Yes, in the sense that it won't blow up. It's been a while since I obsessed over tube-rollng with the 834p but as I remember there were recommendations for 5751 in the rear tube position. Some thought it a better sounding tube than the ax7 but with lower gain. I don't recall anyone suggesting it for the front position. Presumably at least one of the positions is involved in the RIAA correction circuit so departing from the recommended ax7 might affect the frequency response. In the end I figured why second guess the designer, Tim deP, and returned to ax7s in all positions. Ended up using all EIs which were/are priced sanely.