The 6550 Experience

[Tek465b]

it may be a bit different but the preamp of the univibe is still working and affecting the signal.
the bias control on the univibe may be similar to the dark bulb effect, but anyway, if you set the intensity to zero, wether the bulb is producing light or not, the bulb doesn't affect the process.

Yes thats the point, to have the signal go through the preamp and all the univibe circuit.
About the other statement i have to disagree. or we missunderstood eachother.
Here is my technical understanding:
With the bulb a dim orange(or any single bits of light) i can hear a difference and i can see it on the x-scope also(2 small notch, not moving but changing the EQ a little, with bulb off they disappear and you get a different more natural effect kinda like more headroom more BOG).
My ldr are over 20Mohm(edit 200Mohm) on the dark cycle(my meter top at 20Mohm). just a bit of light and the resistance drop alot and very quickly. I could measure the speed with the scope but i did not bother. can't remember wich one i got but they are glass sealed from smallbear from a few years ago.

edit:
could not get into smallbear my account to get the parts number but i think they are these ones:
http://smallbear-electronics.mybigcomme ... dark-to-5/
(these could work too: http://smallbear-electronics.mybigcomme ... x-hi-dark/)
200Mohm dark resistance.. just a bit of moonlight and it drop alot trust me loll .
With these when the bulb is completly off, it make a difference. The out-of-phase signal are too weak(very high impedance 200+Mohm) and the low impedance in-phase signal dominate and the notch disappear completly(or get well above the frequency spectrum)..There you get the univibe preamp sound . it has more dynamic and appear louder(more headroom was the good word).

[Xplorer]

these cells look like i should test them !

i'll maybe put some device like for the transistors, to test various batchs .. without soldering them.

thanks

[Tek465b]

these cells look like i should test them !

i'll maybe put some device like for the transistors, to test various batchs .. without soldering them.

thanks

I find that switching transistor in the vibe has very little if any effect(at least not any that i could perceive).
What i like is a wide range for the lamp driver emitter POT/trimmer(500ohm/1k). and 68 ohm instead of the 150 ohm for the resistor in serie with that pot.
Thats another change from the original vs neovibe i forgot, original use 150ohm in there. neo use 68 Ohm.
Give a wider range of lamp driver gain control. that with the bias offset mod and you can get almost any bulb in the ballpark.
I have a little secret, i tune my lamp driver bias offset and gain using the scope
I found that if we turn the lamp too bright(probably near or past full intensity) we get some kind of return/diminishing effect(its hard to explain, but the eq change alot and the vibe effect get ugly).
On the scope it look like the notch get all messed up. I think the LDR or the circuit reach a maximum light intensity at some point and the notch get distorted.

[shakti]

Sorry to just be a boring repetitive geezer, but I have to say it again: THIS IS IT! Dave's mods really, really work.

Now, with the new guitar I am using, it is easier to fully appreciate how the amp sounds with 6550s. It's just a much warmer and more responsive sounding instrument, and at that it's closer in sound to Jimi's Black Beauty. And now that I got the voltage bumped to around 540V, the amp is sounding glorious; detailed, clear, warm, girthy and responsive, with a percussive edge and good clean-up. Xplorer, you really, really must try this spec with 6550s!

I will get a clip together eventually, but I still am not sure I can make it justice with my crappy recording equipment.

Lastly, while I am still open to the idea of an "always on" fuzz, I am no longer sure if it's necessary. The amp itself, with the following settings, is mighty close:
Presence 8
Bass 0
Mids 6
Treble 5
Volume one 7-8

Uni-Vibe preamp also sounds more "right" with my current setup than before. No bright cap necessary!

Next I need to concentrate on the fuzz. A West Coast fuzz is on the list for sure, once Dave can find some time. But apart from that, what would you guys recommend? If you forget the "always on" idea for a minute, which fuzz out there do you think has the right sound?

