3 Ch Dual Recto issue

[Gibson07]

HI all. I had a little problem at band practice last night with my 3 Ch Dual Recto and would appreciate your opinions / advice before I take it in to be looked at.

So while warming up on a low-mid volume I noticed a very minor volume fluctuation with a slight tone change. At higher volumes I did not seem to notice it. Later in the night, after maybe 2 hours of play I suddenly lost 90% of the gain from channels 2 and 3 with some volume reduction also.

I ran through all the simple fixes first, swapping speaker leads, leads etc with no luck. I then turned the amp off and let it sit for 20 minutes or so, after which I turned it back on. The same problem was still there, then all of a sudden the gain was back.

FYI I changed all 4 power tubes about 2 months ago but did not change the pre amp or rectifier tubes (all tubes were glowing as normal when this occurred).

Any advice before I take it in and have to spend money on it would be greatly appreciated.

 

[fluff191]

Most likely your V3 preamp tube is dying, but I would just re-tube all of the preamp tubes and save the old ones as spares.

And just FYI, glowing/not glowing doesn't mean a whole lot with preamp tubes.

 

[Gibson07]

Thanks for the information. I better replace those then. Can anyone recommend tubes that I should seek out. I'm a new Mesa owner if you haven't already guessed.

Cheers

 

[domct203]

Double post.

 

[domct203]

What tubes are in there now, and were you happy with your sound before this?

How old is the amp? Did you buy it new?

Dom

 

[Gibson07]

Dom

I cant remeber off the top of my head, I will have a look when I get home and post it up. I did buy it second hand and it still had the original Mesa power tubes in it (which I changed out for new ones) so I suspect the pre amp tubes have had their day.

 

[screamingdaisy]

Dom

I cant remeber off the top of my head, I will have a look when I get home and post it up. I did buy it second hand and it still had the original Mesa power tubes in it (which I changed out for new ones) so I suspect the pre amp tubes have had their day.

It's not so much that preamp tubes wear out... they can last decades if you're lucky. The issue is more with the cathode follower position. Back in 2008 New Sensor lowered the specs on their preamp tubes and they can no longer handle the voltages present in the cathode follower position. The classic symptom of this kind of failure is a volume fluctuation. In a Dual Rectifier the cathode follower is the V3 and V4 position.

For the cathode follower you should use a JJ or Chinese preamp tube. Any of the new production Russian tubes will die eventually. The current stock Mesa tubes are relabelled JJ.

 

[Gibson07]

Cheers, I am new to tube amps so I have a lot to learn. Would you recommend the Mesa 12AX7 or SPAX7-A or are there any other brands that you prefer?

 

[Gibson07]

Dom

The current pre amp tubes are mesa branded 12AX7A Russian 2. I do like the current sound. I am not sure how old it is. Is there an easy way to find out via the serial number or something?

 

[domct203]

Mesa "Russian 2" 12AX7's are re-labeled Electro Harmonix (New Sensor Corp) and ARE NOT recommended for cathode follower positions ( V3 & V4 ).

The EH 12AX7 is a fantastic sounding tube, but is not up to the task in the cathode follower positions for the reasons mentioned above by screaming daisy.

The current Mesa 12AX7 is a re-labeled JJ and would be fine in those positions as well as the older Mesa "Chinese", but they are hard to find. Another good choice is the Shuguang/Penta Labs Chinese 12AX7, as well as any NOS tube.

Trust me, that "Russian 2" is going to crap out on you in V3 and/or V4.

Read Here for more info on this subject http://forum.grailtone.com/viewtopic.php?f=4&t=25102&start=19

As far as the age of your amp, you could call Mesa with the Serial # and they can give you an approx date of manufacture. If you ever remove the chassis from the headshell there will be the date of assembly (month/year) written inside.

Dom

 

[domct203]

Cheers, I am new to tube amps so I have a lot to learn. Would you recommend the Mesa 12AX7 or SPAX7-A or are there any other brands that you prefer?

For the cathode followers ( V3 & V4 ) you can use either JJ or Shuguang/Penta with no worries. You already own a great tube with the Mesa "Russian 2" Electro Harmonix, just keep it out of V3 & V4.

You should also try a Tung-Sol Reissue in V1, and a Sovtek 12AX7LPS in V5. For current production tubes my favorites are V1=Tung-Sol, V2=JJ, V3-V4=Penta, V5=Sovtek LPS. Another good variation of this is using the EH in V1 & V2.

You need to experiment a little to find your preference. Mix and match using the guidelines above and I'm sure you'll find your tone! Just make sure you give the tubes a chance, play them for more than 5 or 10 min (I'll spend days) before you pass judgement, and expect to tweak the amp's EQ to bring out the qualities of the tubes.

You also need to note that current production tubes are nothing like the ones made in the 50's and 60's and you may end up with a dud here or there.

Have fun with it!

Dom

 

[screamingdaisy]

Cheers, I am new to tube amps so I have a lot to learn. Would you recommend the Mesa 12AX7 or SPAX7-A or are there any other brands that you prefer?

The current Mesa 12AX7 is a relabelled JJ ECC83.

SPAX7s are JJs that tested exceptionally well when it came to low noise production, which is further enhanced by adding the rubber shrink wrap to further dampen vibrations.

The SPAX7s are recommended for the input positions (usually V1) as any noise produced in that position will be further amplified by every gain stage that follows it.

Note that SPAX7s are selected for superior noise qualities and not superior tonal qualities. They're useful if you're finding you're getting excessive hiss in your lead channel, but using them in every position like some people do is kind of a waste of money IMO.

 

[Gibson07]

Thanks for the information all. I appreciate it! Time to do some research and do some tube shopping. I'll let you know what I go with and my impressions when up and running if you are interested

Thanks again

 

[screamingdaisy]

On this forum people are always interested in Mesa amps.

 

[Gibson07]

An update for you. Thanks for all the great advice, and based pretty much on said advice I have ordered the following:

1x Tungsol Reissue 12AX7 for V1
2x JJ ECC83 / 12AX7 for V3 and V4
2x Sovtek 12AX7LPS for V2 and V5.

As I live in Australia and had to order online (or pay through the nose at a local supplier) so they may take a few weeks to arrive, but I look forward to (hopefully) an improved sound!!

Thanks again for your help.