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Changing from Class A/B to A, Pentone to Triode, lower plate voltage, MESA/Boogie amps

In mid-November 1998, I asked Mesa/Boogie rep/designer John Marshall: what is the lowest possible tube power-amp wattage, of all the Mesa/Boogie amps and all the settings and setups? Is there any way to run any of the Mesa/Boogie tube amps at 7 watts, or even much lower, without using a Hot Plate or Yellow Jacket, while getting full power-amp saturation?

He said:

With the early version of the Mark III, a Simul-Class amp, when in Class A mode, it's 15 watts. The newer Mark IV is currently being made. It's a Simul Class amp. When Class A is selected, and when Triode rather than Pentode is selected, it is 15 watts.

He also mentioned "the early version of the Mark II" but I'm not sure it has 15-watt capability.

The later Mark III, no longer made, does not have triode mode; it is always in pentode, for a minimum possible level of 25 watts, when Class A is selected.

Currently made: The Blue Angel amp has 3 settings:
2 6V6's, for 15 watts
4 EL84's, for 33 watts
Both, for 38 watts
He didn't specify anything about Pentode/Triode setting, or Tweed vs. Full setting, but he said the minimum power is 15 watts.

Also currently made: 20 watt Subway Blues, and 20 watt Reverb Rocket. My site only lists amps *below* 20 watts, because I consider 20 watts to be very loud and high-powered (whereas the amp magazines call them "small" and "low-powered"). A *truly* low-powered amp would be 50 mW, 0.5 W, or 5 watts.


I am interested in power reduction capabilities of Mesa/Boogie amps. There are so many power-reduction possibilities, I would like to know how low you can go. Of all the Mesa/Boogie amps, of all the possible settings and setups, what is the lowest power possible? I am willing to consider swapping down to smaller power tubes as well.

The Mesa/Boogie Mark IV - does this get very low power, less than 30 watts? 2-page review, page 39, Guitar Player May 1991:

The Simul-class technology enables you to switch from Class A/B down to Class A, for lower power.

The Pentode/Triode switch enables you to switch from pentode to triode mode, for lower power.

With these two reductions, the article states that the 85 watts have been reduced to 30 watts. The article then goes on to state yet another option, but does not mention the wattage resulting from the following feature:

The 3-way power switch (Full or Tweed, or Off) enables you to lower the tube voltage and power, for a looser sound (and for lower power?).

Does switching from Full to Tweed reduce the power to below 30 watts? If so, then what would be the wattage resulting from all three of the above power reductions?

Can you use these together, to get it down to 15 watts?

The Simul-Satellite combo amp has the above features. The Mark IV also has speaker mute, which I guess involves a load so that the DI outs have power-tube saturation.

Can you change to lower-wattage tubes, such as using Yellow Jackets, to get even less power?

Isn't there a way to run some Mesa/Boogie amp down to 7 watts or less, with some combination of settings and setup?

Dan C. wrote:

>Would 5-15 watt tube amps only be beneficial to people that play the blues or mild distortion? If someone was interested in metal or other extreme hard rock sounds, then their best bet would be a 50 or 100 watt amp (with built-in preamp distortion), right?

>I'm asking because I'm planning on buying a MESA/Boogie Trem-o-verb amp and pulling 2 tubes and one of the rectifier tubes to get it down to 50 watts (and to save money on tube replacing), but your posting made me wonder if it's too much. I'm guessing you were talking about blues or mild type distortion so this wouldn't apply to me, but just wanted to make sure.

You say you wonder "if it's too much". I guess you are wondering whether pulling so many tubes would reduce the power too much to get great tone. I do think that 5-15 watt amps tend to use configurations that produce a creamy power-tube breakup, which is great for Beatles and blues and classic rock, rather than the hard breakup which is used for Metal. I suspect that as you pull tubes to lower the power, you are bound to head toward softer power-tube breakup -- I've seen this pattern throughout the amp reviews.

