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Old 2nd April 2006, 05:09 AM   #1
zxx123 is offline zxx123  United States
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Default 6V6 ->EL84 with 12AT7?

I like EL84 . I can see some schematics
such as driving EL84 with EF86, 6SL7, 12AX7, etc.

However, EF86 and 6SL7 are not welcomed because my amp case is very small. 12AX7 has too much gain.

How about 12AT7 with EL84? Originally, this idea is from SE 6V6.
Absolutely, I need to adjust bias first of all. However, they use almost same current under plate voltage 250V with same load resistance(5K).

How about your idea?
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Old 2nd April 2006, 05:32 AM   #2
rdf is offline rdf  Canada
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Hi zxx123. 12 volts across 130 ohms as shown to the right of the schematic implies 92ma through the EL84. It won't be close. Off the top of my head in the range of 6 volts is more likely. I recommend leaving the 250 in place to start, it's close to my favourite and trades off increased 2nd harmonic distortion (and in my tests reduced upper harmonics) for a little more power. Everyone has a preference, check ten schematics you'll find ten operating points. The 6V6 values are a safe place to start and sound pretty good.
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Old 2nd April 2006, 05:50 AM   #3
zxx123 is offline zxx123  United States
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Quote:
Originally posted by rdf
Hi zxx123. 12 volts across 130 ohms as shown to the right of the schematic implies 92ma through the EL84. It won't be close. Off the top of my head in the range of 6 volts is more likely. I recommend leaving the 250 in place to start, it's close to my favourite and trades off increased 2nd harmonic distortion (and in my tests reduced upper harmonics) for a little more power. Everyone has a preference, check ten schematics you'll find ten operating points. The 6V6 values are a safe place to start and sound pretty good.

Thanks, you are right.
I post corrected one again. (It was my mistake!)
Can you recommend me any power transformer for this 6V6 and EL84 project? I think the 2ndary should be 220V or little bit more, but I cannot find proper one in tubesandmore.com
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Old 2nd April 2006, 05:21 PM   #4
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Think about a doubler B+ supply as used in "El Cheapo". Smaller caps. in the doubler stack will lower the rail voltage. Follow the "extended" CLC filter with a RC section and you should be able dial the final B+ voltage value in exactly.
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Old 5th April 2006, 12:15 AM   #5
amperex is offline amperex  United States
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I am not a fan of 12AT7 sonics. How about Telefunken ECC85 (6AQ8). Lower gain than a 12AT7, but should have enough gain.
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Old 5th April 2006, 12:47 AM   #6
SY is offline SY  United States
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Quote:
I am not a fan of 12AT7 sonics.
Used properly (not often done!), it is stunningly linear. The bad rep comes, I think, from all the poor circuits that chunk it in.
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Old 5th April 2006, 05:13 AM   #7
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SY,

just how exactly do you bias a paralled AT7 tube driving a 2a3 tube instead of 6v6 at 5k load?

gabriel
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Old 5th April 2006, 11:39 AM   #8
SY is offline SY  United States
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If it were me, I'd run one section as a voltage amp (2mA current, 375V supply, 120k plate load), the second section as a cathode follower.
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Old 5th April 2006, 06:12 PM   #9
JimW is offline JimW  United States
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Default 12at7

12at7 works well in srpp configuration as a 2a3 driver. Gordon Rankin's "baby ongaku" used this tube. I use it as a 2a3 driver in a much less ambitous (cheap) amp and it works very well.
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