The 6550 Experience

[JimiJames]

Sweet !

Just finished my amp !! a few tweaks , bias, voltage charts and it'll be nice i suppose.
i just played it a bit, with the bias pot down to zero. it' looks ok , cleans , saturation and 45/100 tone are there and i'm relieved that the preamp used worked this time.
i previously used this preamp in my first 45/100 build and there was a bug impossible to find. i rechecked every components after unsoldering some legs, changed a few résistors and caps. there was nothing very out of spec so i'm surprised but this time it seems to be alright. cool

i'm going to use this one for the west coast Dave Weyer mod.

http://imgur.com/a/MaMkT

[shakti]

Very nice build, Adrien!

One problem you'll run into with a West Coast mod is that the 69 SLs had two stages of filtering in the preamp, as well as more dropping resistors. So you will end up with higher voltages throughout the preamp. I still think your 69 build is a better candidate for modding, especially as you seem to not like it that much in its current state?

[Xplorer]

Thank you !

Dave, Thorleif, what do you think ?
higher voltage is still ok ?
what does it imply ?
Dave told me it'd be ok, when i sent him this modified layout of the 45/100 ( components written in red ), according to what he said.

http://i.imgur.com/swEIwRN.jpg

the irony is that i purshased a dynaco OT , maybe for nothing now .. and Dave sent me some 100uf 400 caps to put in the 45/100.

your remark made me think that this two stage filtering and more dropping resistors may do a difference regarding the amp's DNA , compared to the 45/100 DNA. And i remember Dan's work ( billy batz ) , with lower preamp filtering. it gave a very pronouced bog DNA. it may be a point to look at.

So at least one interesting thing, if it's still something possible to do, would be to still make the mod into the 45/100 , and compare it to the same mod, but into my SL ( just the way you did it, without changing the transformers, without changing the 50/50 caps, and just with 6550 , 2k2 and the values you tweaked ) .... and i could compare both to your results.

What do you think ?

[shakti]

I think you would be in the right track with that latest idea.

Don't take this the wrong way, Adrien, but I don't really understand why you insist on doing these mods with a 45/100 as the starting point? I know that you prefer it to a stock SL, and that you feel it has more of the "BOG DNA", and I'm not going to argue against that. It's just that none of us know what it is about the 45/100 that strikes you as more BOG than a SL. Is it the higher voltage? Lower filtering? The impedance of the power supply? The higher primary impedance of the OT? Or perhaps just KT66 vs EL34 (or 6550 for that matter)? The bass circuit preamp? And in that case - is it the size of the coupling caps? The negative feedback amount? The size of the mixer resistors (that matters too!)? Shared or split cathode? V2 bypass cap or none? Volume 1 bright cap or not?

Out of all the things that we know or that we think we know (due to circumstantial evidence) about what was actually used for the BOG recordings, a 45/100 is not one of them. There are no photos after late '68 that shows Hendrix using one (actually I can't even remember if there are any as late as that...a black flag was used in October '68, but a 45/100 I'm not sure).

Which is why I think the best starting point for experimentation is with the gear that is most likely to have been used; a '69 SL, but possibly with some mods. You can try as many or as few of those mods as you wish. I am starting with the simplest, most effective and most likely ones. Looking at the one known photo of a purported Hendrix/West Coast amp, we can see it has
1) a shared cathode (was it there when Hendrix played it?)
2) V2 bypass cap appears to have been changed, but we don't know when
3) PT is a Dagnall T2562, but wiring is sloppy...has it been put back after the fact?
4) OT is original, as are the screen grid resistors
5) Bias circuit has been messed with...possibly to install 6550s at some point?

Again, don't take this the wrong way. I am curious to hear what you find. And I see you've changed your modded 45/100 layout to approximate *some* of the '69 SL features (dual filtering in the preamp, for instance). But to me it seems like you latch onto *some* of the things that Dave mentions, and not all, and it seems arbitrary to me which parts you leave out and which you include. You may well end up with a tone monster with this idea, but it's equally or more likely that it takes you further away from your tonal goal IMHO. Unless there is some info from Dave that I missed...such as the "big mod" amp being a 45/100 from the start...but then again, where are the photos showing Hendrix using one?

