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

[daveweyer]

You won't see huge visual differences in some of these modded 1959s.
But you should see a 20K on the cathode of V3, you should see 4 green sandy surfaced 7 watt tubular (with a slight bulge in the middle) power resistors with a great big W printed right on the side, the value being 2.2K, and you should see TWO of the plates of the output tubes stopped with 47 ohm 5 watt resistors (some 2 watt carbons).
Marshalls had an oscillation problem up in the above 50KHZ range when under square wave clipping conditions. Using one plate stopping resistor per side eliminated something they call "lumped constants", where all the little capacitances and inductances add up at the same place and cause enough phase shift to make an oscillator out of the amp.

If my notes here in an old spiral bound notebook are accurate, the Governor should have 545 volts on the plate, 100uf filter caps, and a 12AT7 in V3 position. I thought that the power transformer was a Drake 1204-43, but it might have been the 1203-80.
At any rate, I can tell you that after a dozen or so mods, the sweet spot seemed to be with 560 volts on plates of 6550s, set up with 25 ma bias and dropped screen voltage to about 530.
One critical factor is the transformer regulation, and I hand picked transformers by testing them.
The filter caps charge up to peak, about 1.414 times the RMS secondary voltage, but when the amp turns on hard the voltage drops, putting your output stage further into class B. You can mitigate this somewhat by using a transformer with extremely good regulation, using low loss diodes, using a large filter cap, and providing a steady current draw in the amp so that the caps can't quite charge up to peak voltage.
So you may also see a big bleeder resistor, actually two, across the second set of series connected filter caps. Something I used to offset the very small idle current used by the output tubes. (Makes the choke warm, make sure it can handle 90ma)
It is a very simple setup, and doesn't chop the amp to pieces for the mod.
If whoever has the Governor would be willing to measure the plate voltage, we could verify all this.
One has to keep in mind that there is probably more myth out there than actual fact.
I have no real way of verifying the serial numbers given for the amps shipped to West Coast. I think I could recognize some of the mods though.

There were more sophisticated mods in Jimi's amps, split supplies, 5687 driver tubes, different phase splitters etc.
I can explain some of those later if we get that far.

So why did I come to this site???

I have some friends who have been hounding me for years to tell some of this, one of them is Deniz Tek of Radio Birdman fame. I promised I would do it someday if I got time and could find my old notebooks.
So just a few weeks ago a Hendrix lover I know told me they were talking about Jimi's stuff on this site, using quotes from me taken years ago, and told me to check it out. I saw what George was trying to do and watched his little video; pretty devoted to recreating the actual product don't you think?
It just seemed like a place that would really be interested in these stories, most of which have never been given the detail relayed here. George is an amp builder, just like me, and seems like a real decent guy. (He must be, he let me on the forum!)
I thought it might be nice to get some truly honest recollections out there in cyberspace regarding the West Coast Organ and Amplifier Service experience, and our relationship to the Hendrix experience. Everyone has heard the many Kramer stories, and Mayer stories, and stories from everyone in existence who ever touched the Jimi phenomenon. My personal reaction to much of this was, "oh yeah right, if they only knew the half of it", but "setting the record straight" was just too hackneyed and overused--everyone it seems was setting the record straight--and I just didn't want to get into a big argument about it. I mean I could have called Art Thompson and said I want to set the record straight, he's interviewed me before. (I even wrote some articles for his Guitar Player section, but apparently they were too technical and got edited to almost nothing)
So this site felt pretty good, lots of totally devoted Jimi freaks with TONS of knowledge about his performances, sounds from personal experience, and willingness to share.
Might help fill in my own memory gaps.
Maybe word will get around and more folks will join the forum; MAYBE George will even build some custom models using the exact mods we did at West Coast--if you pay him enough! Maybe George's business will boom!
Who knows?

[VelvetGeorge]

Let me speak for all of us here (if I may humbly elect myself) when I tell you that you have found the right audience here and we can't get enough of this info you have chosen to share! We are the obsessed and do tend to take things to the Nth degree. We dig deep and theorize about most every aspect of this stuff. Granted, sometimes we obsess and debate over details that are trivial in the big picture. But, that comes with the nature of the personalities hanging around here.

