Bass Thump: EL84 v. 6L6

[Reeltarded]

I use closed cabinets and I have demands for a pronounced thud that really can't be realized with 84s. There is a physical volume element, and I need to keep the amps just below RMS so I can still use the tone stack to shape the noise.

I don't like a full drive output section. It folds up like paper. If I use the output like that I have to use a parametric to hint at what I intended it to sound like and that is a nasty way to go!

Headroom. I need 50w or nothing gets off the ground.

[rp]

But, I guess I favor the Octals.

Can't offer anything technical just playing experience. 2 6V6s trounce 2 EL84s for richer tone in all amps I ever tried. There's not a 1XEL84 I would bother with except for collector fun, 6V6 SE all the way. In fact if I remove the collector Brit amp cool factor EL84s loose a lot of appeal except for DIY tweaker kicks. 4 EL84s are worthwhile and put some meat on the plate but it's still scallopini vs rib eye. I am very very very glad Dick Denny made his 4XEL84 amp and I've seen so many killer players w/ AC30s that I would never change anything in any way. But personally if forced to choose, EL84s are fun, octals are real.

[Leo_Gnardo]

But, I guess I favor the Octals.

Can't offer anything technical just playing experience. > snip < But personally if forced to choose, EL84s are fun, octals are real.

Trying to get bass out of '84s is like trying to move 3 ton boulders with your '61 Volkswagen Bug. Courses for horses mate. KT-eighty-eight. The more the merrier.

[The New Steve H]

So nobody agrees on anything. Once again, I am shocked.

[Bob S]

No you're not.
&#128512;

[cbass]

I like 7591a nice thump not quite as loud as 6l6gc nota ib ly more headroom than el84
Not tried modern ones though .

[The New Steve H]

No you're not.
&#128512;

I see I am fooling no one.

[pdf64]

There is an inner circle that refers to the TrainWreck Rocket (4 x EL84 output section) as a "Fat Bottom Girl" for the reason that these amps tend to put out a ton of low end.

I recently started using one of my 4 x EL84 amps based on the Dr. Z "Z-Wreck" as a bass amp (I call it the "Tejas Twister"). It really puts out the goods for tone including lots of bottom end. Not a monster bass amp but a very good sounding small venue bass amp with plenty of headroom and more bass response than you might expect: http://diyguitaramps.prophpbb.com/topic18.html

I was surprised by this result but in a very pleasant way...YMMV

I've got a friend who is an AC50 nut; he owns several of them, and after servicing them I like to test them out with the band.
I found that AC50 (2xEL34) make a fantastic bass amp.
I wondered why that was so, as the early tube rectified ones have an LTP and fixed bias, whereas the silicon rectified have a self balancing paraphase and mixed bias.
One silicon rectified AC50 I tried even had a replacement 50W Marshall OT in place of the original, which scotched my theory that the MASSIVE stock OT was the key to the big tone.
The hunch I came to was that it may be related to the open loop power amp, allowing the power amp to make use of the cabs bass resonance, for a bigger 'in the room' sound; with that, a saggy HT may not matter so much.

But that goes against the conventional wisdom that bass amps must be clean and tight.

When I made a 2xKT88 amp for my old bassist, I had this in mind, and in the tweaking stages left options for loose / tight available, ideally switch-able, eg pentode / UL, open loop / global NFB, speakers in series / parallel.
Rather than just arrange things how a bass amp 'should' be.
At every point he ended up preferring the looser option, to the point where I found the response too uneven, but it allowed him to really work the rig.

That 80W tube amp seems noticeably more powerful than his previous 400 watt class D switched mode Genz Benz.

So yes, I can envisage that the Tejas Twister might acquit itself very well in a bass rig.

[Reeltarded]

My rig is all on loads. That class D crap must be measured in some alien way. 2.2kW stands to meet a Major just about straight on.

I blame automotive vendors of those flea market amps. D class amps must be rated x2.5 over reality, at least. I have never seen one do it's business.

