink:
doesn't it? i was taught that the A/B/C suffix was a gain indicator with any transistor!?!
This is true if you're looking at a BCxxx transistor. A/B/C suffix designates the hfe, being A for the lowest values and C for the highest values.
Title: Re: 2n3906 transistors from Tayda
Post by: PRR on November 24, 2020, 10:56:00 PM
IIRC, when 2N devices had different specs, they got different numbers. Occasionally a suffix when an improved device was 100% back-compatible and also suited for bolder designs. 2N301/2N301A. 2N2219/2N2219A. 2N2222/2N2222A. These examples are (IIRC) 20% higher voltage rating, not gain.
Title: Re: 2n3906 transistors from Tayda
Post by: Rob Strand on November 24, 2020, 11:02:19 PM
Quote
IIRC, when 2N devices had different specs, they got different numbers. Occasionally a suffix when an improved device was 100% back-compatible and also suited for bolder designs. 2N301/2N301A. 2N2219/2N2219A. 2N2222/2N2222A. These examples are (IIRC) 20% higher voltage rating, not gain.
Yep.

The numbers extra numbers and letters on the 2N3904/2N3906's are likely to be manufacturing codes.   Plant numbers and stuff like that (not gain).


This datasheet shows some info,
https://www.onsemi.com/pub/Collateral/2N3906-D.PDF
Title: Re: 2n3906 transistors from Tayda
Post by: amptramp on November 25, 2020, 08:35:14 AM
Quote
IIRC, when 2N devices had different specs, they got different numbers. Occasionally a suffix when an improved device was 100% back-compatible and also suited for bolder designs. 2N301/2N301A. 2N2219/2N2219A. 2N2222/2N2222A. These examples are (IIRC) 20% higher voltage rating, not gain.
Yep.

The numbers extra numbers and letters on the 2N3904/2N3906's are likely to be manufacturing codes.   Plant numbers and stuff like that (not gain).


This datasheet shows some info,
https://www.onsemi.com/pub/Collateral/2N3906-D.PDF

Maybe the extra numbers are the best before date, like the one on a carton of milk.  For germanium, this might actually make sense.
Title: Re: 2n3906 transistors from Tayda
Post by: Yazoo on November 25, 2020, 05:28:24 PM
I received some more 2N3906s today and the gain is fairly consistent around 200. I am happy with these. I doubt I will use the Tayda ones.
Title: Re: 2n3906 transistors from Tayda
Post by: iainpunk on November 25, 2020, 06:50:21 PM
for 95% of all applications, the gain is set by the surrounding circuitry, hot the Hfe so i doubt that you will have problems with those sketchy ones. (if you want to lower the gain to be about 1/3rd, just swap the collector and emitter, my secret fuzz trick [doesn't work with most germanium's tho])

cheers, Iain
Title: Re: 2n3906 transistors from Tayda
Post by: Rob Strand on November 25, 2020, 07:13:41 PM
Quote
if you want to lower the gain to be about 1/3rd, just swap the collector and emitter,
The reverse gain is usually only 1 to 10.   (You can also get problem with the BE junction conducting if the voltage exceeds about 10V.)

There's plenty of circuits which would happily work with hFE = 400.
Title: Re: 2n3906 transistors from Tayda
Post by: PRR on November 25, 2020, 10:39:49 PM
Very OLD Ge transistors were sometimes symmetrical. Same gain both ways. (They did not have enough control to optimize the doping.)
Title: Re: 2n3906 transistors from Tayda
Post by: iainpunk on November 26, 2020, 08:51:39 AM
Quote
if you want to lower the gain to be about 1/3rd, just swap the collector and emitter,
The reverse gain is usually only 1 to 10.   (You can also get problem with the BE junction conducting if the voltage exceeds about 10V.)
that's not what my experience with reverse BJT's is, a BC547 with an Hfe 318 in reverse measured Hfe 93, and a BD139 with gain of 85 measured 32 in reverse. that is in circuit, not in a DMM or component tester.
yes, reverse breakdown is a risk, but not so prevalent in 9V circuits, and enough datasheets list the max reverse BE voltage rating that you can account for that with series diodes/LEDs to lower the potential voltage on that junction

