The first check of course is the pinout, and they match.
In terms of operating points, the KT-77 is pretty robust (design max plate voltage = 800VDC, design max screen voltage = 600VDC). It's doubtful that your KT-88 amp was designed such that it will kill this tube, but I'd check with your amp builder.
One overlooked point in tube substitution is heater current draw. If you swap to a tube with significantly higher heater current draw, you my be outside the spec of your power transformer.
In the case of the KT-77 (1.4A draw) and KT-88 (1.6A draw), you'll be drawing less heater current with the KT-77 so you're fine in this regard.
So ... check with your amp builder.
Cheers,
Thom @ Galibier Design
In terms of operating points, the KT-77 is pretty robust (design max plate voltage = 800VDC, design max screen voltage = 600VDC). It's doubtful that your KT-88 amp was designed such that it will kill this tube, but I'd check with your amp builder.
One overlooked point in tube substitution is heater current draw. If you swap to a tube with significantly higher heater current draw, you my be outside the spec of your power transformer.
In the case of the KT-77 (1.4A draw) and KT-88 (1.6A draw), you'll be drawing less heater current with the KT-77 so you're fine in this regard.
So ... check with your amp builder.
Cheers,
Thom @ Galibier Design