please help with a roadster problem(no not the popping)

[farmerboy]

Hey guys,

I am new to this board, mostly because i got my first mesa recently. I absolutly love my roadster, not here to bash but i got some serious problems. I have had my roadster for a little over a month, i had one specially delivered from the factory, i am the only one who has ever played it. Everything has been golden untill the other night. I had played the night before for about five hours, and when i turned it off the night before it was fine. The next night when i fired it up i had absoulutly nothing.

Being an owner of other tube amps, i started trouble shooting. Here's what i've done:

Using my spare set of tubes, i tried to tube swap thinking that it was a bad power tube. worked my way thru all the power tubes with no joy.

Next I checked to see if it had something to do with the settings of my channels, but after flipping switches and turning knobs to every possible confinguration, i still have nothing.

A few things i have noticed:

I have the standard pop when switching to the 3rd channel. I also get a pop occasionaly when i switch the effects loop bypass on the back.

I normally run in spongy mode, with tube recto on all channels & 50 watt, but i have tried switching to diode, bold and 100 watt with no effect.

Power tubes 2 & 3 filliments glow brighter than those of positions 1 & 4. All tubes glow the standard blue when fliped off standby.

recto tubes are as bright as positions 1 & 4.



Any help would be very much appreciated. I have been without a good tube amp for about 5 days now and i think i am starting to get withdraws!!

 

[domct203]

Did you try swapping preamp tubes? This could be a bad 12AX7. Try V3 and V5 first, these positions are notorious for totally destroying a weak tube.

Good luck,
Dom

 

[jdurso]

Did you try swapping preamp tubes? This could be a bad 12AX7. Try V3 and V5 first, these positions are notorious for totally destroying a weak tube.

Good luck,
Dom

+1

If the tube is blown the cap on it might be white or clear.

 

[TheBlackman]

Few obvious, but sometimes over looked things:
Did you check the fuse, power cord, wall outlet/power bar and coresponding circuit breaker? Also, anything in the loop that could be the cause?

 

[farmerboy]

Thanks to all those that replied,

I finally got in touch with a service guy at mesa. He belives that it was caused by always running in spongy mode(never heard of such a thing). Long story short i have to have it taken to a tech to check out. He beleives that the position 2 & 3 power tubes are "red plating" and said that if i want to keep running in spongy, i need to concider using a voltage regulator. Anybody heard of this kind of issue. I never heard anything about running in spongy causing internal problems.

not the best way to start off with my first boogie.

 

[domct203]

I'm no EE, and I'm not trying to second guess Mesa here but I thought 'Spongy' lowered voltage to the amp. My bias probe tells me this is the case with the output section. My Roadster with STR-440's in Bold/Diode run at around 40% of max plate dissipation (431 Plate Volts at 28mA), and in Spongy/Diode that drops to a very cold 24% (353 Plate Volts at 20.5mA), hardly re-plate territory.

I would still at least look for a blown preamp tube. If you are at all uneasy with it then find a local Mesa Certified tech. to check it out. Better safe than sorry, and you don't want to screw yourself on the 5-year warrenty.

I'm sorry to hear of the troubles with your Roadster. Mesa's are known to be very reliable amps, and in the 8+ years I've been playing Recto's I've only had two problems and both were due to bad tubes, not the amp.

One time it was a blown preamp tube in V3. I had the exact same symptoms that you described (fine one day, no sound the next), and after checking I found the tube in V3 had blown (the silver getter flash inside the top of the tube was turned to ashes). Changed it out and all was fine.

Maybe someone else here can chime in on this "Spongy Red-plating" issue.

Dom

 

[domct203]

Also, have a read here:

http://forum.grailtone.com/viewtopic.php?f=24&t=34668

Dom

 

[jdurso]

I agree with Dom... check your preamp tubes. I had your exact same problem a few weeks ago and low and behold, my V2 preamp tube blew its bottom... literally. I would just take a look as if it is the preamp tube, its a very simple fix. At least if its not you KNOW the amp needs to go to a tech... although i question his assessment. Spongy mode will always draw less voltage because thats the whole point of the mode. Let us know how it turns out.

 

[farmerboy]

Thanks guys.

Sorry about being slow to reply. I've been busy rockin the amp!!

It turns out it was blown preamp tubes. The shield springs weren't centered and i guess they knocked off the little "crown" if you will of the tube. Both tubes had gone white. I just don't get how it could have operated fine like that for that long then all of the sudden go bad? Anyway its back to playin' my little heart out. By the way Dom, it was V3 & V5. Any suggestions about the best tubes to use in these positions.

Thanks,
Farmerboy

 

[domct203]

............... By the way Dom, it was V3 & V5. Any suggestions about the best tubes to use in these positions

As far as current production tubes the new Mesa Russian 12AX7 (JJ ECC83S) will hold up well, as well as the 9th generation Shuguang Chinese 12AX7. The Mesa Russian-1 (Sovtek) and Russian-2 (EH) 12AX7 don't handle those positions very well. Before I took to NOS/VOS tubes I would run a JJ 803S (longplate) in V3 and the Shuguang in V5 with good results. My favorite for V3 is a Vintage GE 17mm longplate, and a Vintage RCA 12AX7 or Mullard CV2024 (12AT7) for V5.

Dom