The 6550 Experience

[Xplorer]

thank you for the info, that's definitely something to try. i will, as soon as i secure the amp with some better heaters résistors.

but it's not so bad, it's actualy interesting regarding the Jimi Hendrix tone archeology.
with this cap, and no fuzz involved, it gives some tones that look a lot like the bright tone Jimi has on an outtake version of "angel" , and with the fuzz involved, it thickens the tone , giving a lot of Hendrix records, including bog.

my guess is that this cap was left in his amp ( But Dave certainly could tell ) , and Jimi adapted himself to it , and that's why it gives these bright tones sometimes, and some thicker tones the rest of the time. just Rolling down the strat volume, if the fuzz is involved, brings the amp in this bright territory, as heard in room full of mirrors or "burning desire" ( still in the bog show, even if it's a bit bright ) , or "angel" , as well as some other tunes.

if the cap didn't exist in his amp, then i don't know how he got such bright and thinner tones.

angel is even brighter than this beautiful part of burning desire ( which would just be the strat volume rolled down a bit, and the fuzz still involved )

you can hear this angel version i'm talking about, at 1:12 . i can get a bit close to it sometimes, without the fuzz, on the superlead. BUT gien the dates ... 1967 , it couldn't be the west coast amps

http://www.dailymotion.com/video/xxalrh ... enes_music

[Xplorer]

- So ! i got today some more résistors, and this time i simply put them in parallel to each other, and connected to only one pin of V7.
the total volts it gets is 2,16 Vac + 3,58 Vac = about 5,75 Vac . i know it's not 6V but do you think it's ok ?

i may try to combine another value, lower, among the two resistors. it's a bit empiric because i don't know why, the value that P=UI gives isn't enough for the amp. it should normaly be 0,1 ohm but it works better when it's closer to 0,25 ohms.

- one thing that is a bit strange ... the other day the voltage on the pins 3 of the power tubes could go up to 525 - 530 volts , and now, on pin 3 on V4 to V7 , i read 478 Vdc min to 502Vdc max ... ( could it be related to the heaters voltage ?? )
the B+ is still 523 Vdc

but fuck, this quad doesn't look matched anymore. the bias readings say 25, 24, 28, 31 mv ....
i'll maybe swap tubes and see ..
it sounds good though.

Anyway, this amp is fabulous, everything it plays is Hendrix.

- i recognize "Gypsy blood" , Bog , many things that didn't have a really satisfying explanation ... until these last months with Dave, and for about 45 years ... Dave, i'm really amazed, but you already know, since i keep telling it all the time

i'll maybe do some clips tomorrow, with two Ribbon mics , it could be nice.
the really interesting thing that kept us in a grey area for so long is that the later Jimi sounds like a 45/100 but not quite. it also sounds like a Superlead, but you don't recognize the EL34.
so, right there ... 6550 in a special operation mode.

- i actualy enjoy playing it without fuzz, it's just perfect in fact. if i use it with a fuzz, i run into a problem, it darkens the tone too much maybe. i'm not sure how to compensate this thing "naturaly" into the fuzz circuit, for a more transparent effect.
but i think Dave answered this question in another thread already. if there's a way to control this effect with a pot, it would be a mod to do. it's worth it.

- i'll try this V2bypass cap mod , it's the 0,0022 uf if i remember.
isn't it V1B bypass cap rather than V2B ? that's the only place where have a 0,0022 uf .. between the vol I pot and a 100k resistor.
anyway, i tried this one and it got rid of ..... the sound so , that can't be it. but this is the infos i've got :

[Xplorer]

here, a first clip. i didn't edit anything, so sorry for the messy noodling.

i played it mostly dry. also a bit of voodoo vibe univibe and fuzz attempts but the blue fuzz doesn't work so well with this amp. it darkens the tone too much compared to the 45/100.

https://soundcloud.com/xplorer80/150927 ... oast-amp-1

also this one, i don't know the original title of this Hendrix track i'm playing a bit :

https://soundcloud.com/xplorer80/flashing

i'll do more clips later, with more perspective if i can.

