Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: PharmRock on January 29, 2022, 12:46:19 pm

Title: Marshall 18 watt with EF86 and Tremolo (not TMB)
Post by: PharmRock on January 29, 2022, 12:46:19 pm

So I'll start off by saying I had an account over on 18watt which must've used an email account I no longer have, and I've tried to start a new account but am waiting for the administrator to approve me.  The question I am asking may be located in their schematics library but I just can't get access at the moment.

I have a clone of an 18 watt Marshall which has the normal and tremolo channels, just like the original.  A lot of mods on this amp circuit ditch the tremolo and make it into a TMB channel, sort of "Plexi-ish", and keep the normal channel as is.  I was thinking of converting the normal channel (which is currently one triode in Lo input, paralleled triode in Hi input, with a 1-knob tone control) into a single input EF86 channel with a 6-position rotary "contour" tone control. Maybe convert the remaining unused "Lo" input jack hole as a place to install a master volume (as drawn out in Sluckey's Dual Lite...see below for link).

Can this be as straight-forward as swapping out the "normal" 12AX7 channel with the EF86 design Sluckey has in his Dual Lite? https://sluckeyamps.com/dual_lite/dual_lite.pdf (https://sluckeyamps.com/dual_lite/dual_lite.pdf)
And just preserving the tremolo channel "as is"...
https://el34world.com/charts/Schematics/files/Marshall/Marshall_18watt_schem.pdf (https://el34world.com/charts/Schematics/files/Marshall/Marshall_18watt_schem.pdf)

Hope what I wrote makes sense.  Thanks for any advice.

Title: Re: Marshall 18 watt with EF86 and Tremolo (not TMB)
Post by: sluckey on January 29, 2022, 02:12:22 pm

Quote

Can this be as straight-forward as swapping out the "normal" 12AX7 channel with the EF86 design Sluckey has in his Dual Lite?

Absolutely.

I also built that Marshall 1974 18Watt amp. Look at my schematic. Delete everything to the left of the normal volume control and replace with the EF86 preamp. Maybe even put the 180pF bright cap on the volume control.

     http://sluckeyamps.com/18w/18w.pdf

Then you'll have a Dual Lite + Tremolo. BTW, the Marshall preamp in my dual lite is the Trem channel from the 1974 18W sans trem. I predict that the Vox channel will quickly become your favorite in that amp.

Title: Re: Marshall 18 watt with EF86 and Tremolo (not TMB)
Post by: PharmRock on January 29, 2022, 06:43:37 pm

Thanks Steve!  I appreciate the tips and PDFs.  I'll work on a board layout that splices the EF86 preamp in with the tremolo.