You have info and insight so unique that we literally couldn't get it anywhere else. It's valuable and speaks a lot about you that you opted to share it here with us. I agree that you could have "set the record straight" in other context and fought over truths in other arenas. Unfortunately, facts have become overshadowed by legends and myths now. Everything Jimi is epic. Many of those fights would surely be futile.

Please post all you are inclined to here and allow us to absorb it, while researching all we can and connecting any dots that will line up. It will be amazing if we can put lot of evidence together and realize some long lost truths about these amps and mods. It would go a long way to dispelling many of the untrue myths and rumors out there, as well.

I'm excited about the possibilities.

george

[swankmotee]

Yeah Dave we are all sincerely grateful for you taking the time to bestow such knowledge upon us minions! My question is what was your method for testing and choosing transformers? Did you spend much time tweaking OT's because as most of us die hard vintage Marshall guys know they are the heart and soul of the overall tonal character. Any preferences of model and brand since I know Dagnalls were all over the map?

[Xplorer]

love it , it's beautiful.
i'm sure we're all honored to welcome you here. sharing such storys that passionate us and lead us to many discussions before, is fantastic, and all that with great humility from you.

yesterday i played along with the Fillmore east concert, machine gun, who knows, power to love etc ... and with this big lesson : fuzz setting with volume at max and fuzz gain to zero, with an unmodded fuzz, i totaly got there on a 45/100 i think , it totaly made sense now. thank you so much for this.
the univibe reacted way better, the octavia too ...
i'll now build a fuzz according to what you said, and see how it goes with my 68 vox wah.

[daveweyer]

The sweet spot for the OTs came in at 5000 ohms. Supposedly 4-6550s should want maybe 2200 ohms or so, like the Hafler transformers used by Sunn, and they will put out a lot of power that way. But they seemed to sound best with a smaller set of laminations and a lower output rating RMS using a 5000 ohm primary. Some of the Marshall OTs fit the bill perfectly, and I tried to save as many of those as possible to have on hand.
I also found one really super combination using a Stancor A-8053. This transformer was rated at 50 watts from 20 to 20KHZ, but was perfect from 30 to 15KHZ at 100 watts, and I was typically getting 160 watts square wave output from the amps which had 560 volts on the plates and 4 6550s. But the transformer was straining, and that sound is just so sweet for crunch guitar. I built a lot of amps with these, not just for Jimi.
If you think that the REAL sound generator is in the output stage distortion/tranny/speaker rolloff, you are really on to something big. It was the major controller of the sound. All the other tweaks were secondary once the amp was well into overdrive.
And the speakers, as most gear freaks know by now, have to be HIGH Q, small voice coil, high resonance, tight cone models, basically following the design of old console radio speakers from the 40s and 50s.
One post was wondering why Jimi sounded different at Fillmore East, well just take a look at that picture where you can see all those large voice coil, lowQ, big magnet, high compliance speakers in the cabs.
Maybe they held up better, but it's doubtful. You should have seen our blown out speaker stack, just filled with JBL D120s. They blew out just as easy, and actually sounded terrible for crunch guitar. They just wouldn't react to the amp freely enough because their Q was too low. I can tell you Jimi did not like them.

[frenchie]

One post was wondering why Jimi sounded different at Fillmore East, well just take a look at that picture where you can see all those large voice coil, lowQ, big magnet, high compliance speakers in the cabs.
Maybe they held up better, but it's doubtful. You should have seen our blown out speaker stack, just filled with JBL D120s. They blew out just as easy, and actually sounded terrible for crunch guitar. They just wouldn't react to the amp freely enough because their Q was too low. I can tell you Jimi did not like them.

well for fillmore i agree the base crunch sound is generated by celestions .... My first theory was that the plexis were feeding directly a mix of celestion cabs and sunn and guild cabs loaded with 15inches D130f speakers .... Now i think the plexi stacks were relatively low volume and mic'ed to P.As and then feeding the 2X15 jbl loaded cabs in great number on the stage so as for them not to break up at all but just retransmitting at higher volume the slightly distorted sound of the celestions with the highest fidelity .....

