6AC10 - Compactron triple triodes
Compactron triple triodes. I got them as they are much cheaper than 6C10s and in my (radio) experience work well as a substitute. The former is 3 x 12AX7 triode sections, the latter 3 x 12AT7 triode sections. A 6C10 is a) outrageously expensive, and b) very hard to find and c) simply 3 x 12AX7 sections. Better off (in the unlikely event that the the substitute doesn’t work as you like)replacing the 6c10 with 2 x 12AX7s. It will leave a bit of a hole though. Still the substitute may work. It should be Ok in a Fender Champ if not as overdriven, (it has a gain per section of 62 as opposed to 100 for the 6C10, but also has 2w plate dissipation each section, not the 1 watt for the 6C10 - which may explain why 6C10s go bad regularly). A 6AC10 is classed as a high u triple triode, like the 6C10. It works in a Heathkit SB-610 monitor scope with no circuit changes.