2270 Differential Pair Transistors

[airtime]

I think if you are worried about failure prone - that notice must be 30 years old. So if they were going to fail - it would have happened by now.

Get it back together with the old transistors and enjoy!

If they blow later on - then worry.

charles

 

[highhosilver]

I think if you are worried about failure prone - that notice must be 30 years old. So if they were going to fail - it would have happened by now.

Get it back together with the old transistors and enjoy!

If they blow later on - then worry.

charles

That is my plan for now, and I am enjoying it as we speak!
Thanks airtime

 

[argybargy]

I can confirm that ZTX795A does NOT work. I had the exact same problem as the OP: high pitched squealing sounds. Yes the pins were oriented correctly and yes, the HFE were matched.

I then ordered what was advertised as 2SA640 from Littlediode on Fleabay, matched HFE and installed... result was no sound from either channel - Nothing. Lights came on, fuse was okay.

Finally, I matched up 2 pair of 2SA992 from a big pile I had left over and installed those. Bingo! Works great.

My 2270 is dated 1975.8.9

Old thread, but hopefully this might help someone.

 

[skibjr]

Exactly my experience as well. I hfe-matched my ZTX795A's perfectly, bent the legs around to the correct orientation and triple-checked my work before powering up on the DBT. No squealing, but no other function either.

I also ended up with KSA992's which worked beautifully - and they had the correct pin orientation to boot. My 2270 was an early-serialed champagne engraved unit, in the 4200's.

 

[Jeeptechfred]

Highhosilver seems to describing ossillation. Could the new components be "too good" or could they have been installed in a fashion that compromised the layout of the amplifier?

 

[wlhd1610]

Use KSA992FBU's and be done with it.....

Bob