Replacement transistors/mosFETs for holton n-channel amp

[chalo]

Some Questions

Hi, I know this thread has been inactive for a while, but I don´t know where else to ask. I´m willing to build this amplifiers and I have a few questions:

1º - I want to use IRFP250 instead of the original 240, it has higher current capability (30A vs. 20A), higher power dissipation (190W vs. 150W) and lower RDSon, which I think might translate in less heat dissipated by the amplifier (correct me if I´m wrong); all of this should make a more reliable amp, I think. In the other hand it has a higher imput capacitance (2800pF vs. 1300pF), which if I´m correct would translate in increased distortion; It is going to be used as a subwoofer amp, do you think this would affect performance in a considerable way?

2º - I am planning to use LM350T (TO 3P metal package),with a heatsink, instead of LM317K (TO3 metal package), the first is a higher current version of the other (3A vs. 1,5A), because it is easier to add this package in the PCB, would it be ok?

3º - I saw some photos of the amp finished and I saw one of the transistors mounted upon one of the output devices, as thermally tracking, is that correct? Is it Q 13?

Thanks in advance, Chalo.

 

[chalo]

Correction

LM350T - TO 3P is plastic package not metal as I wrongly wrote.

 

[andrewlebon]

hi chalo
greetings
1 irfp 250 is being used in my amp have had no problems but they need to be matched
2 mje 350 attached to output transistor
3 use lm 317t more than adequate
thanking you
andrew lebon

 

[chalo]

Hi Andrew, thank you for your fast reply, what might happend if I don´t match my mosfets? mje´s ar in place of Q13? why did you used that insyead of IRF610 (if this is the case)? and last is ok to use a common plastic lm317 (not TO3 metal) I´ve read that it gets pretty hot.

Thank you again.

 

[Samuel Jayaraj]

MJE was in place of Q12 but the component values around that were different. Use Q12 as shown in the schematic.