[Nayyte]

Amperex A-frames have been on for 4 hours and honestly they aren't impressing. I was certainly impressed with them the first 15 mins or so, but now they feel a little one dimensional. Honestly like the magic isn't there anymore. The tubes that I got with the amp are RAM tubes's 6DJ8, a California company that doesn't list on their site who actually makes their tubes. Those tubes while a little too punchy, are exciting in all the right places and have lots of energy. They are A-frames as well. I will compare them when I swap them back in later tonight.

Edit: idk what I'm (not) hearing. I power cycled my DAC and things seemed to get better. I can't differentiate this past being pseudo effect. I think tomorrow I will start up the mjolnir with the RAM tubes first and test a specific playlist, then swap to the Amperex's after a few hours.

 

[Nayyte]

OK so impressions aside, I went on a LITTLE spree last night.

What did I get you say? Well to follow some advice by @ShortBtwnHdset, I ordered a pair of NOS Matsu/Mullard 12AT7 here: https://www.ebay.com/itm/395245407111
I wasn't going to pull the trigger but the seller sent me an offer for $40 off so it was honestly too good to pass. I figure its good that I get these now since not that long ago they where less than $50 each, and I got them for $68 each here. Sooooo that's good, right

Ordered some tube adapters from Pulse store too, out of stock on tubemonger so hopefully they wont take too long to get to me.

 

[ShortBtwnHdset]

Hey Nayyte! The adapters are quality made, and expand the flexibility of the Mjolnir by a huge margin. Pulse didn't make a 5670 adapter at the time, got a cheapie somewhere else online. Pulse is usually pretty fast with shipping, shouldn't take long. Haven't personally tried the Matsu tubes, closest Japanese brand I've tried was a Mazda, that particular set had one that was slightly microphonic, so didn't persue any further eval.

I get the feeling your not sold on the Brimar CV4003. Look thru the thread, you'll find a lot of people who love that tube specifically in Mjolnir. I've read it sounds most like an expensive Mullard, love mine, stocked up on several spares, they're just that good. If money's tight, put it on your radar for future, they really are worth it.

Happy Listening!!!

 

[Nayyte]

Hey Nayyte! The adapters are quality made, and expand the flexibility of the Mjolnir by a huge margin. Pulse didn't make a 5670 adapter at the time, got a cheapie somewhere else online. Pulse is usually pretty fast with shipping, shouldn't take long. Haven't personally tried the Matsu tubes, closest Japanese brand I've tried was a Mazda, that particular set had one that was slightly microphonic, so didn't persue any further eval.

I get the feeling your not sold on the Brimar CV4003. Look thru the thread, you'll find a lot of people who love that tube specifically in Mjolnir. I've read it sounds most like an expensive Mullard, love mine, stocked up on several spares, they're just that good. If money's tight, put it on your radar for future, they really are worth it.

Happy Listening!!!

Throughout my 8+ years in my own personal hifi , one thing I have figured out is that no matter how many good reviews I read about x product, there is no way that I can know if I will share others enthusiasm without testing for myself. Because of that I usually tend to make purchases based on my own standards and gravitate to the little known, the sparsely reviewed, products that not everyone else is using. Not saying I wouldn't like the Brimar tubes, but I often stay away from things that everyone likes, in multiple areas of all my hobbies. Someday for sure, but not today.

For example, I bought the Hifiman sundara's on release and paid a lot for them. Despite all the positive reviews from my favorite youtubers at the time, I thought they sounded like ass. Same thing happened for the original Verum ones, and the Gold plannars. That was a while ago and I took a break from midfi planars after that. Relevant sure but I am venting here lol.

 

[Slade01]

@Nayyte sorry those tubes from Brent Jesse stopped impressing. May I ask - do you know if those Amperex tubes were US made or Holland made? I'm curious to know as I've heard they have different takes on sound.

Tube Rolling can be a challenge, and you're right despite reviews, having heard it for yourself, and in your particular gear can be strikingly different from expectations.

For me personally, I never liked the 6DJ8/6922 family, in nearly any amp that used them. In the MJ2 and similar amps in general, I thought the 12AU7/12AT7 and especially the 5670/2C51 were the way to go.

