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Old 29th October 2005, 09:41 AM   #1
Pano is offline Pano  United States
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Default ECC88 at 12 volts

I've been reading few posts on this forum about low voltage tubes. Mostly everyone here says they don't work well.

The reason I ask is that buddy lent me his Musical Fidelity X-10D to have a look and listen. I was very much surprised to see that it runs on 12 VAC!

Having never seen a tube run so low, I was curious how this thing could work.
The X-10 is a line stage, said to work in pure class-A. M.F. sold a lot of them and they got rave reviews. The thing doesn't have any gain, and seems to have almost no sonic signature. It's supposed to work well between a CD player and amp, like any line stage.

The 12V thing baffles me. Even my old Neuman and Schoeps mics with their tiny tubes used an external 90V supply.

Most of the advice on this forum is that low voltages can work, but never very well. Any comments? I can post a schematic if need be.
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Old 29th October 2005, 09:49 AM   #2
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I believe the voltage is multiple after rectification
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Old 29th October 2005, 09:58 AM   #3
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Indeed the X10-D works remarkably well (I had one for years and I loved it). I think the point most people would make is that the ECC88 can sound even better if supplied with about 100V. If diy'ing, why force a tube to the least of its abilities.
Far from the x10d having no sonic signture - I found it filled out the sound and extended the top end a little.

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Old 29th October 2005, 10:15 AM   #4
Nisbeth is offline Nisbeth  Denmark
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Default Re: ECC88 at 12 volts

Quote:
Originally posted by panomaniac
Most of the advice on this forum is that low voltages can work, but never very well. Any comments? I can post a schematic if need be.
There are plenty of low-voltage tube designs around, and also plenty of tubes designed for low-voltage operation. A good example is the headphone amplifier by pete millet (www.diyforums.org) and a lot of the designs discussed in the headwize diy-forum (www.headwize.com). Still, I'd be very interested in the MF-schematic if you have it. If you can't post it here, you can email it to me


/U.
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Old 29th October 2005, 05:08 PM   #5
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You can certainly use a tube at 12V. Just don't expect more than so many microamperes

Tim
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Old 29th October 2005, 06:18 PM   #6
moamps is offline moamps  Croatia
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Quote:
Originally posted by jaudio
I believe the voltage is multiple after rectification

Yes, to +/-30V DC.
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Old 30th October 2005, 03:08 AM   #7
Pano is offline Pano  United States
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We have a winner!

Moamps is correct. +/-30V I should have measured the thing to begin with.

Seems strange to start with 12V and then mutliply. But it works.

I'll post a schematic ASAP.
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Old 30th October 2005, 04:21 AM   #8
wa2ise is offline wa2ise  United States
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Default Re: ECC88 at 12 volts

Quote:
Originally posted by panomaniac
I've been reading few posts on this forum about low voltage tubes. Mostly everyone here says they don't work well.

The reason I ask is that buddy lent me his Musical Fidelity X-10D to have a look and listen. I was very much surprised to see that it runs on 12 VAC!


Does the 12V AC come from a wall wart? If it's still AC, they could run it into the secondary of a 12V transformer and get 120VAC to rectify for some real B+ voltage. It wouldn't need to be that big; a transformer like those used in digital clock radios would be adequate.

Many manufactureres use wall warts to avoid the hassle of getting test lab approvals (like UL or the various European test labs).
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Old 30th October 2005, 06:03 AM   #9
Tyimo is offline Tyimo  Hungary
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Default MF-X10-D schem.

Hi!
I know only this schem of MF-X10-D, but I am not sure is it real...

Check it.

Greets:

Tyimo
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File Type: jpg musicalfidelity-x10-d-schematic.jpg (38.2 KB, 798 views)
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Old 30th October 2005, 06:49 AM   #10
Pano is offline Pano  United States
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Hey Tyimo,
Yes, I have that schematic too. It's good. A few of the values are different. But not much.

The 12V does come from outside, I just used a 12V 1A transfo that was handy. There is no transformer onboard, it is all stepped up via doubling (guess).

The big caps are at only rated at 35V, not much margin there. I'll try to get a value on all the componants and some voltages around the board.
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