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Old 21st December 2011, 08:06 PM   #1
Einric is online now Einric  United States
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Default My First Tube Preamp

Hello,

I'm wanting to build a tube preamp to feed my LM4780 Audiosector kits.
I will be paralleling the lm4780s to make mini monoblocks.

I'm needing something with volume control to make sorts of a dual mono mini integrated amplifier.

The project needs to be simple since it is my first tube project.
This leads me to E-Bay of course, I KNOW, I'M SORRY.
Here is what I'm looking at,
Buffer Tube 6N3 HIFI Audio Preamplifier Pre-amp -B3 | eBay
I honestly don't think it will be the best thing since sliced bread but I'm also looking at this like a learning experience.

Any opinions about this item?
Any CONSTRUCTIVE thoughts that might help?

The listing says it requires 150-200VAC, that's no problem but I was wondering what the difference would be with a 200V or a 150V input?
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Old 21st December 2011, 08:13 PM   #2
SY is offline SY  United States
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It's certainly cheap! Without a schematic, it's difficult to say much more. My main worry would be reliability- having a hot rectifier right next to temperature-sensitive electrolytics is not a good idea.

BTW, you're right next to one of my favorite pizza spots ever, over in Belgrade (Damasco's).
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Old 21st December 2011, 10:43 PM   #3
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First let me say I know nothing. I just put togeather built boards and pieces parts in boxes. I am planing to use this preamp with a pair of magic eye tube vu meters because they use the same voltage transformer. I have the two tube version with the solid state rectifier and it does sound good to my 50 year old ears. When I first got it I ran it with two transformers (second one backwards) to give me 140 v ; 10v under spec. Then I got an antek transformer at 160 v ; 10v over spec. I couldn't hear any difference between the two power sources. I use it between my cd or dac and t-amps and I like it cause it seems to smooth the sound and make it not as dry and harsh.
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Old 21st December 2011, 11:29 PM   #4
Einric is online now Einric  United States
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SY,

I agree Damasco's is a good slice.

I am looking at taking all of the capacitors and relocating them to the bottom of the board this should help with overheating.
Then I was planning on building a heat shield that is mirror like so I can see the tubes glow from the front of my enclosure.

I'm mainly concerned with voltages and tube types.
Are there any issues with these tubes used?
Are there any drop in replacements that would be better down the road?
Would there be any benefit to using higher voltages instead of lower eg. 200 v.s. 150 or somewhere in between?

Thanks
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Old 22nd December 2011, 12:09 AM   #5
SY is offline SY  United States
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Well, the problem is that without a schematic, you can't really say anything about whether the tubes are used appropriately or what the effects of varying B+ are (note that the 6N3 is the rectifier, the ad doesn't say what tubes are used for the audio). You have to trust the designer- and that may or may not be a good idea, there's a lot of really bad Chinese "designs" being sold on EBay for cheap. There may be some good ones, I don't know, but I haven't seen them yet. OTOH, it's $30...

Excellent ideas about thermal management!
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Old 22nd December 2011, 12:18 AM   #6
Einric is online now Einric  United States
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It looks to me like this kit uses two 6N3's and one 6Z4.

These undoubtedly are Chinese 6N3's is it possible that their naming/numbering scheme is different?

The 6Z4 looks to be the rectifier tube.
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Old 22nd December 2011, 12:29 AM   #7
dtaylo3 is offline dtaylo3  United States
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You may just want to buy the completed amp on their page instead.

It's called the "Finished 12AX7+12AU7 Tube Pre amplifier Preamp"

I would not expect too much, but you never know.
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Old 22nd December 2011, 12:37 AM   #8
Einric is online now Einric  United States
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I would not expect much either.
BUT.....I'd rather not expect much from $43 and have a learning experience than have a Face->Palm for $200.
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Old 22nd December 2011, 12:40 AM   #9
SY is offline SY  United States
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Good attitude.

Is this possibly the same unit?
Need help with a Tube preamp Kit (6Z4, 6N3)
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Old 22nd December 2011, 12:56 AM   #10
Einric is online now Einric  United States
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That setup is very similar but broken into two pieces.
I think I remember reading that post a while back.
If the worst thing I have to worry about on this kit is changing the pot and swapping for 5670's I will be a very happy camper.
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