[Xplorer]

Simply because i intended to have this 45/100 made for mods and experiments. And also because it features the big drake transformer and i don't want to pull it off àd place it inside the superlead, just too lazy. So it'd be close to a superlead, featuring the sl OT, and the drak PT + 6550 àd 2k2.
I figured that the rest would be tweakable easily to make it SL like.

I can build a second power cap board too, so i can swap it.

And, you convinced me to also do the west coast mod on my SL.
Easier, no much more work.
Also, it could be interesting to test this franken west coast 45/100 and compare with my west coast SL..

Regarding the amp pictures, there's no picture of that special night at the fillmore, + the videos can't show enough, and this night sounded different...
So without enough evidences, we can't conclude anything.

In the end, since i have another SL chassis + nos components to complete a bit, i could perhaps use the dynaco on this one ( but later ) and make it west coast. Then getting the el34 SL back together, and end up with a 45/100, a tweaked or black flag JTM 100, a west coast SL,

Maybe it was a superlead but anyway, as you noticed, i rather follow what works.
The west coast SL could very possibly work for me too, and make more sense to you. we'll see

Since i have another SL chassi, i may use the dynaco + the nos components i have to make it a west coast, then put back to stock my SL 69, and end up with :
A stock 45/100, a tweaked franken JTM 100 or west coast modded or Black flag, a dynaco west coast superlad, and a stock el34 SL ( i still like it anyway . Maybe it'll be modded to VH specs for some fun ).

[shakti]

You know you need them all, Adrien!

In my 100w arsenal, I have (all clones):
- JTM45/100 (stock with KT66s)
- JTM100 black flag (the early dual rectifier version, with EL34s)
- '68 12-series (EVH style if you will, but slightly increased screens filtering and lower plate voltage around 460, the classic EL34 Marshall crunch amp)
- '69 SL with some West Coast mods (6550s etc)

They all do something different!

[Xplorer]

i see in your list that you have a lot more amps ! very cool !
two heards on the top on each others, multiplied by one or two, on the top of various cabs, it's fantastic.

later in the years to come, clones of a sound city / cp103 , an AC30 1965, a brian may deacy amp , and restoring a 60' super reverb french replica - Shades" amp. and maybe resoring a JMP from the 70' , green board.
that should cover all my needs !!

[daveweyer]

Well what's the real difference between a 45/100 and an SL, just a few refinements in the power supply for the preamp and nearly identical circuits otherwise, wouldn't you say? That is, excepting the rectifier system which was the Fender style "full wave center tap" system. As far as I can tell, that would be the main "DNA" difference in the two products, because the SL used a full wave bridge system. That system was used to increase reliability in the output tubes by lowering the plate voltage and of course the screen voltage, which also meant that in order to get 100 watts of power, the P-P primary impedance of the OT had to be lowered quite a bit. The bridge system also lowered the cost of the transformers, since there were less turns of wire (it had to be a larger gauge, but there was still a savings in cost and weight). Marshall had discovered that in order to use an output tube in pure pentode mode, that the voltage had to be lowered, and also realized that for the higher voltage units they would have to use "ultra linear" mode, whereby the screens are connected to a tap on the output transformer windings so that their voltage lowers along with the plate during the high current half of the cycle; you can see this system in the Majors, the 1966 1967 1968 type models.
It's the only safe way to run the screens at high plate voltages.
Anyway, that power supply input system is the real difference between the models; there isn't any reason why a 45/100 couldn't be turned into an SL, but it will probably bring the 45/100 DNA with it.
And the other way around would most likely be the case too. Jimi's SL models most likely kept the bridge input system except for a couple which I changed to full wave CT, and they would look just like SL amps too. We know he carried some older models around too because a few of them are still floating around with mods and the regular stenciling.
For reliability, the 2K2 screen resistors are essential on the high voltage units, unless you use the screen taps on the OT, which Adrien can do since the A431 has them specifically for that purpose. The mod would have the DNA of the "Majors".
One can also obtain, as I did, some transformers for the SL system which will give over 500 plate volts; I hand picked the Dagnalls for regulation on the HV, some of them providing well over 500 volts.
I would say for the SL DNA, one would be best served by using the full wave bridge input system, irrespective of the plate voltage--the A431 will work great in that application too, especially with higher plate voltage.

[daveweyer]

Adrien those pics of the amp build make my back ache! Maybe after thousands of them I am just happy to see how much effort you all put into them yourselves. That 45/100 is so neat it looks like a Hiwatt.

