The 6550 Experience

[daveweyer]

This thread goes from tubes to fuzz and then back again, but I thought I'd update with a note that I have not gotten to the circuit boards that Xplorer sent yet. It's on my list to do.
I wonder where Bill is on his original type 6550 experience in a modded Marshall.
The latest I am hearing from Vox engineer Bob Hovland is that the KT150s are a very good audio tube with a lot of expressiveness.
Did anyone get their own 6550s and put them to work in their own Marshall?

[Xplorer]

no, not yet. i can't afford 6550 tubes for now, but the rest of the components, including those 12at7 you sent to me are ready, along with some 2k2 10 watts. i might not need to change the 50/50 uf caps,on the superlead, right ?

[bill bokey]

Bill Bokey, haven't seen you around lately. Are you just waiting to spring a killer amp sound on all of us based on a newly constructed 6550 modded SL?

This thread goes from tubes to fuzz and then back again, but I thought I'd update with a note that I have not gotten to the circuit boards that Xplorer sent yet. It's on my list to do.
I wonder where Bill is on his original type 6550 experience in a modded Marshall.
The latest I am hearing from Vox engineer Bob Hovland is that the KT150s are a very good audio tube with a lot of expressiveness.
Did anyone get their own 6550s and put them to work in their own Marshall?

Hi all !

I've been really busy lately and have not yet found the time to work on my 6550 SL.
I'll keep you posted asap

[daveweyer]

Good to hear from you Bill. It's a busy time. I haven't got the fuzz boxes all going yet either.
I'm also looking for old photos of West Coast Organ and Amp, or at least pics of me at a West Coast bench.
Looking for old tape bits as well to share on the forum.
Supposed to be some time here one of these days.

[Xplorer]

oh yes, pictures of that time would be very nice ! and tapes ...

i'm trying to figure a place with plenty marshalls, cabs, guitars , prototypes ... a big place

[Xplorer]

guess what guys ....
now that i'm using my superlead again , but with a different amp setting ( Dave's , with much presence ) , and the blue fuzz volume up and gain down Jimi's way ... it sounds so much like bog to me through my G12H30 75hz.

so i like both the 45/100 and superlead for BOG !
i admit.
Now i can imagine what it would be to play three heads : one stock 69 SL el34 , one 45/100 and one 6550 SL WC !!

[Froumy]

Clips, please! Did you get the 6550's?

[shakti]

And I am finally experimenting with my setup again! I hinted at a guitar change in a previous post, and now that I've done the deal I can divulge a little more.

I had a left hand CS 69 black/maple Strat for late period Hendrix tones (played right hand). Unfortunately, it was a pretty awful guitar...an impulse buy on Ebay (when was the last time you saw a left hand CS black/maple 69, right?). On paper, a very cool idea, but the guitar had the personality and charm of a Dick Cheney cardboard cutout figure. Thin, plinky, harsh, no sustain and warmth...I am exaggerating a bit, but it was a thoroughly uninspiring guitar.

It was only after I saw those recent clips of Steve Webb that I decided to get over my silly anti-70s Fender stance. As you all know, 70s Strats have a spotty reputation. Mostly with good reason - for the most part they are nowhere close to a good 60s one, but nevertheless a good example leaves most CS product in the dust for tone alone. As for attention to detail, CS are generally good, but for tone they are very hit and miss, and mostly miss IMHO...and even the good ones fail to match a good vintage example, be it a 60s or 70s one.

Anyway, after hearing the great tones Steve Webb got out of his '75, I realized there was a local shop which had a similar '75 black/maple one. RIght hand, of course, but that only makes it more usable for other things besides Hendrix lookalike competitions (which I am bound to fail miserably at in any case). I am still getting to know it and tweaking the setup (using 10-38s tuned down makes it hard to get a little relief from the truss rod), and I put in my standard recipe of Callaham bridge with Raw Vintage saddles and springs in place of the awful die-cast stock tremolo. But it is, without a doubt, a much, much better instrument; warmer, more articulate, more responsive, more sustain. It has obviously been played a lot, which is always a good sign. I like it, and it definitely takes my tone one step closer.

Now, on to the amp. To recap, I am using a stock 69SL build, but with a few tweaks:
- shared V1 cathode
- 6550s biased cold ("class B")
- 12AT7 in V3
- mismatching OT and cab so primary impedance is more like 3.4k
- 47k negative feedback at speaker jack, so essentially 47k@8 ohm due to the mismatch

I just did two things:
1) took out the volume bright cap (I had a a 5k ceramic cap). I know I said I really liked it a while back, but as I've done so many times with these bright caps, I almost always end up taking them out again. I removed it from my 68 build as well. It may work well in a larger room and at loud volumes, and when daisy-chaining or running a very long chain in front pf the amp. But for most settings, it is too large and makes the amp kind of harsh and hard to find the sweetspot. I got too much gain and breakup at any setting. So for now I am leaving it out, and I will try again with a smaller value as the final tweak once I get everyhting else dialed in, to choose the most practical value for my own setup (depending on the signal/effect chain, room, etc). I feel I get close to BOG tones this way, as I had too much breakup that was a little harsh, and it was just hard to get those in-between tones.

