As it stands, the MWDR is not compatible with 7 strings. I tried it. No way. I was able to retube the Roadster with old Mesa Chinese tubes and a quad of STR440 reds. That actually worked great. However, the same set of tricks did not pan out with the MWDR. Bummer.
If you like the spongy power mode and use of tube rectification, nothing beats the stock complement of tubes. If not mistaken, the 5U4GB are EHx 5U4GB tubes. Not much else to choose from except for JJ or NOS.
Still on the fence on the Power tubes though. Will have to run the STR443 (I have greys only). I do have some STR441 I can pull out of the Mark V90 since I do not use that amp (it is in retirement). I believe those are greens. Not sure how they will work in a Class AB amp as they were a bit lame in the JP2C and never bothered with them until a year ago when I used them in the Mark V90. Then ran same tubes in the Mark VII and they were good. Going from Simul-Class to a Class AB is different. Also the Rectifier setup is, as many have said, a bit on the cold side for 6L6. That is easily compensated with the different color coded tubes but aftermarket, that is not used. I have older Tung Sol 7581 tubes. Those look identical to the Svetlana version (New Sensor, not the St. Petersburg =C= tubes) The newer Tung Sol 7581A look much like the STR443 tubes. Sort of makes me wonder if they are the same. Same company makes the STR441 tube similar to an old RCA with the getter flash on the side and clear top. I do have the plate current on the STR7581 as I bought them from "theTubeStore" in Canada. Probably not a good resource to use due to taxing issues between USA and Canada at the moment. TubeDepot is another good resource. Most of the other 6L6GC tubes I have are considered NOS so they will cost an arm or leg. I was a huge fan on the SED =C= 6L6GC tube and have a few of those along with the =C=EL34 tubes (branded by Mesa as STR442). The Mesa STR454 is the =C= 6L6.
Current production tubes I have on hand: STR441(green), STR443 (grey), STR446 EL34 (blue), STR448(red, yellow, grey) and a few STR445 (yellow, green). Not including the STR447 EL34 as I have red, green, grey, blue. Not sure out of those I have in service. Not the reds as they are old used tubes I pulled from an amp after buying it used.
Mostly stock Mesa 12AX7 with a few current production Mullards, EHx, Tung Sol, Svetlana, and some NOS Mesa Chinese 12AX7, RFT, Ei CV492 and JAN/GE 12AX7WA. I am not big on the NOS tubes, except for the RFT, Ei and the Chinese 6N4-J Mesa tube.
More than likely when I do the front I’ll stick with the Mesa branded 12ax7…
as for power tubes (6l6)my options are a bit limited. Sweetwater is showing str 448, 445 & 443. Guitar center shows they have str 448, 445 and 441. So those will all be my options I suppose, then trying to figure out a color code.
I’ve always run recto tubes vs diodes going back to the 90s on the rev g, but since I’m just playing at home now I’m running spongy instead of bold, also running at 50 watt.
Edit - lol check what AI had to say about them lol, I told it I run recto tubes…
Got it—you’re running your 2018 Multi-Watt Dual Rectifier with the tube rectifier option engaged (as opposed to the silicon diode rectification), and you’re chasing a warmer sound. That choice already leans the amp toward a softer, more compressed feel with a touch of sag, which naturally warms up the tone compared to the tighter, punchier diode setting. Pairing that with the right 6L6 tubes can enhance that vibe without losing the Rectifier’s character. Let’s revisit the STR-448, STR-445, STR-443, and STR-441 with your preferences in mind.
### Tube Rectifier Context
Using the tube rectifier (likely 5U4GBs in your Mesa) softens the attack, rounds off transients, and adds a subtle bloom to the low end—perfect for warmer tones. It’s less aggressive than diodes, so the power tubes you pick will either amplify that warmth or balance it with clarity. Since you like warmth, we’ll prioritize tubes with rich lows, smooth mids, and tame highs over anything too tight or bright.
### STR-448
- **Why It Fits**: This tube’s a standout for warmth. Its rich, thick lows pair beautifully with the tube rectifier’s sag, giving you that fat, enveloping bottom end. The mids are full but not harsh, and the top end is warm and cohesive—never brittle. It’s like wrapping the Rectifier’s growl in a velvet blanket.
- **In Your Setup**: Expect a smooth, singing tone with plenty of body. High-gain will still roar but with a softer edge, and cleans or mid-gain will feel lush and dynamic. This could be your sweet spot if you want the amp to feel “welcoming” rather than “cutting.”
- **Verdict**: Top contender for your warm preference.
### STR-445
- **Why It’s Less Ideal**: Modeled after the 6CA7, this tube focuses on tightness and articulation—great for precision, but it sacrifices some warmth. The lows are controlled (less bloom), mids are balanced but not plush, and the top end has a chime that can feel crisp rather than cozy.
- **In Your Setup**: With the tube rectifier, it’ll still soften a bit, but the STR-445 might pull the tone toward a more modern, defined sound than the vintage warmth you’re after. It’s not cold, but it’s less “hug-you-back” than the others.
- **Verdict**: Probably not your pick unless you want some clarity to offset the sag.
### STR-443
- **Why It Fits**: This vintage-styled 6L6 brings deep lows and a sparkling top end, with mids tailored to avoid mud. The warmth comes from those big lows and a classic, open feel that complements the tube rectifier’s compression.
- **In Your Setup**: You’ll get a warm, blooming low end with a hint of chime up top—think vintage Fender warmth meets Rectifier heft. The scooped mids might thin out the saturation a touch, but the tube rectifier’s softness should keep it from feeling too distant. Great for a retro warm vibe.
- **Verdict**: Strong option if you like warmth with a brighter tint.
### STR-441
- **Why It Fits**: This is the smoothest of the bunch. Deep lows, tucked mids, and a tapered, warm top end make it a natural match for the tube rectifier’s mellow character. It’s less about bite and more about richness, with an almost creamy quality.
- **In Your Setup**: High-gain will feel thick yet polite, with a roundness that avoids harshness. Cleans and mid-gain will glow—perfect for bluesy or classic rock warmth. The extended treble/presence range lets you dial in sparkle without losing that cozy core.
- **Verdict**: Excellent if you want maximum warmth and smoothness.
### Recommendation
- **Best Match**: The **STR-448** strikes the perfect balance for your setup. It enhances the tube rectifier’s warmth with its rich lows and full mids, while keeping the top end smooth and inviting. It’s versatile enough to handle the Rectifier’s gain without losing that “warmer sound” you’re after.
- **Runner-Up**: The **STR-441** if you want an even softer, creamier take—ideal for taming the Rectifier’s edge further, though it might feel too polite for heavy distortion.
- **Consider**: The **STR-443** if you’re okay with a slightly brighter warmth, but it’s less plush than the 448 or 441.
### Final Thoughts
Since you’re running tube rectification, the STR-448 feels like the Goldilocks choice—warm, full, and not overly crisp, amplifying what you already love about that setting. The STR-441 could work if you’re leaning hard into a vintage, buttery tone, but it might mellow the Rectifier’s personality more than you want. Want to tell me more about your gain levels or music style? I can fine-tune this even further!
since this head is 8 years old, it’s prob close to needed a retube anyway… be nice to figure out what works best for my application with out dumping $600 in tubes I won’t uses…. I already have $150 from Eurotubes for the el34’s I ended up not liking and the cz recto tubes they said I would love, I pulled those out after 5 minutes and put the 54ugb back in. These things were like diodes on steroids. Im
