[Nayyte]

If you want to improve tube filament heating circuit before final closure the chassis there is way to do that by increasing capacity of two 1000uF/25V capacitors near power switch. Voltage for heaters are controlled by two voltage regulators LF60A with fixed voltage of 6V and according to data sheet up to 0.5A with limit of 1A. Jason Stoddard is clever guy and decide to use high PSRR for low frequency of this regulator to control also maximum current by limiting capacity of input caps. With ripples ca. 1.8 V current limit is ca.400mA. With increased capacity on input we get smaller ripples more room for voltage regulator. As usual there is no free lunch. On power on when tubes are cold and resistance is quite low heater circuit will go with 1A so for 300mA tubes which could shorten tube life.

Just bought a MJ2 and already digging around for mods I could do. I came across the 5687 tube variety. Same 9 pin mini design as 6922 but pins 6-9 are swapped around so a converter is required. Only problem is that in order to run in 6.3V, pins 4 and 5 need to be tied together between pin 8. Other wise its between 4 and 5 for 12.6V. On top of that the current draw is 900mA! I think these two things are the only differences but not sure.

Assuming I was to mod the MJ2, I would set up the heaters to be 12.6V @450mA or original 6.3V but I would have to figure out how to squeeze 900mA out of it. Really not sure if its possible without completely gutting it all.

@gumisb "current will be over 3 times higher" - so you tell me there is hope?

Thinking about this for fun of course. Also because I have a mild aesthetic issue with short plate tubes that the MJ2 takes stock.

 

[ShortBtwnHdset]

I had considered for a time doing an external PS for just the heaters and then piping it in. Something like this:

https://glass-ware.stores.turbify.net/lvregulatorkit.html

I stopped thinking about it very seriously when I started trying to figure how I would wire and ground it. It would require:

A. an external box, transformer, and umbilical
B. running wires directly to the tube sockets
C. disabling current tube heater circuit, including possibly cutting circuit board traces

Another idea I played with is having a parrallel circuit to the tube heater to give an extra half amp or so. Grounding and matching the existing circuit shied me away from that, and it would still have some of the other mentioned problems. It would take a person FAR more qualified than me to design and implement, I'm a hack at best with some soldering skills.

 

[Nayyte]

I had considered for a time doing an external PS for just the heaters and then piping it in. Something like this:

https://glass-ware.stores.turbify.net/lvregulatorkit.html

I stopped thinking about it very seriously when I started trying to figure how I would wire and ground it. It would require:

A. an external box, transformer, and umbilical
B. running wires directly to the tube sockets
C. disabling current tube heater circuit, including possibly cutting circuit board traces

Another idea I played with is having a parrallel circuit to the tube heater to give an extra half amp or so. Grounding and matching the existing circuit shied me away from that, and it would still have some of the other mentioned problems. It would take a person FAR more qualified than me to design and implement, I'm a hack at best with some soldering skills.

Yeah it seems like it could be worth it. Problem is that the results would probably be minimal for the effort. There are a crap ton of already compatible tubes for the MJ2. I think I'm much better off just experimenting with those.

 

[Slade01]

I had considered for a time doing an external PS for just the heaters and then piping it in. Something like this:

https://glass-ware.stores.turbify.net/lvregulatorkit.html

I stopped thinking about it very seriously when I started trying to figure how I would wire and ground it. It would require:

A. an external box, transformer, and umbilical
B. running wires directly to the tube sockets
C. disabling current tube heater circuit, including possibly cutting circuit board traces

Another idea I played with is having a parrallel circuit to the tube heater to give an extra half amp or so. Grounding and matching the existing circuit shied me away from that, and it would still have some of the other mentioned problems. It would take a person FAR more qualified than me to design and implement, I'm a hack at best with some soldering skills.

I was about to say that you're better off putting those efforts into just modding your MJ2, but I see you already have a "heavily modified MJ2". LOL. Is the tube rolling much more effective/distinct with the modded version?

 

[ShortBtwnHdset]

I was about to say that you're better off putting those efforts into just modding your MJ2, but I see you already have a "heavily modified MJ2". LOL. Is the tube rolling much more effective/distinct with the modded version?

I love mine, not likely to replace it! I ended up doing some more bypass caps mods to it (no pics, as it ain't pretty and still havent put any effort into closing off those exposed caps. Maybe someday! If I could do it over, I might have chosen slightly different caps in some area's (Mundorfs have good stage depth but not particularly good width and can be a hair bright). I ended up bypassing the input Mundorfs with Jupiter copper foils, really needed some copper in the mix, and it helped.

Tube rolling is a joy for me, can really differentiate some of the finer differences in tubes. I did the mods because I wanted to stick with my Mjolnir, checks off the right feature set for me (high power output, works with both high and low sensitivity HP's, tube input stage only, can work in either balanced or single ended operation, really MAX flexibility), it just needed some finess. And now I've collected a good base of tubes, should last me for years to come.

