Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bruno on November 22, 2010, 06:50:40 am
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I'm building a small test bed right now... and I'll be trying several pre amp and power amps too. I was thinking about trying to put an ef86 pentode before typical fender blackface preamp. Which would make it: ef86 - triode - tonestack -triode.
Is this worth it, or should I not even try to do so?
Thanks
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Why not try the EF86 as a gain recovery stage, after the TS? In > 1/2 triode > plate driven TS & gain pot > EF86 & volume pot.
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or something similar to the Matchles Clubman..
http://www.prowessamplifiers.com/schematics/matchless/Matchless_Clubman.html (http://www.prowessamplifiers.com/schematics/matchless/Matchless_Clubman.html)
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I'm building a small test bed right now... and I'll be trying several pre amp and power amps too. I was thinking about trying to put an ef86 pentode before typical fender blackface preamp. Which would make it: ef86 - triode - tonestack -triode.
Is this worth it, or should I not even try to do so?
If you don't put it in the #2 position and want it in #1 then you may like it w/ a CF afterwards w/ the tone stack after in it's usual place. I have one that way and it really worked out well.
I have another amp where I used two EF86s for #1 AND #2 postions, it's really sweet w/ a lot gain. But, you'll likely have to knock some signal away w/ a voltage divider. That #2 tube position can also become more sensitive to the microphonics issue when it's used at a higher gain. Just something to be aware of & if you experience it you can dial it down easily by playing w/ your load and screen resistors.
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Why not try the EF86 as a gain reconvery stage, after the TS? In > 1/2 triode > plate driven TS & gain pot > EF86 & volume pot.
+ 1 for FYL
Kagliostro
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The EF86 has a LOT of gain all on it's own. In the position you are suggesting in front of a blackface preamp, it will be hard to control all of the gain and you will lose any clean sound unless you stick in divider networks. A better approach is to stick it in V2, or put it in the front of the amp with a cathode follower after it, and then the tone stack. Run lower gain like Merlin recommends and the microphonics and gain levels will be more manageable, and the amp will sound great.
Greg
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Selmer Zodiac:
http://www.vintagehofner.co.uk/selmer/schematic/zod3.html
12AX7-triode - tonestack - EF86