Metropoulos Forum

Just curious. Obviously they're rated for 25W each and a lot of people tend to be conservative, but most of the time the rating is conservative... Just wondering where reality lies.

Please specify if your G12M is an original, reissue, or a Heritage.

I've used a JTM45/100 unattenuated into a 1970 1935B cab, i.e. 55Hz G12M speakers each rated 25W. I don't tend to do that for longer periods of time though, and I don't dare to run a fuzz into it when unattenuated.

I also have a 1967 4x12 which has a set of original 1967 G12M 20W speakers (true 20W speakers with the white voice coil former). I have tried the same JTM45/100 unattenuated into that cab and it sounded glorious, but I did it with my heart in my throat... OTOH I do regularly use a 1986 (50W, 2xEL34) unattenuated into that cab and it has not been a problem.
FWIW, Clapton seems to have used just one G12M cab in the studio when recording Fresh Cream with a cranked 45/100. But then again he would have had access to replacement speakers...

So my answer is probably; not very far, but I am not going to push them any harder. Obviously the rarity of the speakers plays into that.

I have 25W G12M Greenback Reissues loaded in a Metropoulos 68 True Replica Cabinet. The farthest I have pushed mine are: 1959HW vol. 10 Rock Crusher -8 dB. I assume this is not very far, but I'd rather be on the safe side until I find out for sure how much these speakers can handle safely. (How much of a Plexi that is, because IDK if it's true that a 100W Plexi is actually 200W at full volume)

So for me 100W Plexi vol. 10 attenuated -8 dB.

That's not pushing them very far at all. Figure 160W output with amp on 10.

-3dB is half that; 80W
-6dB is half of that; 40W
-9dB is half of that; 20W

So you are probably pushing that cab with all of about 25-30W of power. Come on, you can do better than that!

Analogman88 wrote:I have 25W G12M Greenback Reissues loaded in a Metropoulos 68 True Replica Cabinet. The farthest I have pushed mine are: 1959HW vol. 10 Rock Crusher -8 dB. I assume this is not very far, but I'd rather be on the safe side until I find out for sure how much these speakers can handle safely. (How much of a Plexi that is, because IDK if it's true that a 100W Plexi is actually 200W at full volume)

So for me 100W Plexi vol. 10 attenuated -8 dB.

Most old Plexis with less than 500v on the plates put out 110-115w clean (volume at around 4) before edge of breakup or clipping, however you want to refer to it.

At 10 they put out 180w plus. One of my amp gurus measured an old Super Lead with 560v on the plates at 220w cranked to 10. Not all of them do this, just some with a different PT.

But if you build your amp to spec, then you're going to put out 180w-190w for sure at 10 on the volume knob. As for the reduction in db, depends on how accurate your attenuator is, but shakt's numbers look right.

You should be able to go -4 db without any issues, if your speakers are good. No guarantees, obviously!

Good luck!

Yes, cranking 100w heads with greenbacks is risky indeed (although the contemporary celestion greenbacks often handle more than 25w). A friend recently tried a major into two 4x12s with RI Greenbacks. The speakers broke up more than he care for, and sounded mushy, but they did not blow. I've personally used a 4x20w scumbacks with a 45/100 with 510v on the plates. The amp delivers around 70w at the point of breakup and much more at full distortion, so I had to be careful.

A 1978 Super Lead - everything on 10 through a 100 watt marshall cab (4 x G12C) for hours. Sounded good, survived just fine... still using the same cab and speakers
470V on the plates, 4 EL34's

Er.....I have blown some up - is that pushed far enough ?

If an amplifier have 4 tube at the output it doesn't mean that it's a 100 watt. They are less than that.
Dual rectifier for example with 4 6L6 is just 55 watts of clean unclipped signal... Fender Twin with same tubes is ¬70 watts of clean signal.
When amp clips, the feedback doesn't work, and amplifier's gain is way higher, but only if the clipping is like of a SS amp - Real rectangular shape. OT of a tube amps, cannot produce same straight line of a DC, like SS amps do, and there is blocking distortion of the power amp kicks in, when the power tube clips. It's possible to have that effect for a real short periods of time though... So they are (tube amps) more forgiving in that area.
Bottom Line is that if you don't play with uber-high-gain-fuzzy distortion and speakers wattage is matched to a amp wattage - it's OK. Like 4 x G12M for a "100w" head.

Some times speakers fail and amp is not the reason.

Haze13 wrote:If an amplifier have 4 tube at the output it doesn't mean that it's a 100 watt. They are less than that.
Dual rectifier for example with 4 6L6 is just 55 watts of clean unclipped signal... Fender Twin with same tubes is ¬70 watts of clean signal.
When amp clips, the feedback doesn't work, and amplifier's gain is way higher, but only if the clipping is like of a SS amp - Real rectangular shape. OT of a tube amps, cannot produce same straight line of a DC, like SS amps do, and there is blocking distortion of the power amp kicks in, when the power tube clips. It's possible to have that effect for a real short periods of time though... So they are (tube amps) more forgiving in that area.
Bottom Line is that if you don't play with uber-high-gain-fuzzy distortion and speakers wattage is matched to a amp wattage - it's OK. Like 4 x G12M for a "100w" head.

Some times speakers fail and amp is not the reason.

I think you have it backwards. A quad of EL34s, like in a Marshall 1959, have been measured at 100 watts clean while the volume knob is NOT maxed. The same amps have been measured at between 160 and 195 watts while completely maxed out, depending on the particular amp's B+ voltage.

Just saying how many valves you have doesn't mean much. With the right voltage and impedance you can get real low output out of valves. For instance, Marshall use two EL34s to get 25W out of their small Silver Jubilee. Trainwreck do the same with their low powered Express. Marshall even get 5W out of a single EL34 in their SL5 because it only runs at 250V.

Littlewyan wrote:Just saying how many valves you have doesn't mean much. With the right voltage and impedance you can get real low output out of valves. For instance, Marshall use two EL34s to get 25W out of their small Silver Jubilee. Trainwreck do the same with their low powered Express. Marshall even get 5W out of a single EL34 in their SL5 because it only runs at 250V.

Right, and I even said depending on the B+ a 1959 is measured at max between 160 and 195. The vast majority of amps talked about here are JTM45, JTM45/100, 1959, 1987, 2203, and 2204 heads. Sure that's not EVERY amp we talk about, but it's about 90% at least.

But that wasn't even really the point of the thread. I was wondering what the true breaking point of a 25W Celestion G12M Greenback was.

I was responding to Haze13. Sorry for not being clear.

Measured by whom?
I'm working as tech and have worked on different amps, and non of them were really 100 watts or 50 watts.
Sine wave in the input, with the scope connected to the load and looking at the output before clipping.
That's why I wrote about Fender and Mesa - because I've checked the output and there were others.
GilmourD, have you seen the 100w of Clean power from the 1959 Plexi EL34 or it's just what every body says?

I've personally seen 48W clean sine wave from a 2 x EL34 Marshall that I built and that was with a 10Ohm Load on the 8Ohm Tap. 460V HT with 3.5K Primary on the EL34 and a GZ34 rectifier with only 32uF Mains Filter so there was a lot of sag.