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Old 2nd February 2008, 12:38 AM   #1
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Default Ebay Tube Preamp Kit

I'm looking for a tube preamp for my T-Amp and found this on Ebay. Any opinions on it?

http://cgi.ebay.com/ws/eBayISAPI.dll...MEWA:IT&ih=002
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Old 2nd February 2008, 12:45 AM   #2
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IMO, you should pass it by. A PCB of dubious quality does not whet my appetite. Also, that "kit" is far from complete. Where's the chassis? Where are the switches and controls?

I suggest you look here and exercise a little patience. Mr. McShane should be ready reasonably soon.
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Old 2nd February 2008, 12:45 AM   #3
rdf is offline rdf  Canada
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The schematic's wrong or you'll have 99 volts on the amp input. The pictures show a couple large film caps, they're probably just missing in action on the schem.
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Old 2nd February 2008, 01:43 AM   #4
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I agree with these guys; with poor quality passives (metal oxide resistors? Sheesh!), semi-unknown circuit, obscure tubes, no chassis or PS, it's not worth the trouble it'll take to make it good. Better you build your own goodness, if you got to make a chassis anyway. I have a real simple circuit that works like crazy:

Click the image to open in full size.

I have a small schem almost finished that shows the power supply as well, if you're interested.

If it doesn't appeal to you, there are lots of other possibilities out there. The thing is, those guys aren't saving you enough (if any) work to spend the sixty bucks there. Might as well go for the gold.

Aloha,

Poinz
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Old 2nd February 2008, 02:47 AM   #5
tinitus is offline tinitus  Europe
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New Aikido pre from broskie, runs on 24V and can be driven from a cheap switchmode supply

http://www.tubecad.com/2008/01/blog0132.htm


If you choose one with high voltage supply, it may become a bit expencive, and you might just as well build a integrated

http://www.engineeringvista.com/audi...el-1/index.htm

http://www.tubelab.com/SimpleSE.htm
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Old 2nd February 2008, 03:12 AM   #6
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I thought this looked suspect. I also saw the 24v aikido and have been waiting for the kit to come out. Thanks for all the good advice.
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Old 2nd February 2008, 03:47 AM   #7
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Poinz,
Sure, lets see the complete schematic. What kind of gain are you seeing with your preamp? input/output voltages?

Thanks,
Sal
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Old 2nd February 2008, 05:44 AM   #8
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Tomorrow, Sal, it's late.

Av = 5
Zin = 100K (or pot of yer cherce)
Zout = 200Ω
Hum+noise ~ 20µV

It's a butch circuit.

More in the morning,

Poinz
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Old 2nd February 2008, 09:45 AM   #9
poynton is offline poynton  United Kingdom
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Quote:
Originally posted by Eli Duttman
...............A PCB of dubious quality does not whet my appetite. Also, that "kit" is far from complete. Where's the chassis? Where are the switches and controls?

........................



Quote:
Originally posted by bcrescen
I thought this looked suspect. .........
Hey, guys. A little harsh unless you have seen the preamp kit etc.!!!

I have had a couple of items from this seller.
OK, the quality of boards and components may not be top grade but...

They work, first time
Communication with the seller was excellent
dispatch was immediate
Price and postage were reasonable for what you get


What more could you ask?
You can buy transformers and there are some excellent cases around too.
As for dubious circuits, see post 4. QED!

Be constructive and objective in criticism, please.

Andy
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Old 2nd February 2008, 11:10 AM   #10
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Quote:
Hey, guys. A little harsh unless you have seen the preamp kit etc.!!!
Andy,

I have had first hand experience with some of these boards. I will agree with you that the communication with the seller is excellent and that the seller offers a number of items such as transformers and power supplies. I made three boards and have had questionable results on each. The circuits can be improved upon meaning the selection of parts and values are off. When the circuit is completed you will most likely have to re-engineer it to obtain the correct values to get the tube operating along the correct lines. Its not worth it....

As mentioned....the Aikido will provide a superior result. If you follow the blogs everything is laid out for you. Pick a tube and it lists the resistor values and the current draw. Its a piece of cake.
There are circuit boards available that you can purchase or you can wire it point to point if you wish.

Andy, there are a lot of well meaning guys here that are just trying to lend a helping hand. My suggestion is to follow the path they are suggesting. This will lead to a project being completed that will provide hours of pleasure and a feeling that you did something correct the first time out.
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