Hi all, last year I completed my Hiwatt DR201 (4xKT88circuit) which I use for my bass guitar. Its worked fine, sounds great and has had no reliability problems despite being used regularly at high out puts at band practice and gigs for several hours at a time. However, when the amp is turned from standby to on (regardless of warm up time) there is a loud thump. I've copied the original Hiwatt circuit and used almost identical transformers (Partridge). Can anyone suggest what might cause this and how I might modify the circuit to prevent it? Also I recently read that modern KT88's dont handle the plate voltage that the originals did-is this true? I've got a plate voltage of 700vdc. I'm currently using sovteks of which I've had one failure, but I'm sure thats more down to it being moved about alot than an issue with the valves. Any help much appreciated.
Cheers Just