Marshall origin 20 watt combo with greenback 30 watt....risky?

[daz]

It's cathode biased EL34's, not 84's. They limit them somehow, not sure how because theres no schematic.

[J M Fahey]

Chiming in to suggest same as others: measure, do not guess [tm]

Originally seeing "20W" in the name I thought "no big deal, another 20 MKT Watts 2 x EL84 amp" , MKT being:"Marketing".
NONE even reaches 20W RMS (even less 25, do you hear Mesa and Peavey? ) BUT THEN I read "2 EL34" on the brochure.

So this is not a propped up EL84 amp but a tamed down EL34 one.

And as "tamed" Lions and Tiger owners find out, one day their "pet" badly mauls and/or kills them.

Meaning: I wouldnīt worry about regular "20W" amps, not sure at all about this one.

Easy to test: drive amp to squarewave into an 8 ohm resistor (or whatever impedance your speaker has) , and measure that with a true RMS voltmeter.
Do the math: if >30W RMS simply do not us that speaker, period.
Voice coil does not know waveform or frequency, all it cares is RMS which is a *thermal* rating, go figure.

Or simply take the safe route: if you like Greenbacks, (I do ), get its reinforced Brother, the Creamback, if I donīt remember wrong rated 65W which should be ample.

[daz]

Yes, as i said in my above post in response to Dude, it's EL34's and i have tried all the different 34's in it i have. Funny, always hated JJ EL34 but for some reason in this amp i prefer them even to my fav set i have....winged C's ! Anyways, i already made up my mind on the speaker issue....I'm just gonna get the GB and use a 1x12 or 1x10 ext cab for band use and just the 1x10 combo with GB's at home. At one point i thought i had decided on a creamback but i read a lot of reviews and read some things about the difference that i didn't like. So not gonna chance it. I want the exact GB sound and too many people were saying the creamback is different..

[The Dude]

My bad. I assumed it was an EL84 amp being 20 watts. You know what they say about assuming.

[Enzo]

My first mental image was an AVT20.

[J M Fahey]

Sadly you canīt beat Physics.

Creamback *is* a Greenback but with a heavy duty voice coil, everything else is kept the same.

I havenīt repaired one yet , so no autopsies so far, but I guess a regular modern round copper on Kapton voice coil, glued with Epoxy.

Both things quite heavier than original Nitrocellulose adhesive and paper former coil, which of course make speakers "slower".

Same engine (copper and magnet) and heavier load (former and adhesive) and: Acceleration being Force/Mass means acceleration, in Musicianīs terms "snappyness" will be less, there is no way around that.

That said, Creamback is *closest* possible to original sound, if you want larger power handling.

In your case, best would be using TWO Greenbacks

[J M Fahey]

My bad. I assumed it was an EL84 amp being 20 watts. You know what they say about assuming.

Hey!!!!
Benny Hill ASSUMED his grateful Father in Law would put him in charge of part of his fortune if he made "a little" sacrifice

[pdf64]

It's cathode biased EL34's, not 84's. They limit them somehow, not sure how because theres no schematic.

Amp max power output is determined by the HT voltage (at high output level) and the OT primary impedance.
The valve type is chosen so that it can accommodate the voltage and current levels resulting from that arrangement, whilst being likely to achieve a good service life.

If the HT is reduced to about 300V, and the OT impedance is increased a bit above the usual 3k5 ish, then a push pull pair of EL34 will only be to put out about 20W. And they should last a long time.

What will do a lot will (usually) do a little

[Mick Bailey]

Interestingly, the amp uses two secondaries in series for the HT (100v +130v). I wonder why they did this, rather than use a single winding?

[Enzo]

Transformer used in other models perhaps?

[pdf64]

Maybe a lower power mode, with the HT down at about 200V with the 130VAC winding, was being considered?

[Jazz P Bass]

Hmmm.
If Marshall chose a 50 watt speaker in their 20C combo amp why would the OP want to choose a 30 watt speaker and then wonder if it will be ok.
Just a thought.

[daz]

Hmmm.
If Marshall chose a 50 watt speaker in their 20C combo amp why would the OP want to choose a 30 watt speaker and then wonder if it will be ok.
Just a thought.

Because i want that sound !!! Origin players practically to a man swear the origin sounds like it was made for that speaker, plus they say it overdrives quicker which this amp really needs being so clean I have to boost the heck out of it. So adding speaker grind it desirable in this situation. In any case i'm going to use a ext cab with it for 2x10 or maybe a 12 in the ext. Thats only going to be for live use tho, at home it will be just the combo which will never be louder than 2 on the master.

[Jazz P Bass]

"Because i want that sound !!! :

Ok.
They are nice sounding amps.

[daz]

"Because i want that sound !!! :

Ok.
They are nice sounding amps.

Ahhhhh....turns out the sound i wanted is NOT what i thought the BG was from all the descriptions and above raving reviews. Anyone wanna buy a greenback 10? LOL. So much for trusting reviews and descriptions. Wish i'd gone with the creamback i was considering too.