Tuning the RA100

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bandit2013

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I recently obtained a lightly used Mesa Boogie Royal Atlantic head. Sign off date was February 27, 2012. Almost 2 years in age. The amp was well maintained and the tubes were worn out (not surprised). On the same day the amp arrived, I also got my shipment of SED =c= EL34. I bought them primarily for the Mark V. I did have a chance to try them in the V before committing them to the RA. In honesty, they sounded like the TAD6L6GC-STR (almost), they did not have as much grunt as the EH EL34 after they burned in. However, the SED =C= EL34 performed unbelievably well in the RA100.
The RA100 had a few changes in the preamp as well. Most of the tubes were Mesa brand except for V5 which was a JJ labeled tube. For start, to wake up the Hi/Lo gain channel and to smooth up the tone, the GOLD Tung Sol 12ax7 really made a difference. I installed the standard Tung Sol in V2. Left the original 12aT7 in V3. For the clean channel, I tried a few different tubes but what really made a difference in V4 was a JAN/GE 5751. Tone controls were less neutral with the lower gain tube. Improved brightness which was lacking, and the bass was more defined and not soft. V5 I used a vintage Mesa Chinese tube from the 90's that I had (tube has the square getter). For the reverb which is essentially a driver tube I made use of the Penta Labs 12ax7 tube (which is also Chinese). Along with my tube order, I also got a new Sovtek 12ax7LPS (matched triodes) for the PI (V7).

Impressions, I just could not stop playing the amp. Power soak tone also changed with the new (or in some cases old) tubes. Hi/Lo channel has improved bass response. Not as relaxed as it was with other tubes. The treble is sweet and not so dominant as it was. The Tung Sol tubes offered a perfect blend of tone from low to the high end. Since I am using the V30 that I had in storage for a very long time, they really sound great with this amp, now better with the tube roll. I would say this amp sounds better than any of the recordings on the Mesa Web site. For 70's through 80's rock this amp can't be beat. I thought the Mark V was killer but the RA100 makes ACDC, Led Zepplin, and even Scorpions type music sound more like it should. When it comes to getting the Deep Purple tone, the Mark V seems to handle that very well.

I would definitely recommend a JAN/GE 5751 for V4 (1st and 2nd gain stage for the clean channel), Tung Sol Gold 12ax7 for V1. I think I need to get a new 12aT7 for V3, I seem to have a slight bit of hum in the amp. I will try a different tube in there just to see if I can remove it. It may be motor noise from the fan, I believe it can be turned off so I will check that out. The hum was there with the original tubes, so that has not changed with the new tubes. Only tube not changed was V3. Also the noise goes away when the power soak is turned on. It is not bothering me since it is low level noise which becomes unnoticeable when you are playing. I could also defeat the reverb and see if it goes away. When I got the amp, the reverb cable was unconnected. I installed white cable towards the rear, black towards the transformer (next to the hidden reverb kill jack).
 
Seems that this amp is not as tone sensitive as the Mark V with tube changes. Differences seem minute vs dramatic.
=c= EL34 sounds great but would be better without tube rattle. KT77 sound even better. Those are incredible in the Mark V as well as the RA100. Still have the EL34 tone, love the harmonic overtones in the Hi settings.

I collected all of my Mesa tubes, I had a few lightly used ones that came in the Mark V. They actually sound good in the RA100 vs the Mark V. Learning how this amp saturates and adjustment of the tone controls makes a difference. I have also tried the amp with a few different speaker combinations that I am using with my Mark V and Mark IV. Seems that the traditional sized 412 with V30's sounds the best. Actually it is not all that bad with the Mark V. Smaller cabinet makes a difference than the larger Standard 412 recto cab. The WGS Blackhawk or Jensen Black Bird would probably do well with this amp.
 
I've had my RA for a year and a half now. It still has all stock tubes. Normally I would have tried all sorts of tube combinations, but have just not felt the need. The RA sounds great with stock tubes. Mesa have done a really good job of squeezing the tone out.

So far all I have tried are some SED 6L6 tubes out of curiosity. They did sound good, but the EL34s had to go back in.

My band is looking like getting more active this year so I'll have to look at re-tubing soon and will make sure I try a few of the tubes you have mentioned.

The RA does seem fairly sensitive to speakers. The V30s sound great, didn't like the C90 so much. By far my favourite speaker with this amp so far is the Creamback.
 
When I got the amp, the tubes were basically spent. Prior to buying the amp, I ordered some tubes for my Mark V. =C= EL34 have the best tone, but noisy mechanically. I doubt that they are all noisy but this set seems terrible. I have a set of EH EL34 which also have similar mechanical noise problems. The KT77 on the other hand sound sinister in the Mark V, and tame in the RA100. They are quite similar to the =C= EL34 and nearly the same cost. If you have good luck with the Mesa Tubes, by all means stick with them. I believe they are relabeled Sovtek. Paying the extra money for selected tubes is probably worth it. I do not notice the rattle when using Lo/Hi but I do hear it with the Clean.

The last order I made for SED =C= 6L6GC and the =c= EL34 are somewhat disappointing as both sets have mechanical rattle sounds. I can wait for them to go back into production if it ever happens. There are alternatives to consider. If the KT77 tubes last as long or longer than the NOS relableled SED (original Svetlana) Groove Tubes GT6L62-R were the best sounding 6L6GC I have used since 1989. I believe the variants of the EL34 may be out of the desired tone spectrum for the RA. However, the KT77 (Gold Lion) kicks it up slightly in the Hi/Lo. Not much difference in overall tone between =C= EL34 and the KT7& with the RA. In the Mark V, extremely huge difference. I probably will not buy JJ tubes any time soon. The 6CA7 sounded great but they died within 2 weeks of use.
 
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