'?? differences in biasing GEC KT77 compared to EL34 in JMP marshall'

[Bonenut]

hi folks ,
i have just got two healthy looking GEC KT77s for my '69 small box 50 watt marshall...
i believe unlike the new JJ 77s they are not a straight plug and go replacement for the existing EL34s. can anyone talk me through their experiences with these valves ? will i have to change a resistor in the amp near bias pot and if so , what values are a good starting point?
or is the bias pot usually of sufficient range to suit? [p.s. i am not very knowledgable in biasing amps and usually just use good old stock valves and my ears while watching for redplating with no big problems so far!]

all advice much appreciated....

[Blue Strat]

The only way you'll know is to plug them in and check the bias. No one can answer this without checking the bias range of those particular tubes in your particular amp.

Shoot for about 35mA. If you can't get low enough, increase the value of the bias range resistor by one standard value. If you can't get high enough, decrease the bias range resistor by one standard value.

[Bonenut]

Thanks Mike!