Simul 2:90 Issue - Where to Start Troubleshooting?

[IndyWS6]

I had an issue with the Simul 2:90 that I use for power in my rack rig during a gig on Friday. Towards the end of the second set, the output from my cabinet dropped considerably (less than half) and the tone had no balls to it. Even on my highest-gain preset, there was barely any crunch to it and it should have been ripping. On a clean patch, it was almost inaudible. Cycling power didn't help, so I scrambled and ran straight to FOH from the 11R for the rest of the show. For reference, I had something similar happen a couple of months ago, but at the time I thought it was a problem with the electronics on one of my guitars. I unplugged, plugged back in and cycled power on the rack and everything was good. In fact, I have had no problems using the rig for about a dozen gigs since then.

We played back-to-back this weekend, so I took a tube head as a backup on Saturday. If I run the rack rig out and use the power side of the tube amp, all is good. It's not a definitive test, especially if the problem truly is intermittent, but my gut tells me that the signal chain in the rack is not the source of the isue. When I fired-up the rack rig to test, it was fine with the exception that I have a faint intermittent "crackle" or "static" type of noise coming from the cab (similar to an AC-induced type of line noise). It's barely audible, and it's not constant, but it's there. I didn't use the rig because it was an important show and I didn't want to scramble again if it failed mid-song.

I have done a lot of troubleshooting (cables, connections, loops, etc) and I am certain that the problem lies in the Simul 2:90. Here are some facts:

• I bought it used, but it was advertised as essentially new-in-box with almost zero time on the tubes. No reason to doubt that
  I have used it for about 30 4-hour gigs over the year that I have owned it
  It never gets hotter than one would expect. There is reasonable airflow in my rack. The problem does not seem to be heat related
  The power tubes all appear to be normal (no wierd colors, obvious arcing, etc)
  My cab is wired for stereo and the loss of volume and grunt occurs on both channels of the amp

I would have to ship that heavy mother to Mesa or drive at least two hours to get to a qualified tech. It would be great if I could fix it myself, or get to a shortlist of possible reasons for the issue before doing so. I can swap tubes and am more than reasonably handy with electronic gear, but I don't have the tools or experience needed to work on a tube amp. I have no desire to be electrocuted.

If it was a power tube issue, I would expect it to be one side or the other. If it was a pre-amp tube, I wouldn't expect for it to be intermittent. Suggestions?

I apologize for the long post - just trying to provide enough details to skip past the obvious things.

Thanks in advance...

 

[SDMF38]

Which version is this? Series one with the blue light had a problem, with the molex connector getting hot and losing contact with the other end, and eventually the power amp would not work.

 

[IndyWS6]

Which version is this? Series one with the blue light had a problem, with the molex connector getting hot and losing contact with the other end, and eventually the power amp would not work.

Looks like the date on the bottom says 2010 and it has a red light on the front that, I assume, is original. Here's some photos (hope they show up...)...

 

[IndyWS6]

P.S. Pay no attention to the Serta Sheep in a "69" pose on the nightstand...

 

[IndyWS6]

Any of you amp experts have ideas?

 

[jerrydyer]

I dont know where your at, but out here are a bunch of old boogie guys that could fix it. Michael Campion is out here and can direct you and James Art Reno is still here in CA. you might have to shi out here. Ive never been inside one. I think they had a simple layout back then so a real tech out your way should be able to figure it out. I had the strategy 400....

 

[IndyWS6]

I dont know where your at, but out here are a bunch of old boogie guys that could fix it. Michael Campion is out here and can direct you and James Art Reno is still here in CA. you might have to shi out here. Ive never been inside one. I think they had a simple layout back then so a real tech out your way should be able to figure it out. I had the strategy 400....

Thanks... I'm hoping it's something "simple" and someone on here can steer me in the right direction. I don't have it out of the rack yet (still in the gig trailer...), but I'm going to pull the cover off and look for anything obvious. Short of that, it will go to a qualified tech.

I'm near Indy and there's really only one person I know of that works on tube gear. I've heard good and bad, so I'm a little leary. If I can't zero in on the issue with help from forum members, I'll probably have to put it on a truck heading towards CA. Hell, it might still be under warranty - need to check that.

I may hit you up for contact information if I need to look someplace other than Mesa...

 

[IndyWS6]

Hello? Beuller?

<crickets chirping bump>

 

[SDMF38]

It is one of the newer ones, but pull the top off and look at the molex connector to the board,
This is where I'd start.

 

[jerrydyer]

I dont know where your at, but out here are a bunch of old boogie guys that could fix it. Michael Campion is out here and can direct you and James Art Reno is still here in CA. you might have to shi out here. Ive never been inside one. I think they had a simple layout back then so a real tech out your way should be able to figure it out. I had the strategy 400....

Thanks... I'm hoping it's something "simple" and someone on here can steer me in the right direction. I don't have it out of the rack yet (still in the gig trailer...), but I'm going to pull the cover off and look for anything obvious. Short of that, it will go to a qualified tech.

I'm near Indy and there's really only one person I know of that works on tube gear. I've heard good and bad, so I'm a little leary. If I can't zero in on the issue with help from forum members, I'll probably have to put it on a truck heading towards CA. Hell, it might still be under warranty - need to check that.

