Adcom GFA-555 Help Needed

[BargainBrad]

Hello,

I picked up an Adcom GFA-555 with a blown left channel. As you can see, I've circled in red the burnt resistors (R1 and R7) and transistor (Q8). I'm assuming the problem is a blown output transistor, but I wanted to see if anyone has experience with this particular problem. If you agree that this is the most likely cause, I plan to update the left channel with the following parts (and later upgrade the right if it works as planned):

Q1-Q3, Q10: 2SC2240 (need 4 per channel) - Replace with KSC1845-FTA
Q4: 2SC2912 - Replace with KSC3503 DSTU
Q5: 2SA1016 - Replace with KSA992-FATA
Q6: 2SA1207 - Replace with KSA992-FATA
Q7: 2SA1210 - Replace with KSA1381 ESTU
Q8,Q9: 2SA970 - Replace with KSA992-FATA
Output Transistors
Q11: 2SB595 - Replace with MJE15031
Q12: 2SD525 - Replace with MJE15030
Q13-Q16: 2SB554 (PNP) - Replace with MJ21193G
Q17-Q20: 2SD424 (NPN) - Replace with MJ21194G

Does this seem right? Does anyone see any problem with these choices? I will do the caps as well.

Your help and advice is much appreciated.

 

[FootFungus]

For Q6 you probably want to use a KSA1381. Q9 and Q10 you might want to use something beefier, as the KSC1845/KSA992 are pretty lightweight as far as current handling in the limiters.

 

[BargainBrad]

In looking at this more closely, it appears the Q1 transistor had a short. This resulted in the R1 and Q8 blowing. I tested Q7 and Q2 and they are normal. Do you think it is safe to replace Q1, Q8 and the two blown resistors and fire it up, or would you test anything else first?

 

[FootFungus]

You can. I'd replace Q1 and Q2 as a hfe matched set. At minimum, I'd use some smaller quick blow fuses for the rail fuses. If you have a variac or a dim bulb tester then I'd make use of those.