Vintage Telefunken 12AX7 Tube Review

| November 19, 2013

Tubes? What Century Do You Think This Is?

By Michael W. Dean
The Freedom Feens
Genesis Communications Network
Co-Host

 

Figure 1 - TubesLeft: Tung-Sol 12AX7 tube.      Right: Telefunken 12AX7 tube

deanmichael2CASPER, WY — The transition in audio production from analog to digital over the past couple decades has been a boon for radio. No more splicing tape, and no more finding the right tape or piece of tape. And don’t get me started on those dreaded carts. I’m thankful they’ve been replaced by a click on the screen. Tape hiss is something I don’t miss either.

However, in some ways, digital audio production is too clean. So after ditching tubes and tapes for transistors, integrated circuits and hard drives, some people have gone back to analog for one phase of the audio chain: the pre-amp.

Tube pre-amps and compressors have sonic attributes that cannot yet be replicated with digital modeling. Tubes provide a warmth that comes from semi-random, subtle distortion on certain harmonics. That sounds like it would be a bad thing, but it’s actually a good thing.

Tube pre-amps used to be in every radio and music studio. Not so anymore. Tube pre-amps are one reason (of many) why Frank Sinatra and Black Sabbath both sound better than most music today.

Tube pre-amps can make today’s talk radio sound better too. And in the past few years, the price of decent tube gear has gone down remarkably.

Tube gear between your mic and the rest of your signal chain is a worthwhile investment. And the difference can be heard even after sending your show over a codec, up to a satellite, down from a satellite, through more signal processing at the affiliate, and out onto radio receivers.

My co-host and I both run our Electro-Voice mics through Presonus Studio Channel pre-amp/compressor/parametric EQ units. (They’re about $300 retail. I’ll do an upcoming TALKERS article to review this unit at length.)

The Presonus is a great piece for your rack, but like most tube gear these days, it ships stock with a generic Chinese 12AX7 tube. The Chinese generics are not good. I’d recommend tossing them in the trash as soon as you get the unit and replacing with at least a Tung-Sol 12AX7. These new Russian tubes run about $15 each on Amazon, and last about a year of daily use. They sound much better than the generic Chinese ones. Neema and I have been using the Tung-Sols since we’ve been on radio.

I can hear some readers saying “Buy American! Not Russian or German or Chinese!” But American companies don’t make great tubes anymore, because there’s not enough of a market to justify the price of manufacture, since they have to be made by hand, and some of the raw materials need to be imported anyway. Blame Congress and tariffs, not me.

Recently a fan of ours who is a fellow audiophile sent us each a vintage early-to-mid 1960s German Telefunken 12AX7 Tube. They are rare, coveted and sound even better than the Russian tubes. They are marked “COMPUTOR”, and were made for mainframe computer arrays, back when computers took up whole rooms. These tubes are hard to find, and will run you $50 to $150. eBay is a good place to look. Make sure you buy them from sellers with lots of positive feedback, and make sure you get one that has been tested.

Most audio pre-amps use a 12AX7 tube. But read your manual or look online to make sure yours does before shelling out for a Telefunken 12AX7.

The Telefunken sound is warmer and fuller than the Tung-Sol tubes. Below is a short before-and-after audio file. The difference is subtle, but absolute to the discerning ear. I’ve encoded the MP3 at 320k to preserve the nuances.

freedomfeensgraphic2

 

 

 

 

Changing the Tube 

First MAKE SURE THE UNIT IS UNPLUGGED! Then remove all the screws from the top of your pre-amp. Make sure to set them aside somewhere where you won’t lose them. I recommend an empty glass. And keep them away from pets and little kids. Cats think that screws are bugs and will try to bat them around.

Don’t directly touch the glass on tubes, your finger oils will reduce a tube’s lifespan. Pick up the tube with a piece of tissue paper.

Figure 2 - Tube to ChangeTube to Change

With the thumb and forefinger on one hand, hold the little circuit board that the tube socket is attached to. Grasp the tube you’re replacing firmly yet gently with the thumb and forefinger on your other hand. Gently wiggle the tube left and right while pulling it slowly away from the socket. If the tube you’re removing is a Chinese generic, throw it away. If it’s a Russian Tung-Sol with some life left in it, set it aside and save it as a spare. I usually put it back in the little box it came in and write “USED” on the box with a sharpie. Always keep a spare tube on hand.

To put the Telefunken in, do in reverse what you did to remove the old tube. With the thumb and forefinger on one hand, hold the little circuit board the tube socket is attached to. Grasp the Telefunken tube firmly yet gently with the thumb and forefinger on your other hand. Make sure to line the pins up correctly, there’s a space in the socket for the place where one pin is missing on the tube. Gently wiggle the tube left and right while slowly pushing its pins into the socket. Then replace all the screws. Plug the unit in, and let it warm up for a couple minutes for optimum sonic quality.

Bottom Line

Spending $100 or more on a pre-amp tube is not for everyone. But if you’re really into getting the best audio you can get, these tubes have no equal. If you have a tube pre-amp, I’d recommend indulging in a vintage Telefunken tube at least once in your lifetime. It’s worth it for that classic 60s sound.

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Michael W. Dean is co-host of The Freedom Feens which is syndicated by Genesis Communications Network, and can be heard every Saturday and Sunday from 12:00 noon to 2:00 pm CT. Michael Dean also runs the free audio tip website Creamy Radio Audio. He can be emailed at mwd@michaelwdean.com.

 

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Category: Advice, Technical