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

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

Post by daveweyer » Sat Nov 08, 2014 1:49 pm

Alright, here it is, the rest of the story about Jimi's gear, his mods, and whatever else we did at West Coast Organ and Amplifier Service to help him get his sound and keep his band running.
If you want to know anything about it, please ask. I won't know every detail of every gig, but maybe between what you all have been able to find out and deduce from the study of all his performances and other forums, we can make pretty good guesses about what went down.
I can tell you that Jimi was process, I'd do a mod, it would go into the field, Jimi would tell me what happened (sometimes the amp would tell me), and then things would be changed to try to become more in line with Jimi's vision, which was also changing as his career went along. Mods were done over and over, some he liked and we kept. Other techs did other mods, mostly on the east coast, and we were not in communication about what was changed on either side. Sometimes I'd get an amp back and look inside and go "what the hell is this?"
I believe the wildest amp mods were mine, no one I saw took them quite as far, and a lot of other techs didn't want to touch them. As far as I know, all the amps, pedals and effects were modded to some degree or another, with particularly good amps being left mostly intact, often leaving them more vulnerable to blowing up on stage.
It's tough to get everything you want and still have it be robust enough to play it live.
From what I've heard, some of the original amps are still around, although it appears that they have been returned to stock, which is kind of a shame because that wasn't what Jimi used to get this or that sound at any given performance.
There is a thread on "The Next Level" about the "Governor" amp, if that was really it which was being sold, and there was an article on "Musicplayer.com" which had listed all the serial numbers of the amps Marshall shipped to us for Jimi's '69 tour, only the page has now been removed, the dreaded "404" error.
I guess the numbers were listed in the March 2005 issue under the heading "The Gear of Jimi Hendrix".
Maybe some of you have seen it or have copies of it.
Any other info you might have to expand the story would be helpful too, so throw in whatever you know about, it might make me remember some forgotten detail.
Fire away!
DW

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

Post by Tone seaker » Sat Nov 08, 2014 5:40 pm

So from what I have read in the other post you are saying that you all took the EL-34's out and put in 6550's and put base speakers in the cabs.

How hot were the tubes biased?

Which Bass speakers were they? The pre rola 25w or 30w or something else?

Also what mods did you do to the amps and can you tell me more about the Govenor amp?

Thanks for all this its really great :)

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

Post by Xplorer » Sat Nov 08, 2014 6:25 pm

Fire !! :) that's so cool David ! love this, it's like Christmas

first : i'm currently trying a fuzz ( a simple dunlop blue hendrix fuzz, very classic bc108 circuit ) with the volume at max, and the fuzz gain at zero and let me tell you that something is really happening .... it should need the few mods you were talking about, to adjust the input and output caps for basse and trebles perhaps, and the 50k input resistor etc ... but now i understand a few things , that's fantastic :)
will do a fuzz clone of what you said to hear and analyze better.

if Jimi came to you with one of his early jtm 45/100 or superleads later, what would be the typical mods that you'd do to satisfy him ? i mean, i'd like to do these mods on my current 45/100 build so ...

were you involved into the gears of Jimi, for the Fillmore east concerts ? machine gun, who knows .... he has a red fuzz with white knobs there so ....

i'm so happy to test new things and hear such storys. playing machine gun with the fuzz this way, wow, i understand some things now, it makes sense ...
compressed tone, while cleaned from the fuzzy tones, powerful, great sustain, it indeed needs some 50k resistor to let the original guitar signal to breathe , it also needs a bit more gain like you described, but i see now ...
and i'm sure i'll can still play star spalngged banner with the fuzz this way anyway, i'm surprised.

could you describe , from your memory ( and do you have some documents you'd be ok to share with us ? ) what you did on amps, one after the other, with comments on how it worked, how pleased jimi was , etc ?

and what mods did you do on his wahs for example ?

that's it for now : )

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6550s

Post by daveweyer » Sat Nov 08, 2014 8:24 pm

The 6550 thing.
Folks have been incredulous for many years about why I would remove those beautiful sounding EL34s and KT66s, and replace them with 6550s. But I did do that, and it wasn't because we didn't have plenty of Mullard EL34s lying around.
There were essentially three reasons, reliability, loudness and tone. Well, wasn't the tone actually better with the EL34s? Probably, at least from the normal blues/rock perspective at less than ear-splitting volumes.
But at higher volumes, all that smooth subtlety starts to matter less, ESPECIALLY when you have some effects first, and part of your tone is generated there and you are more and more relying on the amp just to broadcast what you have already generated. This is an important point, and it touches upon what Swankmotee is saying about needing the fuzz all the way up to get certain Hendrix sustaining tones. But we'll get to that in a minute.

