Derek Trucks' 100 watt Marshall

toneman · Post by **toneman** » Sat Sep 06, 2003 6:30 am

I worked on Derek's amp this week. This is a continuation of his 100 watt reissue Marshall that I did gfor him a year ago.
Originally I replaced all tranny's(o/p, choke and mains) and replaced all the filters with original values of 32uf@ 500v, replaced all signal path componets and converted the circuit to the original `67 era specs( as the `67 seems to be the preferred tonality). The current reissue is not what the old one's were and is more closely related to the early `70's metal panels.
Derek's complaint was that the amp didn't cut through and didn't breath. Well, the amp put out 90 watts clean and around 110 flat out. the B+ was about 445-450V depending on wall voltage. He also had one bad tube which caused the amp to really only put out around 65 watts.
I installed a new set of Svetlana(or now called "Winged C") EL-34's and I replaced the mains(or power) tranny with a bigger one from Mercury Magnetics wonderful line of clone transformers. The power supply went up to 525v for the B+ and the amp now puts out around 130 watts clean and 175 watts flat out. this should be enough to give Derek the volume level he needs with the Allman Bros.
I've know most of the guys in that band since I was 15(in 1968..) and they have always played loud but with alot of dynamics (which is the key ingredient!) Everyone in that band is a player's player and I've been lucky enough over the years to play with everyone at one time or another(except Derek..I'll have to do something about that.)
Anyway, it may sound simple replacing the mains tranny but there's alot more involved. I had to re-do the bias circuit as the voltage was too far on the negative side to bias the valves correctly and had to check that other componets would handle the 75v increase as well.
anyway, I'll be delivering it to him tomorrow afternoon at the Greek here in L.A. I had also loaned him my metal body Dobro last week so I'll get that back too...

rictified · Post by **rictified** » Sat Sep 06, 2003 10:13 am

Yeah those guys are GREAT musicians, they have almost a jazz sensibility, the better I became over the years the more I appreciated just how good they really were (and are) Did you know or jam with Berry Oakly? He was a monster bass player, totally original style and great sound. Their jams are a joy to listen to as are their studio songs. One of the greatest American bands, IMHO.

rictified · Post by **rictified** » Sat Sep 06, 2003 10:16 am

By the way Don,
What can you do with a mid to late 70's SVT head? white rocker switches.

toneman · Post by **toneman** » Sun Sep 07, 2003 9:58 am

Bob; I knew Berry & Duane. They, besides The Beatles & Stones, etc. are my favourite band.
Late `70's SVT..? recap it and retube it.

rictified · Post by **rictified** » Sun Sep 07, 2003 12:26 pm

You can't almost double the wattage like the Marshall? ha ha, Oh well.
What are the best kind of tubes for an SVT in your opinion?

toneman · Post by **toneman** » Tue Sep 09, 2003 5:43 am

On an Ampeg you'd have to go to larger power and output tranny's. I think those are big enough. The 100 watt Marshall's that I do are turned into what the original plexi's were like. Alot of them had a power tranny that put out anywhere from 520v-600v during the time from `66-`68. When you up the B+ supply like that you will certainly increase the power output of the amp. Also, I use the Svetlana EL-34's which are the only one's that can handle the plate voltage. Most new El-34's are lucky if they handle 500v let alone 600v!
Marshall's power tranny's varied alot during that time period as did the o/p tranny(but not nearly as much).
Your SVT has always been the same power and o/p tranny.
Best tubes... You might try the Svetlana KT-88's! Great tube. I have those in my Sound City Bass 150.

rictified · Post by **rictified** » Tue Sep 09, 2003 10:46 am

Yeah, it's heavy enough now, thanks.
I knew someone who's bass player supposedly had had two extra power tubes put in his SVT, I don't know where they would have fit, and my friend (a keyboard player) said that he didn't hear any difference anyway. That would have definitely warranted new trannies too I'm sure, so was probably a fabrication, what do you think?

admin · Post by **admin** » Tue Sep 09, 2003 10:48 am

Don and Bob: Jim Marshall is in Fredericton, N.B. in early October 2003. Do you have any questions for him?

rictified · Post by **rictified** » Tue Sep 09, 2003 11:21 am

Well Peter, only this: Will he be giving any free samples away?

admin · Post by **admin** » Tue Sep 09, 2003 3:25 pm

I have no heard that mentioned Bob. If you send me a Marshall amplifier, however, I will get it autographed for you.

mortivan · Post by **mortivan** » Wed Sep 10, 2003 8:13 am

There's a thought!

rictified · Post by **rictified** » Wed Sep 10, 2003 8:49 am

Postage paid?

toneman · Post by **toneman** » Mon Oct 13, 2003 9:24 am

Up-Date: We played in St.Petersburg, Florida Oct. 3rd and who was staying at the same hotel and also doing a gig in town that night like us... Derek!!
Derek and I had a nice, but short visit before we each had to run off to sound checks.

kennyhowes · Post by **kennyhowes** » Mon Oct 13, 2003 2:20 pm

Derek's organ player Kofi was my next-door neighbor in Atlanta for a year.