hello these days my amp would play and the sound would go low and back to regular sound without touching the sound nobs of the amp.

i beleive its time to change some tubes.

whats wierd is last tiem i changed my tubes since then everytime i turn off the amp there are clicking/sizzlling sounds and i brought it to be check and got said not to worry is that true?

i just talked to a luthier and ive been told i should not only change the tube but bias it as well?

i am from canads what price should this service be arround? 

Is it possible to get el34 the same one that came with the amp originally? The person who changed ly tubes lst time said its not possible.

thank you in advance.

David