18Watt design
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18Watt design
I am laying out a new 18w scratch build. I will be utilizing an EF86, and 2 12AX7 preamp tubes. The power section will be 2-EL84's with a 5Y3 rectifier. I am going to add a full tone stack and would like to add a negative feedback circuit. I am studying the Vox AC-15, Selmer Zodiac Twin 30, and the Marshall 18 Watt circuit. Are there any more areas I should be searching for ideas? Any advise would be appreciated! Thanks
Re: 18Watt design
Ok I don't know if this is correct or if the values are correct, but the ground connection simulates a presence pot and cap and the resistor is the NFB. The stock schematic shows a 47K to ground
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Cliff Schecht
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Re: 18Watt design
So you want a fixed presence or a presence pot?
As far as circuits, don't forget to look at some Fender and Gibson amps. For Fender the 15W stuff is almost all 6V6 based but there was a Tremolux that was made with EL84's (only about 180 were made though). Also for Gibson, there's about a zillion different models (not even looking at old Epiphone stuff before Gibson owned them) with a lot of fun circuit ideas that differ from your standard Fender/Vox/Gibson schematics. Spend some time at www.ampwares.com and search through their Gibson archive.
As far as circuits, don't forget to look at some Fender and Gibson amps. For Fender the 15W stuff is almost all 6V6 based but there was a Tremolux that was made with EL84's (only about 180 were made though). Also for Gibson, there's about a zillion different models (not even looking at old Epiphone stuff before Gibson owned them) with a lot of fun circuit ideas that differ from your standard Fender/Vox/Gibson schematics. Spend some time at www.ampwares.com and search through their Gibson archive.
Cliff Schecht - Circuit P.I.
Re: 18Watt design
Thank you. Looks like the Tremolux has what I need!
18 watt boost circuit
Here is a pic of my new 18W build using carbon comp resistors. The tone is incredible. I am using an EF86 preamp tube for my amp and I am trying to incorporate a foot switchable boost. I am using a shared cathode on my tube between pin 3 and pin 8. I have a 2.2K for my cathode resisitor and I added a 25uf 25V electrolytic that can be switched on and off by the footswitch. It is not adding any boost to my signal. I tried adding a 47K beween the 25 uf and the 2.2k and didn't help. Any ideas what I might be doing wrong? Any insight on this would be appreciated.
Last edited by 9VOLT1967 on Wed Oct 19, 2011 10:43 pm, edited 1 time in total.
Re: 18Watt design
Problem solved. My footswitch jack was providing ground to 25uf cap. Installed isolating washer to jack. The boost control now works great. The control boosts as it should now!