[shakti]

I think you're definitely on the right track! Especially with the Uni-Vibe engaged it's sounding very close. Now with an always on West Coast fuzz, we could have it nailed!

[Xplorer]

thanks Thorleif

but i'm sorry i didn't show all the possibilitys of this amp, i basicaly played it attenuated on a single g12h30 75hz pre rola.
and everytime i record something for a clip , it sucks, i'm not warmed up and i do BS. Someone should record me when i'm just having fun, without telling me

settings :

vol 7
pres 9
basse 3
medium 9
trebles 9

the blue fuzz doesn't work as well as with the 45/100, for bog tones, but in some cases it could very well perform perfectly also. i need to test more.

i played with a wah and the fuzz, and i could definitely get the wilde parts of "gotta live together" , but what i've recorded wasn't fine enough to let you guys hear it.

the Voodoo vibe doesn't have the same preamp i think. i'd have to test with a clone someday. too bad, i sold recently my megavibe.

also, i'd like to test this mod in a proper build, with the right 560 v transformer.

but these elements being not faithfull to the originals, it shows that it gets there anyway, so good news !!

i remember all the talking about curly cables responsible of this tone ... lol ... maybe, very little, but it's all about the amp.

when i play it with some faithfull slider's reproductions of the fender 69 ( better than the current CS69 ) , it sounds abit like a telecaster ( maybe the strings ? they sound too new ) .
i prefer to play this amp with my gold lace sensors pickguard, it's very good in every conditions and amps. surprising, given the "bad reputation" they have , if i'm correct. they're perfectly good pickups, and quite silent. low output.
they're from a 91 jeff beck strat.

yes, experimenting the west coast fuzz with it would be really great for sure.

[Xplorer]

About this mod from Dave, i realise that it was more or less the same on Angus Young's 45/100 .

from this website : http://folk.ntnu.no/roef/JTM100.html


Pictures indicate that both Cream and the Jimi Hendrix Experience used Super 100 amps extensively in 1966-67. These amps (especially #3B) are commonly thought to have been used on Fresh Cream and Are You Experienced – something that seems probable if we judge by ear (however, Disraeli Gears might have been ##4 or 5A). The Who is reported to have used all the early 100 watters (##2-4) live on guitar, bass, and PA, and some of these amps may have been used by Free as well. Also, Malcolm Young of AC/DC is reported (by Marshall Law magazine) to prefer a 100W plexi with white back panel ( so a 45/100 .. ) (alongside a Superbass). According to Ritchie Flieger, the amp Malcolm used on Ballbreaker had 625V on the plates of the KT66s (suggesting it is a #3B or possibly a #4A). However, the choke is rumoured to have been replaced with a big resistor in order to reduce screens voltage and increase tube life. Finally, Eric Johnson is supposed to have used several recreations of this amp over the last years.

but i doubt it was the choke that was replaced by a big resistor ( or was it, really ? ), i'd rather think that it was like Dave said : more voltage on the plates ( here, 625 v on the plates of the kt66 ) and big résistors on the screens.

funny, i was about to to the west coast mod on my 45/100 at first, then i went for the SL as it should.
i could almost have turned my 45/100 into an angus Young amp beast ! lol
and say "hey, it doesn't sound Hendrixy ! "

[daveweyer]

You also might try doing shared cathode on V1, then send the bright channel signal through a .002 to V2. This was a pretty common Jimi mod, and seemed to help control the super-bright tone. Sometimes you can eliminate the .68 on V2 as well, depending on how bright the amp is. Also try coupling into the phase inverter with a .005.
Just a few little tweaks to do combinations with.

[Tek465b]

You also might try doing shared cathode on V1, then send the bright channel signal through a .002 to V2. This was a pretty common Jimi mod, and seemed to help control the super-bright tone. Sometimes you can eliminate the .68 on V2 as well, depending on how bright the amp is. Also try coupling into the phase inverter with a .005.
Just a few little tweaks to do combinations with.

this is exactly how my amp is setup right now, except for the .005 pi cap.
It really make the brightness perfect.

