A question about transistors

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A question about transistors

So I am building a board that calls for two BC850 transistors in a TO92 style package.  This is a bipolar NPN transistor.  I really don't know a lot about transistors so please bear with me.  I looked everywhere for BC850, but I've completely struck out finding any in the TO92 style package.  I find some in an SMD package, but that would be ugly to adapt.  I tried googling equivalents, but what I found was mostly either other stuff I can't find or things that are also not readily available in a TO92 package.

 

My question for anyone who knows about this stuff is whether other Bipolar NPN transistors that I have on hand in a TO92 package like a 2N2222 or a 2N3904 would work?  Maybe a stupid question, I can see that it might depend a lot on the circuit in question.  I'm wondering maybe even which one might be the more likely choice of those two if I was going to just try it.

 

Unfortunately I don't know how to get ahold of the people who designed the board.  When I google it I mostly find youtube videos and web pages and stuff that appear to be in Russian.

 

 

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Possible replacements?

This site lists several possible replacments at the bottom of the page.

 

https://www.el-component.com/bipolar-transistors/bc850

 

Justin.

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Might help to know what baord

Might help to know what baord you're building and how these transistors are being used. For example, in a switching vs. analog/linear circuit.

 

My guess however is that the venerable 2N3904 would probably work OK. Can't hurt to try.

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Bipolar "small signal"

Bipolar "small signal" transistors are generally pretty interchangeable, but Jeff is right that a lot depends on how it operates in the circuit. One thing you may find is that newer transistors have higher GBW (gain bandwidth product), which can change the behavior if the transistor is used to filter a signal.

It's also possible that the circuit is using obscure properties such as avalanche breakdown; that would make substitution a lot thornier.

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justinmc wrote:This site
justinmc wrote:

This site lists several possible replacments at the bottom of the page.

 

https://www.el-component.com/bipolar-transistors/bc850

 

Justin.

 

Unfortunately all of the suggestions there also are not TO92 packages.

 

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jeffmazur wrote:Might help to
jeffmazur wrote:

Might help to know what baord you're building and how these transistors are being used. For example, in a switching vs. analog/linear circuit.

 

My guess however is that the venerable 2N3904 would probably work OK. Can't hurt to try.

 

 

This is what I'm trying to build:

 

https://github.com/AlexEkb4ever/MURMULATOR_classical_scheme/blob/main/img/scheme.png

 

The transistors are part of an audio in circuit, which I assume would normally be mostly for tape input to an emulator.  For what I am planning to do it is probably not critical anyway.  I've got lots of 2N3904 so I think I will try it with that.

 

 

 

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softwarejanitor wrote
softwarejanitor wrote:
justinmc wrote:

This site lists several possible replacments at the bottom of the page.

 

https://www.el-component.com/bipolar-transistors/bc850

 

Justin.

 

Unfortunately all of the suggestions there also are not TO92 packages.

 

This one is TO-92 and lists the BC850 as a SMD version of it.

 

https://www.el-component.com/bipolar-transistors/bc171b

 

Justin.

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In this circuit ...

... you can use any small signal NPN transistor with a sufficient current gain (beta, "hfe" on the multimeters who have a transistor test socket). The BC850 datasheet says hfe is 450 (very high for a NPN) while the 2N3904 only is guaranteed to have hfe >= 100 at typical conditions. I don't think that the circuit requires a very high beta, so you could try any NPN you may find in your stash, but check it with the multimeter to have a decent beta, say, 200...250. It's always worth a try ...

 

But watch out for the EBC sequence. Many European transistors have that in reverse. You can easily find out with the multimeter, too. If the beta is high, you can read the EBC sequence from the socket in the multimeter. If you get a very low reading in the single digits, C-E is reversed (yes, the bipolar transistor has some current amplification even in reverse mode).

 

- Uncle Bernie

 

 

 

 

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Hi Uncle Bernie!

I don't know much about it, but I'm very interested in what you read there in Russian? If you need any help I am always at your service.

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UncleBernie wrote:... you can
UncleBernie wrote:

... you can use any small signal NPN transistor with a sufficient current gain (beta, "hfe" on the multimeters who have a transistor test socket). The BC850 datasheet says hfe is 450 (very high for a NPN) while the 2N3904 only is guaranteed to have hfe >= 100 at typical conditions. I don't think that the circuit requires a very high beta, so you could try any NPN you may find in your stash,

 

Luckily CBE is labeled on the board.  It sounds like the 2N2222 might be a better guess than the 2N3904 because from what I google it sounds like it has a typically higher hfe.  I have several meters but none of them has a transistor test on it.  Sounds like something useful to have.

 

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Macintosh_nik wrote:I don't
Macintosh_nik wrote:

I don't know much about it, but I'm very interested in what you read there in Russian? If you need any help I am always at your service.

 

Thanks for the offer.  I forget sometimes you are in Russia because your English is so good.  I was able to read the web pages using Google Translate, but the exact information I was looking for wasn't there.  I obviously couldn't understand what was being said on the Youtube videos.  One of them the guy points to the transistors and I can understand him say the word transistor but the rest of it I don't get.

