Re: Fire up antique tubes

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In Reply to: Fire up antique tubes posted by elektron on August 13, 2006 at 14:59:14:

This a common myths - like so many in HiFi circles - that comes from having a little bit of knowledge and extrapolating it broadly. Cathode stripping is a problem with high powered tubes and it more so with certain cathode materials. But the "high" I refer to is for tubes designed for industry that dissipate hundreds of watts and more. I've been at tech for over 35 years and I've not seen any evidence that cathode stripping occurs with those tubes used in USA consumer equipment - every thing up to about 50W plate dissipation. "Standby" switches on musical equipment - which would help prevent cathode striping if that was an issue (not!) - were originally installed to allow a tube amp with a couple of minutes warm up to stability to be instantly available when a musician took a break or changed instruments (changed a string).
After all, the striping comes from the cathode electrons attraction to the positive plate voltage and you've got to get in the thousands of volt region for this to ususally be significant.
Now bringing up any tube slowly on a variac - etc., - is "nicer" to the heater as the on/off start was long identified with heater failure - nothing to do with cathode stripping! And one can always insert a diode in an AC heater string with a bypass switch to initially warm up the tubes before full heater voltage. But nothing about this has to do with age - if a tube has been carefully handled and not knocked around a 40 year old tube should warm up as well as a new one - after all the inside is in a vacuum and it doesn't "rust" in there . But if a tube has been roughly handled a resistance check between elements - especially with the tube horizontal - should show up any misaligned element that got knocked around. Has nothing to do with age 'cept the more years just give more opportunity for "hard knocks."
Rob

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Follow Ups Full Thread

Topic - Fireing up a NOS tube - ahlgren11@telia.com 11:47:43 08/13/06 (8)

Re: Fireing up a NOS tube - P-90 21:35:09 08/14/06 (0)

Re: Firing up a NOS tube - Jimmy 04:59:34 08/14/06 (0)

Fire up antique tubes - elektron 14:59:14 08/13/06 (4)

Re: Fire up antique tubes - Rob Mercure 08:18:56 08/14/06 (3)

Cathode Stripping and other things - elektron 12:05:20 08/14/06 (2)

Re: Cathode Stripping and other things - elflow 12:58:29 08/14/06 (0)

Re: Cathode Stripping and other things - Rob Mercure 12:39:54 08/14/06 (0)

Re: Fireing up a NOS tube - tubers 12:57:38 08/13/06 (0)

Follow Ups

Re: Fire up antique tubes - Rob Mercure 08:18:56 08/14/06 (3)

Cathode Stripping and other things - elektron 12:05:20 08/14/06 (2)

Re: Cathode Stripping and other things - elflow 12:58:29 08/14/06 (0)

Re: Cathode Stripping and other things - Rob Mercure 12:39:54 08/14/06 (0)

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