(on a side note ; god this automatic corrector is a pain in the ass )

[Xplorer]

+ 1 , you convinced me frenchie

[shakti]

Again to Dave:

- did you mod the bias supply in any way? Meaning the resistors adjusting the bias range, and also the bias grid resistors (stock were 2 x 220k)?

[frenchie]

+ 1 , you convinced me frenchie

look even in the crowd pics on the upright corner , oh big surprise ..... another big ass sunn cab ;

http://www.wolfgangsvault.com/crowd/pho ... 9-34A.html

he obviously tried to augment the spread and volume of his plexi stacks , without setting his plexis on the verge of explosion ....

[daveweyer]

Lots of good threads.

The bias supply; yes the bias has to be changed to get the 6550s to idle at 25ma.
The 220K grid resistors are too high to prevent negative grid current, or positive grid current from a gassy tube from altering the bias for the rest of the tubes. The safest way to control this is by making the grid resistors as low as possible, less than 50K. But to do that you have to change out the phase splitter to a tube which can drive a lower impedance, and then lower the plate load on that tube as well. In the original cathode coupled phase inverter circuit which Fender copied, and then Marshall copied in turn, had a 12AT7 or other high Gm tube using one 28.75K plate resistor, and one 33K plate resistor. You can see the 82K and 100K resistors changed in about the same ratio to allow a low Gm high Mu tube to work in the circuit. This was done entirely for cost reasons, as Leo Fender explained to me, just to save one extra stage. He wanted to get all the gain, and split the phase in the same tube, using just one stage to drive the output tubes. Well, it worked, but the cost was a lot of blown tubes.
Just do a test; hook up your Marshall or Fender with 4 output tubes up to your guitar, turn everything up, and just let the guitar sit in front of the speakers. Put the amp in a dark room. Now as everything feeds back in a howling mass of distortion, look inside the EL34s and watch the screen grids get red hot. Then watch the plate seams in the middle of the plate, and you will see them start to glow. Then notice that some of the tubes are getting hotter than the rest, a lot of times one tube in particular. They are not all working equally.

The super trems had an extra tube, and you could use the other half of that tube to create the original cathode coupled circuit. Just make that half of the 12AX7 the input gain stage and send its signal to a 12AT7 (or even better a 5687) in the phase splitter position. It takes almost no parts. The 12AX7 plate is direct coupled to the grid of the 12AT7, the 12AT7 has the lower value plate resistors and a 33K cathode resistor, no other parts in the cathode circuit.
The feedback is then taken to the cathode of the 12AX7, and the plate leads to the output tubes are reversed to account for the phase change. This circuit gives you balanced feedback to the output tubes, a much higher open loop gain (about 300 for the original Fender design, about 1000 for the modded circuit).
The extra gain makes for a lot more change in the presence control, and you can vary the feedback to suit the amount of gain you want in the output circuit, PLUS, you can use a separate supply for the screens, because that takes more drive to the output tubes for the same power.
You need to change the grid stopping resistors on the output tubes to 10K from the original 5K to help with high frequency oscillations.

Now it seems from the posts there is growing evidence that Jimi had discovered re-amplifying his Marshall stack was the way to get it louder and preserve his equipment.
I can tell you I had been harping about that for a long time. Had Jimi lived we might have seen the fruits of all that talk in the form of a formal system I had worked up and had been building for some of the Hollywood pentatonic guitar slingers who wouldn't play through anything but a 59 Fender Bassman.
It was a special re-amping system which relied totally on the sound of the first tube amp and speaker setup to get the tone, response, feedback, etc.
Jimi was all ears, but very busy too, and getting a bit scattered.

