| Author | Message | ||
     Jens V. |
Maybe it's a FAQ and I might even start a heated debate over a really simple question, but here we go: "Can anyone recommend me what tubes to put in my HD130?" Right now it has a set of old Sovtek EL34's. It needs adjustment so I thought that I would put new tubes in it as well. As I am playing mostly rock, I suppose that EL34's are the way to go, but I would really appreciate input on what brand to choose and what to look out for. (And it also goes for the 12AX7 tube as well) Cheers Jens | ||
| Steve Kennedy |
The few output tubes that come to my mind are: The JJ EL34 has a reputation for a great-sounding EL34 that will stand-up to the high plate voltage of a Music Man HD-130. These will probably not last as long as a true 6CA7 type but a lot of people prefer the sound of this tube. The Electro-Harmonix 6CA7EH is a "physical copy" of the tubes that originally came with your amp...the Sylvania 6CA7. Since this tube copies the physical spacing between the tube elements found in the original Sylvania 6CA7, it is qualified to work a long time in the high plate voltage environment of an MM amp (unlike a traditional EL34 design). I haven't yet listened to the pair I bought as spares. The new and *spendy* Groove Tubes 6CA7GT is made in the U.S. with the original "recipe" and tooling of the original General Electric 6CA7. While they cost about $80/pr., they may be the closest to the originals in sound and construction. This information is not based on a personal bias toward any one tube type, just based on observations. The MM 410-65 I am currently running has old Amperex EL34 tubes in it and I haven't had any reason to change them in the last 8 years! My other 410-65 has the original Sylvania 6CA7 tubes in it and they are still alive and well (although a bit tired) after 30 years! Of course, my amps are not getting daily use either. I have a 210RD-100EVM that has Sovtek EL34 tubes in it and these seem to work OK, they don't stand-out as a particulary definitive sounding tube (of course, it is hard to tell when using the EVM loudspeakers!). The 12AX7 is used as a phase splitter, so I would think that any decent quality type would work fine. Even a 12AX7 that suffered from microphonics in a tube preamp stage would probably work fine as a phase splitter! I would NOT use a cheap Chinese tube here... if the phase splitter fails in a certain fashion it could result in a meltdown of the output stage and take a set of tubes and maybe even an output transformer with it! If in doubt, spend a little more on a JAN military 12AX7 equivalent from one of the online tube stores that carry them. These are more physically "rugged" then the cheapies and should work great in the phase splitter circuit. Steve | ||
| Jens V. |
Thanks Steve Usefull info as always  . Will go down to my local tech, armed with your input, and have a chat with him. Cheers Jens | ||
| Michael Kaus |
I wou ld say JJ's for MM's at this point. I have been using them for a few years now and they are played pretty hard and don't fail. They handle the high voltage of our amps the best of anything that is out there now. I have many sets of NOS Sylvania's and I CHOOSE to use the JJ's instead. The 12ax7, I concur with Steve-get a good one. THe new JJ long plate isn't quite out yet but it promises to be good. Other than that, I would say NOS if you can get one reasonably priced. The JAN tubes are great and pretty cheap too. Mike. | ||
| michael kaus |
By the way, I posted this somewhere(too damned old to remember where), but be careful of buying Tung Sol and Mullard off of Ebay or these places. Somebody bought the rights to the names and are re-labeling Sovtek junk with these fine old names. I am pretty sure it was New Sensor and they will NOT be the real deal. Mike. | ||
| Steve Kennedy (admin) |
NOS (New Old Stock) Tubes are becoming increasingly risky to buy from strangers as it is relatively easy to play "musical tubes" and swap boxes around to get the biggest return. Buyer beware... stick with suppliers you trust. Steve | ||
| Jens |
A quick followup question: I checked out the JJ tubes and found that there is one named EL34 and one named E34L. It seems that the E34L is more geared towards the high voltage that MM amps have. Any opinions on the two tubes? Jens | ||
| Michael Kaus |
The E34L is the one you want. THey are what I use in the 2-10 65. They handle higher voltage better. By the way, please have it biased when you get the tubes replaced. THese amps run close to/at 700v on the plates and they were tough on 6CA7's back when they were building good tubes. I run mine at 21mA of idle current and get good life and great sound and haven't smaoked a set yet. The 12ax7 is used as a Phase inverter and if you order a pair/quad from Eurotubes, their 12ax7/ECC83 works just fine. Mike. | ||
| chris williams |
A quick question that has probably been answered somewhere already: I was pulling tubes in my 212HD 130 last night and noticed that, behind the far right tube, there is another slot for what appears to be a 12ax7 or other tube close in size. I looked back at the little tube schematic sticker on the inside of the amp and, from left to right, it lists 12AX7 Pre, followed by 4 6CA7s, without making any mention of this other slot. any ideas? | ||
| Steve Kennedy (admin) Username: admin Registered: 03-2002 |
First, the 12AX7 tube that the amp does (or did) use was not in the preamp, it is in the output stage and is used as a phase splitter to develop the push/pull signals required by the output tubes. The only jacks that most MM amps have behind the output tubes are the RCA connectors for a Reverb tank and/or the footswitch. If you have another tube socket back there, somebody has been messing with your amp at some time and it is probably a special interface for some custom mod. I have never seen another tube socket in an MM amp (unless it was added as a mod). Steve |