How can you tell tubes in preamp going bad

[PJN]

I have an Aikido 9 pin all in one preamp that I built and used for several years. I had taken it out of service when I started building SS class A amps (Pass) because I was afraid the voltage spike on the outputs at startup was killing the expensive JFETS in the front end of the amps. But It did sound great. Recently took it out of storage and noticed distortion in the vocals while playing. It sounds almost normal, nothing like a hiss or a buzz, but some garbling of the vocals is noticed. I'm going to open it up and check the power supply voltages, but I was wondering if this is symptomatic of aging/dying tubes.

Thanks,

Paul

 

[mike567]

I would start checking capacitors. Tubes mostly just get weak.

 

[DF96]

Could be the valves, or resistors, or capacitors. The first step is to check DC voltages.

 

[picowallspeaker]

Contacts in tube sockets ?
Generally I find that problem in all the switches in old integrated amplifiers...

 

[PJN]

I checked everything out, nothing amiss. Pulled tubes and cleaned pins with deoxit, reinstalled, that did the trick. Aikido singing sweetly once Again. Thanks all.

 

[kevinkr]

What is the input impedance of the amps you are driving?