Hey guys,

Something I kind get my head around. I've been playing around with a jc18 for a while, but I cant get to tighten it up. When palm muting and playing low notes it just seems like there is a lot of sag. (Or compression) Like how low notes get squashed by a fuzz. 

I did make the 2nd gain stage cathode switchable between 10 and 5 k

Its most prominent when the gain is turned all the way up. (Also gain on the high input seems very low) b+ Voltages seem to add up though. Also I have replaced all preamp tubes multiple times, tested with different cabs, load boxes. etc. the problem is there with the master low or high, so it's deffinately in the preamp section.

Should I suspect the power supply? Any other jc18 of px18 owners that can reflect on the tightness of their amps? It either has to be the Power supply, blocking distortion or grid conduction?

I love to hear what you guys thinks!

Generally, because of the bright cap across the gain pot, a JCM 800 stylle (or should I say 2203/2204) preamp can get muddy with Gain on full, depending on your pickups. 
Keep in mind, that because of the bright cap, you have alway full gain for higher frequencies, and you somewhat "fade in" lower frequencies. Now, with that you can pretty easily find asweet spot for the lows not getting muddy. This is how I dial in my Jubilee clone to dapt my different guitars, since also has a bright cap across the gain pot.

If this is not satisfying, or a solution for, and it still sounds muddy to your ears, it would be best to give us some good sound sample of the behaviour. Then we can estimate if this is rather normal or sounds like if there's something wrong.

Hey,
I just built a PX18 and the thing just sounds killer. Depending which guitar i play i get more sag but i can tighten it up by rolling the bass down a bit. Have you checked your connections? Sometimes a solder joint can look fine and its not making proper connection...

Marco.