kicker transistor brand

[Hexhclass]

Amp is a kicker ZX350.4


Amp had a blown PS and two bad output TIP35/36
I replace the outputs with same part number but brand was ST.The channel is playing clean audio but these outputs is heating up even at idle.I tried them on the next channel and same thing.The outputs are good i have used the same batch to repair other amps with no problem.Do i need to get the same brand outputs for this amp?

 

[ultra]

I think there is nothing wrong with your replacement transistors, even though they are old in TO-218 case. I believe if you try a set of the KEC brand transistors to the burnt channel you will see exactly the same. So, you probably missed something in the repair of that channel.

 

[Hexhclass]

The heat follow the the transistor when i tried them on a next channel.

I also took two output from a good channel to try in the repair channel and it works fine.In
fact that's the first thing i did just to make sure.

 

[nigelwright7557]

Perhaps the bias needs setting up again with new transistors ?
Is there a bias adjust pot ?

 

[Perry Babin]

Increasing the value of the B-E resistor or decreasing the value of the B-C resistor on the bias transistor should re-bias the circuit.

 

[PapaZBill]

This amp is fixed bias, If the heat follows the ST replacement transistors,I would recommend using KEC's.

 

[ultra]

i was wrong in my estimate. After checking both pdfs it seems that the ST brand transistors have a lower gain. Wouldnt that mean that they should run cooler than the KECs?

 

[EWorkshop1708]

Try using a multimeter on diode-check to check the Vdrop from the B to the E terminals of the transistors. Check them OUT of circuit. Compare the new ones to the old ones to give us some idea of their differences. That can help us figure beta and junction size.

A beefier transistor with lower gain will usually have a lower B-E voltage, but not always.

 

[Perry Babin]

The threshold voltage is what's critical for the new transistors. For class B amps, the bias is set to just under the threshold. If the replacements have a lower threshold voltage, that could cause the biasing to increase to class AB and the outputs will pass current at idle. Making adjustments to the bias resistors can reduce the bias back to class B, just as you'd have if there was a bias pot.

If you adjust the bias resistors, you need to run the amp up to thermal shutdown, monitoring the idle current along the way, to confirm that the bias settings are OK from a cold start all of the way to thermal shutdown.

 

[PapaZBill]

Here are the locations and values of the biasing resistors Perry refers to:
R (b-c) R346-2.26K 1%
R (b-e) R347-1K 1%

A replacement alternative for the output transistors would be KTD718 and KTB688, if the KEC's are unavailable.Which will perclude any biasing changes.

 

[PapaZBill]

Just for clarity the locators R346 & R347 have counterparts in the remaining 3 amps
as follows:
R146,R147
R246,R247
R446,R447
As I'm sure you will have determined.

 

[Hexhclass]

I lower the 2.26k to 1.5k and the heat is gone at idle.
I run the channel for about 30 mins and all seems well.I did not monitor the current draw,
was mostly checking for heat difference.I will run it to thermal and monitor the current draw.

 

[Perry Babin]

Kicker amps may be different than those where I've tried interchanging the 2S type transistors with the TIP35/36. Years ago, I suggested that the TIP be used in place of the 2S transistors. After repeated failures, I was baffled until I tested to thermal. The TIP transistors were OK with the bias configuration when cold but as the temperature increased, the bias current didn't hold (thermal avalanche). That's why I always recommend running to thermal shutdown and monitoring the idle current.

The 718 and 688 may be OK in this amp but they're rated for much less current than the TIP35/36 and may not be universally interchangeable.

 

[PapaZBill]

Based on my schematics the 2004 and 2006 models use 688's & 718's, and 2008 where changed to TIP's. I took a closer look and realized that the emitter resistors where changed from .2 ohm to .1 ohm and T1 turns ratio was increased to accomadate the TIP's. However there where some revs to raise the thermal shutdown threshold to accomadate a lower impedances value for Kicker component speakers, which complicates the issue. Looking at the pic Ian33 posted shows .2 ohm with TIP's. Which further clouds the issue. I'm inclined to agree with you Perry, and using the 688 and 718 would not be recommended.

If I where doing the repair I would have replaced the TIP's with KEC's, but I have a bit of an advantage as far as an available source of parts, which Ian33 may not have.So, having said that if lowering the resistor value in the bias circuit and testing for thermal shutdown works, great! I came here to not only offer my experience with Kicker amps, but to learn more about the art of electronic repair, and this is a good example!!