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Old 4th January 2006, 10:27 AM   #1
beamnet is offline beamnet  Netherlands
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Default 12 volt preamp

Hi guys,

I got this cute miniature 6ag5 tub from a friend i traded with.

googling for an application i came across a radio citcuit using it in a 12 volt application.

Just out of curioity i powered up mu 12 V dektop supply and plugged some resistors 'n caps in my breadboard.

Within a short time i was hearing audio, after a bit tinkereing i am hearing GOOD audio.

Looks all cool on the scope. Don't know how to measure distortion, but it sounds teriffic.

Now i am suspecting there is some drawback, else we would all hook tubes to low voltage supplies.

Could anybody enlighten me why this isn't done more?

I am thinking: 12 lead acid battery and make a hummless phono!
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Old 4th January 2006, 10:36 AM   #2
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This IS being done and is already a very famous approach in the headphone amplifier scene. The most notable implementation mates it with a buffer output and is called the Millet Hybrid Amplifier.
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Old 4th January 2006, 01:51 PM   #3
lineup is offline lineup  Sweden
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12 Volt is maybe to overdo it.


But there are a few tubes that do reasonably well at lower voltages.
Say between 50-100 Volt.
But some values of performance will not be optimal.
What will suffer I do not know, as I am no tube expert.

One tube that can run a bit lower (than 200 Volt) is 6DJ8/E88CC/6922.

Here is a thread about same topic:
Running tubes at lower voltages
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Old 4th January 2006, 03:12 PM   #4
owen is offline owen  United Kingdom
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Nope, these are tubes designed for 12V operation - typically for car radios!

Thought about finding some, but in the end I have too many other things to do!

Owen
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Old 4th January 2006, 03:27 PM   #5
beamnet is offline beamnet  Netherlands
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which tubes?

Bas
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Old 4th January 2006, 05:04 PM   #6
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For 12v single triodes we have the 12AE6A, 12FK6, and 12FM6.

These are all designed for car operation and can thus run well off a 12v SLA.
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Old 4th January 2006, 05:16 PM   #7
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The 6GM8/ECC86 is a LOW voltage relative of the 6922. It's a fine Dutch product.
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Old 4th January 2006, 10:21 PM   #8
316a is offline 316a  England
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Hi ,
I don't know about the space charge valves mentioned earlier but the ECC86 looks like a safe bet . Otherwise if you can stretch to 50v or so , miniatures such as 3S4 are a possibility and there are many subminiature types that run at low voltages . Steve Bench has a battery phono stage on his site , maybe a good reference ?

cheers

316a
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Old 5th January 2006, 04:10 AM   #9
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I have a bunch of NIB 12CN5 and was thinking of a battery amp myself. These are IF pentode but ought to work at lower frequencies I'd think. You can actuallly get 4.5 mA plate current happening with 12 volts B+. Here's data on this baby. http://www.nj7p.org/Tube1.php?tube=12cn5
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Old 5th January 2006, 04:19 AM   #10
lineup is offline lineup  Sweden
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Quote:
Originally posted by Eli Duttman
The 6GM8/ECC86 is a LOW voltage relative of the 6922. It's a fine Dutch product.
6GM8 is tube design especially for 12 volt supply ( in car battery operation ).
At plate 12 Volt will run like 2.5 mA
At plate 6 Volt will run like 0.8-1.0 mA


I guess that when plate 6 Volt, the supply is 12 Volt
and anode resistor is like 5 kOhm
and cathode resistor 1 kOhm

Heater is 6.3 Volt / 330mA
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