How do I check output voltage on my Marshall Super Lead 100 vintage 1971 head?

[Steve Conner]

When the Super Lead comes out of the freezer, its first question will be "What did the chicken do?!"

I think by the time the TSL came out, Marshall had toned down the output stage considerably so it made less power when overdriven, in the interest of keeping Russian and Chinese tubes alive. I heard somewhere that the earliest 100w Marshalls would make nearly 200 watts when driven flat out, but I can't remember the source.

[J M Fahey]

Well, sticking to raw Physics, we have an amp that can put out more than the speakers can take.
And that's not "opinion", so it clears the waters somewhat.
Basically there's 2 options:
1) the best sounding, time tested one: use 2 cabs!!!!
25 Million Marshall users can't be wrong, and that's where the "Stack" name, concept and powerful visual image comes from.
2) although using higher powered speakers *is* the simplest option, I don't push it too far (it depends on firehouse taste of course) because the Greenback *does* have a special sound.
Unfortunately in great part it comes from its use of thin round copper wire, wound on a paper former , glued with Nitro lacquer, and having the speaker components also glued with Nitro.
Which being a stuff that weakens around 65ºC, bubbles and disintegrates at 90ºC and burns with orange flame at 120ºC (it's nitro cellulose after all, similar to what's used in smokeless powder) means 25W RMS is the absolute maximum.
No kidding.
You "improve" anything (go for Epoxy adhesives ; Kapton former ; etc.) and you kill the original sound.
3) attenuators, well ... attenuate.
But also modify the sound
Mainly because they are resistive and speakers are not, by a long way.
So any resistor in series will kill damping (this is not bad, really) but any parallel resistor will damp or kill the resonance peak so you lose "thump" and high frequency impedance rise, and you kill (or damp) bite.
4) ***Personally*** , I would add a Power Soak, to lower power by lowering +V .... and leaving *everything* else untouched: waveforms, impedance, inductive kick, the works.
By the way, using *this* kind of "attenuation", tubes suffer *less* and transformers, filter caps, etc. work cooler and last longer.

[Gtr_tech]

For me, it is a matter of using the right amp for the job. It makes no sense to me to use a 100w amp strangled with some tranny toaster power attenuator when a 20-30w amp would work just as well and need no power attenuation. 100w amps are not really needed these days when we have high powered PA systems that do a better job of dispersing the sound evenly when the cab is miked. They are best used for clean headroom with some sort of pedal or preamp in front of it.

I like Enzo's car analogy. I"ll use that often too because its something we all can relate to. To me its like driving a 70 Chevelle behind a dumptruck going 30 MPH and redlining the Chevelle trying to push the dumptruck. How long you think the motor will take it before it blows?

So....I was just trying to explain the risks involved when a high plate supply high wattage amp is dimed constantly into an attenuator for long play times. The smoke will come out eventually....count on it. I didn't appreciate the OP coming off like some petulant 15 year old kid.....

[Jazz P Bass]

It also would helpif the speakers where wired in parallel.
The series/ parallel arraigement is too risky. (ie: one series blows, you now have two speakers)
Has the OP ever stated that he operates the amp at 12?
Just curious.
And what was the exact 'failure' of the speakers? (open coil?)

[Gtr_tech]

Sounds like he's overdriving the amp to me. That thing putting out even 50w into a 4-12 of greenbacks...even tho they are a low power spkr, would be melt yer face loud. And the number of wrecked speakers suggests they were hit with some clipped output. Not that a non clipped wave won't heat up a coil to the point of burning open, but a clipped wave will sure do it faster.

So....to the OP: tell us exactly how you are using this amp so we can get a better idea of whats goin' ahn.

[firehouserecording]

I was playing at nine, and yes the coils burned open. That situation is very clear to me at this point. I've always done that. I never knew it was such an issue. The funny thing is, the other time I blew two speakers was with lower volume an a distortion pedal. I know I'm a moron, but I never knew my setup was so out of balance.

Thanks again, everybody. The Marshall never made it to the freezer, because the freezer broke, but that for another forum. The Firehouse taste, Juan, is 100 watt Marshall through 25 watt greenbacks. I was taught that trick by a world famous producer. We have all listened to his records many times. He just never mentioned that this setup was so overpowering, and I never knew to ask. I thought it was 25 watt, as opposed to 30 watt only. I love the sound. When I record, I am sticking to the formula. I will pay for the re-coning.
I have a 4x12 cab with 75 watt speakers, but I won't be able to use both cabs in the isolation closet that I have built, and it will obviously lighten the load on the greenbacks which is not what I want to hear on my recording. I guess I will just use the 75 watt cab for rough recordings and rehearsals. I will buy a power soak, and hope it sounds great on recordings. I'll probably end up selling the power soak after I hear it, though.
My bottom line is, I need to be able to record the sound of my current setup, but lighten the load off my speakers. I guess that's an impossibility, so I will just do it sparingly, and pay the speaker guy.

Isn't petulance next to Godliness?

[Steve Conner]

Oh, I see, it has to be Greenbacks to get the mojo.

