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#1 |
diyAudio Member
Join Date: Jul 2012
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Hello all.
I am trying to make use of 10 nos ef86 tubes I have.I also have 2 ecc82. I have built a valve phono stage,so I want to make a preamp at line level. I don't need tone control Can anyone recomend a schematic many thanks |
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#2 |
diyAudio Moderator
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#3 |
diyAudio Member
Join Date: Feb 2009
Location: Calgary
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Funky with C1 and R3 across the anode load on V1. Looks like they may have had some issues with RF oscillations on the input stage. Or didn't want such oscillations to return in issues in the field.
Just an observation.... ~Tom
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Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits. Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right |
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#4 | |
diyAudio Moderator
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Quote:
![]() "A CR network (C1, R1) shunting the anode load produces an advance in phase which increases the stability of the amplifier at high frequencies." More here >> Mullard 5-10 |
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#5 |
diyAudio Member
Join Date: Jun 2004
Location: Hillside
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R1 is the 1M resistor on the input. What does that have to do with the anode load?
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#6 |
diyAudio Moderator
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#7 |
diyAudio Member
Join Date: Aug 2002
Location: Eire
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I can't think of any situation where the gain of a ef86 in a preamp would be anything but a disadvantage. It then requires copious amounts of negative feedback to kill the gain - and a preamp is definiately one of those situations where there is little need for feedback.
This tube has no other place than a phono preamp in my opinion. Shoog |
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#8 |
diyAudio Member
Join Date: Jun 2005
Location: Dk
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#9 | |
diyAudio Member
Join Date: Apr 2010
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Quote:
Why not strap it as a triode to reduce the gain? |
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#10 |
diyAudio Member
Join Date: May 2007
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The OP was asking about preamps, so why post circuits for power amps?
The network at the anode of the EF86 is to stop feedback loop instability (typically in the low ultrasonic region); the input stage itself is very unlikely to suffer from RF instability. The EF86 has no place in a modern line stage, as it has far too much gain. Keep a few as spares (for your phono preamp?) and sell the rest so you can buy more suitable valves. |
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