 

[Nayyte]

My first high-end amp from schiit, really awesome! I had no idea this thing was built so well, really like the wrap around aluminum body. Could I ask for some tube recommendations? I already own a tube amp that is pretty neutral and smooth, so I would love something with grit and warmth but not too much punch. I've heard that the USA Sylvania 6922s are pretty good. I've read through Brent Jesse's website about all the variants. The tubes in now just say RAM on them and idk what they are, they sound good but sort of average.

 

[Slade01]

My first high-end amp from schiit, really awesome! I had no idea this thing was built so well, really like the wrap around aluminum body. Could I ask for some tube recommendations? I already own a tube amp that is pretty neutral and smooth, so I would love something with grit and warmth but not too much punch. I've heard that the USA Sylvania 6922s are pretty good. I've read through Brent Jesse's website about all the variants. The tubes in now just say RAM on them and idk what they are, they sound good but sort of average.

I love the old chassis designs from Schiit and built like a tank!

If you’re sticking with the 6DJ8/6922, then maybe try throwing in some Gold Lions 6922 or Amperex (A-Frames) 6922. Sylvanias are good too…they are lively and dynamic sounding.

 

[Nayyte]

I love the old chassis designs from Schiit and built like a tank!

If you’re sticking with the 6DJ8/6922, then maybe try throwing in some Gold Lions 6922 or Amperex (A-Frames) 6922. Sylvanias are good too…they are lively and dynamic sounding.

Nice, those are the ones I ordered, the Amperex holland "A" frames from Brent Jesse

 

[Slade01]

Nice, those are the ones I ordered, the Amperex holland "A" frames from Brent Jesse

Also, if you plan to tube roll a bit for the MJ2, I would also recommend getting socket savers. They elevate the tubes up a tad higher and it's easier to get them in and out of the amp.

 

[ShortBtwnHdset]

Hey Nayyte, lots to check out. I would buy adapters, 6Dj8 to 12A*7 and 6DJ8 to 5670, and shop those as well. Look at places like Langrex and TubeMonger. If you search this thread a bit , you'll come up with several highly recomended and reasonable tubes to shop for.

 

[Nayyte]

Hey Nayyte, lots to check out. I would buy adapters, 6Dj8 to 12A*7 and 6DJ8 to 5670, and shop those as well. Look at places like Langrex and TubeMonger. If you search this thread a bit , you'll come up with several highly recomended and reasonable tubes to shop for.

Thanks. I've had my time rolling 12au7 and I honestly don't like them. Maybe some day again. I'm going one at a time here and placed an order from Brent Jesse for some amperex "A" frames.

I've been listening to the MJ2 with my HD600s tonight with some nos 6dj8 "ram" tubes from Yugoslavia. They came with the amp from the previous seller and they are certainly doing more for me than any 12au7 I've ever heard did. Yeah yeah I know this is a totally new amp for me but, this has to mean something still.

 

[ShortBtwnHdset]

Hey, sorry I didn't make it clear. I meant the ADAPTERS are 6DJ8 to 12A*7, the tubes you might want to check out are 12AT7's, those have similar gain characteristics to the 6DJ8. You'll find scores of posts in this tread on some good tubes in that family, mainly because they tend to be less collected out than the 6DJ8 ones. Check your Brent Jesse pages for 12AT7 derivitives, ther's lots he recomends. Several on this thread had good luck with Brimar CV4033's from Tubemonger, great tube especially in this amp. Telefunkens and Siemens are pricey but nice, heck, there's alot to choose from.

 

[ShortBtwnHdset]

Hey All! All the talk of tube rolling and recomendations from the new Mjolnir owners gave me the bug again! 1st package to arrive are Brimar 6060's. I only have an hour burn in time on them, but I can definitely tell they are from the same manufacturer as the CV4033's, warm and inviting. Some have said they are as good as a Genelex A2900. I don't feel they are at that level. While I was on Tubemongers site, got a spare set of CV4033's, and a set of Brimar CV4024 12AT7WA's, listed as 6201's with Tronix printed on the tube. It's a gamble, but I really love my GE 6201's 5 stars in this amp, hoping the Brimar may be even better. Will post when I get them in. Here's the pics.

 

[Nayyte]

6dj8 Amperex Holland RCA's came and are installed

So far everything is great. Smoothness and instrument separation are what I notice most. Soundstage is less of "I'm in the audience" and more of a holographic intimate bubble around my head, which is my preference! Never new my HD600's could dig so deep until this! ZMF lambskin pads as well help a ton.

The A frames in the tube reflect the heater glow in such a slick way, really happy with these tubes!

 

[ShortBtwnHdset]

Hey Nayyte! I think I have a pair or two of those! My fav for glow are the GE5 star 6201's and the 5670's, they seem to be a good degree bighter than most.

Did some tube rolling last night, came up with a great combo. Siemens E88cc's in the DAC, and Brimar CV4033's in the Mjolnir. Just Magical, sound is both extended, liquid, with a great soundstage, just a wonderful sound!

Anyway, Happy Listening!!!