 

Right now I am waiting on some 10k SMD resistors and some Dsub15 connectors to complete this board.  I also need to figure out which way a couple of 3v3 SMD Zener Diodes go on the board.  The markings aren't clear to be on either the diodes or the board.

 

I'd love to ask about the transistor and the diodes but I can't find any contact information and even if I did I am not sure they speak English.  If I do get ahold of them I might have to ask you to translate for met.  I appreciate your offer of help.

 

 

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The part with the two

Indeed the part with the two transistors is an audio amp that allows you to load software with you smartphone (or a Walkman) through an audio jack, so even if you leave that part out for now the Murmulator will still work.

 

Btw, once you build it, if you have some spare time can you please try this and let me know how fast it ishttps://github.com/xrip/pico-xt

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CVT wrote:The part with the
CVT wrote:

The part with the two transistors seems to be an audio amp that allows you to load software with you smartphone (or a Walkman) through an audio jack, so even if you leave that part out the Murmulator should still work.

 

 

That's exactly what I had in mind.  I was thinking about building a "Pico Transporter" by designing something based on the Murmulator on an Apple II card.  It would be extremely similar to what you've done with your ESP32 Softcard except for doing VGA out.  I also want to try building one of these using the direct HDMI out to see if that works.  If it does, it would be interesting to adapt that to the Ralle Palaveev A2VGA design to make one that didn't need the add-on VGA->HDMI controller but was directly A2HDMI.

 

I would think that the RPi Pico may be faster than the ESP32 so it might be a faster emulated PC.  Also direct VGA output should allow full CGA/TDA or better output without the limitations of NTSC/PAL composite.

 

I was also thinking about whether it would be possible to combine both the A2VGA and the murmulator functions on one board, probably needing two Picos, so that it could automatically switch between Apple II video going out VGA/HDMI and the emulated PC video.  That would truly make it be more like the old Applied Engineering PC Transporter.  If that's not possible I was thinking a modified version of the A2VGA that sent the pre-resistor network video signals by an interconnect cable to the Pico Transporter card which could switch between that and it's own video.  That would use up 2 slots but still provide the same level of functionality.

 

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I am thinking now that

I am thinking now that probably the 2N2222 will probably work, maybe even the 2N3904.  But I think I have some 2N2222 on hand so I will try that first.

 

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softwarejanitor wrote:...I
softwarejanitor wrote:

...

I would think that the RPi Pico may be faster than the ESP32 so it might be a faster emulated PC.

...

 

Actually it's slower. They are both 32-bit dual-core ARM based processors, but the ESP32 runs at 240 MHz, while the Pico runs only at 133 MHz.

 

However this emulator could be faster and software can make a huge difference. For example the version of Doom that is on the Murmulator as well as the ESP32 SoftCard is based on PrBoom, which was optimized to run much faster than the original Doom. If the original Doom had these optimizations when it first came out, it would have ran on a 386 DX 33 MHz PC as fast as the original did on a 486 DX 66 MHz PC.

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CVT wrote:softwarejanitor
CVT wrote:
softwarejanitor wrote:

...

I would think that the RPi Pico may be faster than the ESP32 so it might be a faster emulated PC.

...

 

 

Very interesting.  I didn't know the ESP32 was that much faster.  It will be interesting to see how fast Pico-XT is then.  What little I can find about it, it sounds like it at least is capable of "Turbo-XT" kind of speed, which back in the day at least usually meant an 8-10MHz 8088, although sometimes was 12-16MHz.  Even if it only is comparable to an 8MHz PC-XT, that's still fast enough to run an awful lot of the 1980s MS-DOS software.

 

If it isn't as fast as the ESP32, then maybe I'd consider building a ESP32 Transporter card, maybe with a Pico on there for Apple II video out.  It will be interesting to see.

 

 

 

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If you want to play with an

If you want to play with an ESP32 that already has a VGA output and a PC emulator, I highly recommend this boardhttps://www.olimex.com/Products/Retro-Computers/ESP32-SBC-FabGL/open-source-hardware

 

(Not offering economy shipping to the US is total bullshit though. For this size and weight it only costs $7 to ship through BG Post -> USPS with full tracking and things get there in 2 weeks or less.)

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CVT wrote:If you want to play
CVT wrote:

If you want to play with an ESP32 that already has a VGA output and a PC emulator, I highly recommend this boardhttps://www.olimex.com/Products/Retro-Computers/ESP32-SBC-FabGL/open-source-hardware

 

(Not offering economy shipping to the U

 

That is interesting...  Maybe this instead?  It looks to have similar features:

 

https://www.aliexpress.us/item/3256803812536259.html?spm=a2g0o.detail.0.0.14179i1m9i1mz

 

It's less expensive by a couple bucks and under $5 shipping to US.  Of course that shipping from China through Aliexpress is usually a super slow boat.

 

 

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This board will work too. You

This board will work too.

 

You can also purchase Fabrizio's and help support him by doing so, however right now it's out of stock: https://www.tindie.com/products/fabgl/fabgl-esp32-board-16mb-flash-4-mb-psram-33v-io/

 

He is the author of the FabGL library. I have been looking at his code and the amount of work he put into it is tremendous.

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