Quick question about BJT transistor

[DrGonz78]

I am fixing a Hartke bass amp and need to replace a shorted 2SA1266. I have a 2SA1015 on hand and was wondering if this is a good replacement? The main difference in the part is the Collector dissipation of 625mw for the 2SA1266 and 400mw for the 2SA1015. Does the rating of collector dissipation matter that much? If so what is a better part to use if I was cross referencing? I tried cross referencing the part and just got a bit lost in it all. All I know is that I don't want to buy a NTE290A and I can always find a 2SA1266 online. I really wanted to see if I have something similar that will work as a replacement first. Any help is always much appreciated thanks. These are the links to the two different data sheets.

[soundguruman]

SEMICONDUCTOR 2SA1266 Pack of 10, Electronix

I have used 290A and they worked just fine. That was 3 years ago, still working.

[Jazz P Bass]

If the transistor is rated at 625mw collector dissipation, then that is what you should shoot for.

Unless you want to sit down & analyze the circuit, go with what the designers chose.

Without seeing the actual circuit, I would assume that the 400mw part will most likely fail.

The other way around would probably be o/k.
Sub a 400mw part with a 625mw.

[52 Bill]

What does the transistor do in the circuit? Is it really dissipating that much power? If it is used as a low level signal amp, then the difference in the power rating doesn't mean that much.

It really comes down to usage.

[DrGonz78]

Thanks for all the replies you guys! Yeah I don't have the schematic but I have one that is nearly exact on the output section. The transistor is on the output section Q4 and I am pretty sure it is part of the bias circuit. The NTE290A might work okay in this situation and I have a 2SA1268 transistor as well. The 2SA1268 has 100ma max rating and the 2SA1266 has 150ma rating. Not a huge difference on a lower powered amp. Here are some data sheets and the schematic.

[52 Bill]

The transistor is on the output section Q4 and I am pretty sure it is part of the bias circuit.

Q4 is the pre-driver not a bias circuit part. The input feeds into Q2, the front side of the differential pair. The output from Q2 is then sent to the base of Q4, which in turn feeds the bases of the two driver transistors Q5 and Q6.

[DrGonz78]

Just to update a bit on the correct data sheet for the 2SA1266. It is made by KEC and the collector dissipation is 400mw. The other BJT I have is the 2SA1015 and it basically matches. I did some research and found that HFE code for the 2SA1266 is Y, as printed on the case. That means the HFE is between 120~240 for 1266 transistor. I measured HFE on the two 1015's I have and one was 243, the other 329. The 2SA1015 has GR89 as its class of HFE which can be between 200~400. I wound up trying out the 2SA1015 transistor(243hfe) to replace Q4 and now instead of 4.5vDC on the output it is only 325mv. Still need to think this one out a bit and not sure the effect between the classes of HFE on the circuit.

I will check some more on the amp tomorrow and get some voltage tests going. Just thought I should post the updated data sheets if anyone was curious. There are also 2SA1015-Y type transistors and those would be an exact match to the 2SA1266-Y that I have now. So I guess I learned something new to me. Took a while just to even figure out how to find the right manufacturer for the each transistor too.