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Author Topic: Tube mics: How Long Before Full Performance Is Reached?  (Read 407 times)

klaus

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Tube mics: How Long Before Full Performance Is Reached?
« on: January 10, 2017, 01:18:35 am »

I posted this earlier today on Gearslutz, but that thread eventually spun out of control, so I saved my post to an island populated by adults.

In my experience, the most relevant factor when using tube equipment is stability of performance: after what length of time will the equipment’s performance be stable enough that no further gain or eq-adjustments are necessary?
This is a relevant consideration, so that takes, edits and punch-ins are predictable, seamless, and don’t vary audibly from one to the next.

In that regard, it has been my experience that the longer you wait, the more stable the performance of tube equipment becomes. The only downside: increased wear, which can be financially prohibitive when replacing high quality specialty tubes.

A reasonable compromise must therefore be found between relative performance stability and reasonably low tube wear.

Here is my data for that sweet spot, from 30 years of experience:

AC701: 15 minutes
VF14: 15-45 minutes, depending on condition of tube
EF86: 10 minutes
6 and 12 Volt Nuvistors: 15 minutes

Miniature preamp tubes (12 Axx/ECC xx, etc.): 20 minutes

Another important question - how will on/off cycling affect tube life - is very hard to generalize.
Many well-designed power supplies for tube equipment ramp up gently and slowly, minimizing wear damage, while other mic supplies or supply sections of mic preamps are primitive, affording minimal ramp-up periods which can decimate tube life.

Here, again, a reasonable compromise between stable performance and tube wear would suggest to turn off tube equipment overnight, with more expensive tubes shut down even for a lengthy lunch break (2hrs+).
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Klaus Heyne
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Jim Williams

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Re: Tube mics: How long until full performance is reached?
« Reply #1 on: January 10, 2017, 11:04:41 am »

I agree with those timetables, they have also served me well. There have been some older cranky gear that needed a bit more time, mostly older components that needed to settle.

Modern stuff doesn't have those issues, it's just the tubes themselves.

As to extending tube life, one of the most damaging aspects is feeding the high voltage B+ to the tubes before the heaters have ramped up. I read something about stripping gas or elements away from plates.

This was the reason Fender guitar amps have a standby switch. That allows the heaters to ramp up before hitting the plates with the high voltage. If I had an unobtainium tube for an old rare mic I would consider installing a standby switch to extend it's life.
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Dan Popp

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Re: Tube mics: Wait how long until full performance is reached?
« Reply #2 on: January 10, 2017, 04:43:10 pm »

Gentlemen, do you have a recommendation for warming up "subminiature" tubes?  Or are they just a category of "miniature" tubes?
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Piedpiper

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Re: Tube mics: Wait how long until full performance is reached?
« Reply #3 on: January 10, 2017, 06:40:01 pm »

Some mics and preamps have timers on them to delay the high voltages until the filaments warm up. A tube rectifier on the high voltage supply can have a similar effect. Thus, it is not always necessary to have an actual standby switch.
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