[Xplorer]

thank you.

it features already a shared / split switch, but i always play on shared cathode.

removing the 0,68 uf, i should try, even if it's already cool.
Now just double checking :

send the bright channel signal through a .002 to V2

is it the 500 pf bright channel cap near the 470k that you're talking about ? changing the value to 0,002 uf ?

Also try coupling into the phase inverter with a .005.

sorry for my ignorance, do you talk about the 0,022cap phase inverter near the big blue 50uf on the picture above ?
you recommend to put a 0,005uf in parallel with it ? what should that do ?

i think you recommended also to try some lower nfb résistors, like 27 k instead of 47k, am i correct ?

thanks !

PS : i'd have another question. i'm thinking of using my 2nd 45/100 power transformer into a new SL west coast build , so it'll deliver 560 volts or more. ( and i'll transform this 45/100 into a 67 black flag, with the proper PT and OT. i'll also get this current SL back to stock with EL34 )
Now what OT would you recommend again please, for this west coast Superlead ? a stock one ?

[Tek465b]

the .0022 is to replace the .022 V1 coupling cap on the bright channel, i think you already have a .0022 in that position since you use a superlead and not a jtm45/100.

the .005 is to replace(not parrallel) the .022 at v3 pin 2 pi input from the treble pot, that will restore the brightness after you remove the stupid .68 on v2 cathode if you find it too dark..
i think thats a really good combination.. you will probably like that alot For the sake of BOG you should really at least give it a try.
Our hearing are more sensitive to high frequency(bright) when its really loud. i think you said your using an attenuator and playing at very low level, maby thats why you find it a bit dark. or its your guitar/speaker.
I like alot of NFB, low NFB resistor value.

[Xplorer]

the .0022 is to replace the .022 V1 coupling cap on the bright channel, i think you already have a .0022 in that position since you use a superlead and not a jtm45/100.

the .005 is to replace(not parrallel) the .022 at v3 pin 2 pi input from the treble pot, that will restore the brightness after you remove the stupid .68 on v2 cathode if you find it too dark..
i think thats a really good combination.. you will probably like that alot For the sake of BOG you should really at least give it a try.
Our hearing are more sensitive to high frequency(bright) when its really loud. i think you said your using an attenuator and playing at very low level, maby thats why you find it a bit dark. or its your guitar/speaker.
I like alot of NFB, low NFB resistor value.

very cool, thanks tek ! will disconnect one leg of the 0,68 right now, and i'll work on the 0,005 this week end

what's the resistor value that you've got on the NFB ? lowering the value gives more NFB ?
i supposed i imagined it wrong, having this reference in my head where brian may explains how on the vox ac30 they removed all the negative feedback , hence why i imagined they just removed the resistor at some point

[Xplorer]

i just removed this 0.68 and with some clips i can test with and without. indeed, this cap brings some highs, but i don't know what to decide, with or without .. i still like it with the cap in, but i'd need some more perspective, with time.
i'll see tomorrow, i can't very loud it's 3 am here, and i don't know if the neighbours are here or not
of course there's one simple way to discover this .....

[Roe]

About this mod from Dave, i realise that it was more or less the same on Angus Young's 45/100 .

from this website : http://folk.ntnu.no/roef/JTM100.html

...

yes, that's one of Malcolm's amps.

[Xplorer]

yes you're right, i don't know how i could switch Malcolm with Angus ..

[Xplorer]

so just a little feedback about the 0,005 uf between the treble pot and V3. i tried it with an RS silver mica 5000 pf but it made the break up a little bit strange, hard to describe. i think i'll remove this one and get back to 0,022 uf.
but it was Worth trying, thanks.

sorry to ask this again Dave, but for a west coast SL new build, which output transformer would you recommend please ?
i remember that for the power transformer it was fine with a dynaco, although i'll probably use a 45/100 PT there.

thanks