And the higher voltage in the preamp just gives you more headroom before distortion/compression, the disadvantage in the early Marshalls was more hum and noise in the preamp because of less filtering. But you can have it both ways by simply adding another stage of filtering like the SL, only not dropping the voltage as low, i.e. small resistor between the stages.
Larger caps like I sent you also help.
Do you wonder why Marshall went to larger caps in the SL? And even larger in the Majors? Another DNA difference.

[peter25]

Hey Dave,
I'd like to ask you one more question about the OT. Xplorer got a Dynaco. is this the OT that you used to put in when you modded a Marshall? And how do these compare to the Drakes. The 1202-119 (1,9k primary) and the 1202-132 (2,2k primary)?

[Xplorer]

Thanks a lot Dave for the explanations and for the compliments, i appreciate, especially coming from you who saw countless Marshalls ! and some of the most mythical ones.

i think i understand what you mean about the input power system, full wave center, and full wave bridged. i mean, i don't see how it looks like electronicaly but you point a clear difference.
But i warn you, i may make you repeat yourself when it'll be time to mod it ! ha ha. picture yourself a monkey see monkey do guy, who understands just a bit, just enough to build it and do little mods.

i think it'd be interesting to test the mod in both amps, 45/100 and superlead. that's what i'll do.

For now, Thorlaif, guys, i'm amazed, this amp sounds really great, and i should definitely show you an A/B test between without fuzz volume and without univibe, and with both .

with the input bias rolled down a bit just enough to let the wah breath , this fuzz lands perfectly for the bog tone, since it pushes the signal just enough ( still clean sounding ) , and the input and output caps are of the right value to my ears.
amazing how it lands perfectly. without it, the sound is the amp's DNA alone , and it's a bit bright and thin. the fuzz removes some of this brightness and adds thickness as well as giving some more range for the cleans, making you reach the right break up caracteristic to bog , if you pick just a bit harder.

Now , the fuzz alone doesn't make the whole work. you need the univibe, and the Voodoo vibe has quite a high output, just perfect.
Same on the other way : the univibe alone can't do it.
now both ... with both their volume at max ( and intensity to zero on the univibe + fuzz gain to zero ) , plugged into this amp DNA, Here you are .... marvellous, EUREKA. i urge you to try.

i'll do a test sometime, with some Ribbon mics, maybe in a blumlein stereo arrangement.
A : Strat > amp
B : strat > univibe > amp
C : strat > fuzz volume > univibe > amp.

i'll do this test with : the 45/100 , the west coast 45/10 , and the superlead west coast.

the only thing i need is a mod on the fuzz, switchable, to push it even more, into the machine gun Wilder stuffs, when he "switchs it on" ( already on for the cleans i think, as you know ) .

Dave, i have caps and diodes, and perforated paxolin left. i could build a custom input power board , to put into the 45/100. will it be all , along with the layout i did show you, made according to what you said ?

i don't want to pollute this thread but if i can simulate the whole thing to do visualy on a layout, before i do it on the amp, i'd feel better, with less doubts. always affraid to miss some important things to do.

i'd probably do the same on a superlead layout, with your directives and Thorleif's values.

[daveweyer]

Peter,
The Dynaco was handy to get back in the day at West Coast Organ and Amp, so I sometimes used those for output if I had a higher voltage supply. Their primary impedance is around 4K, which means if you use them on a lower voltage amp you have to use the 16 ohm tap for an 8 ohm cab to get maximum power from the tubes.
And depending on the DNA you want, you can also use the OT screen taps on the screens and get a bit of that Marshal Major sound, since it had the same hookup for the screens.
Your tubes will also last a lot longer that way if you play loud a lot. Other than that, it was a very good sounding transformer, better than the Dagnalls.

Now Adrien has this theory that maybe the BOG tones are coming from a 45/100; I see all the question marks from the members here because it really doesn't make sense logically, especially considering BOG was later stuff, and Jimi had a dozen SLs to use---why would he use and old 45/100 for any of it, after all, the 45/100s blew up all the time.

Probably no definitive answer. But I can tell you that I basically made a couple of his SLs into 45/100s with the mods, even the full wave center tap rectifier system was used. But those amps also had the extra preamp filtering of the SL, and the choke. So there is a slim chance that the 45/100 DNA got into BOG without any visual evidence being obvious in the performances.