[daveweyer]

Jeez I'm glad somebody got something done! Way to go Shakti!
Now if that guy would just get off his ass and get the West Coast 3 transistor fuzz going...............

[Tazin]

Next I need to concentrate on the fuzz. A West Coast fuzz is on the list for sure, once Dave can find some time. But apart from that, what would you guys recommend? If you forget the "always on" idea for a minute, which fuzz out there do you think has the right sound?

I was under the impression that the Dunlop JH-F1 was a good platform to start with.....

[shakti]

Yes, it's on my shortlist. Anyone compared it to an Analog Man BC108 Sunface? The smaller size is a little tempting.

[shakti]

Just to keep the momentum up here, though completely on the side of the topic:

With my particular amp, which is a very detailed replica of a particular batch of early '69 amps, I get a pretty loud pop when switching it to standby. My B+ side is wired exactly like the originals, with a bridge rectifier mounted on the inside edge of the chassis. AFAIK the originals didn't have any capacitors to bleed off and discharge any standby switch pops. Any recommendations on how to get rid of this pop? None of my other Marshall builds do this.
I have 5.6k grid stoppers on each output tube, but this isn't a squeel which you can often hear on amps without grid stoppers, rather a loud thud/pop.

[Tek465b]

Use a capacitor across the standby switch contact, am not sure but something like 0.0047uF(or 0.047) should work(make sure the voltage rating is correct).

[Xplorer]

Sorry to just be a boring repetitive geezer, but I have to say it again: THIS IS IT! Dave's mods really, really work.

Now, with the new guitar I am using, it is easier to fully appreciate how the amp sounds with 6550s. It's just a much warmer and more responsive sounding instrument, and at that it's closer in sound to Jimi's Black Beauty. And now that I got the voltage bumped to around 540V, the amp is sounding glorious; detailed, clear, warm, girthy and responsive, with a percussive edge and good clean-up. Xplorer, you really, really must try this spec with 6550s!

I will get a clip together eventually, but I still am not sure I can make it justice with my crappy recording equipment.

Lastly, while I am still open to the idea of an "always on" fuzz, I am no longer sure if it's necessary. The amp itself, with the following settings, is mighty close:
Presence 8
Bass 0
Mids 6
Treble 5
Volume one 7-8

Uni-Vibe preamp also sounds more "right" with my current setup than before. No bright cap necessary!

Next I need to concentrate on the fuzz. A West Coast fuzz is on the list for sure, once Dave can find some time. But apart from that, what would you guys recommend? If you forget the "always on" idea for a minute, which fuzz out there do you think has the right sound?

.... And i really , really want to do this ! of course !
as soon as i can buy some 6550. which did you try ? modern tung sol ?

yes, you should post some clips, and close up pictures of what you did, and how your amp is set ! please

Next I need to concentrate on the fuzz. A West Coast fuzz is on the list for sure, once Dave can find some time. But apart from that, what would you guys recommend? If you forget the "always on" idea for a minute, which fuzz out there do you think has the right sound?

difficult to say, because like univibes, i think that fuzz dépends on the amp used, and here it's a particular modded setup so it's tough to say ...

i'd think low hfe silicons, and a particular attention to the input and output caps, to fit the amp you're using.
also a nice tuning of the résistors values, to have a smooth lively sustain.
+ a special care to the signal presence, thanks to an input bias.
always ON or not, the always ON test should be a good start too, to see how it matchs the ball park tone. then you can figure a bit how it goes if you increase the settings for more gain.
i think that the always ON theory is about a subtle layer that has quite a cool effect on the univibe response, and on the amp response.
i'll of course start with the Dunlop blue as a start, when i'll get the amp together.

[neikeel]

Ok so I am going to go with this. I'll use the Winged C 6550s I have in the 69 amp and see what gives. I will see if my Mk2 Bender gets any way there, but I suspect not (can't find my Octafuzz!!)

