I am a very newbie to good quality headphone equipment and now that my
Little Dot DAC_I Digital to Analog Converter and the
Little Dot MK IV with SE better tube option has finally arrived from China it completes my system along with my Sennheiser HD 600 headphones. And I am becoming absolutely amazed by the sound once
Little Dot MK IV headphone amp burnt in.
Consequently I want this sound they are giving me to last the rest of my life. My new headphone amplifier uses the uses two M8100/CV4010 driving tubes and two 6H30PI (gold-pin) Power tubes in a tube solid-state hybrid design.
When they finally wear out should I expect the power and driving tubes to wear out together? Should I only replaced them in match peers and trust my seller to match them for me? Will the degradation from what I am hearing now be gradual and subtle or very noticeable? And if anyone knows these tubes could you give me a guess as to their life expectancy?
Wow, this thread was from way, way , way back! I haven't posted here for a while.
6H30 is a fairly common tube nowadays that got popular when Balanced Audio Technology (BAT) first begun to promote it in their products back in the early 1990s. Now ARC uses them too for all their preamps. This is a fairly rugged tube, but sounds a bit more linear, dynamic, and cooler than the traditional 6DJ8/6922/7308 variant that it had replaced. I am speaking of NOS tubes here. I had compared my preamp, a modded ARC LS-25 Mk I using 6922 tubes, to its successor, the LS-25 Mk II which uses the 6H30 tubes, and that was my conclusion.
I am not familiar with M8100/CV4010, but a quick search revealed that there are a lot of Mullard NOS tubes available for decent price. So you should be OK. I have friends that have been using more up-to-date ARC preamps and phonostages that uses the 6H30 tubes. They swear that there is a big difference between the current production ones vs. ones from the 1980s. And those are getting more expensive than NOS 6DJ8/6922/7308 tubes.
Some gears drive tubes harder than others. There was a preamp from CAT that would kill any NOS tubes within a week or two. The only one that would survive in it was the Sovtek 6922s. In most gear, tubes don't just "die", like you wake up one morning, and it doesn't glow any more or no sound is coming out. What will happen is that the sound will just degrade over time. You might occasionally have a tube failure where you see flashes and the tube dies of an untimely death. But there are always exceptions. My friend's 6550 power tube died in his ARC Ref 5 preamp, and it took down some other stuff with it, so he had to get it serviced. Another guy with a pair of old ARC Ref amps told me that when a power tube dies, it takes out the resistor that is soldered to the circuit. So you have to resolder a new one on top of replacing the tube. There are two things that age the tube. One is the amount of time you have the amp on, but the other is turning on and shutting off which ages the tube faster than just leaving it on. So I would recommend if you are just stepping away for like an hour or two, leave the amp on. But if you are going to be gone longer than that and won't be turning them on 3 or 4 times during that day, then turn it off. It's a judgement call. But remember turning the amp off and back on will require some warm-up time for the amp to sound good.
For normal listening, you can probably replace tubes every 2 to 3 years. But I am sure other owners can provide you with better recommendation. Depending on the life expectancy of the 6H30 vs the M8100 and how hard the amp drives each set of tubes, you will most unlikely to need to replace both pairs at the same time. But it would be a good idea to swap the particular pair out at the same time, not just a single tube. Keep the old tube as spares as you never know when one might die on you. As for tube matching, there are a lot of different opinions on that. First, you need to find out from the manufacturer how the tube is being used. For example, many of the tubes used in preamps such as the 6DJ8/6922/7308 family as well as the 12AU7, 12AX7, and the 6H30 have two "sections" within the tube. For one of my old ARC phonostages, PH3 SE, I learned from ARC that each channel is actually using a section in each of all 3 tubes. So it was more important to have the internal sections of each tube matching each other than say have 3 identical tubes. And I've rolled plenty of tubes through all my gears. Back to tube matching. Most dealers these days match by measured outputs. So if you subscribe to this, find a reputable tube dealer and they can provide you matched tubes and charge you a little bit more. I've tried tube that measured differently and honestly cannot tell discern any different in sound or volume level. Others in the NOS circle also subscribe to the thought that tubes should not only be from the same manufacturer, but also from the same plant, same manufacturing date AND same batch. Of course this would be hard to achieve as the supply is dwindling. I usually just tried to make sure that they are from similar manufacturing date, from the same plant and have the same internal structure. For NOS tubes, they did change design of tubes over time, so the sound signature do change, so it is important to make sure you are buying the "same tube".
As for matching tube output, I use an old military TV-D/U tester to test all my tubes. It measures the transconductance. Don't ask me what that means. As far as I know, there's not a tester out there that you can buy (as a consumer) that will test the 6H30. So you can only rely on the retailer. And I don't even know what they use to test. Maybe they have one of those old curve tracers or something.
One last thing, when you swap tubes, the amp will not sound "exactly" the same, as different tubes manufactured from different period will have a slight variation in sound signature. And tubes from different manufacturers will have bigger differences. That is part of the fun with tube equipment as you can tube roll to change the sound of the gear. Some gear will have bigger changes with tube rolling, but some may not.
