I need help troubleshooting this amplifier

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I need help troubleshooting this Amplifier. The issue I am having is that the 3906 along with the 47ohm connected to its collector keep burning out. I tried many times to figure out the issue but had no success in finding what could be causing it. By the way the voltage in is 80v.
P.S. if you have any different amp designs that use the 2n3055 transistor and a similar power, feel free to share them.


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You need to tell us what power voltage you are using. Real 2n3055 not more than about 55 v. 2n3904/6 don't have much Vceo, they should limit this amp to a 30 v power supply. 2n5401/5551 have more voltage standoff, work up to 70 v. MPSA06/56 or MPS8099/8599 might be cheaper to buy. Use real On semi, fairchild, or ST transistors from a distributor. Instead of 2n3055 which might be counterfeit, use MJ15015 from a distributor. It can stand a little more voltage.
2n3904/06 don't have much power rating and make poor drivers for TO3 transistors. this amp A prehistoric amplifier: The Archosaurus - Page 6 - diyAudio
uses TO126 drivers, which can take a heat sink. MJE340/350 may be more available in the US for the drivers than BD131. Use the above transistors in the front end instead of the exotic (here) BC557/548.
If your 47 ohm is burning out go to 2 W or 3 W. Once it burns it would probably take out the 2n3906.
With the same number of transistors, but some of them TO220, I'm listening now to an Apex AX6. You don't really need 4 output transistors below 60 W/ch. Retro Amp 50W Single Supply
You just need a lot of heat sink. I'm using fans on the heat sink. My choice for the drivers these days would be MJE15028/29, also the VAS. Fast transistors that make the high tones more pure. AX6 has harmonic distortion down to the .0x% range.
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If you actually applied 80V to 2n3055s then the top two have probably shorted and the emitters of the lower two are now open, which then allows the 47 Ohm resistor to burn.
And as Jo mentioned 2n3906 and 2N3904 can not be used above 40V.
And the base of the 2n3906 is connected to the wrong side of the diode.
The 470 Ohm resistor is probably a bad idea.
A 1uF input cap is probably too small unless you intended to filter everything below 500Hz.
I assume you know this amp has no gain.
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Unsolder the bases of all 3055's , the circuit should function unloaded as complimentary emitter follower. It burns because of high voltage across 470 ohm , why , any upper transistors base collector leakage or short can cause.
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Unsoldering the bases is not going to do anything. Disconnect the collectors.

Work on your circuit with 15 to 20VDC and limit the current to 100mA until you work out the problems and have it working. Then raise the voltage slowly while watching the current. A common trick is to use a light bulb in series with the power supply as a current limit.

Almost certainly your circuit has a fault that destroyed your transistors in an instant when you first applied powered to it. This is classic audio amplifier learning and it has happened to most everyone who has built an amplifier.
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