[Xplorer]

+ 1 , you convinced me frenchie

look even in the crowd pics on the upright corner , oh big surprise ..... another big ass sunn cab ;

http://www.wolfgangsvault.com/crowd/pho ... 9-34A.html

he obviously tried to augment the spread and volume of his plexi stacks , without setting his plexis on the verge of explosion ....

frenchie, i'm sorry, where ? i don't see them

http://i.imgur.com/5sFQWBt.jpg

[frenchie]

+ 1 , you convinced me frenchie

look even in the crowd pics on the upright corner , oh big surprise ..... another big ass sunn cab ;

http://www.wolfgangsvault.com/crowd/pho ... 9-34A.html

he obviously tried to augment the spread and volume of his plexi stacks , without setting his plexis on the verge of explosion ....

frenchie, i'm sorry, where ? i don't see them

http://i.imgur.com/5sFQWBt.jpg

there's one under the balcony up on the right ...you can barely see the aluminium dust cap ....

[Xplorer]

Lots of good threads.

The bias supply; yes the bias has to be changed to get the 6550s to idle at 25ma.
The 220K grid resistors are too high to prevent negative grid current, or positive grid current from a gassy tube from altering the bias for the rest of the tubes. The safest way to control this is by making the grid resistors as low as possible, less than 50K. But to do that you have to change out the phase splitter to a tube which can drive a lower impedance, and then lower the plate load on that tube as well. In the original cathode coupled phase inverter circuit which Fender copied, and then Marshall copied in turn, had a 12AT7 or other high Gm tube using one 28.75K plate resistor, and one 33K plate resistor. You can see the 82K and 100K resistors changed in about the same ratio to allow a low Gm high Mu tube to work in the circuit. This was done entirely for cost reasons, as Leo Fender explained to me, just to save one extra stage. He wanted to get all the gain, and split the phase in the same tube, using just one stage to drive the output tubes. Well, it worked, but the cost was a lot of blown tubes.
Just do a test; hook up your Marshall or Fender with 4 output tubes up to your guitar, turn everything up, and just let the guitar sit in front of the speakers. Put the amp in a dark room. Now as everything feeds back in a howling mass of distortion, look inside the EL34s and watch the screen grids get red hot. Then watch the plate seams in the middle of the plate, and you will see them start to glow. Then notice that some of the tubes are getting hotter than the rest, a lot of times one tube in particular. They are not all working equally.

The super trems had an extra tube, and you could use the other half of that tube to create the original cathode coupled circuit. Just make that half of the 12AX7 the input gain stage and send its signal to a 12AT7 (or even better a 5687) in the phase splitter position. It takes almost no parts. The 12AX7 plate is direct coupled to the grid of the 12AT7, the 12AT7 has the lower value plate resistors and a 33K cathode resistor, no other parts in the cathode circuit.
The feedback is then taken to the cathode of the 12AX7, and the plate leads to the output tubes are reversed to account for the phase change. This circuit gives you balanced feedback to the output tubes, a much higher open loop gain (about 300 for the original Fender design, about 1000 for the modded circuit).
The extra gain makes for a lot more change in the presence control, and you can vary the feedback to suit the amount of gain you want in the output circuit, PLUS, you can use a separate supply for the screens, because that takes more drive to the output tubes for the same power.
You need to change the grid stopping resistors on the output tubes to 10K from the original 5K to help with high frequency oscillations.

Now it seems from the posts there is growing evidence that Jimi had discovered re-amplifying his Marshall stack was the way to get it louder and preserve his equipment.
I can tell you I had been harping about that for a long time. Had Jimi lived we might have seen the fruits of all that talk in the form of a formal system I had worked up and had been building for some of the Hollywood pentatonic guitar slingers who wouldn't play through anything but a 59 Fender Bassman.
It was a special re-amping system which relied totally on the sound of the first tube amp and speaker setup to get the tone, response, feedback, etc.
Jimi was all ears, but very busy too, and getting a bit scattered.

if only i was able to decrypt everything and do a layout of such mods, i'd do it on my current amp build ! and buy some 12AT7, 5687 , stancor OT , 6550 ... well, on my next 69 superlead.

may i ask you what about the 45/100 mods ? you kept the kt66 and did somethings ?

it seems that the re amplifying system of Jimi sounded right ? but i can't know anyway, i'm just thinking of the final mix, which blends the room sound, and the mic near the main marshall speaker.

when i get into a stadium or a big concert hall, it's allways a bad sound when they start to use some standard kind of speaker walls, re amplifying the "small" guitar amps. it allways struggles with the acoustic, and it's very bassy . it killed the last jeff beck concert i saw at the grand rex .

such Equipment that you know :
http://www.electrovoice.com/sitefiles/p ... 009_37.jpg

i guess it was really great to see such Hendrix performance , made with big walls of marshalls only. but if the re amplification is made with special cares, sure, it can be nice too !

