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organ
02-14-2005, 07:17 PM
My pre has a standby/on switch. From what I understand, it's the B+ hitting the tube on a cold start that reduces its lifespan significantly. I believe tubeheads call this "Cathode Stripping".

My pre have a ss rectifier so there's no 'slow start'. In standby mode, the heater voltage is applied to the tube and it's lit up. No B+ yet. Once I set it to 'on', the B+ is applied and sound can be heard.

So what I do when I want to listen is first set the pre on 'standby' for a few minutes to let the tube warm up and then set it to 'on'.

So my question is.... Does the high voltage being applied instantly when set to 'on' shorten tube life? This is after a few minutes of warming up with only the heater voltage.

I know that with a tube rectifier, the B+ is applied slowly. But with my pre, it's applied instantly. So will this instant B+ hurt a tube that's already been warmed up by the heater?

Maurice
RuSsMaN
02-14-2005, 07:30 PM
Only a VERY few tube rectifiers offer a soft start. 5Y3 is one of the few.

The standby on the GT should be engaged for at least 30 seconds, before switching to 'on'. What it is doing, is letting the plate and cathode stabilize, before applying B+. It will affect power tubes in amps moreso than lower voltage drivers/line tubes, like in your preamp - but they put the feature there for a reason, so I always used it.

Cheers,
Russ
madmax
02-14-2005, 07:30 PM
It is my understanding that if the tube is warmed up with the heater then all is ok. I'm sure the startup curve makes it even easier on the tube but by how much I don't know. Probably insignificant.

madmax
organ
02-14-2005, 07:45 PM
Sweet. Thanks a lot for the replies guys. Glad I was doing the right thing. If I'm going to be home for a few days, I don't turn it off. I just put it on standby before going to sleep.

Russ,
I love the GE 6DJ8 you sent me along with the pre. You know, the one with the black stuff sprayed inside the glass to prevent RF noise from getting in (or something like that from what I've read). I want that little tube to keep on kicking so I give it a lot of TLC.

Maurice