Melted Op Amp Zistors?

[velo]

Did the transistors in this old ALTEC op-amp melt? Should I replace them? ...or maybe replace the whole op amp? Not 2520 style socket. I will have to run jumpers?

 

[Khron]

Does it still work / pass audio?

Those might be some pre-TO92 package, resin-filled? They kinda resemble the bottom of box-cased film caps.

https://res.cloudinary.com/rsc/imag...uto,w_540/c_pad,h_303,w_540/F6167935-01?pgw=1

 

[Tubetec]

Id be a little surprised if blown transistors didnt cause a few of the resistors on the board to burn up as well , or at least leave scorch marks . Often a blown transistor will have pock marks on the front surface where the print is . I havent seen transistors with that dimpled top before , compare cold readings with the other similar parts.

 

[velo]

Does it still work / pass audio?

Those might be some pre-TO92 package, resin-filled? They kinda resemble the bottom of box-cased film caps.

https://res.cloudinary.com/rsc/imag...uto,w_540/c_pad,h_303,w_540/F6167935-01?pgw=1

The channel strip I pulled it from works at least as a preamp without engaging any of the EQ or other effects. I mic'd kick drums and they sounded great.

These must be ~55 years old.

Id be a little surprised if blown transistors didnt cause a few of the resistors on the board to burn up as well , or at least leave scorch marks . Often a blown transistor will have pock marks on the front surface where the print is . I havent seen transistors with that dimpled top before , compare cold readings with the other similar par

 

[Tubetec]

Yes but someones been at it much more recently ,
If it sounds good , trust your ears .

 

[abbey road d enfer]

Did the transistors in this old ALTEC op-amp melt?

No. Some transistor packages were exactly like that.

Should I replace them? ...or maybe replace the whole op amp?

If they work, no.

 

[velo]

I tried breaking these in keeping power on for 24 hours or so. One of the channel strips in this 2-channel rig was no longer working after that. After recycling power, the bad strip goes out with a pop bang after less than one minute--just enough time for me to hit record, turn around, and start playing Channel One Suite in honor of that bad channel.

What is the most common reason for a popping out? I see a spike in the audio output and then silence...like a capacitor discharging and then not recharging. These units are solid-state.

 

[abbey road d enfer]

I would suspect primarily an electrolytic cap.

 

[velo]

I would suspect primarily an electrolytic cap.

Well, the good thing (?) is that I've two channels so I can check voltages and timings between the two with various signals.

They both ran fine for several hours today with an SM57 and me tapping my thumb on the mic after being powered off for over 24 hours. Previously I had Beta52A from a 26" kick drum.

Getting closer (?) but since there are three discrete op amp boards per channel in addition to the motherboard circuit so I am not sure where to begin.