Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

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Coleo
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Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

Post by Coleo » Sat May 04, 2019 10:44 pm

Hello, another day, another issue with my beloved dual rec roadster 100w head. I use the amp maybe 5 to 10 hours a month at bedroom volume, so not abused at all, but this happens from time to time. Tonight, I was playing a song switching between clean channel and channel 4 and it cut out totally.

Right now, Channel 1 and 2 = NO SOUND
Channel 3 and 4 are anemic and brittle, basically sound like a gritty and unsustained guitar with no growl.

Settings:
Channel 1: 50W recto
Channel 2 50W recto
Channel 3 50W recto
Channel 4 50W recto

EDIT: Just flipped the switches to 100W across all channels and it came to life in each channel, then within 5 seconds died and had same output as the 50W setting.

Any help on easy tube fixes/swaps or other are appreciated. I rarely play, so when I do it means I have time and when the amp stops working its annoying to spend the precious time trouble shooting and swearing. Thank you!

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Re: Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

Post by domct203 » Sun May 05, 2019 6:13 am

What brand of 12ax7 are in V3 & V5? Those are cathode follower positions and weak tubes in those spots can create the issue you describe.

Best to use only the current Mesa 12ax7 (which is a JJ), or a Chinese made tube (NOS/VOS seem to be fine also). Anything made by New Sensor Corp (Sovtek, EH, Tung-Sol reissue, Millard re-issue) have shown to fail in cathode follower use.

http://forum.grailtone.com/viewtopic.ph ... 2&start=19

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Re: Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

Post by bandit2013 » Sun May 05, 2019 10:01 am

+1 on the cathode follow circuits.

Sounds more like V5 may be the culprit if you are using the FX loop in active mode but this issue would be consistent with all 4 channels. You can bypass this circuit completely if you turn off the FX loop function on the back panel. This will also disable the master and solo boost controls so be prepared to reduce the channel volume controls. V2 can also be responsible since the clean channels uses V2A and the high gain channels use V2B. How old are the preamp and power tubes? It may be time for new tubes, If this be the case I would also replace the both Rectifier tubes when you replace the others. If you normally run 50W all the time, you can try swapping the two Rectifier tubes with each other as well as the inner and outer pair of power tubes. In 50W power mode, only the outer most pair of power tubes are used, the inner pair is just idle with only heaters active, cathodes are disconnected and not contributing to the output. You can try swapping the two sets of power tubes inner to outer and vice versa and keep the 50W power setting. Odd that CH1&2 would cut out and not 3&4 if it was a power tube issue.

If it was a power tube issue, say one cut out, it generally sounds worse and more distorted before the one tube in operation red plates. Had that issue only once but that was a Simul-Class Mark V. Never had this type of issue with the Roadster but does not mean it cannot happen. If it was a Rectifier issue, possible but usually takes out the fuse when they fail.

If it was a strobe mute issue (strobe mute grounds the grids on some tubes (reverb circuit) before and after FX loop) to silence the channel pops. If there is an issue with the channel change circuits it may be getting stuck in strobe mute (not the same thing as the amp mute control) that will have a relatively low impedance on select preamp stages and depending on gain setting it you may hear a very weak signal but you may have to max out the volume controls. I would suspect V2 being the culprit of the issue more so than a preamp circuit fault with one of the JFETS. You can opt for no reverb and move V4 to the V2 position to see if that helps.

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Re: Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

Post by Coleo » Sun May 05, 2019 3:21 pm

Thank you both for the reply. I took it apart just now and confirmed Mesa 12AX7 in V 1-6.

The power tubes are mesa 6L6 GC and the other 2 on the right are not matched (is this an issue?), one is a mesa 5U4GB and the other an ElectroHarmonix made in russia.

I have 1 spare 12ax7 here, but feel it may be worth replacing all of them as starter. Thoughts on this?

I am limited technically with amps so appreciate the simple fixes!

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Re: Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

Post by domct203 » Sun May 05, 2019 4:45 pm

Coleo wrote:
Sun May 05, 2019 3:21 pm
Thank you both for the reply. I took it apart just now and confirmed Mesa 12AX7 in V 1-6.
If the Mesa 12ax7’s say ‘Russian-1’ they are Sovtek, ‘Russian-2’ and they are EH, both are questionable in cathode follower use. The current Mesa 12ax7 will not have ‘Russian’ or ‘Chinese’ stamp on them, those are JJ’s and are safe to use.

