Replacement for 2N5912, MPSA42 and BCV62C

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I have to repair some old equipment and need replacement for 2N5912 Dual N JFET. Found that replacement chip is LS5912, but I can't buy it i my country. Can I use two identical JFETs instead and which one? Any recommendations will be greatly appreciated !

I'm a little desperate for NOT BE able to REPAIR my power stage.
I NEED THE HELP OF A CHARITABLE SOUL.
PLEASE have someone help me to replace the subject transistors
 
You can readily purchase sets of 5 LSK389 or LSK489 on ebay. It's a much better part. However, getting it to work in circuit might require adjusting resistors elsewhere depending on how the Idss current differs between the 5912 and the LSKx89 device...
THANKS FOR YOUR QUICK AND ATTENTIVE RESPONSE.
My availability of "measurement tools" are very limited and scarce; I have a good multimeter but NOT oscilloscopes, etc. `Therefore I thank you that on the image that I attach, help me to select the components that I must change / adjust so that the circuit is NOT negatively affected by the substitution that I propose of the 2N5912 by LSK * 89.
This dual transistor is very hard to find. Can I also use 2 of type LSK170. (seeing the circuit would be A or B).
Can I eliminate the constant current current diode J511 ?.
Also what changes would you suggest to IMPROVE THE FINAL SOUND?
YOU CAN ANSWER IN PRIVATE MESSAGE
View attachment Etapa de ENTRADA.pdf
 
You can readily purchase sets of 5 LSK389 or LSK489 on ebay. It's a much better part. However, getting it to work in circuit might require adjusting resistors elsewhere depending on how the Idss current differs between the 5912 and the LSKx89 device...

THANKS FOR YOUR QUICK AND ATTENTIVE RESPONSE.
My availability of "measurement tools" are very limited and scarce; I have a good multimeter but NOT oscilloscopes, etc. `Therefore I thank you that on the image that I attach, help me to select the components that I must change / adjust so that the circuit is NOT negatively affected by the substitution that I propose of the 2N5912 by LSK * 89.
This dual transistor is very hard to find. Can I also use 2 of type LSK170. (seeing the circuit would be A or B).
Can I eliminate the constant current current diode J511 ?.
Also what changes would you suggest to IMPROVE THE FINAL SOUND?
YOU CAN ANSWER IN PRIVATE MESSAGE
View attachment Etapa de ENTRADA.pdf
 
HI.
IS NO ONE IN FORUM THAT SEEING THE SCHEME CAN HELP ME?
I HAVE ALLOWED A TIME TO SEE IF SOMEONE COULD DEDICATE A "LITTLE TIME" TO MY SITUATION WITHOUT DEPARTURE.
THE LSK389 TRANSISTORS DO NOT MEET THEM BY ANY SITE AND TO REPLACE THE 2NK5912 BY 2SK170 .... WHAT ADJUSTMENTS SHOULD I DO ACCORDING TO THE SCHEME ATTACHED?
 
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Changing from a dual to individual JFET transistors is possible but is a poor solution. To do even that properly, you will still need more than just a desire to repair your amplifier and a multimeter. This isn't just a simple 'replace this', 'replace that' and turn the power on job so please, read a little about this first before yelling at the forum in capital letters and so, appearing to demand help. Well, that doesn't help you at all.

There are many parts that can only be bought from a few places in the world. The pro. repairers among us have become accustomed to this and usually now deal through Ebay which is simple and painless. It's just a fact of life but now you can use search engines like Google to locate them in seconds. MPSA42 at least, is available everywhere, including Spain. BCV62C is available from all Farnell and RS distributors in Europe, including Spain, AFAIK.

There are several threads on this same same problem already and there are several Ebay sites selling replacement 2N5912 parts - from generic copies to military spec. This should be your first choice if you want to succeed. I think that messing about with unmatched, discrete or unknown parts of the wrong specification will make the task too difficult to get acceptable results for a beginner or even for the average DIY with some repair experience. Don't try to improve the circuit unless you really know what you are trying to achieve and how to go about redesigning it for that specific product.

By the way, you neglected to tell us what amplifier you refer to for some reason but in any case, you must use the obsolete JFETs and not MOSFETs here.
 
The (genuine) SK170 is much better than the 2N5912. The drain-source current varies between specimens.
BC550 would do in the place of MPSA42.
The J511 is needed, but I would omit the BCV62C, using a resistor and a variable resistor, respectively.
Please be careful to identify the pins. This will upset the DC balance of the amplifier! I should not be held responsible for any damage.
 