[Leo_Gnardo]

I've got a friend who is an AC50 nut; he owns several of them, and after servicing them I like to test them out with the band.
I found that AC50 (2xEL34) make a fantastic bass amp.

Roger THAT, got one!

One silicon rectified AC50 I tried even had a replacement 50W Marshall OT in place of the original, which scotched my theory that the MASSIVE stock OT was the key to the big tone.

Same here, but the Marshall OT looked much the same as the Vox size wize.

The hunch I came to was that it may be related to the open loop power amp, allowing the power amp to make use of the cabs bass resonance, for a bigger 'in the room' sound; with that, a saggy HT may not matter so much. But that goes against the conventional wisdom that bass amps must be clean and tight.

I think you're on to something.

But it still takes some (put Arm & Hammer muscle flexing arm here) power. Unless you're playing with an acoustic outfit, can hardly do less than 40W of good - octal - tube power. If you want to get there, that's gong to take 6 EL84's. A sort of EL84 mini SVT if you will. I have seen a German made mono hi fi amp with half a doz EL84 and its owner likes his reggae, has 15" speakers in his home stereo, & a pair of those amps, that keeps him happy in his living room. Try to keep up with most any drummer live, the minimum I've seen work is a good ol' Fender Bassman with 2x15 ElectroVoice cab.

[rp]

The hunch I came to was that it may be related to the open loop power amp, allowing the power amp to make use of the cabs bass resonance, for a bigger 'in the room' sound; with that, a saggy HT may not matter so much.

Does "open loop" mean no negative feedback?

I just re-looked over at the schematic, I had never noticed and am pretty surprised it doesn't have NFB (and neither does the AC100!) I one day really want to build an AC50, and a bass amp, I don't need anything big for the latter so this might be a good way to kill two birds... so thanks for the tip.

BTW for bass were you running a 12AU7 on V1?

[teemuk]

That class D crap must be measured in some alien way. 2.2kW stands to meet a Major just about straight on.

IMO, most class-D amps have very realistic ratings. The problem is that people falsely think that output power ratings are any sort of indicator of perceived loudness.

[pdf64]

the Marshall OT looked much the same as the Vox size wize

Ha, in readiness for this moment, I thought on to take some details of a stock AC50 OT when I had one with me last; also in case memory acted to fade the scale of the thing!

Stack thickness = 2.5" (~174 laminations!) x 3" x 3.75"
Primary z = 3k4

A regular 50W Marshall Drake 784-139
Stack thickness = 1.5" (~76 laminations) x 3" x 3.75"
Primary z - 3k3

Just as a matter of interest, the OT used in the DrZ EZG50
Stack thickness = 2" (~144 laminations) x 3.125" x 3.75"
Primary z = 5k5

So the AC50 OT truly is a monster.

Yes, open loop = no (global) negative feedback.
If you follow the regular silicon rectified schematic with mixed bias, the 47 ohm unbypassed EL34 cathode resistors will add a little local feedback, which in this configuration should act to increase the amp's output impedance.
As opposed to decreasing the output impedance, which is what regular global NFB does (though when overdriven, the NFB can't operate).

And yes, a 12AU7 seems to work out much better in V1, whether for guitar or bass.

IMO, most class-D amps have very realistic ratings

Do the headline power output numbers tend to be measured on a continuous output basis?
I figured that they may be a momentary peak, which couldn't be sustained.
I've shied away from testing my theory, as my dummy load may be a victim if the power output really did live up to the claim.

[M Fowler]

I gave my daughter a TW Rocket head running pair of 6L6's, diode rectified for use a her bass amp and it works very well for that purpose. Non gigging just practice.

So not an AC50 but in my simple mind it is very much like an AC50.

[Reeltarded]

That class D crap must be measured in some alien way. 2.2kW stands to meet a Major just about straight on.

IMO, most class-D amps have very realistic ratings. The problem is that people falsely think that output power ratings are any sort of indicator of perceived loudness.

Truly, the consumer needs a relative comparison that matters in the real world... but there is no way this thing hangs with a Crown MT1200 and it's <48%.

It weighs 3.5 pounds though. (shuts up)