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OPA2134: Counterfeits?

Part Number: OPA2134

I obtained some OPA2134PA DIP op-amps from a friend to test. For my test circuit I am using:

+/- 13.5 volt supply, 100 nF and other bypass caps

Signal input 4.5 Vpp sinewave, 65 KHz, centered at 0V

Gain about 4 (RG/RF)

I have parts with third line on DIP reading 9AK52FM. These parts faithfully reproduce the sinewave. First line is the BB symbol. Second line reads OPA2134PA.

I have parts with third line on DIP reading 43AGFKM that output a sawtooth instead. First line is the BB symbol with (R) symbol. Second line reads OPA2134PA.

Are the parts with third line 43AGFKM legitimate?

Thanks in advance.