Potential New JP2C Owner

The Boogie Board

Help Support The Boogie Board:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

ntotoro

Well-known member
Boogie Supporter
Joined
May 12, 2024
Messages
86
Reaction score
35
Hi, everyone!

A friend of mine has a Mesa JP2C I'm contemplating buying that is sounding weak... really weak. I'm not too familiar with the nuts and bolts of these, but I've heard tons of clips and know the thing isn't right.

Clean channel seems strong and loud enough, channels 2&3 are just weak, regardless how I set them. Low-gain, even cranked and with the gain knob pulled out, bright and thin.

There is also some muffled popping coming when plugged into a cab. I reseated all the tubes, thinking that would be the first thing to try... no dice. No better, but also no worse. Do you all think it's a preamp tube? I found a tube layout diagram, but hoped you all would have far more experience and guidance.

Thanks!

Nick
 
Do you have any other 12ax7s to swap in and compare to? That's usually step one. If that's not it, then it's time for repairs maybe.
 
Looking at the tube task chart in the manual it looks like all the tubes have some influence on channels 2&3.

IMG_2208.jpeg


https://mesa-boogie.imgix.net/media/User Manuals/070494-JP2C-160317-download.pdf

Dom
 
Thanks, I'm gonna save that... and get at least four new preamp tubes to roll LOL! Maybe swap positions... doesn't necessarily have to be multiple bad ones.
 
Agreed. The current Mesa preamp tubes are JJ’s, just be sure to get them from a reliable vendor.

Sometimes the shotgun approach is warranted, and gives piece of mind that you have all good tubes.

If you do change them all out you don’t overlook the phase inverter (V5).

Dom
 
Agreed. The current Mesa preamp tubes are JJ’s, just be sure to get them from a reliable vendor.

Sometimes the shotgun approach is warranted, and gives piece of mind that you have all good tubes.

If you do change them all out you don’t overlook the phase inverter (V5).

Dom

The tubes that are in there now are a mix of two JJ's and three Mesa branded tubes. Does that sound like the way it would have left the factory?

Is the LPS still considered the "go-to" PI tube?
 
If a retube of the preamp doesn't fatten it up, don't overlook potential power tube issues. Also, is the 100/60 watt switch in the 60-watt position? That can sound a tad thinner, especially if you're used to the 100 watt setting. Your ears get over it quick though...
 
This is based on my observations with a 2016 model. Newer models will have different transformers so the results may vary.

I would first look at the power tubes. If they are Mesa tubes, there should be a silver label on them, usually on the plastic base of the tube. On that label will be a three letter code. RED (obvious), YEL (yellow), GRN (green), GRY (gray) and BLU for blue. The red or yellow bias codes will have more headroom and less power tube distortion. JP2C does rely on that power tube saturation. Green or grey is what you should have in the amp. The Class A/B power section is different than the Simul-Class used in the Mark IV, V or VII that will drive that extended class A (push-pull) into saturation or distortion with ease. You do not have that with the JP2C so you need a power tube with early onset of distortion in the green, gray or even blue bias colors.

When the STR440 tubes went out of production, I had tried a few of the other offerings like the STR441, STR443, and eventually the STR445 and STR448 before settling on the Mesa STR415 NOS tubes that are not easy to get. the STR445 in green or the STR448 in gray bias colors were the closest I could get to the STR415 characteristic. The STR443 was a bit lame, they were ok I suppose but not great. I got those in the gray bias color. The STR441 tubes in green were very lame. I did not get any distortion from the amp with those, if I did, it was not very impressive. When it comes to the power tubes in a class A/B amp, the onset of distortion may make or break the full gain characteristics of the amp.

Side note: some amps are better served with the higher headroom in the red or yellow bias color ranges. Roadster is one prime example. Reds actually sounded the best. Most of the drive characteristic is from the preamp. MWDR on the other hand, the green or gray range was really good. Note this is based on the STR440 tubes. The other models STR441, STR443, STR445 and the STR448 may or may not behave all that great in those amps. The same can hold true for the JP2C. Depends on the tube impedance as well as the onset of early distortion. This amp seems to perform much better with more power tube distortion than the other amps like the Roadster or even the Mark VII.

A note on the alternate Mesa tubes: STR445 tubes vs the others, they are a very tight fit due to the slightly larger pins. They will fit into the socket, just takes a little patience to seat them properly. Those are the stock power tubes Mesa uses on the Mark VII and the MWDR.

STR448, tube length can be a problem. They are longer than the original STR440, which is about the same size as the STR415 tubes. I could not make use of the metal tube cage after I got them into the amp. Cage would not fit. they are difficult to install but it is possible if you angle the tube and get the pins aligned properly.

