Apologies for the very green question. I have built kits before and know I prefer certain parts in specific locations if at all possible but to be honest do not understand the math/science behind it. This amp will be a stock (but I do intend to upgrade to the C4S, unsure about the iron yet). I was wondering what ill effects there would be if I used a few resistors that were slightly rated different than what comes with the kit (watt rating will match or be higher in the replacements that much I do understand). Specifically these:
Kit: Possible substitute:
1.27k ohm 1.3k ohm
249k ohm 250k ohm
620 ohm 600 or 680 (prefer the 680's brand if possible)
C4S
Kit: Possible sub:
270k ohm 330k ohm
OK, the 1.27k is actually a 1% resistor but it does not need to be better than 5% - I like metal film for stability and low noise in this position.
The 249K is a grid resistor and can be anywhere from 150K to 500K, so again the fact that it is a 1% part is not critical. It does not carry any DC current so carbon or carbon film are reasonable alternatives. (Metal oxide has a poor reputation for sonics so I'd stay away, though I've never done the experiemnt myself.)
The 620 ohms is indeed the bias resistor. It's a 5% part and should be rated at least 2 watts; it dissipates some heat so stability is important. The value is critical; I would not use a 680 ohm part, and in fact would not stray more than 5% (and even then, only if you can get a 1% part to replace it).
The 270K in the C4S is the LED bias and can deviate 10% without problems, however it does drop 350 volts and must be rated to withstand at least 400 volts DC, working voltage not dielectric strength. We have had some bad experiences pushing resistor working voltage ratings, so a 500v part would be more confidence-inspiring.