And I really want a definitive answer about the contribution of playing speakers loud. Certainly a 4x12 cab is the only way to go, for Metal, and the most popular speakers now are Celestion Vintage 30s. Is it crucial to drive that cabinet hard, at the 100 or 50 watt level? What would happen if you took a scaled-down power-amp that itself had the same Tone as a 100 watt power amp, but used it to drive the same cabinet as usual? Would the cabinet sound the same but quieter, or would the cabinet response have an inferior Tone, as well as being quieter? I have heard contradictory assertions about people's speaker response (speaker Tone) at lower power levels.

>The Trem-o-verb is a more versatile version of the Mesa/Boogie Dual Rectifier Solo head. Some people say that Mesa/Boogie amps are as good as or better than Marshall amps, for Metal. Metallica, Dream Theater, and Foo Fighters are a few that use Mesa/Boogie amps.

I read that the amp used for Ozzy's first solo live album Speak of the Devil is a .22 Caliber Mesa/Boogie, with Brad Gillis. (But this isn't the same tone as Metallica.) I do think that you are most likely to find the appropriate power tubes and class and plate voltage in a 50 watt setup -- using Class A/B with two 6550s should be the hardest type of power-tube saturation. When you switch to another tube type or switch to Class A or lower the plate voltage, you will get a creamier, softer power-tube response. And most attenuators will compromise your Tone proportionately to the amount of attenuation. I suspect that the best Tone is with a loud 50 watt amp, though I think you should be able to get satisfactory Tone at lower power levels, if the components are all scaled down in a balanced way. I would try using only a single Celestion Greenback 25 watt speaker in a 4x12 cabinet, though this would lose the supposed phase cancellation comb filtering of having 4 speakers.

Someone wrote:

>I've heard that the Mesa-Boogie Tri-Axis was good, but even James Hetfield of Metallica has to hot-rod it to get it to sound the way he wants. I actually heard the Tri-Axis once, but I'll have to give it another listen--it looks to be difficult to dial in your setup.

From http://www.amptone.com/g046.htm -- Complete list of tube amps under 20 watts:

Mesa/Boogie. [15 watts with 6V6 option?] Heartbreaker amp. EL34 or 6V6 adaptable. ($1499 for head-only version). 2x12 combo version $1699.

Mesa/Boogie Mark IV - does this get very low power, less than 30 watts? 2-page review, page 39, Guitar Player May 1991. Tweed Power switch - Class A disconnects the 2 centrer tubes, cutting output in half. 3-way power sw: Full, off, tweed; tweed lowers the tube voltage and power, for a looser sound. Can't you use these together, to get it down to 15 watts? And maybe change tubes, to get even less? The Simul-Satellite combo amp has the above features. The Mark IV also has speaker mute, which I guess involves a load so that the DI outs have power-tube saturation. Isn't there a way to run some Mesa/Boogie amp down to 7 watts or less, with some combination of settings and setup? [to do: post that question to the newsgroups]

Mesa/Boogie - Blue Angel $1000 (combo version). Tube head or combo. 1 ch. 5 ctrl knobs. Progressive linkage switches between the 2 6V6, 4 EL34, or all 6 power tubes, for 15, 33, or 38 watts. No ftsw, no mst vol, no master eq. Reverb, par fx loop, Celestion 90 watt custom spk. Fan. Depth control for FX loop. A variety of out jacks for different ohms. Options: head only, $899. 2x10, $1000. 4x10, $1099. Reviewed in Guitar Player Sep 1994. "This is a sweet sounding amp with much power-tube sponginess; not for metal or loud clean tones. Turning the volume knob more than halfway adds more saturation than loudness. Capable of detailed clarity, but not at high volumes. The overdrive is always creamy even with chords, never muddy; your playing retains articulation and individual strings. Not a bad sound in it. Designed for classic tones, for subtle dynamic and tonal contrasts."

This large block is from a newsgroup posting by attenuation expert Steve.

Brian Denuyl wrote:
> I was wondering if I could get your opinion on the THD
> Yellowjackets. I have a Hiwatt DR-50 and a '65 Marshall JTM-45 which
> are both too loud to use in the clubs in which I play. What do you think about these things?

Steve wrote:

Well, I am very happy with them. I have only used them in my THD
"Plexi" amp which normally uses EL34'--so there is no real way
of knowing how they will sound with your amp without trying them.
Mine cost $120 for the pair--which is fairly reasonable considering
what you get.

