Gain issue + 443 vs 440 power tubes

[user 83985]

Hey guys. Bought my JP-2C a year and a half ago and when I play through it now, CH 2 feels as it has lost a considerable amount of gain...so bad it feels like I have the volume knob on my guitar rolled down. Even with the gain pulled and on max there is no feedback and palm mutes in drop C sound really weak and thin, unlike how it used to sound. I have the shred mode engaged on that channel as always, using an EMG 81 with a brand new battery and a mogami gold instrument cable, now plugged straight into amp, and a mogami gold speaker cable to my cab. I unplugged my effects loops cables from the amp to see if that was the problem since I run the 4CM through some pedals and a midi switcher. Unplugged my two notes captor X and didn't help. Nothing in my signal chain has changed since I've had it, just the sound. Guessing that it is probably a tube issue but not sure where to start..power or preamp (Power tubes aren't red plating). Also, I wondering which power tubes you guys had in yours stock and what the sound difference between 443's and 440's is? Mine came stock with 443's but not sure if maybe I would benefit from 440's for a harder metal tone? Any help is appreciated to get this beast back up to par. Thanks.

 

[tjt73]

Normally I would say it sounds like a tube issue, but, if it were it should effect channels 2 and 3 not just 2. They use the same tubes. Are you just using shred on 2 or 2 and 3? As far as power tubes I've gone the opposite. Mine came stock with 440 and I switched to 443. Made only a slight difference.The 440 are a bit crisper. Slight EQ change and it sounds the same.

 

[Lokair]

First set ch2 and ch3 to about the same settings if ch3 is doing good and ch2 is wonkey then(turn off the EQ's for this on both channels and turn off the efx loop, make this as simple as possible, turn all reverbs to 0.) , take and start by replacing preamp tubes one by one(take tube v1 out put in fresh tube , try amp if no change replace tube v1, and try swapping out tube v2 and so forth),tube v1, v2, v3, v4 . If this does not fix the issue then its time to take it in for service. Channels 2 and 3 share all tube gain stages so I think your issues could be in the channel . In all likelihood your gain pot could dirty on ch2 but it could also be something less obvious that good amp tech will find quickly with the proper tools. The power tubes really do not do anything other than amplify the pre signal so a problem with them would be across all channels not just one.

Afew things to note before taking it in, check all other functions , shred works on ch3 , eq1 on ch3 works as intended(or eq2 for that matter), the effects loop works, on ch3 , the footswitch works as intended. if your gonna have it for service may as well have anything else fixed too.

The 443 is the stock tube for the JP2C, So that is not really the issue here.

Lok

 

[user 83985]

Just received some new Mesa preamp tubes so I will start with your advice and see what happens. Thanks for the help! I have noticed that after playing CH3 it is also lacking the gain as well. I use CH3 for my leads so the issue is not as noticeable on the single note and legato runs but with big chords the sustain and feedback just isn't there. Do you guys pull the whole chassis out to switch tubes, or just take off the front grill? Only have changed tubes in a triple recto some still getting used to the Marks. Thanks again guys!

 

[tjt73]

I just take the front panel off to change the tubes. It's much easier getting in there. Good luck. Hopefully you get it sorted out. It's a great amp.

 

[user 83985]

Well, I went and changed every single tube in it to try to solve the problem and the sound hasn't improved at all. So I packed it up and sent it to Petaluma to see what's wrong with it (no decent repair shops near me at all.) Thanks again for the help, hopefully here in a few weeks it will be back with me sounding like it should.

 

[El Rey]

Well, I went and changed every single tube in it to try to solve the problem and the sound hasn't improved at all. So I packed it up and sent it to Petaluma to see what's wrong with it (no decent repair shops near me at all.) Thanks again for the help, hopefully here in a few weeks it will be back with me sounding like it should.

What was wrong with it?

 

[bandit2013]

It has been almost 2 years since this post was made. Anything to report?

I would have tried replacing the power tubes before shipping it out. Sometimes they can drift due to use and become weak in character. If that did not make a difference, then it gets a trip to California.