Boston gt24

[mike49504]

This amp has a blown power supply its using 75333p as the fets wondering if i can switch them over to a irfz48

 

[Perry Babin]

The IRFZ48 should work but it has slightly more gate capacitance so you may need to change the gate resistors if they're 100 ohms or higher. The Z48 is also rated for less current. If this is for a paying customer, you should use the original parts.

 

[mike49504]

its 1 of my own amps i bought from a guy for $10.00 it was blown


If i use the irfz48's what do i need to use for the gate resistors they are using 56 ohm surface mount they say 560 on them so guessing it 56 ohm

 

[Perry Babin]

The 56 ohm resistors are sufficient if they're within tolerance.

 

[mike49504]

I guess ill have to order some 56 ohm resistors cause all i have right now is 10 ohm and the resistors that are in the amp are blown in half

 

[I Am An Idiot]

Perry, do you need pics of a GT-24? I have to work on one tomorrow. I did take pictures of the Memphis 500.

 

[Perry Babin]

Sure, bring me some photos of it.

 

[mike49504]

back to this amp im thinking of using the irfz44's for the fets instead of the 75333p and switching the gate resistors from 56 ohms to 47 ohms wondering if this will work

 

[Perry Babin]

The Z44s are rated for less current so the amp may not be as reliable. Either the 56 or the 47 ohm resistors will work.

 

[mike49504]

would the irfz46n's be a lil better then the 44's?

 

[Perry Babin]

Yes.

 

[mike49504]

I replaced the fets (75333P's) with IRFZ46N's and changed the gate resistors from 56 ohms to 47 ohm's .

The amp is stuck in protection mode wondering where i begin to check??

All output's test good

 

[Perry Babin]

Post or email me a photo of the inside of the amp.

babin_perry@yahoo.com

 

[mike49504]

If i pull the rectifiers out amp powers up and idles fine. And doesnt go into protection with the rectifiers out

 

[mike49504]

So since i pulled the rectifiers in the amp and it powers up and doesnt go into protection. Does that mean the problem is in the output section?

 

[Perry Babin]

With the rectifiers in the circuit, does it attempt to draw excessive current or do you read any excessive DC offset on either channel (measured directly on the speaker terminals for each channel)?

Have your scope probe on the bridging terminal of each channel and watch for a pulse of DC as the amp tries to power up?

 

[mike49504]

It doesnt draw excessive current. With power ,ground,remote hooked up no DC on outputs.

IF i put my meter leads on the left channel and then apply remote voltage it has 12volts of dc on outputs for 2 to 3 secs the goes back to 0 volts. I also checked the left channel with my scope and it has dc upon power up for a few sec's

 

[Perry Babin]

If it's only the left channel, that where you need to start troubleshooting. I'd suggest pulling the outputs and checking them for leakage. What outputs are they using in this amp?

 

[mike49504]

They are using IRF540a's and SFP9540's for the outputs

 

[mike49504]

Ok if i pull the 9540's out of that channel amp powes up. So i replaced the 9540's and amp goes back into protection with them in circuit