Jimi Hendrix' Gear and Mods at West Coast Organ and Amp

[cvh]

also, i’m still confused on the screen voltage regarding the sweet spot; bc if i can figure out that value, then i can reverse engineer different locations to tweak...

but at two different times you say the sweet spot varies:

“...after about a dozen or so mods...560V on the plates...tubes biased at 25ma...dropped screen voltage to 530.”

also, “...600V on the plates and 300V on the screens is the sweet spot...”

so which is it? maybe dave or someone can chime in, i feel like the voltage is the most important part of this mod.

[revolver1]

Still here Dave,

Haven't posted because I need to test drive the amp with the new value P.I tail resistor to see if I like it more than the stock 10K. The lock down has been great for getting things wrapped up but I cant make much noise because all the nighnours are home.

Need to get this stuff into a rehersal studio really but I got side tracked with other amp builds. It's an addiction and I got it bad.,,,

[revolver1]

Did you have any more news on the production West Coast amp?

[FloPoeKo]

A good day to everyone!
Quick Question: Has anyone here ever thought about or already attempted to load the 3-Transistor-Fuzz with silicone (PNP) transistors?

[daveweyer]

I did. I tried it out with some early GE silicons that Thomas Organ used. It actually worked better but did not sound the same, so I scrounged the 2N591 germaniums from early Allen Organ amplifiers to send out to a few forum members to try out. I'd send out more but I'm out of amplifiers to rob. If you find an old Allen 20 or 50 watt amp with germanium devices, get it, because they used a hand-picked for low noise 2N591 in the preamp section, and the current gain was often over 100--even up to 180. They also used a GE 2N525 in several places, so those amps are a good place to find the right transistors.

[FloPoeKo]

I did. I tried it out with some early GE silicons that Thomas Organ used.

Do you have any recommendations on the gain-selection? I mean, I wouldn´t bother for the sake of experiment if it turns the fuzz into something very different.

[daveweyer]

Use low beta types, with gains preferably of 100, 150 and 70 for Q 1,2, and 3 respectively. NOS pieces will probably have lower gain. Any small signal device will do. Old GE types like the 2N3900 might work about right. OC 71 and OC75 and 76 are probably in the same range. Try to keep the same ratio of current gain between the stages.

[Xplorer]

I didn't want to keep posting unless someone was around to read it and maybe think about it. Xplorer held down the fort for years!

ha ha

[daveweyer]

Well Xplorer, it's nice to know you are alive. Without you, who is going to comment on everything???

[Xplorer]

Well Xplorer, it's nice to know you are alive. Without you, who is going to comment on everything???

ha ha ha. I'm sorry, i got more and more busy these last years, i never imagined i'd had less and less time.
+ you already know i'm amazed and my interventions would become sterile and there's not much i could add for the moment. But i miss the forum and our conversations for sure !

my attenuator did some smoke, i don't know why, plugged to the west coast. i have to open it and check what's wrong before turning the amp ON again ...

The west coast fuzz is still on the list of to do's ..
Hope you're doing great ! i see that the forumers are still here too !

[cvh]

ah, good to see the wrecking crew is still here! i feel like i know y’all after dwelling on these pages even though i’ve never met any of you. thanks for all the wisdom!

[PhilSt]

Well, Looks like Hendrix black strat has also gone through west coast organ.
Check out the sticker on the neck plate.
https://www.pinterest.de/pin/403846291563839875/

[yladrd61]

Jimi in Maui both shows blue ray video and remaster CD or vinyl will be released in November.

[SmellsLikeAmp]

Hey Dave

I just finished going through the whole thread and am really interested in trying some of your mods. Amp building has been my hobby for over 15 years now and I do have some "experience." I have a Sunn model T copy that I built with Triode Electronics Dynaco iron and thought it would be a good candidate but it only has 2 output tubes. I am intrigued by the 5687 phase splitter being juiced by a paralleled triode 12ax7. I just finished another Marshall 18W project and really love the first channel with the paralleled 12ax7 preamp stage. I have been building mostly audiophile type home stereo stuff recently and noticed that the 5687 is widely regarded by Audio Note, no less. I have a pair of Bogen MO100 PA amps that use a pair of GE 6550A's and an EZ81 for screen regulation at 330V while the plates sit at around 620V for 100W. The phase splitter was modified by Quicksilver who pretty much copied the rest of the amp for its first high end stereo amps. I have heard of bass and guitar players use them for back ups while touring.

You sound like you really know what you are talking about technically and I would like to know more about the other amps you modded for Hendrix like the Supro 6420 Thunderbolt and the Guild. My computer does not let me see some of the pictures and schematics posted on the thread but a third party image hosting site would. I own a Gretsch Pro Bass that has an almost identical circuit to the Thunderbolt but sounds nothing like some of the better examples on youtube. Most specimens actually don't sound that strong but I think maybe the ones with lower voltages and the tube rectifier are the ones that sound the best. I read in guitar magazines that he used it for maybe Jimi James and the Blue Flames and for his recordings with Curtis Knight and that he borrowed a black Les Paul with soap bars for these recordings. They were supposed to be really fine sounding examples. The speaker is a huge part too with a small voice coil like you say (C15PS?) I built a 1690 Supro Coronado that I love using a speaker with a one inch voice coil and floating baffle that I think is key and is why my Valco made Gretsch does not sound that great. Thanks for being so generous with all your knowledge and I have learned a lot this past week reading up here on the forum. A seperate thread for other amps you modded for rock starts like Neil Young or Grand Funk would be great too!

[Tone seaker]

looks like he used big and small bottle tubes
https://www.bing.com/images/search?view ... ajaxhist=0