Hope that helps.
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Re: Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

Post by tbonesullivan » Mon May 06, 2019 3:37 pm

The Russian 1 does not have the spiral filament, so they are usually fine in Cathode follower positions. The Russian 2 tubes were either EHX or Sovtek LPS tubes, and can torch in the Cathode follower positions.

Any of the Slovakian or Chinese tubes should work fine in those slots. Also a great place for ANOS old production tubes.
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Re: Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

Post by domct203 » Mon May 06, 2019 5:56 pm

tbonesullivan wrote:
Mon May 06, 2019 3:37 pm
The Russian 1 does not have the spiral filament, so they are usually fine in Cathode follower positions. The Russian 2 tubes were either EHX or Sovtek LPS tubes, and can torch in the Cathode follower positions.

Any of the Slovakian or Chinese tubes should work fine in those slots. Also a great place for ANOS old production tubes.
From the link in my first post (Mesa TSB)
”For the past few years, Mesa has been using two types of 12AX7 tubes: ones originating in Russia (Sovtek EH), and ones originating in China.
The Russian (Sovtek) tube is NOT reliable as a cathode follower. Of the tubes we are using today (March 2008), ONLY THE CHINESE 12AX7 IS RELIABLE AS A CATHODE FOLLOWER.”


Mesa specifically states that their branded Russian tubes are not reliable in the cathode follower positions. At the time of this TSB there were two Russian 12ax7, the ‘Russian-1’ was a Sovtek, the ‘Russian-2’ was an EH. My 2007 came loaded with ‘Russian-2’ 12ax7’s, without a doubt all EH tubes.

If you are chasing a volume drop issue, per Mesa do not use either of those tubes in the cathode follower positions.

I personally use (and prefer) JJ’s in V3 and V5 in my Roadster and have never had an issue.
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Re: Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

Post by tbonesullivan » Tue May 07, 2019 9:57 am

domct203 wrote:
Mon May 06, 2019 5:56 pm
From the link in my first post (Mesa TSB)
”For the past few years, Mesa has been using two types of 12AX7 tubes: ones originating in Russia (Sovtek EH), and ones originating in China.
The Russian (Sovtek) tube is NOT reliable as a cathode follower. Of the tubes we are using today (March 2008), ONLY THE CHINESE 12AX7 IS RELIABLE AS A CATHODE FOLLOWER.”


Mesa specifically states that their branded Russian tubes are not reliable in the cathode follower positions. At the time of this TSB there were two Russian 12ax7, the ‘Russian-1’ was a Sovtek, the ‘Russian-2’ was an EH. My 2007 came loaded with ‘Russian-2’ 12ax7’s, without a doubt all EH tubes.

If you are chasing a volume drop issue, per Mesa do not use either of those tubes in the cathode follower positions.

I personally use (and prefer) JJ’s in V3 and V5 in my Roadster and have never had an issue.
What I had read elsewhere is that it only affects the Spiral Filament design Sovtek tubes. The 12AX7 WA/WB/WC are much older designs with standard filaments, which do not have the spiral filament that the EH, Svetlana, Tung Sol, Mullard Reissue, etc have. This is why the WA/B/C light up much more when on: they don't have the spiral filament, which is usually completely encased in the plate structure.

It's that filament design that is not as tolerant of high Cathode to Heater voltages, which are technically at or above the design limiting value. The original datasheets for Companies like Sylvania and Philips list this voltage as 180 or 200. The cathode followers used in the Rectifier put 216V and 210V on V3 and V4 from what I can see.

Anyway, the 12AX7WA/B/C aren't exactly anyone's favorite tubes anyway, so I also just stick to Chinese, JJ, or old production tubes in these positions.
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Re: Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

Post by Coleo » Tue May 07, 2019 10:15 am

domct203 wrote:
Sun May 05, 2019 4:45 pm
Coleo wrote:
Sun May 05, 2019 3:21 pm
Thank you both for the reply. I took it apart just now and confirmed Mesa 12AX7 in V 1-6.
If the Mesa 12ax7’s say ‘Russian-1’ they are Sovtek, ‘Russian-2’ and they are EH, both are questionable in cathode follower use. The current Mesa 12ax7 will not have ‘Russian’ or ‘Chinese’ stamp on them, those are JJ’s and are safe to use.

Hope that helps.
Thanks. These ones have no printing on them so assume they are the JJs. I couldn't locate any tubes in town Sunday but will try again this weekend and report back. Would the power tubes also be culprits or likely a set of preamp tubes for the fix?

