Boat autopilot remote (question about transister choice)

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The discussion centers on the suitability of using BC337 and BC327 transistors as replacements for 2N4402 and 2N4400 in a boat autopilot remote circuit. While the BC337 is an NPN and the BC327 is a PNP, participants note that the continuous collector current rating of the replacements is higher, which could be beneficial. The consensus suggests that as long as the transistors are rated to handle the required currents and are correctly configured, they should function adequately in the circuit. Additionally, attention to pinouts and frequency response is advised to ensure compatibility. Overall, the choice of transistors can be flexible if the basic requirements are met.
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Hi,

I'm about to build an autopilot remote for my boat, manual found here:
http://www3.sympatico.ca/ericn/Files/Other/DIY Autohelm ST4000.pdf

In the scheme I need to use two transisters, a 2N4402 (PNP) and a 2N4400 (NPN) as illustrated here:
circuit st4000.PNG


As I don't have these transisters can I use a BC337 and BC327 which is what I have. I guess what I'm asking do the specs of the transister matter? Both have emitter voltage of 5V but mine have a Continuous Collector Current of 600ma rather than 200ma on the sketch above. But in the sketch, aren't they just used to re-direct current in this case really? Does the Continuous Collector Current matter?

Kind Regards,
Peter
 
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Aren't the BC327 and BC337 both NPN transistors?
 
hutchphd said:
Aren't the BC327 and BC337 both NPN transistors?

No, the BC327 is a PNP and the other a NPN
 
I remember myself asking very similar question and then reading this: https://www.edn.com/design/analog/4429969/Choosing-Transistors
 
Borek said:
I remember myself asking very similar question and then reading this: https://www.edn.com/design/analog/4429969/Choosing-Transistors

Hi Borek

Thanks for the reference, but I don't feel that it answers my question specific to the circuit that I'm looking at.

Br, Peter
 
I personally don't see any reason why they should not be interchangable and I guess its only a plus that my Continuous Collector Currents are rated higher than the ones in the sketch as I suppose it means that they can handle more current without the magic smoke..

Br, Peter
 
pslarsen said:
Thanks for the reference, but I don't feel that it answers my question specific to the circuit that I'm looking at.

Not directly, but it explains how to choose the transistor and why in most cases - as long as you follow some simple rules - choice doesn't matter much.
 
Borek said:
Not directly, but it explains how to choose the transistor and why in most cases - as long as you follow some simple rules - choice doesn't matter much.

I guess what its sayning that the current out is the sum of current in and since my trasistor choise has nothing to do with the currents flowing into it then the only thing that matters is whether is a NPN or PNP as long as its rated to survive the currents in the system.

Br, Peter
 
If your replacement capacity is bigger you seldom get in trouble. If there is any high frequency in signal be sure to check freq response of replacement. Good luck
 
  • #10
Many thanks
 
  • #11
Also be careful to check the pinouts on the transistor: I think one of your list is not the "standard" EBC configuration. Be sure to check.
 
  • #12
Ok I will
 

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