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Old 2nd February 2003, 02:18 PM   #1
Elkaid is offline Elkaid  Canada
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Default Low voltage Tube Schematic

I found yesterday this thread where a motherboard manufacturer is using tubes on their motherboard as a low power amplifier.

Computer with integrated tube amp

Do you have any schematics on low voltage tube amplifier ?

What are your impressions about the 6922 used as a low power amplifier ?

Thank you !


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Old 2nd February 2003, 02:43 PM   #2
SY is offline SY  United States
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Ahhh, the triumph of marketing.

The 6922 will not be particularly linear with a low plate supply. A Nuvistor would have been a better choice if such things were still made. I'm still in hysterics about the marketing-driven idea that after running the signal through thousands of transistor junctions, Everything Will Be OK if we put a tube somewhere in the line. Looks cool, but so would the same tube with just the filaments powered up. Just as useful, too.
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Old 2nd February 2003, 02:56 PM   #3
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Default ON THE BRIGHT SIDE...

Hi,

All marketing aside,I now that for line level stages the 6DJ8 family can be run successfully at 24 V B+.
Italian Stefano Pugini has once presented a complete 24 VDC battery powered preamp using the 6DJ8.

If you like to take a look:

PAENG

I can only assume that on the MB from Aopen they run it at a very low B+ .

Cheers,
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Old 2nd February 2003, 03:06 PM   #4
hifi is offline hifi  Sweden
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The other thread stated that a 300V DC to DC converter was being used.

/micke
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Old 2nd February 2003, 03:10 PM   #5
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Default STRANGE TACTICS

Hi,

Quote:
The other thread stated that a 300V DC to DC converter was being used.
Could very well be...only 300 VDC for a 6922 is way too much.

Does anyone know the function of that tube there?

Cheers,
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Old 2nd February 2003, 03:28 PM   #6
SY is offline SY  United States
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Default Re: STRANGE TACTICS

Quote:
Originally posted by fdegrove



Does anyone know the function of that tube there?

Yes. Marketing.

300V as a supply is not necessarily too much, and isn't too different that what I use in my own preamp/xover. The critical thing is what voltage ends up at the plate- which you well know. If you're going to run a tube in that 6DJ8 family in a linear way, you need current- with a 20K plate resistor (pretty moderate value) and 10 ma of zero-signal current, you'd end up with 100V on that plate, pretty close to that tube's sweet spot. Likewise, 50K and 4 ma, though the gain/linearity tradeoff would be an interesting one.

Yes, you CAN run tubes in the 6DJ8 family at low plate voltages (24V was your example), but for swings of a couple of volts, the distortion will be higher than good engineering practice will tolerate. Maybe that's what some designers are after, but it's not hi fi, it's signal processing.
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Old 2nd February 2003, 03:32 PM   #7
dhaen is offline dhaen  Europe
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Hi,

I would guess they are cathode followers, otherwise the output Z would be rubbish.
SY's point still applies about the voltage, hence the big output couplers.

Would I bother with it?...no.

Cheers,
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Old 2nd February 2003, 06:08 PM   #8
EC8010 is offline EC8010  United Kingdom
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Default Marketing

Studer once made a studio analogue to digital convertor that included a valve which was visible through a window in the front panel. The heaters didn't glow enough, so an orange LED was mounted in the centre of the valve socket to add a bit more glow. I don't know what electrical function the valve performed (if any), but the unit had a control labelled "Angel Zoom." I kid you not.
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Old 3rd February 2003, 01:47 AM   #9
halojoy is offline halojoy  Sweden
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Cool A tube radio, output stage operating from 12VDC B+

A tube radio with a "power" output stage operating from 12VDC B+

the 1st audio tube. You may have to select a somewhat different value to get good audio. The tube used here is another 12V tube, the 12AE6.

The amount of audio output power isn't much, about 50mW. Similar to that of a transistor radio. The output tube is a space charge tetrode, a 12K5. Except for pin 5, it will fit the same socket connections as a 50C5. Pin 2 is the control grid, and pins 5 and 6 of the 12K5 are the space charge grid, which connects to B+. This tube was intended for output stage transistor driver circuits in car radios.

12 V Tube radio

12 V Valves from the 1950-ies

Low-voltage phono preamplifier by Stefano Perugini

Quote:
In the world of the vacuum tubes it is inusual to meet with devices able to work at a low power supply. Among the signal triodes it is natural to think about the ECC86/6GM8; with its maximum plate voltage of only 30 volts, a transconductance and an internal resistance of 3.6 mA/V and 7K respectively, it represents the canonical choice when you want to elaborate the audio signal at low levels an low power supply. A series of experiments convinced me that, however, the use of valves, apparently not suitable for this aim, as the E88CC/6922 and E188CC/7308 (very similar tubes but not the same), can produce better results from the sonic point of view even at a low power supply. Between the two, I have fully preferred the E188CC/7308 because in this appliance I have found a better alectric response and a more pleasant sonic feature.
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Old 3rd February 2003, 02:14 AM   #10
halojoy is offline halojoy  Sweden
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Default ECC86/6GM8

ECC86/6GM8

ECC86 datasheet PDF

Headwize Tube Amp uses ECC86/6GM8

Click the image to open in full size.

halo - the low voltage tubeman
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