Hi,

I'm curious to know if there are any major differences between batches of TL071's with regards to performance?

I've constructed a simple triangle wave generator that oscillates at 49kHz with about 5Vpp output using two TL071's (one as a comparator and one as an integrator). The waveform was excellent.

At some point I had to change out the TL071's and install a couple of replacement TL071's, without changing any other circuitry I had a completely different waveform at a different frequency (see below).

Now much closer to a sawtooth waveform at about half the frequency. I've noticed each IC has the part number i.e. TL071, but that there is also another number either starting with 06 or 98 usually, are these variants of the same IC?

 

I threw in a different TL071 again (this time with another part number starting with 1A and I've returned to my original signal).. Guess they do mean something.

 

Can you post clear, well focused photos of the good and "bad" TL071?

Is it possible that you have an inferior knockoff?

What are the good and bad frequencies?

 

And while at it, please post the schematic; if the circuit is well designed, the opamp should be able to vary a lot without having much effect on the output signal.