Telefunken ECC83/12AX7

Tonight, I dug out a Harmon Kardon A30K stereo preamp/amp that has been sitting on a shelf covered in dust and spider webs, hasn't been powered on for at least two decades. According to the internet, it has all original tubes, four 7408 (6V6) outputs, and these 12AX7s. And a 12AU7.

What's so special about these Telefunkin tubes, where sometwat on the internet is asking $500 per, NOS?

Are they nuts, or just fishing? This amp worked when I put it up, and reading all the tube stuff restore projects here, I am now inspired to do the same. I wanna play, is there room in the sandbox for me too? 

Gene

They do get that sort of money at times.  I have a pile of those that came out of old stereos.  I have not found any  which did as well over time as your average American brand.  None sound great, and most are noisy.  Contrast with a similar situation GE/RCA/Sylvania, those always seem better.  I have never heard a NOS Tele, and the experience has not inspired me to do so for extra $$.  Take the $$$????......

There are guys who will pay silly money just for originals because they have been brainwashed into thinking they will sound better than current production. I once bought a box of very old valves, sight unseen, from a guy and had a good rummage through it. Checking type numbers on eBay I found one, that was still in it's original box, that was fetching well over £100 . I put mine up for sale and sold it for £150.

I suggest you do something similar.

Cheers

Ian

All I can say is my NOS Telefunken ECC803S beat any other ECC83 or 12AX7 brand new or old tubes in noise performance (20-30dB better) in my D-LA2A.

I remember at the beginning of the D-LA2A project one member trying anything in it, but wasn't satisfied with the noise performance.
To be on the safe side, and to exclude building or measuring setup errors etc I did send him a pair of ECC803S to compare.
He already tried every brand and model he could find.
I had no chance to get my tubes back (and he was willing to pay a high price).

In my experience, the smooth plate Tele 12AX7 is noticeably quieter and objectively subjectively better sounding in some circuits.  They would be wasted in a Marshall amp, but can make a huge difference in a mic pre.  Obviously the phono preamp stage of your HK would be the place to try them vs other brands.

For another opinion and possibly a chuckle, http://leedsradio.com/blog/?p=261

Edit: objective/subjective!

I listened to different tubes in a overdriving tube guitar circuit and the vintage ones I had KILLED the new production.

dmp said:

I listened to different tubes in a overdriving tube guitar circuit and the vintage ones I had KILLED the new production.

Click to expand...

In general, I agree.  I was talking specifically about a smooth plate Telefunken 12AX7, which is a high dollar tube even compared to a vintage RCA 12AX7 which will probably be better suited to the distorted guitar amp.

[silent:arts] said:

All I can say is my NOS Telefunken ECC803S beat any other ECC83 or 12AX7 brand new or old tubes in noise performance (20-30dB better) in my D-LA2A.

Click to expand...

If there was that amount of difference in noise then there must be something seriously wrong with the circuit or its implementation. It sounds to me like the regular  tubes were oscillating supersonically which is a common cause of excessive noise in poorly designed or constructed projects. Probably the slightly lower gain of the Telefunkens was enough to stop this oscillation and give the impressive improvement in noise performance.

To put this into context, I regularly build tube mic pres with brand new 12AX7s in the front end that produce up to 70dB of gain and they achieve a noise level within a few dBs of the theoretical minimum. There is no way a 20dB improvement can be made without defying the laws of physics.

Cheers

Ian

Has anyone done any measurements on the actual miller capacitance in 12ax7s or do most stay close within the datasheet spec? I have always wondered if this is a major contributer to the sound of tubes, especially in high gain amps with large grid stop resistors.

iampoor1 said:

Has anyone done any measurements on the actual miller capacitance in 12ax7s or do most stay close within the datasheet spec? I have always wondered if this is a major contributer to the sound of tubes, especially in high gain amps with large grid stop resistors.

Click to expand...

I have never seen any evidence that they are anything other than close to spec. Layout and stray capacitance can make  difference as well. The degree to which  Miller effect affects frequency response depends mostly on the source impedance and the stage gain. In many guitar amps the stage gain is set deliberately high and the input impedance is also set deliberately high (via a series resistor) so the -3dB point is often quite low. It will get worse if stages are cascaded because the source impedance seen by the second stage is the output impedance of the driving stage and if this is a 12AX7 it can easily be 40K or more.

Cheers

Ian

I'm not much of a tube guy. I don't currently use any tube based equipment. At one point I wanted to see if  could use a pair of K+H UE100's in my mastering setup. In the EQ sections it didn't matter what tubes I used. I tried a bunch of new and old tubes. I could never hear a difference. The output amp was another story. Only  Valvo and Telefunken tubes sounded right. It was enough of a difference to think the units went from unusable to useable.

Gold said:

Only  Valvo and Telefunken tubes sounded right. It was enough of a difference to think the units went from unusable to useable.

Click to expand...

I've had this experience with 6C5 and 6J5 comparisons in the same circuit, 6J5's never sounding right, yet they are interchangeable on paper. 

