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

[Tone seaker]

I think the tube mod could have been pretty common. I read Jimmy Page changed his out to 6550's or something else

[daveweyer]

Shakti,
There are some pretty good Russian knockoffs of the 6550, the plate sat ratings are now approaching the old American versions.
Don't change the 220K resistors from the output grids to the bias supply, THAT WON'T CHANGE THE BIAS.
Bias the tubes with the little supply; remove each cathode one at a time from the common connection and measure the current in the tube with a meter, should be 25ma to 30 ma.
Try a 12AT7 in the phase splitter spot and change the lower cathode resistor to a 22K or a 15K depending on sound. Try the original resistor first and compare sound.
Go ahead and mismatch the OT impedance to get close to 4K on the primaries.
Try the feedback from each tap and check the crunch factor.
Add extra capacitance on the filter caps and check for sound and crunch, dial it in for best feeling.
Do tests louder than the unmodded versions, so you can approximate where Jimi played the amps.
Try bypassing the first stage cathode of V2, with an electrolytic, and then a film cap. See which one or both sounds best with your speaker setup.
Make sure the plate voltage is better than 500 volts. Try using 2.2K resistors on the output screens and check for sound, after you try it with the 1K resistors.
Let us all know here on the forum how it sounds to your ears, and what Jimi performance it invokes, and then we'll take it from there. Fun stuff........

DW

[shakti]

Thanks Dave. I need to find some 6550s first though. Anyone have a recommendation?

I know the 220ks don't change the bias, but I had read that 6550s and KT88s need lower value resistors to operate safely. Even EL34s work healthier with lower values, but can usually take. I don't understand the technicalities of it enough to say why that is though. Hiwatts use 100k in those positions, regardless of whether it's an EL34 or KT88 amp.

I'm a little confused by what you mean by the "lower cathode resistor" in the PI though. Do you mean the 10k "tail" resistor?

On V2 I have a .68uF WIMA film cap, which was typical of those Feb/March '69 Super Leads.

I'll be sure to report what I find. I know others (BillyBatz for one) have tried 6550s with great success.

[Xplorer]

it's going to be fun !!

Dave, can this be made also on a 45/100 with modern kt66 ? sending 560 volts thanks to the bigger screen resistors ?
unmodded, it's advised generaly to avoid it.
then if it's ok, i'll order a 12AT7 ( which brand preferably ? ) or 5687 ( ? ) and 4 x 2k2 10 watts résistors to test it too.

thorleif, please let us know and post clips please once you did this and some with the fuzz volume to max and fuzz to zero ... adjusting the strat tone and volume for Hendrix territorys.

[Xplorer]

i told Billy about our new member some days ago, and he was very pleased, i wish he'd join us to talk about it.

unfortunately his soundclips page isn't available anymore, i'm not sure to have copys of it. with some 6550 he got some very interesting results regarding the bog tone.

[Tazin]

Looks like Dave's seal of approval.

[daveweyer]

Just a little note on the grid resistors for the output tubes.
The value is based upon the tendency for the output tube grid to draw current if the tube gets a little gassy (and they all do, especially with hard work), and of the tube draws negative grid current, which can happen if the resistor value is too high, meaning that it will alter the bias the other way.
Fender chose 220K because it was the maximum allowable practical value which would drain off any current from the grids of the power tubes.
In more comprehensive designs this value would be much lower, clear down to zero in transmitting service using inductive input systems i/e. a coil with a high AC impedance and nearly zero DC resistance.
So lower values are safer, but they cause distortion in the phase splitter stage if you are using a 12AX7, and they also cause the maximum gain of the stage to be reduced.
So those are the trade-offs. With a 12AT7 in that position, the plate resistance of the tube is reduced, and it will drive a lower grid input resistance--one of my mods if I was able, just to save output tubes.

Oh, and a note on the 5687, it only has a gain of 16, but it will drive anything. It also has the filament connections on 4/5 and 8, so plan accordingly if you intend to use one.
This tube is best used in the situation where you use the second half of the trem tube as the gain stage in the power amp, and then use the 5687 as the driver. It will actually take the output grids to positive peaks, for even more output power.