[shakti]

Do it Neil! Will be interested to hear your comments. The few other things I also did was to mismatch (8 ohm into 16 ohm load), use a 12AT7 in V3 (subtle, but maybe a bigger difference with higher voltage?) and a shared V1 cathode.
Be sure to try both standard voltage and higher voltage and see what you find...

[daveweyer]

It's probably been a little difficult to pick up the idea of using 6550s in the super leads and 45/100s just based on my telling of the story of Jimi's amps so many years ago. I always thought to myself that if someone really did those mods they could find out for sure if that was what they heard in Jimi's tone on so many revered cuts. So it pleases me to hear that there is now some empirical evidence being gathered which tends to support my revelations of how Jimi got his tone. As this goes on it should become even clearer, especially if those tones are shared on the forum to a so called peer review group of other tone seekers.
I sometimes wonder if I should have come forward years and years ago to tell all these stories about Jimi and his equipment, but there was something about those folks who were making their livelihoods out of piggybacking on a dead man which really bugged me, so I resisted the whole idea, thinking that if the time and circumstances were right I might talk about it. When Art Thompson from Guitar Player magazine called me for that famous interview, I had a platform to reveal just a tiny bit of information I thought might be helpful, but was disappointed to find out that they got some of the facts wrong, and truncated quite a bit of the story to save time and space.
Even then though it appeared that the information was revealed too late; many Hendrix freaks in the field outright rejected what I offered as wrong or impossible, the story had already been put together over thousands of articles and interviews, and never really included those things I talked about.

So without folks on the forum actually reproducing those amp changes and effects mods, there was never likely going to be a generalized acceptance of those ideas in the world of Jimi aficionados.
Thanks to the rather generous contributions of those on the forum who were willing to scrounge information to back up my claims, a sort of sketchy story of the West Coast mods has emerged. The stickers on the backs of the amps seemed to help quite a bit, and the photographs of Jimi's amps with what appear to be 6550s went some ways further
to substantiate the claims. I know we've had a serious discussion about whether they are 6550s or not, but it is still evidence, even if not entirely conclusive.

So we had believers right away, some semi-believers, some mostly doubters, some complete doubters, and some outright hostile naysayers.
What encourages me is that skeptical, rational folks are trying the mods and finding out they work. I can't think of a better testimony to all those mods I did on Jimi's Marshalls than that. If it weren't so expensive it would be easy enough to build the whole raster of mods and let everyone try them out for themselves.
Maybe it's too late to matter any more since folks have been working over this stuff for 45 years, but one way or another the West Coast chapter will become part of the record, even if the only ones keeping it are the members of the forum and guests who read about it, and the ones who replicated the designs and found out for themselves.
I really don't get anything out of the deal myself, no reward, no contract, no movie. Just passing on what actually occurred. Glad to hear when things work out as well as they have for Shakti. Kind of makes it worth doing.

[JimiJames]

.
A real big Thanks from all of us here, Mr. Dave.

(My only experience with 6550's was with Lee Jackson's Metaltronix M1000 series.
It has a split design using EL34's or 6550's that you can switch from.


With this particular circuit, I ran EL34's for rehearsals until I finally played my first gig with it. Leads were okay, but lots of other artifacts were lost in the mix. The very next show I thought I'd give the 6550's a spin. Although not as hot at the same volumes; punch, articulation, separation were back. Everyone has a good performance when you can hear yourself and are able to execute what your feeling at that time...

[Xplorer]

Guys, just wondering if the 6550 experience would be a good experience with .....

some new tung sol 6550,
or maybe some TAD 6550 ? i have no idea of what's serious with modern tubes like these, each, over the old RCA 6550 ..

http://www.tubeampdoctor.com/en/shop_TA ... tched_2822

reading this .... wow , it looks like the real deal ! ha ha, but .......... i honestly can't judge tubes, i don't have the knowledge, it's so complex.
.... it looks like there are hundreds of workers, building high end tubes with the NASA specs here , lol. they live with tubes, marry tubes, eat tubes, so they can tell what a good tube is

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