I also have done a bunch of listening to different brand tubes (old and modern) in mic preamps, LA-2A and guitar and bass amp preamps. This involves a controlled test, with the exact same program material, same levels, etc - the only variable is the tube. I record the results then switch back and forth to compare.  I discussed this with Brian,  a very smart guy I work with on projects. His first question was "did you measure bias voltage and current on each tube when you swapped, to be sure they were the same on eqch tube?" I did not. And I thought it was a pretty scientific test. So much for that!

Ever more far out is how certain tube brands exhibit similar sonic characteristics within different tube types - Tele and GE are hi fi, RCA are more round, etc.  Discussed this with Gridcurrent, Oliver Archut, Brian, and my tube connection, an old ham radio guy with an insane knowledge of tubes. We kept coming back to cathode coatings as being the "secret sauce" in different tube brands.

I can make the statement that I've not heard a modern 9 pin Noval tube that was as pleasing to my ears as old tubes. Power tubes are a different story. I've found the JJ power tubes, and maybe Ruby 6L6's can hold up against Mullard and RCA power tubes, at least in guitar and bass amps. No experience in hi fi power amps.

But as good as old preamp tubes sound, $500 per tube is nuts. If I can buy a great GE, RCA, TungSol, Amperex etc 12AX7 for $50, I don't think a Tele ECC83 sounds ten times better. And I have Tele ECC83's my Pultecs, BTW.  I sure didn't pay $500 each!!!

ruffrecords said:

To put this into context, I regularly build tube mic pres with brand new 12AX7s in the front end that produce up to 70dB of gain and they achieve a noise level within a few dBs of the theoretical minimum. There is no way a 20dB improvement can be made without defying the laws of physics.

Click to expand...

You are a lucky guy if all brand new 12AX7s work perfect like this in your Pre.
If I find time I will look if I can find all the noisy (brand new) ones I tested and send them to you.

[silent:arts] said:

You are a lucky guy if all brand new 12AX7s work perfect like this in your Pre.

Click to expand...

I don't think  said that. I have spent a lot of time looking at different brands and versions of 12AX7 trying to find ones that are consistently quiet. I am lucky that my Lindos test set includes a loudspeaker so you can listen to the noise. The other thing you can do is check for microphonics by gently tapping the tube. You can often hear the grid vibrating in the worst examples and you can even hear pinging noises when you turn the tube off as the metal parts cool and contract.

Bottom line is I have found only one 12AX7 which has consistently low noise AND low microphonics and that is the 12AX7WB by Sovtek. There are plenty of other low noise ones but most of them have poor microphonics like the 12AX7LPS for example. For tube mic pres it has always been necessary to select tubes for lowest noise but I have found 90% of the Sovteks are good enough
If I find time I will look if I can find all the noisy (brand new) ones I tested and send them to you.

So you are right, there are plenty of poor current production 12AX7 tubes but the NOS industrial versions I have always found to be even worse.  One problem with buying them is you don't really know their history but it is certain that the many I have tested have always been worse than the Sovteks.

If I find time I will look if I can find all the noisy (brand new) ones I tested and send them to you.

Click to expand...

I would be happy to test them out. Any information that improves our chances of obtaining better tubes must be a good thing.

Cheers

Ian

I'm finding in my RCA console restorations that the particular burn-in conditions affect noise.  Burn in a higher current position makes that tube permanently noisier, probably by 20dB.  This is with new 12AY7's. 

emrr said:

I'm finding in my RCA console restorations that the particular burn-in conditions affect noise.  Burn in a higher current position makes that tube permanently noisier, probably by 20dB.  This is with new 12AY7's.

Click to expand...

What's the work around you use if you don't mind me asking?

scott2000 said:

What's the work around you use if you don't mind me asking?

Click to expand...

I don't use those positions for burn-in!  Do it in the PRE, not the PGM or MON.  220K/8K2 versus 56K/1K2 or 39K/1K2.  I ruined 6 tubes using PGM and MON amps for burn-in.  PRE burn tubes stay quiet when moved to PGM or MON, PGM/MON moved to PRE have higher noise.  I'm looking at an Audio Precision test set along with ear observations.  I need to wire up a stand a lone burn in rig that treats both sections of the tube identically. 

emrr said:

I need to wire up a stand a lone burn in rig that treats both sections of the tube identically.

Click to expand...

This is interesting. Especially if there are
no other positions in a piece...

Tele ECC83/12AX7a go for about 50 on ebay (take your chances) 90 on KCA (trustworthy) and sometimes crazy prices as mentioned above.

Just got done going thru a 67 Fender DeLuxe Reverb equipped with Tele and RCA orange paint 7025's and it is one of the best amps to come thru the shop, dead quiet, you can hear every note equally, overtones, very Hi-Fi sounding,  If you are going to run an amp wide open, i think they would be a waste.

I would say make sure of the return policy, people sell off the bad ones, or they could be fakes.  Look for the triangle on the bottom.