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How to go about matching LSK170 FETs though? You might notice that the diyAudio store no longer offers matched pairs, so just how many parts would be needed to find an acceptable match? The plan is fine if you have plenty of cash and a matching jig setup but at the price of sufficient parts or pre-matched pairs of LSK170, you could probably buy two better performing stereo amplifiers.
 
Dear All:

Having a look to the attached diagram in my post on July 5.
What is the function of Q11 (J511, is a current regulator diode)? Does it set the current at 4.7 mA?

Within my limited knowledge, I ask myself:

This means that the Idss value. of Q10 is set by Q11 at 4.7 mA? and for that reason Q10 could be either 2N5912 or LSK389A or 2 x LSK170A? Or does it mean that having Q10 paired on the 2 channels could I do without Q11? or none of the previous statements is true .....

Sorry if I'm claiming a "nonsense."

Thank you all for your help and patience.
 
Dear All:

Having a look to the attached diagram in my post on July 5.
What is the function of Q11 (J511, is a current regulator diode)? Does it set the current at 4.7 mA?

Yes

Within my limited knowledge, I ask myself:

This means that the Idss value. of Q10 is set by Q11 at 4.7 mA? and for that reason Q10 could be either 2N5912 or LSK389A or 2 x LSK170A? Or does it mean that having Q10 paired on the 2 channels could I do without Q11? or none of the previous statements is true .....

Sorry if I'm claiming a "nonsense."

Thank you all for your help and patience.

Maybe you should read more about LTP (long tailed pair) and how current is shared between transistors.

MPSA42 and BCV62C are available from Mouser.
About 2N5912: maybe IFN5912 from Interfet is equivalent replacement
 
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About 2N5912: maybe IFN5912 from Interfet is equivalent replacement

Interesting, Mouser acts like it is. The IFN5912 minimum Idss is 7ma, so if the J511 is not way out of spec, should be fine.

manuellop, if you get a 2N5912 from somewhere, it will need an Idss greater than 4.7ma, I don't have a datasheet. If the J511 is broke, then you could use some jfets (J112 should work) and short gate to source and select one at about 4.7ma and use it in place of the J511. I don't trust J5xx off eBay, I got some and they sucked.

Mad
 
Interesting, Mouser acts like it is. The IFN5912 minimum Idss is 7ma, so if the J511 is not way out of spec, should be fine.

manuellop, if you get a 2N5912 from somewhere, it will need an Idss greater than 4.7ma, I don't have a datasheet. If the J511 is broke, then you could use some jfets (J112 should work) and short gate to source and select one at about 4.7ma and use it in place of the J511. I don't trust J5xx off eBay, I got some and they sucked.

Mad

Hello Mad.
To replace J511, I thought of 1N5314 or CR470 .... Attached data sheet
Since I am in this process, I would like to improve the entry stage, maybe with LSK389. what parameters are required in addition to an Idss greater than 4.7 mA and paired Jfets?
Can the circuit be improved by replacing or eliminating BCV62 and / or MPSA42?
What importance and / or influence does each of the transistors have on the final quality of the power stage? View attachment CR470 y 1N5314 (Sust. J511).pdf
 
LSK389 would be an improvement. You can also match individual N-channel JFETs like this: connect the gate to the source and to the negative pole of a nine-volt battery. Connect a 100 ohm resistor to the drain and to the positive pole and measure the voltage drop across the resistor.
J511 can be replaced with 1N5314, CR470 or a resistor.
BCV62 can be replaced with any PNP transistors.
For sonic reason, I would keep MPSA42, remove BCV62 and replace J511 with a resistor.
 
I would not modify this amp, you don't know what it will do to the VAS stage or compensation, I would just get it working. Don't remove the cascode (MPSA42) or current mirrors (BCV62)

Mad

And replace the 2N5912 with 2LSK389?
I redirected the previous question. "Since I am in this process, I would like to improve the entry stage, maybe with LSK 389. What parameters are required in addition to Idss greater than 4.7 mA and paired Jfets?"
Thanks for your kind attention
 
Hello:confused:
I have decided to replace the 2N5912 with a pair of 2SK170 GR (the LSK389 DO NOT GET THEM).
My question is, what value should I choose? The closest to 4.7 mA? Can it be any value above 4.7 mA ?, does not the value of Idss matter as long as they are matched?
Thank you for your cooperation.
best regards
Manuel
 
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