In that case, the suggestion earlier, of connecting a 16 ohm, 100 watt resistor in place of a second cabinet, might help. You set the amp to 8 ohms as if you were running two cabinets. Half the power goes to your cabinet and the other half gets burnt up in the resistor. Hopefully this will keep the speakers alive without spoiling the tone too much.

[soundguruman]

It's normal to roast speakers.
This is why, at concerts there is two speaker stacks for one head.
After 40 minutes, tops, the head is switched to a fresh cabinet stack. This prevents the speakers (in the first stack) from overheating and melting.
It's traditional practice, world wide.
The sound of a Marshall is not correct, until the output tubes are over-driving*. This is why we use a power attenuator, not a distortion pedal. That IS the correct way.
If you want the "real" Marshall sound, crank that head up, and throw away the distortion pedal.
Otherwise, you might as well be using a Roland Jazz Chorus 120! Hahahahahahahahahah!!!

*screaming for mercy
**a distortion pedal is a pathetic, weak imitation, why do you even "have" one?
*** I threw all my distortion pedals away, decades ago.

TEST: if you crank the Marshall 100 in the garage, and the neighbors call the police, that means it's working correctly.
TROUBLESHOOT: If the neighbors don't call the police, there is still something wrong with the Marshall. Check your bias...

[DrGonz78]

My thought on playing a live show versus a studio situation is completely different. When I play a show I can deal with a half stack 100 watt Marshall stack and that is what works for a good size club. However, when in the studio I always felt that a half stack never translated very well with recording in general. Not saying I did not use a half stack in the studio, but that it is not necessary or practical in many regards. In particular there is the phase issues between having four speakers and picking which one to choose to position the mic. If you can find a good studio now'a'days that even has the right sized room for this setup that is difficult. At least have one mic on cone and then have a mic in the room. Blending these two mics is what I always found to be that sweet sound. Some even use two mics up close on the cone and then one in the room. Most recording is being done in sub par rooms these days with a real DIY attitude. Nothing wrong with that but those studios that Jimi filled with his guitar are not around as much these days. If you got that old school kind of setup then all the power to you. If you ask the great minds in the recording industry they will recommend a one speaker cab to record with in the studio. A one speaker cabinet gives you clarity in the studio that is really necessary to capture the raw sound of a guitarist. To me it is important to know this big difference when approaching studio work. Hard for most to understand but the real pro recording engineers know what I am talking about. I am sure you all see the pro's and con's in it all. After all I spent many sessions with a large half stack before trying it the other way and in the end I learned this lesson for myself. Take my experience with a grain of salt cuz I still feel everything is still subjective at best. Either way I learned that both stacks and single speaker cabs play a part in the studio, but when it comes down to it there is a big difference between playing shows and studio recording.

[soundguruman]

I think the point was that if you are using 25W or 30W speakers, it saturates, and you have to give the speakers a rest. 40 minutes is about all it takes without flaming
Clipping the output tubes into hard continuous square wave, there might as well be DC on the output...it's just pulsed shaped (frequency of guitar) instead of continuous DC..it makes the 25W greenie pretty warm. mmmm, mmmm, mmmm toasty!
Granted a power attenuator is relieving some of the issue. The speaker pairs are wired series to spread out that heat... Or the load resistor deal...
If you are using your pedals in the studio and turning the amp down low, obviously you are not overtaxing the speaker, but you are not getting the real sound either, hahahahahah!
But sooner or later at proper volume, you gotta swap cabs. Any square wave from distortion pedal or other means is still taxing the speakers harder than a sine wave.

[J M Fahey]

This is why, at concerts there is two speaker stacks for one head.
After 40 minutes, tops, the head is switched to a fresh cabinet stack. This prevents the speakers (in the first stack) from overheating and melting.
It's traditional practice, world wide.

What a truckload of bull manure.
Nobody never ever does or did that.
Ridiculous suggestion.
If you have 2 cabinets and one head, you just plug *both* and play all night long without trouble.
Which by the way doubles sound pressure, punch, thump, oomph, you name it.

[Gtr_tech]

Why there was backlines with several stacks back in the late 60s/early 70s is to have spares ready to go in case one blew up. And they did....

[acorkos]

Doyle's book, in the appendix section, has a reproduction of a Marshall Tech bulletin from back in the day...
100 watt Lead amp
115 watts RMS at clipping
170 watts into 4 ohms @10% distortion.

i imagine back then they were testing the amp into a 4 ohm load probably consisting of four 16-ohm 4x12's loaded w/greenbacks

[Steve Conner]

Yeek.... Seems like it could easily make 200W when mashed into hard clipping then.

[firehouserecording]

Yes, Soundguruman, I agree 100 percent. I don't own any distortion pedals. I only own a clean boost pedal (it's called Time Machine). I play my Marshall jacked most of the time. I referred to a distortion pedal in an earlier post, but that was owned by a guitarist who is now in jail for drowning his girlfriend's puppy. I do own a JC-120 though, and that comes up big for me time and again.
I'm still going to max my head it into my 75 watt 4x12 for non recording times. For recording, I am going to use my 25 watt cab. Loudness isn't a problem.
I can't afford to blow speakers when I am recording a customer, though. Do you suggest the attenuator over a dummy load? Either way, if I don't like what's coming through the speakers, I will go full throttle with my own recordings.

Thanks,

Paul