Tube Heater Question

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Mr P

Tube Heater Question
« on: 11 Oct 2018, 05:07 am »
I recently sent my Lampizator DAC in to be upgraded.  As part of the upgrade the tube heater circuit for the DHT power tubes remains energized when the unit is in standby.  My question is this, does leaving the the DAC in standby with the power tube heater circuits energized shorten the life of the tube?  I also verified that no high voltage is applied to the power tubes when in standby.  Thanks.

FullRangeMan

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Re: Tube Heater Question
« Reply #1 on: 11 Oct 2018, 05:20 am »
I recently sent my Lampizator DAC in to be upgraded.  As part of the upgrade the tube heater circuit for the DHT power tubes remains energized when the unit is in standby.  My question is this, does leaving the the DAC in standby with the power tube heater circuits energized shorten the life of the tube?  I also verified that no high voltage is applied to the power tubes when in standby.  Thanks.
My question is this, does leaving the the DAC in standby with the power tube heater circuits energized shorten the life of the tube?
Yes in this case the tube timelife is being expended.
90days x 24hours=2160 hours, sorry for the bad news.

Docere

Re: Tube Heater Question
« Reply #2 on: 13 Oct 2018, 02:05 am »
I recently sent my Lampizator DAC in to be upgraded.  As part of the upgrade the tube heater circuit for the DHT power tubes remains energized when the unit is in standby.  My question is this, does leaving the the DAC in standby with the power tube heater circuits energized shorten the life of the tube?  I also verified that no high voltage is applied to the power tubes when in standby.  Thanks.

Short answer: It's likely; I would not leave filaments on in standby.

Long answer: There are several mechanisms that affect tube lifespan: plate dissipation/heat; plate voltage and/or current; filament use; filament voltage accuracy; filament warm-up; on/off duty cycle; B+ application relative to filament voltage application; mechanical failure... It is hard to say whether leaving the filaments on continuously will be a contributing, or sole limiting, factor in tube life in your case.

Also, Directly Heated Triodes don't have "heaters". DHT cathodes (filaments) are directly connected to the power-supply, causing the cathode to heat up and release electrons. In contrast, Indirectly Heated Triodes (IDHTs) have a heater connected to the power-supply - the heater causes the cathode to heat up and release electrons.



Cheers.

FullRangeMan

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Re: Tube Heater Question
« Reply #3 on: 13 Oct 2018, 02:30 am »
I would add a soft start as a factor to extend tube life.
Below a GM70 schema where cathode wire is heated directly,
this M shape cathode wire measure about 40cm long!

The 2 strips below are the cathode in the 6C33, the small filaments fell apart/removed, the grid is visible around the cathode:

« Last Edit: 13 Oct 2018, 04:11 am by FullRangeMan »

Mr P

Re: Tube Heater Question
« Reply #4 on: 13 Oct 2018, 09:22 am »
Thank you both for your input.