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?
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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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....
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....
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.
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.
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.
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.
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
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
Hey JAZZ2250 and Timsch75 - I'm in San Antonio and know several fantastic DIYers in Austin. Shoot me an email and I'll hook you up. You may want to try and make the next LoneStar Bottleheads meet in Austin to check out lots of different gear and topologies. Pre's, amp's, box speakers, horn speakers... we do it all.
webmaster@wardsweb.org
webmaster@wardsweb.org
Actually every commonly used octal rectifier that I have ever seen is pinned out the same. Wire it up for the 5Y3 and you will be able to use a large number of rectifiers without changing a thing. Keep your eyes open for used rectifiers as they are pretty rugged and won't cost much. I buy used 5V4s when I find them and haven't had one test bad yet and I like the coke bottle shape.
Again, when you start playing with tubes that have higher ratings (and cost more) than the 12AU7s the soft start is nice so it is worth it to have these on your list when out looking. In the mean time a 5Y3 is as good as any for what you are doing.
Good luck and be careful of the high voltage.
Again, when you start playing with tubes that have higher ratings (and cost more) than the 12AU7s the soft start is nice so it is worth it to have these on your list when out looking. In the mean time a 5Y3 is as good as any for what you are doing.
Good luck and be careful of the high voltage.
Are we gold plating turds again ?
Compared to what ? Another 12AU7 perhaps ? That wouldn't be difficult ! A TFK 12AU7 in a Foreplay is like having a set of $1000 alloy wheels on a car worth $500
Now someone please tell me that a $100 TFK 12AU7 sounds better than a $10 Sylvania 6SN7GTB in the same application . Do the TFK's actually represent good value for money (I've always wondered about that) compared to other 12AU7 ? I always list the ones I find on Ebay . One interesting point to note : TFK 12AU7 have far higher transconductance (about 2.8-3mA/V) compared to other 12AU7 (2.2mA/V) . Perhaps the resulting extra gain gives the perception of better sound , but who knows ! 
316a
mg16 said:
Compared to what ? Another 12AU7 perhaps ? That wouldn't be difficult ! A TFK 12AU7 in a Foreplay is like having a set of $1000 alloy wheels on a car worth $500
Now someone please tell me that a $100 TFK 12AU7 sounds better than a $10 Sylvania 6SN7GTB in the same application . Do the TFK's actually represent good value for money (I've always wondered about that) compared to other 12AU7 ? I always list the ones I find on Ebay . One interesting point to note : TFK 12AU7 have far higher transconductance (about 2.8-3mA/V) compared to other 12AU7 (2.2mA/V) . Perhaps the resulting extra gain gives the perception of better sound , but who knows ! 316a
tfk foreplay
Hi,
Extra gain,(if they do have more gain than others), has nothing to do with what I'm hearing.
I have tried rca nos, jj tesla current production, and mullards in the foreplay.
I am talking a wider, deeper soundstage with tfk, as well as a more extended top end, and a greater perceived sense of reality in the music, that a tweak of the volume control using the other tubes won't match.
I bought the tfk's used , tested strong on Audiogon for $40.00 each. Money well spent in my opinion.
mg16
Hi,
Extra gain,(if they do have more gain than others), has nothing to do with what I'm hearing.
I have tried rca nos, jj tesla current production, and mullards in the foreplay.
I am talking a wider, deeper soundstage with tfk, as well as a more extended top end, and a greater perceived sense of reality in the music, that a tweak of the volume control using the other tubes won't match.
I bought the tfk's used , tested strong on Audiogon for $40.00 each. Money well spent in my opinion.
mg16
I would use a bigger choke, 10H at ~40mA is still quite small.
Also use a slightly bigger first cap and probably only 100uF or so after the choke.
In case you are interested, there is a free power supply design tool to download at www.duncanamps.com
They also have a downloadable tube database which is a godsend.
And the 12AU7 is a great sounding tube in the right circuit...
???
As long as you're happy but not quite the point I was trying to get across ! What sounds worse than a 12AU7 then ?
I'm very interested as I have tried direct comparisons of 12AU7 with 6SN7/7N7 and 7AF7 (cathode battery biased with CCS anode load in an amp input stage) . The 12AU7 I used were French RT , Mullard M8136 , TFK ribbed , TFK smooth and Brimar Cv4003 . I have literally the best part of 800 12AU7 to play with , these were all I could be bothered with ! All sounded euphonic and smeared compared with a bog-standard USA 6SN7 , in terms of 'soundstage' all the best (Mullard M8136) could manage was a diffuse 'tubey' sound . Perhaps this is the attraction , down to taste rather than accuracy I did not notice any of the valves acting as a 'tone control' as some claim , more like a 'loss of focus' control or 'blurr' control
316a
ShiFtY said:
And the 12AU7 is a great sounding tube in the right circuit...
As long as you're happy but not quite the point I was trying to get across ! What sounds worse than a 12AU7 then ?
I'm very interested as I have tried direct comparisons of 12AU7 with 6SN7/7N7 and 7AF7 (cathode battery biased with CCS anode load in an amp input stage) . The 12AU7 I used were French RT , Mullard M8136 , TFK ribbed , TFK smooth and Brimar Cv4003 . I have literally the best part of 800 12AU7 to play with , these were all I could be bothered with ! All sounded euphonic and smeared compared with a bog-standard USA 6SN7 , in terms of 'soundstage' all the best (Mullard M8136) could manage was a diffuse 'tubey' sound . Perhaps this is the attraction , down to taste rather than accuracy I did not notice any of the valves acting as a 'tone control' as some claim , more like a 'loss of focus' control or 'blurr' control 316a
A 50c op-amp? An aiwa mini system?
While that is interesting and cool that you have actually done these comparisons, just remember that plenty of great designs used the 12AU7/ECC82. You don't have to have the "best tube" to enjoy music.
While the 6SN7 may be better sounding in some circuits, it is pretty bad in some ways: high power consumption, microphonic, runs quite hot etc.
ECC82 will be a fine tube for a simple pre-amp. Personally I would use a tube per channel in an SRPP configuration, but thats just my preference.
However, I do actually prefer octal tubes in general, because they are easier to solder.
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