AND TAZIN.......Is that a West Coast Organ and Amplifier Service sticker I see ??? I do believe so!
For some reason, the glue on those stickers just lasted and lasted, you couldn't get them off.
I've had some show up here on some of Jimi Hendrix' old equipment, and after scraping off the layer of oxidation, there it still was.
Here's another bit of history, we got a roll of the stickers which had the wrong phone number on them, and some of them got stuck on equipment before we got the problem corrected. Number should be 462-8683.

And this leads to one more contextual matter, the total screw-ups of everybody at every level and every company in those completely stoned out, care-less, chaotic, balls-to-the-wall times.
You really can't understand the Jimi story completely without contextualizing through that lens.

If this forum will permit me, and be willing to live with a renewed level of uncertainty about the gear Jimi was supposed to have, and played through, I can bring some context to the discussion around Jimi's gear.

Thanks again for your indulgence. Such devoted Jimi and Marshall freaks, how I wish it would have been like this in 1969!
DW

[frenchie]

to daveweyer

If i may point that out you neither confirmed nor denied what i conjectured in page 6 ;

" Could it be that the traynor/yorkville Ysm1 voice monitor on the bar seat next to jimi in the fillmore east show , in fact wasn't there to monitor him his voice or anything else , but to have a nearby speaker allowing him to have a mechanical feedback line next to him ( i guess when it comes to controlling feedback , one speaker is more managable than a whole stack ) , so that he didn't have to travel 5m just to let it scream , but having a device ( well it's not a device technically speaking just a speaker alright ) allowing him to control feedback at hand like almost another instrument or a pedal box ...I mean during the performance you see him often turning his guitar to this monitor ??? "

Can i ask you your opinion about this point ?
Possible or not ?

[daveweyer]

Frenchie,
Sorry I missed that in all the other ideas floating around.
I would answer your question in the affirmative. It might be an acoustical feedback speaker. I have seen him do this, and that was one job of the 66 Guild amp I have mentioned in these posts.
There is a picture of Jimi with that Guild amp floating around on the web somewhere, and it also appears to show the Guild being used as a monitor speaker driver.

Maybe someone has more info on the gig you're talking about and has another idea. But I can tell you that Jimi knew about this close amp feedback idea, and had used it before. It's actually a good idea, saves ears, and in a real loud setting, can help you hear yourself (and others) better. Another benefit of that arrangement is that if you find a speaker which reacts particularly well with your guitar, and provides the feedback in the zones you want, then you are really that much more in control of the out-of-control sustain.

[Xplorer]

"theremin" device for strat feedback fantastic idea. thanks for pointing this frenchie

[shakti]

Looks like Dave's seal of approval.

Is this from one of the purported Hendrix amp you spoke of, Tazin? Can you tell me if you see any (I mean *any*) signs of modding in there?

Dave Weyer - one more thing that wasn't clear to me: you mean you went through OTs to find one with a 5kohm or so primary Z? And you found some among the stock Dagnall C1998s? Nominally they were 1.7k, so that seems like a veeery long stretch.

OTOH, if this really is true, then I should say this to Xplorer: you may not be so far off with your JTM45/100 thoughts. Essentially this mod would have turned a regular '69SL to something definitely closer to a 45/100; bigger glass with a different tone than EL34s, higher voltage closer to a 45/100, high primary Z output transformer (a 45/100 OT is 4k). Can't wait to try this out!

[Xplorer]

OTOH, if this really is true, then I should say this to Xplorer: you may not be so far off with your JTM45/100 thoughts. Essentially this mod would have turned a regular '69SL to something definitely closer to a 45/100; bigger glass with a different tone than EL34s, higher voltage closer to a 45/100, high primary Z output transformer (a 45/100 OT is 4k). Can't wait to try this out!

love to hear that !
i suppose that Dave will confirm it was closer to a 45/100 , despite the envelop.
i prefered to follow my ears despite the pictures ( which show only one night, not the special night ... ) or historians.

