Telefunken ECC83/12AX7

[DaveP]

I did actually settle on two different brand 6SN7s for the outputs so maybe I just tested them by ear until I found two that behaved alike and brought out the best sound to me.... definitely didn't test anything beyond that.....

Push pull output stages cancel even harmonics in the OPT.  If your chosen pair were unbalanced then you preferred some 2H, if they were balanced, then you preferred residual 3H.

DaveP

 

[emrr]

Push pull output stages cancel even harmonics in the OPT.  If your chosen pair were unbalanced then you preferred some 2H, if they were balanced, then you preferred residual 3H.

DaveP

Yep.  And:

Unbalanced PP output stages usually have less low end, because of the current imbalance in the output transformer.  This can be moderate to severe, also affects sound perception. 

 

[emrr]

Less bottom extension than before in an otherwise 'flat' response.  Depending on the transformer, it can be huge, it can be small.  Outside of response, this affects distortion.  This is why some amps have balance trims to make simple current matching possible.  This is why that's regularly seen as a good modification on certain amps. 

 

[CJ]

it is really a matter of "how much do i care?"

a real fanatic might but 10 samples of each 12AX7a/7025/5751/ECC83  etc which might cost a million bucks,

for poor people like me, it's read the hype, try to make a good decision, and hope for the best,

it is fun to plug and play different tubes, but it gets tiring after a while. and what's the point when people are listening to MP3's thru ear buds off their phone?

it is fun to read stuff where somebody had a huge cache of tubes and also had some test equipment, and maybe some friends with ears and unbiased opinions, (blind fold test)

we use electro harmonix because the boss has an account there so he gets a discount, that's how that works, maybe some new Mullards floating around also.

https://web.archive.org/web/20131122141757/http://www.jumpjet.info/Pioneering-Wireless/eMagazines/VTV/VTV14.pdf

back in the early 70's some friend would call up and say"come on over and check out these Mac 2 speakers" so we would hop on over and put  a 1st pressing on a Thorens thru an SAE preamp thru an Adcom pwr amp, and we would stare at the speakers in silence listening as hard as we could for all the details, who does that anymore?  usually music is background noise while we are doing something else like running a jigsaw thru some plywood, 

 

[rock soderstrom]

back in the early 70's some friend would call up and say"come on over and check out these Mac 2 speakers" so we would hop on over and put  a 1st pressing on a Thorens thru an SAE preamp thru an Adcom pwr amp, and we would stare at the speakers in silence listening as hard as we could for all the details, who does that anymore?

I do it sometimes, alone. I should do it more often, best way would be with some of my old friends. I miss it... :'(

 

[okgb]

It's not very scientific , but a friend and I were checking a bunch of tubes because they were used and wanted to grade them as spares,  mostly we  were checking the noise  [ by putting them in the 1st position of a Marshall 800 ]  and recording the results
no audio and the noise spectrum of each type was fairly different, one particular mullard very dull.
not sure to what end [ maybe to see what we were left with ] but on playback started checking two at a time  reversing polarity on one and listening in mono, to see how much would cancel and of course it varied EXCEPT when only two chinese tubes were used the result was a strange hi frequency distortion, random but fluctuating  , kind of like a pinging peak distorted  random clock noise,
now it was at a level & condition that you'd never encounter  exactly , but it was disturbing!

 

[ombudsman]

Speculative dealer prices really aren't the benchmark.  Used real smooth plate telefunkens are fairly common and can be obtained for around $40 each pretty consistently for those that test well. Sometimes you can run into them for $1-5 at flea markets/etc. They last a very long time and there is no real need to find one of the dwindling supply of new in the box examples.

I have consistently found that one of these with clean pins has lower noise than any other option available to me, when I have a problem with noise in a certain 12ax7 socket.

I also think they sound great. But I don't have many so I don't use them except when I really need to which tends to be the first preamp tube in a guitar amp.

 

[ruffrecords]

Speculative dealer prices really aren't the benchmark.  Used real smooth plate telefunkens are fairly common and can be obtained for around $40 each pretty consistently for those that test well. Sometimes you can run into them for $1-5 at flea markets/etc. They last a very long time and there is no real need to find one of the dwindling supply of new in the box examples.

I have consistently found that one of these with clean pins has lower noise than any other option available to me, when I have a problem with noise in a certain 12ax7 socket.

I also think they sound great. But I don't have many so I don't use them except when I really need to which tends to be the first preamp tube in a guitar amp.

I suggest you try a Sovtek 12AX7Wa current production tube. A third the price and the lowest noise 12AX7 I have ever measured.

Cheers

Ian

 

[ombudsman]

I suggest you try a Sovtek 12AX7Wa current production tube. A third the price and the lowest noise 12AX7 I have ever measured.