You've all heard about class A and class AB1 and class AB2 in the output stages of these old Marshalls, and you've probably seen a million amps that could switch to a class A output stage for that wonderful smooth bluesy distortion. What you probably don't know much about is class B operation. In the radio transmitting world, class B was used extensively to get more power out of tubes, and preserve their life. It's a mode of operation where one output tube draws no current at all during the phase that the other tube is conducting in push pull operation. This means that the tube has extra time to get rid of its heat--a whole half cycle of time where it is not dissipating heat--and the power it is able to switch when it is on goes way up.

So when I installed 6550s in Jimi's amps, I set the idle current to just 25ma per tube. What happened then was that during periods of high signal level in the amp, the output stage was operating in class B, because the idle current was already so low that the non conducting tube would immediately switch completely off until it was its turn to conduct.
Class B allowed much higher power output levels without over dissipating the tube, especially the screen grids. Class B also has its own kind of distortion, more at very low levels, called crossover distortion, and a very gnarly barking kind of distortion at high levels, ultra-masculin sounding.

When Jimi heard that in 1968, his ears heard something he could use, and I embarked on a series of tube changes and amp mods which went on till the end of the grand experiment.
So not only do 6550s have more durability, they have a different sound to their distortion, and that sound gets even gnarlier when they are run in class B. No grid current on the positive cycle by the way, just cutoff at the transfer.
A positive grid current amp got made eventually for even more power, but I have no idea where it ended up. I used a 5687 driver tube to generate enough power to drive the output tube grids positive at the peaks.

SO, if you will go to www.rockprophesty.com, and listen to the mp3 of Jimi using the Wah for the first time on stage in Catfish, you can hear what happened when the Wah circuit was energized and he got uncontrolled feedback from the fuzz. Remember, the Wah circuit shorts out the feedback resistor in the Fuzz and the gain goes through the roof, and it isn't pretty either.

Now, here's a quote from Jimi about the fuzz from Roger Mayer's writings, Jimi speaking of Roger:
"He's made me a fantastic fuzztone. Actually, it's more of a sustain than a fuzz."

DO you notice the magic word, SUSTAIN?

Anyway, the mods to the fuzz pedals were all about sustain, not fuzz, not that there was any shortage of fuzz.
And the mods to the amps were all about sustain too, as well as broadcasting that sustain for long periods of time and in a more controlled way. The whole point is that the ENTIRE chain of parts were being asked to give more power and sustain, as well as SHARE the development of the distortion, not rely totally on one little transistor in a fuzz box.
The input resistors on the fuzz tones tamed that screeching which was totally out of control at the beginning, as you can hear.

So the 6550s were part of the whole sound generation chain, and they could really stand up to abuse, especially in class B. The only gnarlier sounding tubes I have heard belong in the sweep tube class, like the 6DQ5. The 8417 was a sweep tube adapted for audio use, very powerful but needed a special circuit, like the Guild Quantum amp that Jimi used for a few minutes of his early career.
If you regulate the screen voltage to 300 or 350 volts you can comfortably use 750 or even 800 volts on the plate of a 6550, and you can do the same thing with an EL34 by the way. This gives you output power levels of 120 watts per pair with not too much strain.

That's part of the 6550 story. They were Tungsol tubes by the way, and the other companies just branded them until they tried to make them themselves, which didn't work out as well.

DW

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

Post by Xplorer » Sat Nov 08, 2014 8:59 pm

too bad, the link doesn't work for me. rockprophecy ?

so in a typical Hendrix amp, you'd put two mullards for example in V1 and V2, then a 5687 preamp tube in V3 , before four 6550 tungsol, with 2k 10 watts résistors on the screens + 560 volts on the plates or even more ?

sorry, this starts to be quite Advanced tech for me, i'm trying to follow :)

the development of the distortion is a very intersting subject. Jimi was Lucky to have the right persons arround him, helping him getting his sounds. unlike us who build our stuffs, maybe too focused sometimes to know better where we want to go, it's interesting to see how Jimi could have a perspective with his ears, on what came to him.

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Re:6550s

Post by daveweyer » Sat Nov 08, 2014 10:01 pm

The early "normal" mod would just leave the 12AT7 as the phase inverter/driver, either Mullards, or those beautiful Telefunkens in the first slots, (there was a short plate RCA which was real good too), put in some current limiting resistors on the output screens that wouldn't smoke if there was a momentary oscillation, like 2.2K 10 W. Then make sure there was a stout power transformer which would deliver at least 550 volts to the plates, and carefully work the grounding system so that the input stages did not "see" any of the power supply ripple, like star grounding technique. Additional power supply capacitance would usually be added, and a replacement of the diodes in the power supply so that they could handle the current peaks from the extra capacitance.
Often a hum balance pot would be installed to get rid of more hum from the filaments, then a good fiddling with the coupling caps, especially within the feedback loop, until the spanish radio station located right below West Coast Amp would call and complain about the volume of the test leaking into their broadcast mics.

