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Old 17th June 2003, 05:43 AM   #1
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Default First time building a tube amp: Help please

I'm starting to make a tube preamp, which is my first tube amp. Main purpose of this project is to learn the tube stuffs, not to make superb-sounding tube amp. After reading a text book and posts on diyAudio.com, I've decided to go with "the famous 12AU7". I know that there are much better tubes and that some (many?) people think that this tube is a piece of S**T. But, please bear with me until I finish this project. Then, I should be able to make better tube amp. I will use the circuit from the textbook, Tube audio design by Bruce Rozenblit, shown below.

My first question will be on power supply. The transformer would be Hammond 272BX with secondaries of 300-0-300 (DC 100 mA), Fil.#1(rct) 5.0 V @ 2 A, and Fil.#2(htr) 6.3V @ 3.0 A. What kind of tube rectifier should I use? Well...actually I ordered a 5Y3GT thinking that this shoud give what I wanted. Is this tube OK?
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Old 17th June 2003, 06:06 AM   #2
Colt45 is offline Colt45  Serbia
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this PT and a 5Y3 will work fine, it is overkill though.

each 12AU7 section will only draw a few mA, and the PT is rated at 100mA, and 5Y3 @ ~150mA.


you could have used a much smaller PT, and a 6X4 or similar rectifier, but whatever.. i guess you can use this for a small power amp in the future.

I would jack up the plate resistor a bit, and drop down the output cap, but i 'spose this will work too.


12AU7 is a neat little tube, despite what the haters have to say about it....
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Old 17th June 2003, 06:09 AM   #3
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A 12AU7 might pull 5mA. No way in heck you need a 272BX for that! If you reduce the current, then it'll fit within the ratings of a P-T442 (an AES tranny) with a voltage doubler.
If you later intend to add say, a 6V6 amp, then a 272BX will be a nice choice.

Tim
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Old 17th June 2003, 06:15 AM   #4
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Quote:
Originally posted by Sch3mat1c
A 12AU7 might pull 5mA. No way in heck you need a 272BX for that! If you reduce the current, then it'll fit within the ratings of a P-T442 (an AES tranny) with a voltage doubler.
If you later intend to add say, a 6V6 amp, then a 272BX will be a nice choice.

Tim
Thanks for your reply, Tim.
272BX is not only for this project. As you mentioned, it could be used in my future project. So, I would like to keep it, if possible.

Jai
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Old 17th June 2003, 12:42 PM   #5
Joel is offline Joel  United States
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Jai,

Then you should probably do what I did and use the 300-0-300 @125mA version for the first project. That tranny has enough horsepower to run an EL84/6V6/6L6, etc, SE amp later on.

Joel
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Old 17th June 2003, 02:07 PM   #6
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Sounds good. Then, could anybody let me know if 5Y3GT would be OK for this project? Or, should I look for any other recitier? Thanks.
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Old 17th June 2003, 02:32 PM   #7
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At lower voltages like you will be using a 5V4 would be great and since it is a soft start it will extend the life of your other tubes especially when you start playing with ones that operate at higher ratings than the 12AU7s.
There are several very good DIY tube guys in your area and the Lone Star Bottleheads have meetings every few months rotating around to different cities in Texas. The last one was in San Antonio on June 7th. These are great for seeing and listening to some great DIY and commercial products.
Maybe we will see you at the next one.
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Old 17th June 2003, 03:29 PM   #8
Joel is offline Joel  United States
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David,

At 10mA of current draw, no damage could ever occur to these tubes' cathodes because of startup conditions. This is something you need only worry about in cases where you have much higher demand.

Also, a 5V4 is an expensive option (relatively), and its extra current capacity is not needed.

Jai, to answer your question, yes - a 5Y3 is fine. A 6X4 is also a good choice, as is a 5W4.
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Old 17th June 2003, 03:43 PM   #9
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Quote:
Originally posted by Joel
Also, a 5V4 is an expensive option (relatively), and its extra current capacity is not needed.
Thanks, Joel. As this is my first project, I would not like to spend too much. So, a little bit cheaper is better.

Quote:
Jai, to answer your question, yes - a 5Y3 is fine. A 6X4 is also a good choice, as is a 5W4.
I will go ahead with 5y3-gt as per your recommendation.
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Old 17th June 2003, 04:48 PM   #10
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Hey, jazz,
I tried to email you off-forum, but your link wouldn't allow it. I'm also an Austin DIYer and was wanting to contact you to get some info on local suppliers, etc. If you wouldn't mind contacting me at timsch75@juno.com, I'd appreciate it.

sorry to everyone else for the space.

tim s
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