I assume you either talked to the guys at THD or received their
literature--so I won't quote their excellent descriptions and
reviews. ( If you haven't received the THD info let me know...).

First, you have to ask yourself if you like the sound of EL84's.
I do! It's one of my favorite tubes. I know little about Hiwatts...
and as far as your '65 JTM 45 it will certainly sound different
with EL84's. Again, I'm really not an expert (talk to Lord Valve!),
and I don't know if you have KT66's or whatever they are--or 6l6's...

The other thing you have to ask yourself is if you like the
sound of pure class A amps--since the Yellow Jackets will
convert you to that class. Certainly, Marshalls wouldn't
sound like Marshalls if the weren't class AB. Also, your
'65 must be real valuable, so I would certainly consult
THD and other experts before making any alterations--I
have no real technical expertise and would never advise
anyone as regards to modifiying a vintage amp!

On a side note, one advantage of CLASS A Yellow Jackets is that
you can just plug 'em in without any re-biasing. Also--
you can try different kinds of EL84's. For example, you
could try Groove Tubes EL84's rated for low volume distortion
characteristics...I use standard issue Sovteks...

To my ears--and again everything depends on the amp--
Class A is a sweeter, smoother, looser, and perhaps
a little more compressed.

It cannot be emphasized enough that everything in
the sound-production chain is highly INTERACTIVE and
SYNERGISTIC...guitar, pickups, amp [power supply, preamp,
tone controls,output tubes, transformer etc] speakers,

> Both of these
> amps really need to be cranked to deliver their sweet tones and the
> Yellowjackets seem like a viable solution. According to THD, the
> Yellowjackets would bring the amps down to around 23 watts which would
> be about perfect.

A Hotplate will be much more flexible in reducing volume--and maintaining
the original amp tone. The Yellow Jackets are less about reducing volume
than getting a different amp tone...

Something you should consider: The relation of wattage (power) and volume (perceived
loudness) is logrithmical. It takes approx. 10 times the power to double the volume/and
vice versa.

For example: to double the volume of an 50 watt amp you must have 500watts!

To cut the volume of an 50 watt amp in half you must go down to 5 watts!

SPEAKERS are of course, a ABSOLUTELY CRUCIAL element to consider in the quest
for great tone at moderate volume. I e-mailed Weber VST with a question
in this regard:

The Tone of EL84's

Patrick wrote:

"I have been using the Fender Deluxe amp for 4 months. Initially I was
pleased with the clean channel, but wanted a little more breakup without
becoming deaf from turning it past 3. the 2nd channel is supposed to
give a very slight overdrive similar to turning the volume to 5-6 but it
never did the trick. So here is what I did: First, I installed yellow
jackets from THD. They cut the volume down
by half [FALSE! 1/2 Wattage not 1/2 Volume -- Steve]
by emulating a Class A circuit; this allowed me to get that
little bit of drive I was seeking. 2nd: installed a Mojotone speaker
as I was impressed with the sound of the Victoria amp but did not have
the money. Result: a very fine sounding amp in the clean and overdrive
channels, in fact it came very close to the matchless I had been
drooling over but didn't have the money.
Cost: amp 475
Yellowjackets 150
Speaker 70
I don't think I could find a better sound for the total price."


: Whats the difference between the EL84 and EL34? I have an amp that uses
: 2 EL34's, but is too loud. Would this scheme give me the same sound but
: lower volume ?

"EL84's have much lower output and a glassier sound with more his and mids. A
quartet of EL34's can give up to about 120 watts whereas a quartet of EL84s will put
out about 50 watts max. The sound won't be exactly the same but not 100%
different. I suppose 2 EL84s will give around 20 watts which would
definitely be not as loud, this is why I'm interested in them too.I want
to hear them in my 61 Bassman head. Guitar World's review of them in a
Marshall Super Lead said that they made the Marshall sound more like a
Vox AC30.THey list for 75$ a piece. Later,Daniel"

"Valid comments by Daniel. EL84's are sometimes regarded as 'baby EL34's
but I don't agree. They are sometimes percieved as being deficient in
bass, but that's not necessarily true. They do have a different
character and the lower power may lend that impression.

