Ear 834 12AX7 filament brightness when powered up

[sebgreen]

Hi,
I've just finished putting an E834 clone bought off the bay together.

Powered it up for the first time tonight with a single "sacrificial" (noisy as hell) tube in it to see what would happen.

Now the filament voltage is a bit high, and I need to adjust it. What surprised me more is that when I flip the switch, the tube light up like a lightbulb before dimming down to a more normal orange glow.

I am guessing this is due to the lack of a soft start, but is this normal, and if so, is it going to be detrimental to the life of the tubes I'm going to put in it ?

Thanks a lot

Sebastien

 

[petertub]

Hi,
I've just finished putting an E834 clone bought off the bay together.

Powered it up for the first time tonight with a single "sacrificial" (noisy as hell) tube in it to see what would happen.

Now the filament voltage is a bit high, and I need to adjust it. What surprised me more is that when I flip the switch, the tube light up like a lightbulb before dimming down to a more normal orange glow.

I am guessing this is due to the lack of a soft start, but is this normal, and if so, is it going to be detrimental to the life of the tubes I'm going to put in it ?

Thanks a lot

Sebastien

This is normal for a tube made by philips or any of their brands.

 

[MarcelvdG]

The Haltron ECC81 in my RIAA preamplifier has the same behaviour. It scared me at first, until people on a Dutch vintage radio forum explained to me what it was.

It is normal when the valve has a bit of heater sticking out of the cathode tube. This part of the heater does not get cooled by the cathode and due to the positive temperature coefficient of resistance it will get more than its normal share of the heater voltage until the cathode has heated up. The folks at the vintage radio forum claimed it didn't do much harm and apparently they were right, as my preamplifier has worked fine for years.

 

[sebgreen]

Edit : I just put another tube in it and the phenomenon has gone ...

Could it be the tube ? What would cause this ?

Here are some pictures of what happens with the dead TAD tube

 

[sebgreen]

The Haltron ECC81 in my RIAA preamplifier has the same behaviour. It scared me at first, until people on a Dutch vintage radio forum explained to me what it was.

It is normal when the valve has a bit of heater sticking out of the cathode tube. This part of the heater does not get cooled by the cathode and due to the positive temperature coefficient of resistance it will get more than its normal share of the heater voltage until the cathode has heated up. The folks at the vintage radio forum claimed it didn't do much harm and apparently they were right, as my preamplifier has worked fine for years.

I had not seen your reply before posting my edit. That could be the explanation as the other tube i tried has a different construction. Scared me quite a bit the first time ! Glad I asked thanks a lot. I would have been too scared to put my brand ex tubes in when i recieve them otherwise

 

[Brice]

German tubes often to the same.

Agreed. Scary, but nothing to worry about.
This does not indicate anything wrong with the tube and won't make it die earlier.

I've never had a US tube doing it.