As for the popping noise, I was getting that with the original STR440 tubes. I first thought it was a preamp tube. Nope. It was the power tubes. That was the turning point when I got the alternatives, before I knew the STR440 tubes were discontinued. STR443 did curb some of the fizz and did not pop but had too much low end and lack of desired saturation effect. STR440 tubes were far better. That was when I first realized how much of the desired gain characteristic was also part of the power tube section. It is not all preamp tube distortion like many may believe. It is a Mark series amp, not a Rectifier amp. Dual or Triple rectifiers are more preamp distortion than power tube distortion. May not apply to all of the range of Recto amps. I only have two in my collection, Roadster and the MWDR. the MWDR is a bit different and you can get away with more power tube distortion but not the Roadster. It is just an opinion based on observations in finding the replacement for the STR440 tubes.
 
If a retube of the preamp doesn't fatten it up, don't overlook potential power tube issues. Also, is the 100/60 watt switch in the 60-watt position? That can sound a tad thinner, especially if you're used to the 100 watt setting. Your ears get over it quick though...

Man... I have to thank you all, I did come to the right place LOL!!!

I do have it at the 100-watt setting. Wanted to make sure of that, just in case LOL! One thing I did notice, the power tubes wouldn't all sit flat and I wasn't certain that would be an issue. Three of the four would show a gap of roughly .5mm gap where I could see air. Didn't matter what order I put them in. The reason I didn't think the power tubes were an issue was that the clean channel seemed strong and didn't have the muted hiss pop things. Wondering if that rules out V2... ? Either way, might be best just to swap them all out.

@bandit2013

Didn't want to put the entire post since you had some amazing info there. Thanks so much.

The power tubes are Mesa-branded, STR 443's. I've attached a pic of what I see, the small air gap at the bottom. I did turn the pic "upside-down" to make it easier to visualize. Is the silver stripe along the bottom what you mean by the rating? I'll have to look at the actual code later when I get a chance.

Nick
 

Attachments

  • Gap.jpg
    Gap.jpg
    485.4 KB
V2b is used for all 3 channels as gain stages. V2a if the FX return buffer, that would also affect all channels.

V3 & V4 are gain stages for just Channel 2&3 (and the reverb buffers). Start with those.

Dom
 
Ok, I was wrong, it is not silver but mostly black with a thin silver area on the bottom. The color code will be printed on that silver area. I could not see what the code was in the picture, perhaps it is not in view.

The gap is not an issue. Mine do not sit flush to the socket either. Sometimes the screw on the bear claw will interfere. If the pins are longer than normal, that will do it too.

I would agree with Dom, on the V3 or V4. Do you remember where the JJ branded tubes were located? They should be marked as ECC83 on the glass. They will look much the same as the Mesa branded tubes (they are the JJ ECC83) and are bought in bulk without any printing. Mesa prints their name and part on the glass after they get tested and sorted. Rejected tubes do not get the branding and I assume are disposed of. At least that is how I understand it.

Look at the JJ tubes twice, there are ECC88 available too and they look the same. Not the same tube though and should not be used. Way different gain range that is not even close to the 12AX7/ECC83 range. I only state this for a reason, I bought some JJ tubes from Tube Depot. I wanted the frame gride ones, E83CC which are supposed to be an improvement. What I got from them was E88CC. They look identical to the Mesa tube, however the 88 are not the same, much, much lower gain factor and pin 9 is not connected.
 
At least the power tubes are in the bias range that sound better in the JP2C.

Since it was/is your friends amp, have you asked that person if the amp always behaved this way? Was it bought new or used? And why the JJ tubes? There is a slim chance Mesa could have shipped the amp with the JJ branded tubes. There was a rash of tube scarcity going on, more or less related to the pandemic and lack of materials like the glass tubing, compound for the getter flash and stuff. Hard to say, it was difficult to get Mesa branded tubes for the past 2 years. Now things are back to normal.
 
@bandit2013

That's going to be my question today, now that you all have shown beyond the shadow of a doubt that this isn't totally factory. They could even be super low-rated ECC83's. Or just bad.

I currently have the amp to look it over and will replace those two tubes and see how it is, then go from there. I told him about the sound and was met with a "Huh... " so...
 
Last edited:
@bandit2013

That's going to be my question today, now that you all have shown beyond the shadow of a doubt that this isn't totally factory. They could even be super low-rated ECC83's. Or just bad.

I currently have the amp to look it over and will replace those two tubes and see how it is, then go from there. I told him about the sound and was met with a "Huh... " so...
Some people just don't know
 
Long story short... it didn't work LOL!

I had four 12AX7's around and used them in every combination I had to test them, using one of the "original" tubes alternated at any time.. I lost track of how many combinations that was LOL!

It made no difference at all. No better or worse. I noticed turning up the volume that the clean channel had the hiss, also. Off to try 6L6's...
 

Latest posts

Back
Top