Any decent 12AU7 recomendations?

[RothwellAudio]

I'm concerned that using a 12AX7 in place of a 12AU7 may harm the amp?

So can I ask if it is OK to keep using Svetlana's in this way. Any concerns?

Without seeing a circuit diagram it's difficult to say exactly what will happen when using 12AX7s instead of 12AU7s but generally valve amps are pretty robust and there's a good chance that no harm will come of it. Worst case scenario is that there will be more power dissipation in a valve or a resistor than they're designed for and they'll either slowly cook or burn out pretty rapidly. Also, a voltage across a capacitor could rise too high and cause failure. However, more likely than not, no harm will be done.
Bear in mind that the operating points for the amplifier will be different and distortion might be worse, maximum power output might be reduced etc. Best to just stick with a 12AU7 where the circuit is designed for a 12AU7 imho.

[Arkless Electronics]

Without seeing a circuit diagram it's difficult to say exactly what will happen when using 12AX7s instead of 12AU7s but generally valve amps are pretty robust and there's a good chance that no harm will come of it. Worst case scenario is that there will be more power dissipation in a valve or a resistor than they're designed for and they'll either slowly cook or burn out pretty rapidly. Also, a voltage across a capacitor could rise too high and cause failure. However, more likely than not, no harm will be done.
Bear in mind that the operating points for the amplifier will be different and distortion might be worse, maximum power output might be reduced etc. Best to just stick with a 12AU7 where the circuit is designed for a 12AU7 imho.

^ Good advice. +1

[Daru]

I have quite a collection of old 12au7s. You cannot go wrong with RCA cleartops and Sylvania long plates. Both cheap and plentiful on ebay.