K8020 Tube Question

Do the replacement tubes have to be ECC82 in the K8020 preamp? For example, is it a bad idea to use a ECC83 tube? Is the ECC82 the best type of tube to use in the amp?

Amp has been designed and calculated for ECC82. ECC83 has totally different specs.

How about E80CC tubes, they are taller and require more heater voltage. Will the (power supply in) K8020 be OK with that?

Thank you!

Sorry, we have no experience with those tubes.