Cheers

Ian

Thanks but I have never particularly liked the sound of Sovteks and I do not buy any Russian products due to their criminal regime in general and their occupation of Crimea.

 

[Heikki]

Thanks but I have never particularly liked the sound of Sovteks and I do not buy any Russian products due to their criminal regime in general and their occupation of Crimea.

Do you also not buy any electronics in which conflict minerals were used. Russia may be bad but to me child slaves working in mines seems pretty bad too.

 

[ombudsman]

Do you also not buy any electronics in which conflict minerals were used. Russia may be bad but to me child slaves working in mines seems pretty bad too.

I'm not sure a generalized ethical purity test is helpful to a thread about 12AX7s and also not sure what your standing is to challenge me on it.

 

[okgb]

reminds me how every so often  [ less these days ] someone figures they'll manufacture magnetic tape for recording and can't make a go of it, then disappear!  I remember  after  they stopped making a green printed sylvania  6l6 in the 80's  , they just didn't last as long and I had to replace them more often, the modeling stuff is getting closer, so
if the russians or chinese  don't want to make a good tube they'll soon lose out,
trying to controlling a government through spending habits is noble if not futile , where you live , it's harder to find something , anything , not chinese these days [ and I trust none of it ! ]

 

[Squeaky]

A while ago, I built a late 60s-type Hiwatt head and the cathode follower slot ate new production valves. None survived. Amp works fine with NOS Mullard or Matsush*ta in that position. Chemist in me makes me think about materials of construction. People (yes them) spend an inordinate amount of time focusing on materials of construction imparting sound to transformers (think about Pulse Techniques in its new incarnation - there was a PhD metallurgist involved?). Its apples and oranges, I know (valves and transformers). Maybe rutaceae and rosaceae is still too close? I presume there is no doubt that new production valves are constructed with different materials (to the old fellas) to attain the equivalent electronic characteristics? Or not? I don't know and I don't (currently) have the inclination to research the literature. "Spattering" is a good word though.

A propo de rien, I seem to prefer new production valves in the diy 50s/60s Fender guitar amp circuits I build and NOS seem to find their way into the diy Vox, Marshall and Hiwatt stuff. Fairly sure its just my unscientific tube rolling at play. I keep meaning to drop the capacitor values in the output of the Fender stuff I build but then I just decide to that the benefits outweigh the negatives.

 

[ruffrecords]

A while ago, I built a late 60s-type Hiwatt head and the cathode follower slot ate new production valves. None survived. Amp works fine with NOS Mullard or Matsush*ta in that position.

Could be a heater/cathode volts issue. Can you post the schematic? (even just the CF will do).

Cheers

ian

 

[Squeaky]

Thanks Ian,

Attached is the schematic, sourced from the Mark Huss Hiwatt webpage (unbelievable Hiwatt resource). There are definitely some differences between the 727 amp and the classic early 70s Hiwatt. I built it with a 50W output stage.

Regards,

 

[Squeaky]

Here is an amp shot as well.

 

[ruffrecords]

Thanks Ian,

Attached is the schematic, sourced from the Mark Huss Hiwatt webpage (unbelievable Hiwatt resource). There are definitely some differences between the 727 amp and the classic early 70s Hiwatt. I built it with a 50W output stage.

Regards,

There does not seem to be anything particularly unusual there. Which of the two cathode followers is the one that destroys new tubes?

Cheers

ian

 

[bluebird]

Its kind of weird that the power for the last cathode follower (right before the phase inverter) is tapped off the first stage. I've never seen that. perhaps they were trying to keep the heater cathode voltage differential down.

 

[ruffrecords]

Its kind of weird that the power for the last cathode follower (right before the phase inverter) is tapped off the first stage. I've never seen that. perhaps they were trying to keep the heater cathode voltage differential down.

That stage runs from a lower HT than the previous CF so the Vhk requirements should be less, plus the ECC83 has  a Vkf of about 180V which sholud be well over the cathode volts. I suspect it is more to do with getting the bias conditions right for the phase splitter. Quite why they thought it was necessary to dc couple three tube stages I do not know but, since there is no feedback at dc, the dc conditions of the second and third tubes could vary over quite a wide range - perhaps enough to take one of them out. Of course, replacing the dead tube would not solve the problem if it was a dodgy earlier tube causing the dc upset so they might keep blowing.

Cheers

Ian

 

[Squeaky]

My apologies, I should have been clearer. It is the stage preceding the tone control that seems to eat new production tubes (V2 slot). The other cathode follower at V3 is (and always has been) a new production Tung-Sol.

I thought I'd best take the chassis out of its cabinet and measure the voltage at V2 pin 3: ~170V.

Thanks for all the comments and thoughts.

The amp sound great by the way, if not too loud for me to use now. I haven't plugged it in for years.