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Old 31st December 2009, 09:42 PM   #1
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Default Simple SE driver tubes

I'm curious what people have used for driver tubes in the Simple SE.

I made mine for a JJ ecc99 driver tube, and will try a 12bh7a shortly. These tubes have less gain and use a lot of plate current (20 mA). I have an active preamp, so it works well for me.
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Old 1st January 2010, 12:37 AM   #2
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I m still using the JAN12at7, but am interested in others. Have you compared the ecc99 to the 12at7?
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Old 1st January 2010, 04:22 PM   #3
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No, the ecc99 and 12bh7 are the only ones I can use without changing component values. I'll pickup a couple of the bh7 tubes to try soon.
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Old 13th January 2010, 02:46 AM   #4
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I got an RCA 12BH7A from ebay, it looks like it's made by Tung Sol, it has the "12BH7A" printed inside an octagon near the top of the glass. The tube lettering and box are in perfect shape. Price was just under $20, much better than more popular audio tubes.

Sound is a step up from the JJ ecc99. It's a bit more forward and crisp sounding, which I like.

I tried feeding the amp direct from the DAC and using foobar's volume control, and there isn't enough gain for some material, but I think this driver is worth considering if you're using an active preamp and building the Simple SE as a power amp.
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Old 13th January 2010, 05:12 AM   #5
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Originally Posted by Davec113 View Post
I got an RCA 12BH7A from ebay, it looks like it's made by Tung Sol, it has the "12BH7A" printed inside an octagon near the top of the glass. The tube lettering and box are in perfect shape. Price was just under $20, much better than more popular audio tubes.

Sound is a step up from the JJ ecc99. It's a bit more forward and crisp sounding, which I like.

I tried feeding the amp direct from the DAC and using foobar's volume control, and there isn't enough gain for some material, but I think this driver is worth considering if you're using an active preamp and building the Simple SE as a power amp.
Is the 12BH7A a direct drop in in the driver slot? No mods required?
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Old 13th January 2010, 07:33 PM   #6
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Originally Posted by bigjppop View Post
Is the 12BH7A a direct drop in in the driver slot? No mods required?
Actually, you could try it as-is. I think the 12at7 uses ~10 mA plate current, while the ecc99 and 12bh7 work best around 20 mA. I changed the resistor between the anode and CCS (I forget which # it is) to adjust the plate current, the value of resistor you need is on the IXYS datasheet. You could rig a resistor in parallel with the resistor used for the 12at7 so you can try the 12bh7 at 20 mA instaed of 10.

Looking at the ecc99 and 12bh7 datasheets, the tube looks very linear and I wonder if the ccs is helping or not. Might be worth it to try running the 12bh7 resistor loaded instead of ccs loaded.
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Old 13th January 2010, 09:54 PM   #7
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Interesting with the 12bh7. I would think you would have to adjust cathode resistance to properly set the plate voltage. Did you measure that with stock?
I was looking at implementing a similar cathode bias set-up as in the tubelab SE. This way all you do is set the IXYS reference resistor for current and adjust your voltage to put it in the linear range.
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Old 13th January 2010, 10:00 PM   #8
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Originally Posted by SGregory View Post
Interesting with the 12bh7. I would think you would have to adjust cathode resistance to properly set the plate voltage. Did you measure that with stock?
I was looking at implementing a similar cathode bias set-up as in the tubelab SE. This way all you do is set the IXYS reference resistor for current and adjust your voltage to put it in the linear range.
I remember checking on the plate voltage and I decided to use the same voltage the 12at7 uses, so I did not change the cathode resistor value.
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Old 14th January 2010, 01:26 AM   #9
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May I ask, other than gain is there any difference? in my system more gain is a problem as I am using the amps in a full active setup and my tweeter is close to 100 db sensitive while my mids are about 93 db. The only reason I would change is for sonic benifits. I am using a mullard 12at7 and I also have a mullard (Labeled Phillips) 7062 which is also very nice.

Last edited by Pez; 14th January 2010 at 01:31 AM. Reason: Punctution
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Old 14th January 2010, 02:26 AM   #10
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Originally Posted by Pez View Post
May I ask, other than gain is there any difference? in my system more gain is a problem as I am using the amps in a full active setup and my tweeter is close to 100 db sensitive while my mids are about 93 db. The only reason I would change is for sonic benifits. I am using a mullard 12at7 and I also have a mullard (Labeled Phillips) 7062 which is also very nice.
I drew out the load lines when I built the amp, and it looked like the bh7 curves were more linear than the at7, but the ccs makes the load line horizontal, which linearizes the tube to some degree. Also, the bh7 can run at double the current the at7 can, making it a more powerful driver tube. But again, I think the ccs will make the resulting difference smaller.

None of that matters though, I think you have to try it and see. You could just add a resistor in parallel with R13 and R23 using clips to see if you like it. I think I used a 150R resistor, but check the IXYS datasheet, it's been a while... You'll only be out 2 resistors and a $20 tube (if you go top of the line) if you don't like it. IMO, reducing excessive gain is a good thing, although my preamp has 28 dB gain, which is a bit excessive. I'll build a preamp eventually...
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