Resistor on power tube pin 5

[Bluefire_81]

Hi !!!

It's my first post here, been reading for quite long and i've built 2 amps since.

Can someone explain to me the difference between 5.6K resistor on pin 5 of each tube socket and the 1.5K between the two pin 5 of V6 and V7 ( or V4 and V5 ) On a 100W model 2203.

Thanks

BTW sorry for my english !!!

[neikeel]

They are there as 'grid stoppers'. They minimise parasitic oscillation in the output stage.

The 1k5 between the push-pull pairs are ok but do not actually give you stoppers n the inner two of the pair, whereas the individual ones on each pin5 do. This is more effective on higher gained or modded amps. If you go too high you can get some high end roll off. Try any value between 1k5 and 10k as you like. Marshall used 4k7 and 5k6, presumably values that worked for them. The 1k5 only on outer pairs seems to work fine on SB and early SLs.

[Bluefire_81]

Thanks !!!

So better have stopper on each grid to stop oscillation ???

[stef]

That's right