Roadster trouble

Today I plugged into my Roadster and found my amp was not working. The volume was very, very low, it sounded like mud, and there was a very loud hum. When I bypassed the loop it was louder but still does not sound right. I assume there there is an issue with a power tube. The power tubes are all glowing and there is no noise when I tap them. Can anybody give me any suggestions? I don't have any extra tubes right now. I have had the amp since 2007 so I should do a retubing anyway. Can someone recommend a good website to purchase tubes? I also want to try a Tung Sol in V1 since I have been reading such good things about it.

I would say it's time for a re tube, I have orderd from http://www.dougstubes.com a few times, if you have any question you could email him and hes usally quick to respond.

I would change V3 & V5. Use either new Mesa 12AX7's (relabled JJ), or Penta/Shuguang.
In 2007 Mesa was using Electro-Harmonix 12AX7's. These tubes have been proven to fail in the cathode follower positions V3 & V5. With 4 years on them I would also change powertubes.

You can troubleshoot the power tubes by plugging your guitar into the FX loop return.

Doug's Tubes is a great vendor. Give him a call or email and he'll help you select your tubes.

Dom

Pluggin the guitar in FX loop return?????
please explain as i do not know this method!!!

Rkorn said:

Pluggin the guitar in FX loop return?????
please explain as i do not know this method!!!

Click to expand...

For troubleshooting you can bypass the preamp this way. If you plug into the FX Loop Return and there is no sound, or just humming or buzzing, then there is a problem somewhere in the output section. If you hear a normal but somewhat lower guitar sound then the problem is in the preamp.

This is not for everyday playing, just to troubleshoot.

Dom

Sounds like a dead preamp tube.

I agree that after 4 years it likely needs new power tubes too... unless you rarely play it.

Ok I have a shipment of tubes from Dougs Tubes coming in tomorrow. The preamp tubes are:

V1 - Tung 12AX7

V2 - High Gain JJ ECC83

V3 - Penta 12AX7

V4 - Penta 12AX7

V5 - Penta 12AX7

V6 - Sovtek 12AX7 LPS

The manual says V1 is the position closest to the input. On a Roadster head it would be the one to the left when looking at it from the rear? Just want to be sure.

Yes, when looking from the back of the head V1 is farthest to the left, kind of tucked behind the Output Transformer.

Dom

When your new tubes arrive you should take the time to find out which tubes are still good out of your originals so you can have spares. I would swap out V3 & V5 with the new Pentas first and see if that fixes your issues. If it does, keep the original V1, V2 & V4 as spares. V6 is the Phase Inverter and should be replaced every other power tube change anyways IMO.

Also, if you play your amp regularly, especially at band volume, you should change those power tubes as well. Doug can set you up with power tubes that will meet Mesas specs. I recommend SED =C= SV6L6GC.

Dom

Thanks Dom, after what you said before I was already going to change v3 & v5 first to see if I can keep some backup tubes. I did end up getting power tubes and rectifier tubes also. I only use the Roadster in a band situation, not for home practice.

I received the tubes today. I changed each preamp tube one at a time to see if i could find the bad tube. Changed them all and I still had the problem. Than I changed The rectifier tubes. I was sent the wrong power tubes by mistake, EL34s. I changed them anyway to see if it fixes it but I still have the issue. Now I am getting worried now.

Start with the simple things. Verify that all your cables are good, instrument and speaker.

Try plugging your guitar into the FX Return (to isolate and check the output section) and see if you still have the same symptoms. If you have another amp with an FX loop you can use it's FX Send into the Roadster's Return instead. You can also isolate the Roadster's preamp by running it's FX Send into the other amp's FX Return.

I'm now guessing the problem is in the output section.

Mesa is closed on Friday so if you are going to call them do it tomorrow.

Good Luck,
Dom

All cables, cab(s), and guitars are ok. I plugged into the effects loop return and I don't get those problems, it is a loud and pure clean output. I don't have a 2nd amp to connect the loops.

Is it possible that it is the transformer?? It just occured to be that by mistake I plugged my Roadster into a Marshall 1960 Cab that I thought was in mono 16 ohms but it was switched at 8 ohm stereo, the head was at 16ohms. It did not show any symptoms then and I changed it.

If you're getting a good output when plugged into the FX Return i'd say your Output Transformer is fine, as well as the rest of the output section. I would think we have eliminated the expensive parts of the amp.

This seems to be in the preamp, as you have proved that everything after the FX Return works properly, and you are not blowing fuses. Maybe there is the remote possibility that you have another bad preamp tube?

Call Mesa, they will put you on the right track.

I hope it's nothing too serious.

BTW- I know an excellent Mesa Certified tech if you are in the CT/NY City area.

Good luck Brutha......

Dom

Thanks Dom, I will let you know if I need that tech's #. - Bill

Bill,
Just wondering how you are making out with your Roadster. Have you made any progress with this?

Dom