[Xplorer]

i can't tell if it was a 45/100 or not, and as you guys said, there's no evidence, only what i'm hearing.

Probably no definitive answer. But I can tell you that I basically made a couple of his SLs into 45/100s with the mods, even the full wave center tap rectifier system was used. But those amps also had the extra preamp filtering of the SL, and the choke. So there is a slim chance that the 45/100 DNA got into BOG without any visual evidence being obvious in the performances

this could be it, and before you started to discuss with us on the forum, we wouldn't dare to imagine that some SL were turned a bit into some 45/100, it would have been pure fantasy, free speculation and utopia. Do you remember guys ?
Now, what you say follows the DNA we're hearing so this is probably what makes the most sense, from the informations we have, on some historical, technical and ear point of view.

this would make the 45/100 a bog old brother , which still works perfectly for this quest.

i'llm work on some layouts to follow, according to what you said along the threads. later. If you can have a look and bring some corrections if needed, it's very cool.
a bit of simulation before diving into the build blindly is more safe for me.

Oh, Guys ! Happy new year !!!!!!!!!!!!!!!!!
May the tone be with you and have some wonderful times this year !!

[Billy Batz]

Id love for Adrien to play my setups here. Im constantly going from 68 era lead to bass to 45/100. I agree they all sound 90% the same and we make a huge deal about the 10%. Going to a fender or vox puts it into perspective. While I also feel like I cant get BoG with a pure Lead setup I understand that I cant say for sure thats not right. I had a friends over for new years and cut the tip of my left finger opening a waxed beer bottle. I could only listen to a friend of mine play as I switched settigns and amps. When your not playing the rig personally the impression of how different it is drops to less then 5% when you cant 'feel' the dynamics.

Its funny about Dave saying he made a few of his SLs into 45/100s. About 10 years ago I was flammed out of plexi palace for suggesting this. There was a rumor Im sure you guys have heard that Jimi often said the newer amps just didnt have the mojo of the older ones or something to that extent and I offered that it wouldnt be hard to imagine him sayign to a tech "make it soud like this older one" and they would do that by changing to bass values (which at the time I was working on the theory that he used a Bass amp for that same reason). Apparently that idea was too hard for people to deal with. I do understand it. I didnt have an written sources for these ideas just parroting and I understand why people want to flame down unsubstatiated claims but there shoudl be room for pure thought experiments on this bs.

The reason I would see Jimi using a 45/100 that late is simply because it was an album recording not just a show. I admit I dont think it was an actual 45/100 and the biggest question would be would he still have had one or have one available for that show? the idea of a SL modded towards bass is running away with me right now pretty much because thats the only way I can get close with the amps I have.

[Xplorer]

Please Dan, yes, go for it !
your soundclick page doesn't work anymore, and it was very interesting to hear your old clips, and maybe some new ones too.

these 10 % make a big difference to me, but it's in the ball park anyway.
As you said, this record was made for an album + the special night sounds more like a 45/100 ( + there's no much pictures about this one and the movie isn't so useable as an evidence ) and different from the other nights and the baggy's rehearsals, which sound more like the west coast mod. so, since it was in New York, where he probably had his old amps in the new electric ladyland studios .... why not making a change from the first night to the second one, and pick the old 45/100 with an unusual use of it ( later silicon modded fuzz + univibe ) , compared to the Experience days ?

That's pure fantasy which could work regarding this context and what we hear. Now he obviously also had some west coast amps for that night too.

so your speculations got you to the point that you were fired from the plexi palace forum ? wow ! what a good example of how limited is the "go by evidences and proofs" way, which can't work much since anything can hide behind the cabs and head cabs ...

Why are we always coming to the Bog tone ? it's interesting. maybe because it was the most elusive tone Jimi got, contradictory, paradoxal, landing like an UFO among all the tones he had from the various eras. Also difficult to get ( not anymore i think ) , while the others are not so tough to reach.

i think that Dave brought the main missing puzzle pièces and that's fantastic.
One piece , very important : the fuzz . it'd be great to focus more than we do about it, and maybe to do a fuzz thread, with experiments . i'm sure that the first experiments we did, from Dave's infos, could go much further and give even more perspective on this passionate subject.