Please help me find missing transistor...

[Bad silver]

Hi, I am repairing JL 300/4 amp that has missing output transistor. I was looking for exact replacement on the web but couldn’t find it.

I think that the missing transistor is exactly the same as #404 on the 2nd picture, but I am not 100% sure. I’d really appreciate it if you can help me out.

[MOER]

We have thousands of IRF540N in stock. These are IR parts.

Stephen Mantz
Zed Audio Corp

zedaudio@aol.com

[1moreamp]

You have found excellent help.

Good evening Mr. Mantz

I use : http://www.findchips.com/avail

But your in great hands With ZED Audio, thats for sure.

[AndrewT]

Hi,
you're real lucky, that must be about the cheapest high current vFET generally available.

I don't know the circuit, but you may require a matched pair rather than just a single device replacement.

Check the board and tracks around the missing device very carefully.

[Bad silver]

I will replace both of them, but which ones are going to be the best replacement?

Fairchild IRF540A

http://www.futurecb.com/Boutique/Pro...IRCHILD3021342

International Rectifier IRF540

http://www.futurecb.com/Boutique/Pro...CTIFIER3156700

NXP IRF540

http://www.futurecb.com/Boutique/Pro...F540NXP3490802

ST MICRO IRF540

http://www.futurecb.com/Boutique/Pro...STMICRO5984976

[Bad silver]

Does this stand for International Rectifier?

[Perry Babin]

That's an International Rectifier part.

Here's a good site if you need to find the company name from the logo. Surprisingly IR is not on the list.

http://info.electronicwerkstatt.de/b...teile/ic_logo/

Both Fairchild and IR have been reliable for me.

When you replace the transistor, you need to bend the center lead so that it can flex (see attached photo). If you solder it in place and the center lead is perfectly straight, the clamp may not exert enough force to hold the transistor against the sink. Clean the old grease and apply a thin layer of new grease. When the clamp is installed, make sure that the grease is displaced evenly around the transistor's perimeter. If it's not, it may not be mated properly and may overheat.

[Bad silver]

Thanks Perry. While we are on this amp, does anyone know what is the purpose of the black asphalt coating on thyroid? Previous owner told me that this amp was once sent to an authorized JL repair shop where it was coated for some reason.

[Perry Babin]

Coatings are used for various reasons. Sometimes it's to secure the windings so the insulation doesn't wear through on the core or on other windings. Other times the coatings are used to quiet the windings. In some amps you can hear the audio being produced by the transformer's windings at high power levels. Sometimes, the noise is due to rapid changes in the duty cycle (the regulator operating to maintain the target voltage).

This is the first JL that I've seen with a heavily coated core.

[Bad silver]

I received the replacement transistors, but I am not sure if they are the same with old ones...