Can a MJE5742 transistor be substituted for a 2SC2335

Thread Starter

Roque

Joined Sep 16, 2014
156
Hello to you all you tech Guru’s
Got myself an old Technics Sh C01 pulse power supply in for repairs and found a couple of transistors (2SC2335) gone bust have looked online and they seem to be obsolete .... looked into substitution in all transistor page and the only ones I could find are the MJE5742G ... the specs moreover match but the description on many sites state the MJE is a Darlington transistor and that’s where my confusion starts
Any info on the two transistors would be much appreciated and whether I could still use the MJE
Thank you
 

Ian0

Joined Aug 7, 2020
503
The main features of the 2SC2335 are: high speed, high voltage and high Hfe. Uncommon to find all three together.
You would have to look at the application to select a substitute. If you need it that fast, would a lower HFe work?
Or, if you need that much gain, does it have to be so fast?
The MJE is much slower - look at that storage time!
I bet it's in some form of off-line switched-mode supply.
The reason why they have become scarce is that that job is almost entirely done by MOSFETs these days.
Unfortunately, I would doubt you could substitute a MOSFET, but it *may* be possible, depending on the circuit.
 
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Thread Starter

Roque

Joined Sep 16, 2014
156
The main features of the 2SC2335 are: high speed, high voltage and high Hfe. Uncommon to find all three together.
You would have to look at the application to select a substitute. If you need it that fast, would a lower HFe work?
Or, if you need that much gain, does it have to be so fast?
The MJE is much slower - look at that storage time!
I bet it's in some form of off-line switched-mode supply.
The reason why they have become scarce is that that job is almost entirely done by MOSFETs these days.
Unfortunately, I would doubt you could substitute a MOSFET, but it *may* be possible, depending on the circuit.
Thanks Ian cheers
 

Thread Starter

Roque

Joined Sep 16, 2014
156
Hello Gents ,
thanks a lot for the info you all chipped in regarding the transistor 2sc2335 did manage to source a few and replaced them in the technics SH C01 power supply the strange part is Q203 when in circuit the relay RL 201 wont click in ,if i remove the transistor the relay clicks in and i get the required output volrtages +42 and -42 and connected to the amp module SE C01 all works fine .....not sure if that transistor is just used for switching a particular relay ??? will it affect the powersupply unit in the long run or can i omit it which is a silly question to ask since evey component has a part to play ...any advice or info be much much appreciated thank you

Regards
Roque
 

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Dodgydave

Joined Jun 22, 2012
9,463
The transistor in question is a 2SC1815, it's a ramp generator for the 22Khz osc feeding the two 2SC2335 transistors which pulse the Transformers T203/T204 to make the +/- 42V output.

Such a strange design they go to all that complexity to mix linear Transformers with switchmode as well.,
 
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Thread Starter

Roque

Joined Sep 16, 2014
156
The transistor in question is a 2SC1815, it's a ramp generator for the 22Khz osc feeding the two 2SC2335 transistors which pulse the Transformers T203/T204 to make the +/- 42V output.

Such a strange design they go to all that complexity to mix linear Transformers with switchmode as well.,
Thanks Dave it sure is weird ... was thinking to myself if I can’t get it working would just use the linear simple powersupply with some nice filter caps and let it power the amp ... as you mentioned the transistor C1815 is used as a ramp generator ... when left in the circuit the power relay won’t switch on but when I desolder the 1815 the power supply works fine the only noticeable thing is a slight audible tick sound at regular 1 minute Intervals
wonder without the C1815 what’s making the 2335’s pulse ...
 

Thread Starter

Roque

Joined Sep 16, 2014
156
The only other thing to check is the diode SVDN413 in the blue circle, looks like a Diac.
had a read online of the different diode symbols and found these tye tobe be
Transient Voltage Suppression Diode
probably it is sensing something to be incorrect and then tells the transistor 1815 to turn on sort of a protect mode ????? i tried to find the 30V i guess initial spike at collector of 1815 but nothing maybe its too quick for my DMM
 

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Thread Starter

Roque

Joined Sep 16, 2014
156
had a read online of the different diode symbols and found these tye tobe be
Transient Voltage Suppression Diode
probably it is sensing something to be incorrect and then tells the transistor 1815 to turn on sort of a protect mode ????? i tried to find the 30V i guess initial spike at collector of 1815 but nothing maybe its too quick for my DMM
Hi Dave resoldered the diode after testit was ok and resoldered the transistor and guess what ..... works this time hahahah very strange..
thanks a million for your response sir .

Regards
Roque
 
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