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

[daveweyer]

Just so you know how these amps begin; just a ball of wires, transformers sitting all over the bench, a bunch of test equipment to verify how your crazy ideas translate into physical reality. This amp is a Mu follower power amp, some unheard-of concept for a power amp, which is not supposed to work, and so far they're right. But it's getting there.
The whole point is to have a measured amount of distortion at every volume, never quite squeaky clean.
That, and a lot of power from two tubes, 180 watts.
In tonight's test I got 220 watts out of two tubes running in deep class B. 760 volts on the plates. Horizontal deflection amplifier tubes with plate caps.
Thought you might enjoy the process.
Maybe George will post a picture of his design bench too............eh?

[swankmotee]

Nuts man but I love it!!

[daveweyer]

Swankmotee, been missing you. Glad you're back. Yeah, nuts is the right word, but sometimes you even get something to work. Then you get to have a party cause you did it!

[shakti]

Dave,

can you tell me which method you used to measure the cathode current when you biased Jimi's amps? Most of us DIY guys have been installing little 1 ohm resistors between pin 8/1 and ground, so we can measure the voltage drop across them and thus get an indirect measuremtn of total current, but this is not entirely accurate because
1) we need the resistor to be *exactly* 1 ohm, and
2) the measurement includes both screen and plate current

I'm just curious, and ultimately will have to decide by ear where to bias my amp with 510V plate voltage, but it would be nice to get an idea of how you did it.

[swankmotee]

Swankmotee, been missing you. Glad you're back. Yeah, nuts is the right word, but sometimes you even get something to work. Then you get to have a party cause you did it!

Thanks Dave and sorry I didn't reply back to you yet but am recovering from a hernia surgery and haven't felt like doing much of anything. I sure have enjoyed the posts though and did a lot of listening to boots of Jimi's 70' tour ruminating on those heads you modded and the great tones he got on the Cry of Love tour.

[daveweyer]

For setting the bias I just removed the cathode lead and inserted the meter there. But since it's such a pain in the ass it's a lot handier to install a small ohm resistor on the cathode, say a 5 ohm, and just measure the voltage across it. That resistor also acts like a very small self bias adjuster and helps the inherent differences in the output tubes to balance.
You can also see how much difference in idle current you output tubes have. If you check out that schematic of Jimi's 1966 Guild Quantum amp that Xplorer posted, you can see the clever system they provided for measuring the bias and adjusting the tubes to match at idle. You can insert your meter probes from outside the chassis, and also turn the bias controls from outside.
On that Guild Quantum amp you can also see grid #1 stopping resistors of 1K, but none on the screens (because they connect to a low impedance constant voltage source directly, the cathode of the 6GF7).
As I said in my other post, any stopping resistors on the active elements of the tubes help with instabilities, and the values can be staggered except for the cathode resistors. And and Tazin mentioned, sometimes the resistors are left off two of the tubes, either grid #1 resistors, or grid#2 resistors, but with high voltage it's better not to leave off the screen resistors.
The cathode resistors should match closely so your measurements will be more accurate.

[frenchie]

On the subject of woodstock and eventually re-amping ....I wonder if dave can enlighten us about this cupboard on the upper right hand side of this capture ;


http://i1376.photobucket.com/albums/ah3 ... c5c11d.png

i made a quick but closer composite of it using different captures ;



http://i1376.photobucket.com/albums/ah3 ... f4b324.jpg

there are tubes in there ! ( at least preamp tubes shields appear on the composite .)

[bill bokey]

A Hammond organ, used by band that was on stage earlier ?

[frenchie]

A Hammond organ, used by band that was on stage earlier ?

oups yeah .... i think you're right ( google image with hammond organs shows such a layout ) ....
shit why can't we have good usable pics of backstage , or a movie showing the roadies mounting up the whole setup

[daveweyer]

No, actually it's a giant re-amping system, and it was put there precisely to piss off Matriarch!
They just used an organ console to hide the gear from everyone, so it would look like Jimi was just using his West Coast modified Marshalls to get his tones.

[frenchie]

No, actually it's a giant re-amping system, and it was put there precisely to piss off Matriarch!
They just used an organ console to hide the gear from everyone, so it would look like Jimi was just using his West Coast modified Marshalls to get his tones.

ha jimi ... that cunning little brat

[daveweyer]

Swankmotee, best wishes for a speedy recovery, can't be that much fun, what you're going through....
I trust I speak for the others here as well.

