12AX7/ECC83 Valve life

Of the modern production 12AX7/ECC83 type valves which one has the longest life. My Classic 30 eats the phase inverter tube and its getting expensive - especially if you pay to have the 2 triodes matched.

I have been using 12AX7 EH for this but I was just wondering if there is anything better. I seem to remember reading that the Sovtek 12AX7 WA has long life because it is lower gain - is this correct and will it adversely affect tone as a phase inverter compared with the pricier EH?

Al

 

Regarding the NOS idea, I did use a Brimar CV4004 (military grade) valve in this position once and it did last about 10 months instead of 6 or 7 months which is what the current production valves tend to last but the Brimar has tripled in cost over the last 3 or 4 years and are now about 4 times as much as a 12AX7 EH.

The other 2 preamp tubes do last much longer. It's just the phase inverter that doesn't last that long. I know a lot of people recommend that you change the phase inverter more often - generally when you change the power tubes but the phase inverter isn't even lasting long enough to do that.

Al

 

John

Thanks for the advice. Do you have any idea what kind of things could cause the problem or should I take it to a good tech? The thing is that the amp sounds good and I've had no other problems with it.

One thing that does come to mind is that I have a Fender Champ 12 where a power valve did not last nearly as long as I would have expected it to. I was wondering if I am doing something wrong like moving amps too soon after using them before they have had a chance to cool down.

Al

 

John

In the Peavey, they don't stop functioning but the way they go is that the drive channel starts to sound exceedingly nasty - like a cheap 80's practice amp. It once got to the point where the drummer (of all people) noticed and asked what was wrong with my sound! If you leave it long enough the clean channel starts to sound nasty as well although I generally change the valve before this gets too noticeable.

With the Brimar I did swap it into the first position when it went like this and it gave me lots of hissing/fizzy noises.

I try to leave it for at least 5 minutes before moving the amp. A sound engineer once picked the Fender up and moved it while it was on (and had been on for over an hour so it was nice and hot) which I wasn't terribly pleased with at the time. This may have contributed to that one - a pity as I'd managed to lay my hands on a NOS GE.

I've got a schematic for the Peavey and a multimeter so it's probably not beyond me to check a few resistor values. Do I have to disconnect capacitors from the circuit to measure values? I live 2 miles from Chandler's so the other option is to let Dave Petersen have a look at it.

Again thanks for the advice.

Al

 

If the amp checks out, try a NOS Telefunken. Their best 12AX7s are rated at 100,000 hours. This means you can play them 10 hours a day, every day, for 30 years! (According to the claim) Some of the modern production tubes, in comparison, will only last a good 1500 hours.

 

I was wondering how much effect the lack of a standby switch on the Classic 30 (and champ 12 for that matter) would have on valve life.

Al

 

I've had a look inside the Peavey. The problem is that the design (which I guess is cheap to build) is a pig to work on. Taking measurements of plate voltage etc. seems impossible with the PCB in place. And if you take the PCB out of the chassis which is quite a major operation then you lose the connection to earth (without some kind of bodge) and you can't switch it on to take the measurements.

The thought of paying someone £40 to £50 an hour (at London prices) to work on the amp when it would probably be an hours work just to take it apart and put it back together again does not appeal. I think I might just put it back together and put it on Ebay, along with the Fender and put the proceeds toward a nice Cornell or Brunetti.

Al