amp bias?

[yankcrime]

i have just recently bought a marshall jcm 800 series 2210 from a classified ad, and i was wondering if anyone would reccomend taking it in to get the bias adjusted. do you think this is necessary?

[Lordathestrings]

I'm not familiar with that particular model, but as a general rule, a used tube amp should be thoroughly checked out before putting it into service.

If it puts out more than about 15 Watts, it probably has a push-pull output stage with a separate bias voltage supply. As tubes age, the bias should be adjusted to keep them operating within a healthy range of conditions.

Another very good reason to have a tech look it over before you use it, is the capacitor condition. Most tube amps, especially the older ones, have canister type 'oil & paper' electrolytic filter capacitors in the power supply. Even when they are used regularly, these caps tend to degrade over time. If left unused for a couple of months or more, the caps can fail dramatically if the amp is simply turned on.