HI Steve, thanks, it's to go in a music from outer space system I've been building, well actually it is already in the system just i've been noticing some spiralous noises and quite a lot of undulating hum/distorted/noise coming from it at times and realised I hadn't paid enough attention to the fact it was designed to run on a different voltage, lazy really, just assumed it'd be fine..... electronics tends to not like my assumptions
"Calculate the voltage on the base of Q3 from resistors R17 and R43"
I hope i'm getting this right, in that i just use a voltage divider calculation?
So here's my calculation based on original component vlaues
15 (v) x 1.5 (R17) = 22.5
120 (R43) + 1.5(R17) =121.5 22.5/121.5 = 0.1851
So the answer 0.1851 needs to remain (or be as close as possible) when adjusting the divider accepting 12v and changing R43?
And with R43 changed to 100K and voltage at 12v
12 (v) x 1.5 (R17) = 18
100 (R43) + 1.5 (R17) = 101.5 18 / 101.5 = 0.1773
Is that close enough?
Actually I stopped here and realized I should be able to calculate, I needed to get some help off a friend though to help me through the steps needed to isolate R43, the calculation needed is;
V source x R17 / V out - R17 = R43
12 x 1.5 / 0.8151 - 1.5 = 95.74
As for the other pairs of resistors, i'm unsure how to calculate these, or at least what calculation is required? Maths is still very new to me, but trying my best to learn and catch up