Tube biasing

[bsco]

Hello everybody...Hope you are having a wonderful time......I was given to sets of EL34's...same brand...GT's....two tubes in a set....I am supposed to install the four of them as a matched quad.....anyway, I installed them and the amp has a triode/pentode mode switch....the amp is a Marshall DSL100H......one set is rated as a 5 and the other set is rated as a 6 on the box.......and both are also labeled medium......I installed the set of 5"s in the two center tube sockets and the tubes rated as a 6 are installed in the two outer sockets.....I set up the bias so that when in Pentode mode, the bias is 60 mV on each side...which works out to about 30mV per each tube.......when I switch to the triode mode the bias changes to around 65mV per side...isn't this the mode that only uses the two center tubes?? If so, isn't that reading too high?? I just wanted to clarify this here first before I proceed......any thoughts and suggestions always welcome......
Cheers

[The Dude]

All 4 tubes are used in both modes. As indicated, it simply switches the tubes from triode to pentode mode. A slight bias change is to be expected. I'd say you're good to go.

[Leo_Gnardo]

There are 2 bias trimpots, no? If that's the case I'd put 2 matched tubes on one side of the push pull pair, and the other matched pair on t'other side. I generally set DSL100's at 70 mA per pair.

Is the triode/pentode switch a factory install? Can't say I've ever seen one of those on a DSL100H but who knows, Marshall's always adding more bells & whistles. It's easy enough to trace from the switch to the screen grids. I've added such switches to 100W Marshalls, and all 4 tubes are involved in both modes. If that's the case then no worries about the bias current reading you're seeing in triode mode.

[bsco]

Thanks to Leo and The Dude for the info as I wasn't quite sure about the increase in bias.....I'll proceed to finish this up so I can get it out of my way.....
Thanks guys....