cheers, Iain
Title: Re: 2n3906 transistors from Tayda
Post by: antonis on November 26, 2020, 04:23:03 PM
I can ensure you, Iain, for a bunch of damaged BC317s conversely fitted in 15V CE (grounded E) amp circuit..
Title: Re: 2n3906 transistors from Tayda
Post by: Rob Strand on November 26, 2020, 05:41:34 PM
Quote
that's not what my experience with reverse BJT's is, a BC547 with an Hfe 318 in reverse measured Hfe 93, and a BD139 with gain of 85 measured 32 in reverse. that is in circuit, not in a DMM or component tester.
yes, reverse breakdown is a risk, but not so prevalent in 9V circuits, and enough datasheets list the max reverse BE voltage rating that you can account for that with series diodes/LEDs to lower the potential voltage on that junction
Interesting.  I've measured the values in test set-ups quite few times and I always get low values.  That's for small signal transistors all the way up to large TO-3 packages.

I only *use* transistors in reverse at low voltages, for example as controlled resistors.   The other motivation for measuring reverse beta is to come-up with spice models (many spice models have dubious reverse parameters and don't work correctly in reverse).

I'd have to check out what's happening.   It's possible BE leakage, promoted by breakdown is helping.
Title: Re: 2n3906 transistors from Tayda
Post by: iainpunk on November 26, 2020, 06:32:55 PM
Quote
that's not what my experience with reverse BJT's is, a BC547 with an Hfe 318 in reverse measured Hfe 93, and a BD139 with gain of 85 measured 32 in reverse. that is in circuit, not in a DMM or component tester.
yes, reverse breakdown is a risk, but not so prevalent in 9V circuits, and enough datasheets list the max reverse BE voltage rating that you can account for that with series diodes/LEDs to lower the potential voltage on that junction
Interesting.  I've measured the values in test set-ups quite few times and I always get low values.  That's for small signal transistors all the way up to large TO-3 packages.

I only *use* transistors in reverse at low voltages, for example as controlled resistors.   The other motivation for measuring reverse beta is to come-up with spice models (many spice models have dubious reverse parameters and don't work correctly in reverse).

I'd have to check out what's happening.   It's possible BE leakage, promoted by breakdown is helping.
now im starting to doubt my measurements, it could have been a fluke, we measured the gain of the BD139 in an amplifier circuit based on the currents through the pins, and the BC547 was at a practicum where we had to measure Hfe of a transistor, among other things.

a good transistor to use in reverse is the BF245, since the gain is roughly the same both ways (its a JFET)

cheers, Iain
Title: Re: 2n3906 transistors from Tayda
Post by: Axldeziak on November 27, 2020, 07:31:54 AM

a good transistor to use in reverse is the BF245, since the gain is roughly the same both ways (its a JFET)


You just saved me a ton of time and worry on a completely unrelated project where a BF245 was suggested as a sub but was reverse from the original schematic. Thanks!

Little things like this are why I read this place everyday.
Title: Re: 2n3906 transistors from Tayda
Post by: iainpunk on November 27, 2020, 10:47:20 AM

a good transistor to use in reverse is the BF245, since the gain is roughly the same both ways (its a JFET)


You just saved me a ton of time and worry on a completely unrelated project where a BF245 was suggested as a sub but was reverse from the original schematic. Thanks!

Little things like this are why I read this place everyday.
not gonna lie, this made my laugh.
there are a lot of JFETs where the source and drain are interchangeable, the BF245 is my personal favourite because it sounds very good in an SRPP style circuit.

cheers, Iain
Title: Re: 2n3906 transistors from Tayda
Post by: Yazoo on November 28, 2020, 12:38:59 PM
After all that, it turns out I owe Tayda an apology. While I did get an order from Tayda recently, the 2N3906s I bought for the same project came from an eBay seller, not Tayda.

So, grovel grovel, sorry Tayda. :-[