meron pa din thud sound even if volume is at zero level. sa ibang amps ko naman upon power on meron thud. ![Sad :(](https://www.pinoydvd.com/Smileys/default/sad.gif)
the tubes have nothing to do with that,
the power amp is a solid state and connected to speakers via relays,
on power down, this relay should turn off quickly,
but on power on there must be a delay of a few seconds,
this the heart of your problem,
ss amps do have turn on/of thuds and so uses a speaker
time delay relay, this is very rare in pure tube power amps...