Nice post from Swankmotee on the Woodstock thread too! We can benefit from his many years of devotion to Jimi and his sound.

And about that link, I think I misspelled it. It should be : www.rockprophecy.com. Listen to the out of control squeals when Jimi engages the Wah circuit plugged into the fuzz. Catfish Blues about 9.29 into it.

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

Post by swankmotee » Sun Nov 09, 2014 12:46 am

I'm trying to find where on the rock prophecy site that Catfish Blues is located but having no luck. Any clues as howto navigate?

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

Post by Xplorer » Sun Nov 09, 2014 6:52 am

can't find this video either. too bad.
i'm posting a "few" of the questions that we have sometimes.

- right, so you've used some 12AT7 instead of some 12AX7 , in V1 and V2 , then a 5687 in V3 ?
then 4 x tungsol 6550 with some 2k2 10w résistors instead of the usual 1k 5w ? and at least 550v on the plates.
then star/ larry grounding technique.
bias down to 25 mA on the tubes.

- any mods on the preamp or other things ?

- what did you do on his guitars ?

- i'm not experimented enough to really understand what's an extra power supply capacitance + diode, and why it's needed. ( i mean, especialy, how to build it ) , but many are, here.
same for a hum balance pot.

- i'm wondering if you were involved into such concerts at the Fillmore east, and what do you think of the machine gun / who knows kind of tones ?

- did you come accross some Roger Mayer mods on his fuzz ? were they very different from yours ?

- what mods would you do in his wahs ?

- i may add that the modern axis fuzz from RM is way too trebly to play some more bassy machine gun tones. i tried with my clone, with the volume way up, and the fuzz down. your definition of the ideal Hendrix fuzz makes more sense to me.

- what transistors , other than the 2N525 GE germaniums would you use into the fuzz you modded, and what typical gain did you choose for Q1 and Q2 ?

- since it was mainly about sustain ( and power ), did you maybe ialso ncrease the input resistors values of his amps ( like 2 or 3 meg ? ) , to optimise the chain for impedance , like you did for his fuzz ?
you talked also about a super high impedance amp, withithin the strat body, for John Mayall tour.

- the 7026 45/100 Hendrix amp features some 470 ohms 5w instead of the usual 1k, or even 2k2 with you, on the screens, i Wonder what positive thing it can bring, since following you, it would damage the tubes and it should require a lower plate voltage, right ? i Wonder why it ended lmodded ike this.

- what Rola speakers model name did you use ? you know, those bassy speakers which could put out 60 watts peak

. i suppose that you don't have photos of these amps and gears Inside, but maybe do you have some documents to share, that we'd be interested to see ?

thank you Dave :)

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

Post by Roe » Sun Nov 09, 2014 9:34 am

Xplorer wrote:...you've used some 12AT7 instead of some 12AX7 , in V1 and V2 , then a 5687 in V3 ?
then 4 x tungsol 6550 with some 2k2 10w résistors instead of the usual 1k 5w ? and at least 550v on the plates.
then star...grounding technique.
bias down to 25 mA on the tubes...
- he said 12at7 in the phase inverter (not in preamp), although he may have been thinking of the 12ax7 possibly? (except for the one amp that had 5687 in the phase inverter)
- increased screen resistors is a common mod, as is star grounding.

550v on the plates would likely require a new, unoriginal power transformer (unless you had a original 1202-43 or an early 1203-80 that put out 600v).
Do you remember what the screen voltage was at idle?
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Re: Jimi Hendrix' Gear and Mods at West Coast Organ and Amp

Post by Xplorer » Sun Nov 09, 2014 9:49 am

thanks Roe, i'm confused, with such things as you see.
then is it three preamp tubes ( like two 12ax7 and the third being the 5687 for V3 ) , a fourth tube ( 12at7 ) , and four power tubes ?

