Jon, there are considerable differences between the technical parameters of the EL34 and the various versions of the 6L6, many of them in the direction of the 6L6 not being able to handle voltages, currents, and power dissipations that wouldn’t be too high for an EL34. That is particularly the case for 6L6s which precede the version that has a GC suffix.
I assume the person who suggested the conversion is aware of these things. But depending on the design of the amp and the nature of the conversion choosing a 6L6-GC rather than earlier versions (i.e., 6L6-GB, 6L6-GA, 6L6-G, 6L6 no suffix) may be preferable or even necessary, and may result in greater longevity of the tubes.
Good luck. Regards,
-- Al
I assume the person who suggested the conversion is aware of these things. But depending on the design of the amp and the nature of the conversion choosing a 6L6-GC rather than earlier versions (i.e., 6L6-GB, 6L6-GA, 6L6-G, 6L6 no suffix) may be preferable or even necessary, and may result in greater longevity of the tubes.
Good luck. Regards,
-- Al