[swankmotee]

Frenchie, I don't think any of those cabs were in the mix for guitar (I have no proof of knowing) IMHO because if you listen to the Baggyrehersal sessions it is obvious that the same main amp was used in both settings. Now keep in mind that the Fillmore was very echoey and had its own stage e.q. that it added to everything as well as the mics that were placed creating their own E.Q. curve to the recording.Its also obvious that the Marshalls were cranked as always and to my old eyes it looks like Jimi reaches back and cuts amp #2 off of stand by during the feedback outro of Machine Gun because the volume level jumps. I have always felt that this was true since the Baggys recording sounds exactly the same tonally and volume level wise to me. After many years of listening this is apparent to my ears.

[daveweyer]

Frenchie,
You bring up a very interesting point. The re-amping idea has evolved, changing from just re-amping to form a wall of cabinets doing basically what several stacks would do ( but being a whole lot more reliable), to using truly huge PA systems to take over from the amps by miking them.
That is a fundamental shift which has occurred over quite a few years. There were a lot of steps in between, with various combinations of each, gradually giving way to the current practice of miking everything and obtaining the power factor through the 100,000 watts of power available in a large venue system.
It would take a thousand Marshalls to get to that point. (sounds kind of fun, I'd like to try it)

I know Jimi was trying both methods. In 1969, the PA systems had a long way to go, most of them being just collections of stuff put together by techno geeks trying to make a living as contractors. All manner of systems were tried, my favorite being the line array, which finally came into its own rather recently. Even the most powerful solid state amps had 300 watts, and sounded rather strange besides. Eventually the wall of guitar amps had to give way, if for no other reason than practicality.

But there is just something about a wall of guitar cabinets which is unobtainable by just miking a guitar amp. The problem is, as you succinctly point out, it is out of the control of the front of house mixer, and the overall sound cannot be controlled to suit the venue, either loudness or tone.

That's a big problem. But in the right circumstances, there is absolutely nothing like it. Of course all the musicians go deaf, since they have to stand in front of it.

My secondary point is this; if you plug a Fender Deluxe, say, into three transformer coupled solid state amps of 240 watts each, into six Marshall style cabinets loaded with high Q speakers, there is an acoustic feedback path between the big speakers and the Deluxe speaker, there is a feedback path between the guitar and the Deluxe speaker, and there is also a feedback path between the guitar and the big speaker cabinets. These paths are mechanical, but they end up having electrical effects, as everything works on everything.
I did this at West Coast for a number of guitar players, one of them being your favorite, completely blowing their minds with the fluidness, the ramping distortion, and the control it gave them; the strings want to play themselves, and you just sort of let them go into whatever they will do.
I never forgot the sounds and reactions from all who tried it. It's where Jimi was heading at the time. Nowadays it is quite fashionable to use a guitar speaker as a mic.
Not advertising a product here, just offering this to maybe make the sounds you are hearing come into focus a little better.

By the way, the 45/100 modded really well, they usually had the transformers I wanted to use. I never kept the KT66 tubes, the transformers on those amps were too powerful. If someone wanted to use KT66 tubes, I'd get a plexi transformer and get the plates down, maybe to 450v if possible, even lower.

Here's another tidbit; Triad made a transformer I liked to use as the PT, had a lot of current, and provided 560 volts for the plates. It was a vertical model, but if you took the end bells off, you could use the Drake covers and it would fit into the chassis, keeping the original Drake number. Sometimes you couldn't tell the mods were there, well, George could probably tell.