Roe, what do you think of the 470 ohms screen résistors on the Dickinson ? since apparently the way to go is to increase these ?

thanks ! :toast:

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Re: 12AX7 and 12AT7

Post by daveweyer » Sun Nov 09, 2014 1:17 pm

In the early amp mod, V1 and V2 were 12AX7s. The phase inverter was changed to a 12AT7. Why? More stability, less tendency to oscillate, more driving power, and not quite as buzzy distortion.
We boosted the power supply capacitance to 100uf instead of 50, and I liked either the Sprague twist-lock cans or Mallory paper covered models. It turns out they both held up very well over the long haul.
Fender switched to the 12AT7 for their amps too, and changed the cathode resistor pair to a 470 and a 22K. I would have most likely changed the pair out on the early mods as well.
Often, I would bypass the electrolytics with a film cap, especially on the input stage, but you have to try it out to see if you like it.

The transformers which came in the new batch for 1969 tour were all upright, but we had a huge pile of Marshall transformers to choose from. The Dagnall 2562 was the usual power trans in those 1959 model amps, but they varied all over the map. The Drake 1204-43 was capable of even more than 650 volts on the output plates, some could provide almost 700, but you had to pick through every one to find them. I used to take them out of other customers' amps who were having trouble with blown tubes and install the Drakes. This gave me a bigger lot to choose from.

There were problems with plate oscillations in those amps too so I'll post the mod for that next.

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Re: Catfish Blues

Post by daveweyer » Sun Nov 09, 2014 2:14 pm

Swankmotee,
I have the Rock Prophecy site up on my screen.
www.rockprophecy.com/shop.html
Just scroll down through a lot of cool stuff on Jimi till you get to the Stockholm 1967 Sept 4 concert.
It's about a 12 minute jam, and at 9.29 the big break comes. Out of control squealing from having the Wah plugged in to the Fuzzface and turning on the Wah.
This is where it all started. Jimi wanted to get control of that squealing, and turn it into a controlled organ like sound that he could manipulate for his musical vision, which was forming at that time. A lot of experiments started with that request, and that happy accident on stage.

In the last post I forgot the modifier on the replacement with Drake transformers in customers' equipment. It should have said lower voltage drakes, or Dagnalls which were supposed to provide about 490 volts on the plates.

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

Post by Xplorer » Sun Nov 09, 2014 2:26 pm

got it, indeed , what a squeal.

may i ask you what kind of experiments and mods you first attempt when he asked you some control on it ? And how did it end up in the end ?

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Re: The Wah Wah Squeals

Post by daveweyer » Sun Nov 09, 2014 9:37 pm

The first thing we did was to reconstruct the setup. At the time, everybody thought that the Fuzzface should go first, not the Wah. I didn't like the idea of the Wah first because it took away the ability to use the guitar volume control to change the distortion in the first transistor of the pedal. Using it that way, you can turn the Fuzz up, and have very good control of it right from the guitar, from no fuzz to complete fuzz. But Jimi wanted it the other way because he wanted to fuzz the Wah. And you can hear what happened at the Stockholm jam, uncontrollable squealing.
Now there are plenty of Fuzzface sites out there who insist you must always put the fuzz first, for the very valid reason just shown.
But if you want the Wah first, you are going to have to find a separate way to control the input gain of the first transistor of the fuzz box. I know Roger Mayer built Jimi some distortion circuits which didn't use the feedback pair in the original Fuzzface, and whose gain was independent of the impedance of the device plugged into the input of the Fuzzface.
But the first step at West Coast was to put a resistor in series with the input node of the first transistor. A 50K pot can give you a lot of variation. (I tried changing the feedback resistor, and even bypassing part of it with a film cap too, but the simplest way was to use a series input resistor)

What Jimi wanted was for the gain to go up SOME when he pushed the Wah button, IF the Fuzzface was also on.
What he lost in gain from the first transistor of the fuzz, would be made up by increasing the gain in the second transistor of the fuzz box. (increase the collector load resistor of the second transistor up to maybe 20K)
Doing it this way gave Jimi plenty of gain to drive the Marshall into absolute clipping when he wasn't using the Wah
without having to turn up the fuzz, and just a small boost more when he punched the Wah into the circuit, which he then could control with his guitar volume and aiming the guitar at the amp at different angles. With this configuration, punching in the Wah actually automatically turned the fuzz up a little.
You can hear how it evolved.
So Jimi had a number of variations of the Fuzzface in his big box of pedals, and I think one of the codes for which one had to do with the knob color or style.

In order to differentiate between Marshalls for instance, I would put some small dots on the West Coast Organ and Amp labels, That way the roadies or Jimi could tell which amp it was.
I think they may have had other means to decipher this as well, paint dots, different knobs, that sort of thing.

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

Post by Tone seaker » Sun Nov 09, 2014 9:55 pm

So it sounds like all his amps were moded. How far back did that go? Also does this mean he had east coast and European people moding his amps also?

I havve some pics of the governor I took of ebay when it was for sale a few years back but the board wont let me post them :(

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