Plate fire one of the best places to remove bass or help tailor it to your desired levels is the cathode cap and resister we want to bleed of the bass here if possible your cathode cap there is basically a low pass to ground in the circuit one of the reasons a 5e3 has to much bass is the the cap resister they use there.
Tubenit up above stated he no longer uses a 22 or 25 uf cap there but has found that a 5uf or 2.2 uf is perfect in that position i will explain why as best I can, with the math of course.
The math for this example is that a 22 uf cap and 820 resister cross over bass at 8hz there are two things wrong with this for one your transformer cant even use anything lower that 20hz in most cases and your guitars low e string vibrates at I think 88hz so to much low end bass is making it into the mix lets look at Tubnits favorite numbers here an 820 resister with 2.2 uf cap cross over at 88hz which is often times were we like to start I will do the math so you can see the formula 1/(6.28x820x.0000022)=88hz or (6.28x820x.0000022)=.01132912 so 1/.01132912= 88.268109 or 88hz So in high gain amps this is important to stay in this area lower adds bass that causes flubby bass that sounds bad in the circuit. Thats why you will see things like .68 and 2.7k or 1uf and 1.8k they all cross over at 88hz.
But were not talking high gain were talking fender here part of the beauty of the sound is in adding some extra bass thats why in my opinion the fender cleans are the ones everyone tries to emulate. So my favorite favorite is a 4.7uf in this position in fender because it crosses over at 41hz which to my ears adds a little extra sparkle to the clean. I have to say I do not understand why crossing over a little lower than the guitars usable frequancy of 88hz adds sparkle to the sound but to my ears it does.
Know there are a couple variables here that I dont fully understand so I cannot explain one is the 3db shelving effect over the next 100 hz from were we start are shelving frequency at, but I will leave that to the more knowledgeable here to explain. Im barely able to wrap my brain around this part of it, but it works to tailer your sound and is a usefull tool to use when modding your amp and trying to remove some unnecessary bassiness to any circuit.
Thanks Bill