 

[Nayyte]

These 6DJ8's are made in holland for RCA. To me they have less resolution, or at least the resolution isn't as wide spread in the stage, compared to the RAM 6DJ8 A-frames I have. Tonally they are also on the boring side with some treble etch that is not pleasant. Nothing about these Holland A-frames is exciting me, frankly they are forcibly putting me to sleep. So odd of a tube in the MJ2 I have to keep turning the volume down after 15 mins due to fatigue. Listen in to instrumental music mainly.

 

[Slade01]

These 6DJ8's are made in holland for RCA. To me they have less resolution, or at least the resolution isn't as wide spread in the stage, compared to the RAM 6DJ8 A-frames I have. Tonally they are also on the boring side with some treble etch that is not pleasant. Nothing about these Holland A-frames is exciting me, frankly they are forcibly putting me to sleep. So odd of a tube in the MJ2 I have to keep turning the volume down after 15 mins due to fatigue. Listen in to instrumental music mainly.

Well not to generalize per se, but what you are saying somehow tracks with my own perception and expectation of the RCA house sound. Warm, laid back, boring. Lol. Though the etch is surprising. But you're right, my expectation when I had a pair (mine were Amperex A-Frame PQ Orange Print, Holland 6DJ8) was more punchy, lively, detailed but smooth (the way you are describing your other set).

 

[ShortBtwnHdset]

The Siemens E88CC's are very impressive, as were the RFT's for me in the 6DJ8 family. Unfortunately, the Siemens had already become very pricey when I was initially shopping; can't find any that aren't outrageously priced these days. The E81CC's are quickly becoming too expensive as well, the RFT's are still reasonable, maybe slightly cheaper in the 12AT7 family.

By the way, look up the 12at7's family at Langrex, a lot of variety to choose from and some good prices to be had. Just a suggestion!

 

[Slade01]

By the way, look up the 12at7's family at Langrex, a lot of variety to choose from and some good prices to be had. Just a suggestion!

If one is going to hit up Langrex, you might as well get your Brimar, GEC and any other British tubes fix while you are there.

 

[shafat777]

I have a set of RTF 12at7 NOS tubes for sale if anyone is interested. I ran these sets exclusively with my modded MJ2.

 

[gumisb]

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.

For really extreme and/or exotic tubes for this amp it's better to go with external power supply for heating. With some tweaking it's possible to go around 500-600mA @6V form what you have by replacing diode bridge with ideal bridge to gain 1.4V and by increasing capacitance before LF60A regulators. According to datasheet load is regulated to 500mA and max output current is 1A so real performance should be tested before implementation. You can always replace LF60A regulators but keep in mind load of transformer.

 

[ShortBtwnHdset]

Hey Gumisb! Did you ever end up replacing the input and output coupling caps of your Mjolnir with better film caps? Seems to me you were considering V-caps as I remember.

Really the only reaason I was considering the heater mods was I wanted to get some Siemens E288CC's while they were still affordable, that ship has unfortunately sailed. I have in stock some of the other slightly taller tubes (6414, E180CC, 6829) but looking at their data sheets, I think they fall within limits.

 

[gumisb]

Yes, I replaced all wima capacitors and some ceramics with PP film caps. I made ideal bridge that fit mj2 to improve heating circuit. I'm able to run 6n1p tubes(600mA) without issue but I'm more on 6bz7 and they run smoothly.

 

[ShortBtwnHdset]

Might we see some pics?

I have been investigating ideal bridges, did you do all voltage rails or only certain ones? Considering the CRC network directly after the bridge rectifiers, did you up the resistance to account for extra volts not wasted by the ideal bridges. Very curious to know your results and methodology!

 

[ShortBtwnHdset]

Hi all! Package arrived today from Tubemonger, they were out of the 6021's so we subbed a different set of CV4033's, plus a backup of the ones I already have.

Tonight, my mission is to clean tube sockets, adapter sockets, tube pins, and equipment connectors. Have some deoxit D5 and some special interdental brushes, see pic. Also, while I'm at it, it's finally time to test orientation of Synergistic purple fuses.

Wish me luck!!!