[Xplorer]

Dave, i found in my archives a little text sent to me by ... i have no idea who unfortunately, i completely don't remember and i didn't note that, i'm sorry, if he recognizes himself, please come over !
it's about a Fender amp used by Jimi, and modded by west coast , here it is :

I have a 1963 Fender Bandmaster that Hendrix used at the Hollywood Bowl,It was moddedwith higher cap at the PI, 2 extra 380PF domino caps and 2,220K resistors going from the filter cap at point B on schematic... West Coast amp repair did alot of work on everyones amps back in the 1960;s(Eric Barret met JH working there) It was across the street from my High School on Highland and Sunset blvd...I was really lucky to meet and to hang with him..First at Music City,he was buying guitars..What he would do is try out 4-5 different strats,buy them take the best bits,and give the others away to pals...Peter Tork of the Monkees,was a pal of mine and Hendrix would come and hang,PT had all these girls at his house most just had a tee shirt on..Really cool guy..In 1971 the Hollywood bowl remodeled the place and I bought a 65 bassman and this 63 bandmaster,Rodger Lynn got a 65 Deluxe..Like VanHalens Plexi they were house amps..Hendrixs could play a Pignose with a wha and it sounded great,Jimi Live and Jimi in the studio are two way different beast... soft spoken nice guy who listened to some stupid high school kid....

[daveweyer]

Xplorer, really great to see that post. Takes me back to Hollywood.
I think there may be a small confusion in the associations, but that's how it is remembering stuff from so long ago.(The original West Coast Organ Service was by the high school, but the shop quickly moved to Melrose and Vine right next to Golden West Musical Instrument Rentals, and that's where all the modding action happened, and where anyone would have seen Jimi, until the business moved again down to Melrose and Vermont into a much larger space. That first move was when it really became West Coast Organ and "Amp")
Music City sent a lot of stuff to us, and he (Eric?) used to hang around from time to time, just checking things out, and listening to the latest mods. Lots of folks did, including Red Rhodes, who was kind of looking at the same space to work in, and would peer over my shoulder to check it out closely. (And he found a nice niche up in the San Francisco area, as I'm sure you are all aware)
You wouldn't believe how many mods I did, especially Fenders, since they were quick and easy. I kept a log of amps I worked on because so many were coming through there, and by the time I left I had worked on over 5000 amps.
It got to the point, after other folks jumped into the hot rod game, that you could not find any more of certain old Fender amps to do. I trained six guys to do mods, so we could do ten a day, sometimes even more, unless we were bogged down with nasty repairs.
All the guys who were selling gear and modding stuff were after me to join up in business with them because they saw how much demand there was, and how much fun it could be to get things really sounding sweet.
Neal Moser was hired in 30 minutes after word got out that West Coast was closing-- word traveled fast in Hollywood!
It was by several accidental breaks that West Coast Organ and Amp grew so fast and touched so many people in Hollywood, a rather remarkable story considering it was started only after the Beatles 1966 USA tour. Jerry Sanders, who was assistant national service manager at Thomas Organ Company and Vox USA, and traveled with the Beatles on every stop of the 1966 tour, decided to quit after the tour and start his own organ repair shop. He advertised in an LA paper for a technician who knew both amps and organs. I knew both since I had also worked for Thomas and Vox, and was hired on the spot. When Jerry saw my long hair, he said, "I'll do the organs, and you stay in the shop and do the amps".
So I became the "Amp" in West Coast Organ and Amp.
Okay, probably more than you wanted to hear..........

[Xplorer]

cool to hear these storys, don't worry
it gives more pictures to the context, please continue.
5000 amps ... wow .....
maybe i'll remember or find who wrote this to me, it would be cool.

among Jimi, Neil Young ... who were the others ? and do you remember some storys you'd like to share ?
i've never been to LA but i can start to imagine Hollywood in the 60' , Jimi Hendrix, some rock stars and actors big partys in cool villas, plaboy mansion, amazing jams, etc ....
I suppose you were quite busy with electronic but all this context came to you at some point, right ?

i'm wondering : how different it is today, local rock band playing classic stuffs, ... compared to the same back then...
today, drums sound super heavy, every time, some of the gears like today didn't exist , etc ... no much cynism among peoples like today i suppose. and things felt more "new", right ? i suppose that some nostalgias of today are quite related to the lack of this feeling : "new and exciting". maybe i'm wrong.

anyway, probably more than you wanted to hear he he ..