at first i thought that since it happend in New York, where Jimi had his new studio, it could have been very likely that he choose his favourite early 45/100 to pilote the whole thing the next night, ( the tone of both nights is a lot different ) if he wasn't pleased the first night with his setup.
no proof of this off course, just a hypothesis, but indeed, if these amps were modded this way, it answers this just like an unexpected scene coming in the suspens scenario of a good movie

now try with the Hendrix fuzz settings, it's fantastic. best univibe tone you'll hear, different reactions, dynamic of the setup, so much things make sense then ... and it tells a lot about the way Hendrix played.
and the octavia used with the fuzz set this way is what everybody was looking for ... 200 % what i hear on who knows , gotta live together etc ...

[swankmotee]

Sorry but I disagree on the settings of the fuzz control being turned way down. After all my years of messing with different settings on the FF the only way he got the huge amounts of Fuzz were having it turned up very high. When you listen to the entire BOG performances it is apparent he used the same amp,same huge amount of fuzz gain on both nights. You can't get the crazy feedback,sustain, and interaction like he did with it turned down. The Octavia definitely had its own gain/fuzz that mixed well with the FF sometimes but on Who Knows and We Gotta Live Together it was on by itself. The question of the monitor in front being an exstenstion cab I don't buy since there would've been horrible squealing/feedback issues along with phasing that would've been hell to control even for Hendrix. And once again, if one has had experience with using this same setup at volume like he did that night you would no instinctively that all those sounds and interactions could be easily had without any reamping.

[Xplorer]

did you try to play bog this way ? it produces the machine gun and other wild tones anyway, even without the fuzz.
it's not like star splanged banner tone ...
one thing i'm sure of too, is that he didn't crank his amps at all. we have some quite opposite views on the subject ha ha
i tried, perhaps in some good conditions and it blew my mind. no fuzz on bog i think. and the octavia and univibe sound better this way. i got much closer to it than with my previous attempts with a lot of fuzz used, cleaned up with the strat volume :

https://soundcloud.com/xplorer80/machin ... one-45-100

[daveweyer]

Shakti,
I don't think the Dagnalls stretched to 4K. If you had to use one, you also had to use a different output winding to get the primary impedance to look a lot higher to the tubes.
If I had some old Drakes, I would use one of those. I found I was also able to use some Woodward Schumacher OTs, and if I put these cores into a case that fit, you couldn't tell unless there was a slight difference in the stack.
I know I retrofitted at least one Stancor OT too. In fact, if I remember this correctly, I saw american transformers in some of the earlier Marshalls, and they were stock.
The point of all this seems to be that the mods I generally did made the plexis into 45/100 amps in disguise.
I think that's probably a fair statement.
I liked the layout of the plexi amps better, because of the ability to use chassis mounted filter caps. The cans had to be insulated, so if I used a Sprague twist lock, I had to do the insulating job myself, at least on the one with the hot case.
I did probably 50 amp mods for Jimi, he had every different kind of amp and Marshall you could ask for; he got them as gifts, picked up used ones, traded for them, you name it.
At any given performance, you really couldn't tell what he was using, even if the amps had West Coast stickers on them.
Amps would show up completely smashed, trannies ripped out, chassis bent beyond repair, so some of the amps were hybrids, collections of parts and pieces from salvaged amps to make one good one with a decent case.
I'll bet if you scour the photographic evidence you will see amps with the wrong front panel layout, the wrong back covers, and so on.
We had quite a fabric recovering operation going at West Coast too, so some of the amps look new, but they're not. Same goes for the bottoms.
You wouldn't believe the chaos in those hectic years of the late 60s. Fender and Marshall, to name a couple of majors. really didn't have control over what they were doing or sending out, and their records have many errors.
I have a Fender Concert amp here, for instance, which is a theoretical impossibility according to Fender records, because it is actually a Bassman, complete with the 5AR4 rectifier-- and it's all stock. This stuff happened every day with these two companies. Something to think about when you believe you have established a chain of custody for one of Jimi's amps.

By the way, if you want the sound of the 5AR4 in your Marshall, you can get part way there by using 2.2K screen resistors.