What is bias a tube amp ? Is it difficult?

Bias determines the operating point of the tube without a signal applied i.e. just sitting there at idle. Some amps want the tubes to be just barely on. Some want them to be biased halfway on.

In most cases it is a simple procedure, some require a multimeter, some you turn a screw until an LED lights up (or just turns off), and many amps have automatic bias so you don't have to worry about it. Any reputable manufacturer should provide a manual with detailed instructions on how to bias their amp. If you are concerned you might want to start with an auto bias amp to see if tubes are your cup of tea.

Don't know enough about those you listed to comment.

When I was toying with the idea of moving over to the tube side, just the thought of biasing with a meter, turned me off completely to the idea of tubes. Getting down on the floor with a meter, checking, obsessing over my tubes? Forgeddabout it. So, I go for a self biasing integrated. Now, after being exposed to the beauties of tubes and becoming truly addicted to the tube sound and if I had the opportunity to purchase a tube amp (that required self biasing) to die for? I'd get down on the floor with my meter and bias away. warren:)

BTW, my SET seperates are self biasing, thank god.

I've had nothing but tube amps for 20 years. I started with the Moscode 600.Several amps latter I moved to CJ. I had the 5's for 4 years and the 8's for about the same amount of time. Both of these have the trim pots for each tube and are a breeze.--So folks don't get the wrong impression, I never did the meter thing. I would just take my amps in to have this done for me. On my Jadis, I ended up waiting till I had 2 bad tubes;then just had all the tubes replaced.---No techie,here.--