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Author Topic: Tube mic - how long does a tube last?  (Read 7844 times)

PaulGasztold

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Tube mic - how long does a tube last?
« on: October 17, 2012, 07:54:44 pm »

How long does a tube last?

My Telefunken AK47 has a miniature tube

I need the mic to be on most of the day, 5 days
a week

I am a vocal coach by trade and often record
and play back the Singer's tracks during lessons
throughout the day


I end up using solid state condensor mics more often
because I don't want to 'wear down' the tube in my AK47


How soon would the tube in the mic need to be replaced
if I left it one 40 hours a week?


What would the tube replacement cost be?


Is it an issue?   Or is there another way to look at it?


Currently I pull out the tube mic for 'important' sessions
but would love to leave it on 40 hours a week 45 weeks a year


Insights are appreciated.


thanks

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klaus

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Re: Tube mic - how long does a tube last?
« Reply #1 on: October 17, 2012, 08:38:19 pm »

In a well designed and maintained tube mic system, the tube can last for years or decades.

Varying factors:

* tube brand/origin (if the tube is of Chinese, Eastern-European or Russian origin, all bets are off)
* strict adherence to factory-recommended power supply voltages, with yearly checks/adjustments
* careful physical handling, avoiding mechanical shock to mic or tube
* proper ventilation/cooling in warm operating environments










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Klaus Heyne
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Kai

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Re: Tube mic - how long does a tube last?
« Reply #2 on: October 18, 2012, 02:25:35 am »

My Telefunken AK47 has a miniature tube

I need the mic to be on most of the day, 5 days.
How soon would the tube in the mic need to be replaced if I left it one 40 hours a week?
I have some experience with tube wear, although obviously much less then Klaus.

Unfortunately the minature tubes wear out much faster then the normal sized ones.

Factory specs telling about 10,000 h for a Telefunken AC 701.
But this is theory.
For mic use the requirements are higher, and lot's of these tubes start to get noisy long before.
I have several mic's with this tube, and I had to replace the tubes quite often in the days I did use them day in day out.
These days the tube was obtainable by Neumann (already quite expensive).
I don't know how the situation is today, if it's even possible to get selected ones at a reasonable price - I doubt.

Other minature tubes used in mic's, like the 5840 just have 1,000 h, something I can confirm, as I had to replace this tube twice since I use a mic containing one.
Fortunately this tube is cheap and easily available.

In my opinion a tube mic is for doing high quality recording.
For practice or teaching mic usage a good FET mic will do.
This wouldn't even be a compromise, as there are classic FET mic's that are very well suited for vocal recording.

Teaching a singer using a mic is much about using the distance vs. dynamics, what happens I I sing extremly close, what to do if I sing extremly loud or high and stuff like that.
It's even more important to teach how to use a handheld mic - few singers know about that.

If you like tube sound with those mics use a tube pre containing an ECC83, 12AX7 or 6AX7  tube in the 1st stage - it will last long and it's easy and cheap to replace it.

And - don't use a compressor for the recording -  but show the singers what it can (or even can't) do after the singing is done.

Regards
Kai
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radiovinhet

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Re: Tube mic - how long does a tube last?
« Reply #3 on: October 18, 2012, 10:07:45 am »

AK47 uses ef732 tube ?
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klaus

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Re: Tube mic - how long does a tube last?
« Reply #4 on: October 18, 2012, 07:02:15 pm »

Unfortunately the minature tubes wear out much faster then the normal sized ones.

Factory specs telling about 10,000 h for a Telefunken AC 701.
But this is theory.
For mic use the requirements are higher, and lot's of these tubes start to get noisy long before.

What data can you cite that the sub-miniature tube AC701 (you called the size 'miniature') wears out "much faster" than a miniature (you call them 'normal') size tube?

My experience does not bear that out. The problem with AC701 which confuses mic owners: it's highly sensitive to abuse (mechanical shock, over-supply of voltages).

In properly controlled situations the AC701 can and often will last decades. It was specifically designed for microphones, like no other tube has ever been designed for since. The sub-miniature types 5840, 6111, and EF 734 which are now widely used in mics, including Neumann's M149 and M147, were NOT design for tube mics but for functions unrelated to audio. Hence the higher failure rate in the field, even after stringent selection.

P.S.:
Please read my AC701 primer
(http://repforums.prosoundweb.com/index.php/topic,1150.0.html)
to better understand why for the majority of AC701s made, there is no quality difference in microphonics between the 'k' version, and the same tube without the 'k' suffix.


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Klaus Heyne
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Kai

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Re: Tube mic - how long does a tube last?
« Reply #5 on: October 19, 2012, 04:57:59 am »

What data can you cite that the sub-miniature tube AC701 (you called the size 'miniature') wears out "much faster" than a miniature (you call them 'normal') size tube?
It's just my limited experience when using several Neuman mic's (KM type) for recording day in day out.
I had to replace so many tubes that I was quite happy when I could switch to transitorized ones to get rid of that problem.
And- yes, we correctly adjusted the PSU's and the mic's were handled carefully.
This was in the early eighties, when those tubes were already quite expensive if you bought them from Neumann.

Nevertheless the numbers are below what one could call statistically relevant.
It might just have been bad luck.
There is one mic (bough used from a radio station) which's tube has lasted until today, even though it had been used the same way like the others - luck.

On the other hand I have some Schoeps CM 60 with EF94 / 6AU6 tubes and never had any problems with those, although I use them quite often and from time to time had forgotten to switch their PSU off, so they really collected some hours.

Is it true that an ECC 83 is a "minature tube"?

Regards
Kai
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PaulGasztold

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Re: Tube mic - how long does a tube last?
« Reply #6 on: October 19, 2012, 08:18:11 am »

The Telefunken site states that the AK 47 Mark II has an  ef732 tube

Does anyone know if the Ak 47 Mark I ( original )  uses this same tube?  This is
the mic I own.

I am curious as to how this information applied to tubes in general, but also specifically to this mic

thanks all for your input!



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soapfoot

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Re: Tube mic - how long does a tube last?
« Reply #7 on: October 19, 2012, 11:50:18 am »

Is it true that an ECC 83 is a "minature tube"?

Yes, it is classified as "9 pin miniature." When introduced in the 1950s, these were quite a bit smaller than octal-base dual triodes like the 6SN7, etc. which were currently in fashion.

I typically hear EF732, 5840, etc. described as "subminiature" tubes. Many of these subminiature types were used in devices like hearing aids in the 1960s.



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Fletcher

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Re: Tube mic - how long does a tube last?
« Reply #8 on: October 21, 2012, 11:23:36 pm »

The Telefunken site states that the AK 47 Mark II has an  ef732 tube

Does anyone know if the Ak 47 Mark I ( original )  uses this same tube?  This is
the mic I own.

Yep - the "mark I" [for lack of a better term] employs a TELEFUNKEN [NOS] EF 732 just like the "mk II".  Things that changed for the "mk II" were the output transformer, circuit board layout [current handling improvement] and a couple of amplifier tweezes to lower noise and get a bit wider frequency response from the amplifier.

Peace
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CN Fletcher

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Jim Williams

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Re: Tube mic - how long does a tube last?
« Reply #9 on: October 22, 2012, 12:13:30 pm »

Tube specs degrade over time. Take any tube that has been in use for several years and do the usual curve trace, noise and microphonic tests and you will find degraded specs. Like a light bulb, they have a limited lifespan.

If you worry about this, keep tested spares on hand. If you have a mic with those tiny subminature tubes, those are usually soldered in with wires so changing/testing them is a PITA.
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