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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 11 Mar 2009, 23:04 
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Hi Everyone, I don't recall if I answered the heat sink question that was asked. If I did, sorry for repeating it. Any of the Oddwatt amps up to KT77/El34 typically have between 20 and 30 volts across the LM317. I use idle current of 125 ma per pair for the bigger tubes and for smaller ones about 80 ma per pair. The dissipation in the worst case is under 4 watts. A relatively small heat sink will do the job. I like to use the extruded metal ones about 2 inches tall and 1.5 wide. For the big tubes like KT88, 6550 and KT90 the current is usually at 180 ma per pair and the voltage across the LM317 can go to nearly 40 volts. The dissipation is now around 7 watts and you need a fairly good heat sink. The extruded multi-fin aluminum ones about 2X2 inches are suitable. Be sure to use heat sink grease and insulate the LM317 from the heat sink to avoid shorting out the tab to ground. If you do the tubes will conduct everything the PS can deliver and probably fail in a very short time.

Good listening
Bruce

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PostPosted: 12 Mar 2009, 03:18 
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One more question (two): the power rating of the resistor that sets the bias current? And have there been more looking into a discrete CCS? I have some FETs that could work.

As I have hinted, I will drop the Oddwatt for a while and get the 50CA10 together. But I would like to use some cheap transformers (ATRA0427 from Frag Jan Zuerst) together with 6V6. The pair I already have are ment for 6T9's.

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PostPosted: 14 Mar 2009, 19:21 
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Hi, Good questions. In anything I design all resistors can be 1/2 watt unless I specify otherwise. The one in the ccs need not be bigger than 1/2 watt. I usually derate parts, so the actual dissipation is well below the wattage I indicate. Now for the second question. Yes there are other CCS circuits available. I spent a lot of time experimenting with power FETs and various configurations and always went back to the LM317s. There were a few reasons. First they are cheap. Second the circuit is extremely simple. Third, most of the FET circuits had a higher minimum voltage. On the negative side. Some FET circuits can be made quieter than the LM317. This really isn't a problem here as the amp is very quiet. I would be interested to hear about others experiences particularly with other CCS ICs and designs. That's what DIY is all about.

Good listening
Bruce

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PostPosted: 15 Mar 2009, 12:59 
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I have been eyeing up some other design that mych looks like the oddwatt, but has the same kind of phase splitter applied to the input tube. This method looks very attractive as well.

http://soundbrigade.diinoweb.com/files/faktiskt/PP6L6.JPG with LM317 CCS

http://soundbrigade.diinoweb.com/files/faktiskt/pwrampnu.gif With 6CB6 CSS

http://soundbrigade.diinoweb.com/files/faktiskt/Sch-V21.gif Dual ECF80

http://soundbrigade.diinoweb.com/files/faktiskt/Stereo_6L6_PP.gif 6BH6 CCS

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PostPosted: 16 Mar 2009, 12:19 
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The first one with the LM317 CCS in the driver stage looks like a good one, and the other one designed by Tim William is rather neat, it uses a 6BQ7 for a change with an 6BH6 to bias it, that would be a cool one to build as a later project, I have no . I kind of wish I had gone the Odd watt route out of simplicity, but it is too late now.

Just thought I would add a comment or two.

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PostPosted: 16 Mar 2009, 12:38 
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But MINUS 590 VOLTS .... :o :o :hot: :hot:

But a smallish transformer and a voltage doubler can solve that.

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PostPosted: 18 Mar 2009, 20:41 
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Hi Everyone, All good circuits in the earlier post. The advantage as someone noticed is that Oddwatts are simple. There are disadvantages depending on how you feel about class A amps. Oddwatts can not be anything but class A push pull. You could do PP parallel, but nothing else. This restricts your power output a bit. Using the LM317 in a separate driver stage is a good thing if you need a class AB output and more power. Still IMHO, the fewer parts needed to do the job the better. Keep the good ideas coming that's what diy is about.

Good listening
Bruce

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PostPosted: 19 Mar 2009, 15:42 
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Thanks for your support!
When I do my DIYing I always try to go for simple designs, and the Oddwatt is such a great design as well as some of the ones I linked to above.
At this very moment I am looking into a SE-design using a dual triode 5998 and a ... dual triode 6201 (as driver). I could end up with 3W/channel with two tubes, one of them the power tube.

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PostPosted: 21 Mar 2009, 12:53 
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Returning to the idea of oddwatting the IP-stage I remember the tube I use in my Stealth - 6SC7. It's a dual triode (u=70, Ra = 53K, S = 1325) but it has the cathodes connected internally:
http://www.r-type.org/pdfs/6sc7.pdf
Guess I have a few laying around, that could be tested.

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PostPosted: 23 Mar 2009, 21:53 
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Hi You might be able to use it as a low power pp output with the cathodes so connected, but not as an SRPP (I suspect you already knew that). I am working on a tube headphone amp that does that with 6J6s. Low power, 1/2 watt about, that will end up as a web project in a short while. A very simple design with few parts, none of which are costly

Good listening
Bruce

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