Roadster Effects Loop not working correctly

[fullreleaseblake]

I recieved my Roadster amp at the begining of Sept., and the Effects Loop worked great at first. When I went to set it up at a show though it wouldn't work for me. When I run throught the effects loop and flip the switch to engage it, I get very little sound coming out of the amp. It doesn't matter what level the send level knob is at, it still running at a volume that sounds like the channel volume is barely cracked open (and this is with the channel volume and the output levels maxed out). Now when I bypass the effects loop and run everything straight into the front of the amp, it runs like normal (all channel volumes run at normal level). I have talked to a rep at MESA, and the tech told me to run a patch cable from the send to the return to engage the loop with out any effects (that way I wouldn't have any potential problems with the effect pedals or additional cables to contend with testing the loop to see if it's working properly. While I understand this logic, I believe that I will end up with the same results, as using the effects pedals with the same cables I would normaly use for the send and return straight into the front of the amp has yielded no problems.
I'm gonna give his suggestion a try when I get home, but I just wanted to know if anyone else has had a similar issue that has been diagnosed.

Thanks,
Blake

 

[pokerrules47]

Hi Blake,

If you do the test and it runs normally, then your amp is not at fault. If the test yields similar results, you may have a problem with your amp. When you say you "flip the switch" to engage it, do you mean the efx loop bypass switch or the button on the foot controller? If it's the loop bypass then you may have a problem with a tube. I have experienced this with my roadster before and I just replaced v4 and everything was fine after that.

 

[KH Guitar Freak]

What the tech is actually saying is that you may have had some sort of connection problem when you ran your pedals into the loop. Plugging a patch cable between the send and return removes the pedalboard from the chain, hence you can see as to whether it was the pedalboard or the loop that was at fault. If it's the latter, I would try changing the preamp valve in V4...

 

[fullreleaseblake]

Same results with the patch cable in the send & return loop. In fact, the "send level" knob does nothing at all as far as the volume level goes. I'm thinking it's a tube issue like what was said in the previous replys. To late to call MESA now, so I'll let'em know in the morning.

How difficult is it to change the V4 tube?

 

[pokerrules47]

Tube replacements aren't typically covered under the warranty. Mesa considers them "user serviceable" parts and also, like wiper blades on a car, are consumable. That being said, They are hella easy to replace. Just read all of my instructions before you attempt this. It's a good idea to learn this, and to keep a full set of power/rectifier tubes and at least 3 pre-amp tubes available for quick replacements. At least one of your mesa pre-amp tubes must be of Chinese origin and reserved for v3 or v5 as these are cathode follower positions.

If you look in the back of the amp, you'll see 6 large tubes, going from left to right are the power tubes (4) and then two rectifier tubes.

The pre-amps are v1 v2 v3 v4 v5 v6 in behind the power tubes from left to right. They are covered by spring loaded tube covers. V1 in any amp is always closest to the input tap. (correct me if I am wrong here) I am 100% sure the roadster v1 is to the left when looking at the back of the head.

Once you get a new tube, your first step is to remove the tube protector strip (aluminum bar) from the rear of the amp.

Remove the two rectifier tubes by slowly rocking them back and forth and pulling them upwards. Don't move them very far from side to side, just a slight wiggle will free them. Once the are free, take note of the "key" position meaning the small plastic pin on the bottom of the tube. You will notice a small nub on the side of the pin. This will show you what position they need to be in when you re-install them. They won't fit any other way.

Once the rectifier tubes are free, push down and turn the tube cover slowly and it will free itself. It's keyed and will "unlock" and pop off. Remove it from the head carefully. Follow the same proceedure to remove the pre-amp tube in v4 as you did the power tube. This time, be more careful as v4 might be damaged and broken. Slowly apply side to side pressure and pull up on the tube until you free it. This time, there is no plastic pin on the bottom to show you the position you need to put the tube in, plus the sockets are inside the chassis, so it's hard to tell. Make sure you make note of the "gap" in the pins so you can put the new one in.

Put the new one in by aligning the pins the way they should be, then applying gentle pressure and rocking the tube like you did when you removed it. You should know right away if the pins are aligned correctly. Do not force it.

Once the tube is installed, you can put the cover back on by gently pressing down, making sure the key goes into the slot (you'll see what I mean). Do not press too hard as you will break the tube underneath it.

Re-install the rectifier tubes, and power it up. If your problem persists, take it into a tech.

If you are successful in solving the problem. Take the time and check v3 and v5 to make sure they are Chinese tubes. My roadster head did not have them install and exhibited very weird sounds until I put Chinese ones in.

I have 8 6l6 and 4 el34 spares. I have 4 12ax7s as spare 2 of which are Chinese.

I was very "squeamish" when I replaced my first tube, but it's basically tantamount to replacing the batteries in your remote. Once you learn how to do it, it's easy as pie.

Hope this helps, and good luck with your amp!

 

[fullreleaseblake]

Replaced the V5 tube and everything's working great now. Thanks for the help guys

-Blake