Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: RobBozic on April 22, 2010, 08:28:33 pm

Title: Doug's Randall preamp
Post by: RobBozic on April 22, 2010, 08:28:33 pm

Hi,

Regarding the heads Doug built for Randall & in particular the preamp layout below

http://www.el34world.com/Hoffman/images/Ranpre.gif

Has anyone built this? If so, how much gain did it have compared to a typical superlead plexi?

Also in this layout there seems to be an error, the treble wiper connects to the B+ & 0.02 coupling cap of the V3 plate. I assume the treble wiper goes to V2 Pin 2, (a dwg error?)

Thanks
Rob

Title: Re: Doug's Randall preamp
Post by: sluckey on April 22, 2010, 08:49:28 pm

Quote

Also in this layout there seems to be an error, the treble wiper connects to the B+ & 0.02 coupling cap of the V3 plate. I assume the treble wiper goes to V2 Pin 2, (a dwg error?)

I agree.

Title: Re: Doug's Randall preamp
Post by: RobBozic on April 22, 2010, 09:11:31 pm

I was watching the Allman Bros. DVD from 2003 & Derek Trucks is using this amp & his tone is really clean & pure.

I was thinking of converting a JTM45 to this preamp & maybe playing around with V3 cathode resistor, maybe 10K unbypassed if there's too much gain.

Still, I'm hoping someone has built this to see what their impressions were of the preamp

Rob

Title: Re: Doug's Randall preamp
Post by: topbrent on April 23, 2010, 04:35:30 am

Here are some absolutely great clips of Derek Trucks from the 2003 "Live At The Beacon Theater"

&feature=related  "Rockin' Horse"

&feature=related  "Desdemona"