I'm on to my third amp build with bits I have lying around. I have an old mains tx and op tx that will let me build an EL84 push pull. I have for the last two amps used a 6sl7 and ECC83 this time I would like to try a EF86 front end. I know it has a massive amount of gain depending on how it is biased so should I use it in triode mode or pentode? What about the tone controls, Fender type or Baxendale? Your help and experiences would be gratefully received.
Phil.
Phil.
If you use the EF86 in triode, the gain isn't all that high and also kinda defeats the purpose of having a pentode gain stage... anyway, by just itself in pentode may not be enough either after the T/S, so you would also want to add a gain recovery and PI section, try look at Dr. Z's Route 66 for some ideas.
It should sound just fine, also the EL84 is easier to drive, you can also add a master volume control after the PI, so you can vary the amount of preamp vs power amp distortion. Seems like a fun project, I am sure if you search around, someone must have done something like it already...
Really nothing new under the sun, although the Tiny Terror does not use the EF86 in its preamp section... same idea though.
So, Phil, it is better to not use the EF86 as the input stage, and als not to bias is for maximum gain, as recommended in http://www.freewebs.com/valvewizard/pentode.html
I have tried this idea with very good results.
I have tried this idea with very good results.
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