Tube Testers: Upgrades and Calibration

[UberVacTuber]

I was wondering if anyone has had a tube tester upgraded and/or calibrated. I've got a Hickok 6000A tester and it still has the old mercury vapor diode tube. I've seen solid-state replacement plug-ins, but I've been warned that these can throw off the calibration of the tester. Has anyone had their tester modded and if so, did it need recalibration? Who would you recommend for this work? I can replace the capacitors and such, but recalibrating is a different story...

Thanks!