+1, As noted above, NO. 6AJ8 tubes cannot be safely substituted for 6KA8 tubes. The two tubes have different pinouts and internal structures: the 6AJ8 is a triode-heptode, while the 6KA8 is a high-mu triode and sharp-cutoff pentode.
Using a 6AJ8 in place of a 6KA8 could result in improper operation or even damage to your equipment. Please be careful.