Going to agree with Nick here, that’s a fantastic amplifier but it’s just not designed to be warm and rich, I’m sure you can maybe tilt it warmer with we300b and maybe a driver swap, but I think you may find that swapping the driver may end up losing some of the magic and balance of that design (the c3m is a special tube). I do think that the WE may help, but it’s going to be more subtle. If you’re looking for a drastic increase in warmth, if you want to keep the amp, you may find that trying to address warmth in some of the rest of the chain such as speakers, cables, source gear, etc may end up creating a more worthwhile impact instead of swapping tubes in the amp. Yamamoto amps are fantastic at what they do, but imo they don’t really offer the lush wet sound of other tube amps, that’s just seemingly by design. Out of curiosity, what does the rest of your chain consist of?
It took a long time for people to catch on to the c3m and c3g but there are (technically speaking) very few better driver tubes. I guess part of the late adoption were they were not publicly sold. I would say the Radu amp i had with c3g drivers (same as c3m but different socket iirc) was very nicely warm and cozy. The mods they are suggesting is a fundamental amp change and i would sell the amp to someone who enjoys it as is then to dive that deep unless you also enjoy the project aspect of it.
@marlboro i would say the WEs will add a certain “golden” air to the mids but they arent super warm or super lush. It may tilt it enough for you, i think the EHs are said to be the most ooey gooey but dont have the technical prowless of the higher end 300Bs.
Probably not, you might get something out of it, outside the triode strapped C3M/G the 6SN7 is about as linear as small triodes get.
The C3M also has a 150mA 20V heater, it’s hard to swap it for anything, so I don’t know what the adapter would do to provide the 6.3V 600mA a 6SN7 uses.
The C3M/G triode strapped are my favorite pre tubes, but they are very linear. And you can’t really roll anything into a C3M socket because of the 20V heater voltage.
They’re actually quite different, just both used for the same telco application. And both use the same socket, just different heater voltages.
The C3M is a much prettier tube with the shield removed.
Triode strapped as they are in most audiophile amps they are both extremely linear.
C3M’s because of the 20V heaters don’t have the Lampizator tax that C3G’s got, they still aren’t cheap tubes, but you can buy them today for <$ than they were originally sold to the telcos for.
The Yamamoto’s were all sold with the metal shields removed from the C3M’s.
Oh darn you are right. I think i mistook them for the f2a tubes which are also telecom tubes. I think the f2a had a sister tube that was the same but different socket. I emphasis i think because now i am doubting myself.
A couple months ago I brought my Yamamoto A08-S to my local repair technician steve@capstoneElectronics.net (located in King George county, Virginia). He did a light re-fresh and cleaning of the amplifier along w/ some very minor repairs.
Currently I’m using my Sonnet Pasithea DAC doing double duty as both DAC and volume control and getting excellent results 
The Pasithea provides excellent blackness, depth and separation in its output really allowing the Yamamoto amplifier to showcase the control and extreme resolution it’s capable of putting forth. Lastly I threw in my 100db+ sensitivity Charney Audio Companion speakers using new 2025 Lowther DX65 transducers and it’s been an audio eargasm experiencing previously unnoticed details in some favorite tracks from a fresh perspective 
I’ve been comparing the Yamamoto 45DHT SET amplifier VERY intensely to my Decware 341.5 EL34 SET and it’s been such an enjoyable & fulfilling experience. Both amplifiers are similar in cost, both builders have a similar build philosophy, voicing though is opposite and what an incredible pleasure it makes to experience the sweetness of the Decware next to the more resolute intensity of the Yamamoto. Gun to my head, I would take the bullet, it’s that hard to pick a favorite, the sound character of each is that beautiful 
The speakers are a combination Horn/Throat design using a long 108” horn, there is no crossover, the drivers are tiny 5”, no tweeters just a whizzer that will sometimes annoy me when there’s a bit too much emphasis around the 2.5khz region and there is a surprising amount of bass, so much so I had to pull the speakers a full 59” into the room to get them well away from the corners.
Charney Audio makes speakers w/ even more intense and expensive transducers and I would pair them w/ any Yamamoto amplifier in a second and admittedly I would do the same using the Decware SET based flea-watts too 
Happy Listening to all, keep posting about your adventures folks 
i so love living vicariously through your experiences and systems 
The bowling shoes?
I am not surprised as the Yamamoto is a common reference when i was searching for custom amps.
Ah dammit, now i can’t get the image out of my head🤣 i’m gonna have to get some bowling/music stickers now to add to the sides of the cabinets to take the theme to the extreme…