EL 34 recomendations.

markj

 I need a replacement pair of EL 34'S. The TAD el34Bs that I've had in my Amp haven't last very long at all. I'm willing to try a different manufacturer. What would you recommend. 

martinw

JJ.

ICBM

markj said:

 I need a replacement pair of EL 34'S. The TAD el34Bs that I've had in my Amp haven't last very long at all. I'm willing to try a different manufacturer. What would you recommend. 

I would recommend having the bias checked first. Many modern amps are biased far too hot (including many Marshalls) and many old amps were either similar or have leaking bias filter caps and/or drifting resistor values which can do the same thing.

If it's definitely OK then both JJs and TADs are fine.

markj

The amp is a H&K puretone head. In the manual it says if using a matched set there is no need to bias the amp. The amp is running in class A.

markj

I originally thought it was the pre amp tubes so I bought a new set but the problem was still there. Extremely bright and noisy.

RiftAmps

markj said:

I originally thought it was the pre amp tubes so I bought a new set but the problem was still there. Extremely bright and noisy.

So how have you diagnosed that the OP valves are faulty?

ICBM

markj said:

The amp is a H&K puretone head. In the manual it says if using a matched set there is no need to bias the amp. The amp is running in class A.

It almost certainly isn’t. But claiming that it is may mean they’re running excessively hot...

DJH83004

I suspect with the 'statement class A and don't need biasing' they actually mean cathode biased, so no doubt are running very hot. If there is no issue with the cathode resistor / bypass cap, then JJs would be the answer.   

ICBM

It should be said that 25W in true Class A *is* just about possible from a pair of EL34s, but not without exceeding the valve ratings, because it would require the OT to be 100% efficient.

But my guess is that it’s running too hot and still in Class AB as well.

markj

RiftAmps said:

markj said:

I originally thought it was the pre amp tubes so I bought a new set but the problem was still there. Extremely bright and noisy.

So how have you diagnosed that the OP valves are faulty?

I put in the old power amp valves that I had. They have stopped the brightness and noise, but they are past it.

markj

In now for repair. Will report back.