2) More importantly, I finally tried to increase the plate voltage. Remember that Dave said this was an important thing. Well, I think he was right. What I was missing with my setup was some of that big, cleanish, bold tone that still has a fair amount of gain. I had around 500V on the plates. By using the 230V primary and with wall voltage probably around 240+ (didn't measure), I now got closer to 550V on the plates. I like it a lot; it's cleaner and "bigger" sounding as one would expect, and sounds closer to BOG for sure. Threw a Uni-Vibe preamp and a non true bypass wah in front, and it was definitely closer than before. Between this mod and the new guitar, it has breathed new life into my BOG tone chase!
I didn't adjust the screens and still have only 1k 5W individual screen grid resistors. If I plan to use it like this I will up the screen resistors. Dave suggested 2k2. I realized that the way I have the screens wired I can quite easily insert a "common" 470R 10W resistor similar to the setup in Hiwatt amps. This should yield about 2.8k for each screen grid, so a little higher. Or I will change each individual resistor. Eager to hear what this does to the sound as well.

Now I am not all the way there yet, more experiments are needed, but it's getting closer still. A smaller bright cap and/or "fuzz buffer" may well be the last ingredients to get all those littel nuances and the right balance between warmth, snap, articulation and gain/sustain.

[Xplorer]

Now I am not all the way there yet, more experiments are needed, but it's getting closer still. A smaller bright cap and/or "fuzz buffer" may well be the last ingredients to get all those littel nuances and the right balance between warmth, snap, articulation and gain/sustain.

yeah, do that !
our setups never were that close maybe , than now !

mine is on shared cathode position on the switch, always. buffer fuzz volume all the way up, and playing a bit with the strat volume from 10 to a bit lower, and the univibe preamp - intensity down to zero - i was surprised this afternoon how it sounded so BOG.

one thing that counts a lot to me, on a strat, is to have the truss rod almost unscrewed ... on my favourite strat the truss rod has no effect. i prefer the necks which have their truss rod tunable from the body side rather than from the headstock, i don't know, i feel that they sound better : same on jimi's black strat. maybe because this big piece of metal doesn't go just Under the nut, and beyond it ?
and well, using some 09 - 38 , very light, pure nickel from fender ( perfection ) and a small curvature from the neck due to the tension of the strings ... it makes it so playable, and believe it or not : the vibrating truss rod ( on certain frequencys ) , brings some sustain and musicality. much better than a CS strat ! lol
strings stil very close to the fretts, but no buzz on any fretts and the right tune anywhere on the neck.

one step closer to your current setup : 6550 ! i wish i could try some but i can't buy anything for now. i have the 12at7 from Dave though.

did you also switch to some 100 uf caps like Dave said ?

about the 5k bright cap : i tried once, but it's maybe better for van halen stuffs than Hendrix, i removed it after an hour.
and i'll remove the 18k on the third preamp tube of my second 45/100. it's kinda nice but for jimi, you don't want that. i'll remove it too at some point.

can't wait to restore my fender super reverb copy , and dig some Hendrix sounds from fender amps , nice cleans etc ..

[chrisom]

Dave, any thoughts on my previously mentioned idea of converting one of my Marshall 9000 Series 50w+50w stereo power amps from using El-34 tubes to 6550 tubes, just for an additional nice-sounding option?

[Tek465b]

shakti, i hate bright cap, don't bother with them .
Need low amp volume setting for undrix(below 7 for me), bright cap ruin it all. Maby 100pf,, not more then 500pf i think.

Xplorer,
about the vibe, when you say intensity to zero, do you mean with the cancel switch or no cancel, just intensity knob to zero?.

[Xplorer]

Xplorer,
about the vibe, when you say intensity to zero, do you mean with the cancel switch or no cancel, just intensity knob to zero?.

yes, i mean, on the non original univibes which have a true bypass, i turn them on, but i set the intensity to zero or close to zero, to simulate the cancel feature on the original univibe
( + on the Voodoo vibe, another thing helps, it's the bias control, it shapes the tone quite a lot if you want to. very cool feature )
together with a fuzz without gain, it brings Jimi's tone ... and yes, volume below 7 on the amp, for me too, and no bright cap or low bright cap value like 500 pf max.

[shakti]

Xplorer,

no, I haven't changed the filtering. Stock values, i.e. 50+50uF all around. I might try 100 for the first stage, but I am very happy with where this is heading. I think part of the reason why we all like that BOG tone so much is because it has such fabulous articulation, and sounds so big, even when it is wild and raucous. Seems to me that having enough voltage to play with is probably an important factor in that, probably even more so when running in class B? Dave will probably be able to say something about that.
SO slowly we are converging in our views about the amp; "big" glass, high voltage and a fair amount of headroom, medium settings on the amp. The preamp differences between bass and lead are not that huge in this scenario, more like tweaks to the tone. Like you, I like shared cathode. I might also try a different value first stage coupling cap (not 0.0022uF) as one of the purported Hendrix amps had a different cap there, but I don't suspect the difference to be very big.

As for the fuzz, we're still all searching, and I am very eager to try an "always on" West Coast fuzz now!

[Tek465b]

Intensity to zero and cancel do not get the same result.
when your intensity to zero, the bulb still lit a bit(dim orange).
I dont know if its because i have sensitive LDR' but there's a hudge difference to me using cancel vs just setting intensity to zero.
Cancel make the bulb completly dark. and actually sound alot better to me. So much that i removed the true-bypass, don't need that on a vibe.

[Xplorer]

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.