Electro-Harmonix 12AX7EH, Sovtek 5751, Sovtek 7025, JJ ECC83S, Ei ECC83

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7x57

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Well, the NOS replacement tubes finally died in my Conrad-Johnson EV-1, so I retubed it last night.

I had been using Vintage Tube Services "perfect picks" which could be termed "perfect pulls" as they are used tubes that test good and were sold at greatly reduced prices making them an alternative to new Eastern European and Russian production tubes. They died about as quickly as the original C-J supplied Ei ECC83 Telefunken long plate copies, well within 500 hours of play. Not going there again.

Since I use a high output moving coil cartridge, I can use a 5751, 6072, 7025 or 12AY7 type on the input, and if you use a moving magnet cartridge, this should be done to lower the gain. Conversely, when using a lower output moving coil cartridge, you can use a high output 12AX7 type in place of the 5751.

The 5751 was replaced with the original C-J supplied 5751 as it was American NOS and still worked well. I replaced the VTS supplied RCA 12AU7 with an old Mullard 12AU7 from 1959 that I found in my tube stash. Still works acceptably well.

The main reason for the original tube replacement was the Ei ECC83 input tubes. They are notorious for going microphonic, but if you can find a pair that are not microphonic they are Telefunken copies made on Telefunken tooling and they sound great. I had a stash of 10 of the late production shiny plates, and all of them were too microphonic for a moving coil preamp. The earlier production with the gray plates are what you want if you can find some, but you will reject a lot due to microphonics. For guitar amp use, the Ei ECC83 is only recommended in the phase splitter stage.

I have the JJ ECC83S in a guitar combo amp where it works fine. These tubes are quite free from microphonics, so they should work well in a moving coil preamp as they also have good gain. Sound is not as bright and sparkly as the Ei ECC83, so if you want a darker sound, try them.

The Sovtek 7025 and Sovtek 5751 were tried in the EV-1, and although they managed to pass muster for microphonics and can be used if I have to use them, I really wanted a set of super quiet input tubes. The Electro-Harmonix 12AX7EH has been known for some time as the tube to tame microphonics in combo guitar amps that really give tubes a good shaking and known as tube destroying monsters. Well, the E-H 12AX7EH was almost dead quiet with my system turned up almost full blast and far beyond my normal listening level when I tapped on each tube with a pencil. I normally listen around 50-60 and the C-J PV14L was set on 90. That means that at about 25 dB above my standard listening level, tapping on the input tubes made almost no sound. WOW!!! E-H 12AX7EH reputation confirmed!

Beside the low microphonics, I am getting  gain a bit higher than the Matsushita built Mullard copy 12AX7 that VTS supplied. The plate noise is also fairly low. The loudest noise now is power supply hum and electrosmog interference. This means I can use the 12AX7EH in the 5751 second gain stage position and use the EV-1 for everything but the lowest output moving coils without a step-up transformer.

Now for listening notes: A bit dry and laid back at first. The sound was not as involving as the old JapaneseMullard copies. 3 hours later, things were getting more involving and the noise seemed even a bit lower. Of course, late at night a lot of electrical usage dies down and electrosmog noise in high gain preamps is not so bad. I used an oscilloscope to monitor my power line waveform, and it is usually flattened a bit at the bottom and top of the sine wave. This can affect audio performance and it is not something removed by line filters. If you install tubes around dinner time and listen until midnight, you will probably notice an improvement just from the power lines cleaning up.

I paid $7.95 for the E-H 12AX7EH back in 2002 as the sales receipt was in my tube stash. They were on sale, and now I wish I had bought more.

If you want low microphonics and low noise for a moving coil preamp, then give the Electro-Harmonix 12AX7EH a try. They are available from a lot of dealers and Part Express lists them for $13.84. In matched pairs they should not exceed $14.95 each from many tube dealers.

I have a lot of NOS and pulls in my tube stash. A lot of them have turned out to be junk. The great old American and European tubes have basically disappeared to discerning people and what few I got from eBay were often junk. Just buy what you need from the best current production tubes and do your own high grading. You may end up not using half of them, but it is still a lot better than paying $50 and up and up and up to those who sell to a few audiophile crazies. The truth is, some of the current production tubes are challenging the best of the past at far lower prices. Go to a hamfest and not a high end dealer if wanting NOS American and European tubes. Those guys are packrats and have stuff that they forgot about until now. I got a few Tung-Sol 5881 tubes that way and they sound great, for about 1/3 you would pay to an audiophile dealer. They also tend to last for decades instead of years as they were industrial/military types.

Also realize that what does not sound good in your equipment might be just right for somebody else or someplace else. My Ei ECC83 tubes might work well in a phase splitter, but far too microphonic for phono amp inputs. When you order matched pairs, they are usually matched for gain only and not for microphonics. The only way to match microphonics is a high gain moving coil preamp or a guitar amp with lots of gain in the V1 position. If you need matched microphonics then is is usually a DIY project in YOUR equipment. Tube testers do NOT come with microphonic testing capability BECAUSE DIFFERENT CIRCUITS HAVE DIFFERENT RESONANT FREQUENCIES. Within the circuit boards themselves you have different vibrational nodes. I have seen tubes that were fairly quiet except at VERY narrow ranges. There was this one tube that would go crazy everytime Emmylou Harris hit a certain high note...........and nowhere else.

ElliottStudio

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    • Elliott Studio Arts
Thanks for sharing this very useful information!  :D

I've noticed what you're talking about with the power 'electrosmog'. Some times my system sounds harsh and other times smooth and sweet. The harshness has been reduced considerably after installing a series mode line conditioner but still not completely gone. Sine waves here are perpetually flattened like you described. With all the junk on the power lines today, it's no wonder that gear utilizing chokes in the power supply sound so much better..