I may hit you up for contact information if I need to look someplace other than Mesa...

ill see if I can get some numbers. I have a close friend bill pomeroy who used to sit in with some of the beach boys for Doheny Fest, he knows all the boogies still so, ill check it out.

 

[IndyWS6]

I dont know where your at, but out here are a bunch of old boogie guys that could fix it. Michael Campion is out here and can direct you and James Art Reno is still here in CA. you might have to shi out here. Ive never been inside one. I think they had a simple layout back then so a real tech out your way should be able to figure it out. I had the strategy 400....

Thanks... I'm hoping it's something "simple" and someone on here can steer me in the right direction. I don't have it out of the rack yet (still in the gig trailer...), but I'm going to pull the cover off and look for anything obvious. Short of that, it will go to a qualified tech.

I'm near Indy and there's really only one person I know of that works on tube gear. I've heard good and bad, so I'm a little leary. If I can't zero in on the issue with help from forum members, I'll probably have to put it on a truck heading towards CA. Hell, it might still be under warranty - need to check that.

I may hit you up for contact information if I need to look someplace other than Mesa...

ill see if I can get some numbers. I have a close friend bill pomeroy who used to sit in with some of the beach boys for Doheny Fest, he knows all the boogies still so, ill check it out.

Thanks

 

[Anonymous]

where are you located?

first thing i'd do is check the preamp tubes in there....they're supposed to act as PI tubes, right?

anytime i hear intermittent hum and weird buzz, dropped output, i always think 'PI' tube...so i would start there.

if'n that dont get you fixed up, a new quad of known good power tubes would be the next step, and swapping them out.

you can also take a peek over at the grailtone.com site....there's a TON of info on there.
do a search for the author Timbre Wolf, that guy is a wealth of 2:90/triaxis and general tube info.

 

[IndyWS6]

where are you located?

first thing i'd do is check the preamp tubes in there....they're supposed to act as PI tubes, right?

anytime i hear intermittent hum and weird buzz, dropped output, i always think 'PI' tube...so i would start there.

if'n that dont get you fixed up, a new quad of known good power tubes would be the next step, and swapping them out.

you can also take a peek over at the grailtone.com site....there's a TON of info on there.
do a search for the author Timbre Wolf, that guy is a wealth of 2:90/triaxis and general tube info.

I'm NE of Indianapolis...

I'm going to get the rack out of the trailer this week and pop the cover off to look for anything obvious. The Molex board connector seems to be a popular place to start looking... Honestly, I'm not sure how the preamp tubes are configured in that amp. It's not really intermittent hum; the loss of volume and lack of grunt is intermittent, in so much as it has happened a couple of times. When I fired it back up to test after the latest issue, I heard some very faint noise that was reminiscent of induced AC line noise, although not exactly the same. It was barely audible, but the rig had been almost dead silent before that, so I figured it was worth mentioning.

Although I'm not ruling out anything at this point, I doubt that it's a power tube issue. It's a stereo power amp with 4 tubes on each side (8 total) and when the volume drop occured, it happened to both sides of the amp. (My 4x12 is wired for stereo, so it's easy to hear that the issue affects both left and right channels). It's not impossible, but would seem improbable that I would have flaky tubes on both sides...

Thanks for the information; I'll take a look at that site and see if I can find anything useful...

Mark

 

[SDMF38]

Well the good news is you have to pull the top to change the pre amp tubes so you can check the molex connector while your in there.

 

[somata]

Start with the tubes. The problems as you describe them definitely suggest a tube problem. I'd start with replacing the preamp/pi tubes and then move on from there. As for the power tubes, they don't always change color or fail before they need to be replaced. On my Dual Recto, I know it is tube change time when my low end starts to get raggedy. I usually get about a year out of them.

I've found Mesa gear to be very solid and reliable, so while it could be a deeper problem, given their track record, the odds are in your favor. You might give them a call and see if they can offer any insight.

If nothing else, we have a great tech here in South Bend!

 

[IndyWS6]

Start with the tubes. The problems as you describe them definitely suggest a tube problem. I'd start with replacing the preamp/pi tubes and then move on from there. As for the power tubes, they don't always change color or fail before they need to be replaced. On my Dual Recto, I know it is tube change time when my low end starts to get raggedy. I usually get about a year out of them.

I've found Mesa gear to be very solid and reliable, so while it could be a deeper problem, given their track record, the odds are in your favor. You might give them a call and see if they can offer any insight.

If nothing else, we have a great tech here in South Bend!

Thanks for the information - I'll definitely be taking a look at the tubes.

Is the tech in South Bend able to do Mesa warranty service?

 

[IndyWS6]

I finally had time to take the Simul 2:90 to the shop (I found an authorized Mesa service location about 30 minutes from me...). He put it on the bench and checked everything. All of the tubes, as well as the caps, transformers and voltages tested "good". Long story short, he couldn't find anything that was obviously wrong. After spending some time with it, it appears that the problem was nothing more than a flaky pre-amp tube. Even though it tested "OK" and the amp wasn't showing the symptoms you would normally expect from a bad pre-amp tube, replacing it fixed everything.

Now I'm back to cranking my rig (with the "Deep" function engaged - see my other post) to levels that will sterilize small woodland creatures