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Old 9th August 2009, 02:42 AM   #11
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I'd be curious to know if you stuck with the LED's or not?
I did not make provisions for putting the LED's directly in the board. After some considerable testing I decided that it would not be a good idea for a board that is designed for beginners.

There is just too much variability in the voltage drop across LED's from the same lot, and the variability of tubes being sold as EL84's is even worse. The required cathode voltage is dependent on the power transformer, the line voltage, and to some extent the operating mode. There is no way to specify a set of parts that works in all conditions. I have found that a set of LED's that works with one set of tubes will lead to red plate death with another set.

I will explain how to make the modifications to an amp after it is up and running. You need to measure the cathode voltage on your set of tubes after they are well broken in using the existing cathode resistors. Then select a combination of LED's that adds up to the same voltage and install them in place of the cathode resistor. You must do this for each tube. This is the only way it will work without adding bias adjustments to the board. That defeats the "Simple" part. Most builders will not do this, so this feature was left off of the board to avoid unnecessary complexity.

This will be explained in further detail after the basic manual is finished.
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Old 12th August 2009, 12:51 PM   #12
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Hi George, from the pictures I've seen around (diyAudio and Tubelab.com) it appears the Simple PP will only be able to take small, nine pin tubes, is that correct?
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Old 12th August 2009, 01:34 PM   #13
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As with my SE amplifier projects there will be at least two. There must be a "Simple" version that you just build, plug in, and listen. It needs to appeal to the widest possible DIY audience. That is what this amp is for. It uses the EL84 / 6BQ5 tube, and produces from 10 to 20 watts per channel. This board is slightly larger than the Simple SE or the Tubelab SE.

It is possible to design a P-P amp using octal tubes that is all on one PC board but the board would be rather large. Most PC board vendors have a non linear price per square inch charge that starts to turn upward rather quickly at around the size of these designs. This is because the boards are made in large panels and then cut up. The scrap costs go up as the board size increases. I decided that bigger amps would need to be built in a modular fashion.

There is another P-P amp being designed in a thread on this forum. It is a single channel driver board using a pair of 6SN7's. it started out as a paper design to drive 6L6 type tubes in class A, AB1 or AB2 using PowerDrive. It evolved into a working driver board. I made sure that the board had the capability for driving all sorts of wierd tubes and I have been using it for just that. The sound quality has been stunning, and I am already making an amp using the pair of boards that I made. Email response has indicated that there is a demand for these, and I can already see that I could use a few, so I will likely get some made. This is definitely not a "build, plug, and play" solution though.

6L6GC AB2 Amp
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Old 12th August 2009, 01:43 PM   #14
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Yes, a PP board for larger tubes would be getting on the large side of things, allowing for space for the tubes etc.
I'm guessing a PowerDrive board of that sort would be quite a way off production?
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Old 25th August 2009, 12:43 PM   #15
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George-

Just curious, did you get your boards yet?
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Old 25th August 2009, 01:45 PM   #16
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Just curious, did you get your boards yet?
The original supplier that I ordered the boards from decided to raise the price once they received the gerber data because the boards were too big to use their standard process. Their prices for Simple SE boards have increased 30% in the past 3 years already. I decided to change vendors for this board, and possibly the Simple SE on the next batch. They will be supplied by another US board house that I have been using for the Tubelab SE boards.

The ship date for the boards was last Thursday. I have not received them yet. Their web site "order tracking" is useless since it still shows orders from 2005 as "not shipped". I have sent an email asking for order status that has not been answered yet. Past experience has shown that I will get an email reply after I get the boards.

I will post a picture of a shiny new board as soon as I have them.

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I'm guessing a PowerDrive board of that sort would be quite a way off production?
It is a safe bet that they won't be available real soon. I have two working prototype boards that are currently mounted in a "breadboard amplifier" to evaluate several different output tube / transformer combinations. This amplifier will be chronicled in the 6L6GC in AB2 thread mentioned previously since that is where it started, and the 6L6GC is still a valid output tube choice. I have found my UTC LS-57 OPT's so that combination will be tested.

The time frame for commercial duplication depends on a lot of things. The two biggest ones are, the time that I have available for Tubelab related activities (largely beyond my control), and the funds available (this will be determined by the success of the Simple P-P).

I have gerber files ready for the board as it exists now, and I may get a small batch made if the test amp works like I think it will. I can see myself building a few amps using them. I have tested a bunch of different tube / transformer combinations in glorious mono using the one working board that I had, and I heard a few "magic sounding" combinations. I have since made a second board.
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Old 26th August 2009, 01:29 AM   #17
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Just curious, did you get your boards yet?
I wrote the reply above from work today. When I got home from work there was a box on my doorstep. It contained 110 boards. Yes, I am building one right now, but it won't get finished tonight.
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Old 26th August 2009, 04:40 AM   #18
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Fantastic!

I guess you were right about not hearing from them until after the boards arrive, lol.
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Old 26th August 2009, 01:42 PM   #19
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God Dang i am giddy with anticipation. Please let us know when they go on sale.!!! Can we preorder?????
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Old 26th August 2009, 02:25 PM   #20
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Can we preorder?????
I prefer not to accept orders for something that is not ready for sale yet. I really have a hard time assessing the time that I will have to devote to creating the manual, since my work schedule varies on a daily basis. Sherri has been away for 3 weeks and she is returning on Friday. She will be here from 1 to 3 weeks, and I must go with her on the next trip. I will be away for 7 to 10 days. I am usually stuck at work for 60 hour weeks when I return from a trip.

I will attempt to get the manual ready before I leave, but Sherri may have other plans (isn't that how marriage works?). I take boards and my laptop with me and ship from the closest post office, where ever I may roam (where have I heard those words before?).

110 boards will not dissapear quickly so there is no need to panic, and I can always get more. Lately board sales have been 1 to 2 per week. The Simple SE did 3 to 5 per week when it was first introduced, but the economy was much better then.
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