Changing Tubes

[TomW]

The power tubes in my Marshall DSL100 need changing and I was just wondering if my amp needs rebiasing if I replace the tubes with the same type of tube but a different brand.

[jordan]

Yes.

Power-amp tubes should always be re-biased, even if replacing them with the same brand. This is because tubes all have different ratings, and your amp will be (or should have been) biased for a particular valve rating.

Pre-amp tubes, however, can be changed without the need to rebias.

[TomW]

Thanks for the reply.
Does anyone know of a good shop in Leeds where they will replace the valves and rebias my amp? What is the average cost?