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Re: Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

Post by domct203 » Tue May 07, 2019 4:48 pm

Coleo wrote:
Tue May 07, 2019 10:15 am
domct203 wrote:
Sun May 05, 2019 4:45 pm
Coleo wrote:
Sun May 05, 2019 3:21 pm
Thank you both for the reply. I took it apart just now and confirmed Mesa 12AX7 in V 1-6.
If the Mesa 12ax7’s say ‘Russian-1’ they are Sovtek, ‘Russian-2’ and they are EH, both are questionable in cathode follower use. The current Mesa 12ax7 will not have ‘Russian’ or ‘Chinese’ stamp on them, those are JJ’s and are safe to use.

Hope that helps.
Thanks. These ones have no printing on them so assume they are the JJs. I couldn't locate any tubes in town Sunday but will try again this weekend and report back. Would the power tubes also be culprits or likely a set of preamp tubes for the fix?
The 12ax7’s should have the Mesa screenprint on them, if there is no ‘russian’ or ‘chinese’ printed on them, but they are Mesa labeled, they are JJ’s.

Doubtful this is powertubes, I would rule out the preamp first.

If you have another amp with an FX loop you could run from the send of the Roadster to the return of the other amp and see if you get sound.
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Re: Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

Post by domct203 » Tue May 07, 2019 4:51 pm

tbonesullivan wrote:
Tue May 07, 2019 9:57 am
The cathode followers used in the Rectifier put 216V and 210V on V3 and V4 from what I can see.
With the Roadster (and RK), the cathode followers are V3 & V5.

The standard Rectos are V3 & V4.
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Re: Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

Post by bandit2013 » Wed May 08, 2019 6:09 am

You can see what JJ preamp tubes look like in the image on the page or if you click on the 12AX7 tube. They have a wide flat metal plate that gets formed into a flat round disc over both triodes, and then there is also a flat extension with a halo getter above that. They are JJ ECC83s. Those will work in all preamp tube positions of the Roadster.

https://mesaboogie.com/tubes/pre-amp-tubes/index.html

As for the 5U4GB rectifier tube, the Mesa brand is the same as the EHX rectifier tube. If they have the same part number on them 5U4G you should be fine. However, if you are going to replace power tubes, I would recommend replacing the Rectifier tubes as well. Especially if you have not changed them since you got the amp. Note: if and when you do change the tubes. Assuming you will be replacing the preamp tubes, do not remove the Rectifier tubes at the same time, do those last as they will not get in the way of access to the preamp tubes. Also it reduces the chance of installing a power tube in place of a rectifier tube. If you forgot where the Rectifier tubes go, they are the two sockets closest to the side where the power cord plugs into.

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Re: Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

Post by Coleo » Sat May 11, 2019 11:33 pm

So here is my update, went to get 12ax7 today at another stores and they only had the SPAX7, which I understood to be better replacements of the 12AX7. So I bought 3 of them and came home. I replaced

V1 with brand new 12AX7
V2 Same
V3 SPAX7
V4 Same
V5 SPAX7
V6 Same

Results? Same. Channel 3/4 brittle and barely working, and for whatever reason Channel 2 has about .5% output.

Settings
- Guitar direct into input
-All channels on 100W, FX switch on.
-I toggled FX loop on and off on the foot switch
-All power tubes glowing, and all other tubes in pre-amp glowing

Next Test
-Switch all channels to 50W. Result: SAME

Next Test
-flip switch to HARD BYPASS, and magically, every channel comes to life.
-flip all channels back to 100w, ALL CHANNELS WORKING

So, seems like there is an issue with the FX loop here.

Appreciate the guidance here again honing in on this, will continue searching for answers. :)

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Re: Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

Post by domct203 » Sun May 12, 2019 6:45 am

Where is the FX Loop send level? If it’s turned all the way down you will be passing very little signal through the FX Loop circuit, even without effects in the loop.
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Re: Mesa Dual Rec Roadster Head- Lost Channel 1/2 AGAIN

Post by tbonesullivan » Wed May 15, 2019 10:52 am

I would definitely mess with the effects loop send level, and see if the pot may need cleaning.

Also it's possible that the effects loop jacks are dirty, and those may need cleaning as well.

Definitely replace the tube responsible for the effects loop, which I think is V5? It's also possible that the tube socket is dirty.
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