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Author Topic: Filament voltage on 6072A - 6VDC or 12VDC?  (Read 4710 times)

AusTex64

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Filament voltage on 6072A - 6VDC or 12VDC?
« on: July 18, 2013, 04:10:41 PM »

What are the advantages and disadvantages of using 12VDC with 6072A heater filaments in series instead of 6VDC with heater filaments in parallel? Will using 12VDC allow higher headroom of the amplifier, or provide any other sonic benefits? I plan to use both sides of this twin triode in my C12 mic build. Pardon my ignorance in advance if this is a stupid question. Thank you.
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klaus

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Re: Filament voltage on 6072A - 6VDC or 12VDC?
« Reply #1 on: July 18, 2013, 05:19:20 PM »

Parallel connection of two heater filaments? To my knowledge, the heater filament in a 6072 tube is only ever connected in one of two ways (parallel is not one of them):

1. Only one half of the twin-triode is operated, and the other is shut down, by means of grounding all elements of the second half, including the second half of the heater filament, which is simple center-tapped to ground. This system is used in ELA M251E, C28A/B, C12, and various copies of these mics. (Curiously, AKG used the second section of the tube, not section 1, for its single-triode models!)

2. Both halves are active, and, aside of the heater filament, are run completely independent from each other. The full-length of the heater filament is used in this case, and its center tap is not connected. This represents what you would call a series heater connection, though it technically is only one uninterrupted heater wire, requiring a doubling of heater voltage to 12.6VDC.
You can either use the second half of the tube as a switchable second gain stage, as it's done in the C12VR/The Tube, or as a completely separate impedance converter/preamp, as it's done in the C24 stereo mic.
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Klaus Heyne
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Jim Williams

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Re: Filament voltage on 6072A - 6VDC or 12VDC?
« Reply #2 on: July 19, 2013, 01:29:53 PM »

Seems many are now going to the 12 volt solution in tube mic builds. It does have some advantages, mostly the use of a common 35 cent 7812 regulator chip to provide clean heater voltage. 6 volt reg's are hard to find and they would need to dissapate twice the heat as well.

12 volts is a bit shy of 12.6, but many respected tube 'experts' claim a slightly reduced heater voltage does not affect performance in a negative way but does extend tube life by quite a bit. They seem to settle on 6.1 volts as the ideal heater voltage. That would end up at 12.2 for series connected heaters. Selecting through a batch of 12 volt 7812 regulators you will find one that is a bit above 12 volts. A LM317 style regulator is the best solution, lower output impedance, lower noise and full adjustable. The LT1085 low dropout regulator is an excellent sub.
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David Bock

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Re: Filament voltage on 6072A - 6VDC or 12VDC?
« Reply #3 on: July 26, 2013, 04:24:08 PM »

Jim is right about a practical solution for 12 heater reg. 12v has the advantage of controlling ripple a little more easily than 6.3v, by a hair.
The first few hundred Soundelux U95 had parallel heaters (6072 tube) as both sections of the tube were active. Later versions went to 12.6v.
The heater operation is not directly related to headroom, once the electrons are hot.
http://www.funwithtubes.net/
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AusTex64

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Re: Filament voltage on 6072A - 6VDC or 12VDC?
« Reply #4 on: August 04, 2013, 12:59:20 AM »

Thank you all for your responses. I am humbled to receive advice from such company. This forum is awesome.
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