Pentodes (like the EL34 and true EL84's) tend to distort gracefully.
Beam tubes (like 6L6's and 6V6's) tend to sound very round but develop
a more agressive edge when overdriven."

>What can I expect to be different about the 84s vs 34s?

"It's hard to pin an exact tone on a tube, since much revolves around
the amps' circuitry and speaker. However, the EL34 usually sounds
bigger, with extended frequency response. Kind of delicate, airy
sound at low levels. The EL84 (again, generalizing) has a more
compressed, chimey tone. Rich, solid upper mids."

Steve points out that the Mesa Boogie Web site has this article by Randall Smith:

>A good example of this is exemplified by the very different signatures of the 6V6 and EL84 power tubes. Both tubes have modest power handling capabilities of around 15 watts per pair. Both were widely used in the 1950s and '60s, which were the formative years of the electric guitar. And both types have nearly identical plate characteristics. Yet their individual musical signatures are vastly different.

>The 6V6 was widely used by Fender during the '50s and '60s for their low power models. These amplifiers were popular with "electric blues" guitarists who often found their amps underpowered, and simply turned them up! Of course the amp ran out of power and distorted heavily. But the distortion quickly became used as a further tool of musical expression when in the right hands.

>Operating below the distortion threshold, the 6V6 sound is "skinny"-not objectionably thin, but bright nevertheless with bouncy, resilient dynamics. When overdriven, the low order second and third harmonics rise to predominance, obscuring the bright high frequencies and "fattening" the sound in a way which is a trademark of American blues. When severely overdriven, the distortion characteristic goes beyond what is desirable, producing an inarticulate low end which is bloated and tubby, obliterating most other frequencies with its woofiness.

>Meanwhile in Europe -- particularly in England-during the same period -- the EL84 was the power tube of choice in small amplifiers. The sound of this tube is very different from that of the 6V6. The EL84 possesses a glassy brightness whose emphasis is in frequencies higher than the bright zone of the 6V6. The EL84's dynamic character seems less resilient and when driven into distortion, higher order harmonics prevail, and an aggressive, snarling bite ensues. Overdriven to extremes, it does not suffer from low end bloatiness but retains a more balanced spectrum with its aggressive midrange character dominating...

Amp mods to convert 15 watt tube amp to 3 watts?

Can you make a simple modification to a 15 watt tube amp to make it 3 watts?

What is the difference between the design of the 5 watt and 15 watt Fender Champs?

Maybe a Laney or Blues Jr could be converted.

SRSN81A at prodigy.com (Joseph Pampel) wrote:

>Michael wrote..
>>I thought the Champ used 6V6 rather than 6L6. 6V6 is the lowest power
>>common power tube, lower than an EL84.

>Like Mr. Fries pointed out, all the Champs except the Champ 12 used 6V6's.
> The Super Champ used a pair of them, all the other CHamps used a single
>output tube for about a 5W output (depending on how the wind blows..)
> As far as "common" low power output tubes, there are numerous tubes
>less powerful than the 6V6/EL84 (which are closer to being the same than
>different IMHO, power wise, load wise etc. You often see them
>interchanged in older low power hi-fi designs as a mof.) The 6AQ5 comes
>to mind; a lower power version of the 6V6 (specs the same anyhow, but max
>plate volts are 275) that looks like an EL84.. or the 6K6, used in
>Fender's reverb unit which is more or less also a wimpy 6V6. Both are
>still plentiful (read: cheap as dirt) in NOS, and run off of a 200-250V
>supply, you won't get much "oomph" out of them. Even the 6V6 features a
>180V spec (in RC-25, and others no doubt) for running class A that puts
>out about 2 watts. The 6K6 specs feature a 100V B+ setting, good for 0.35
>watts. (!) You'll need a 12k load for it, but I bet a 10K would suffice.

> To build a 1/2 watt power amp, you could either run a single power tube at
>low voltages, (as above) or you could use a pre-amp tube (like a 12AT7 or
>12AU7) although it might not get the sound you want. An easy thing to try
>for a low power-power amp is to get a spare Fender reverb tranny (as used
>in the combo amps) and use that with a strapped 12AT7. The output of that
>reverb driver tranny is 8 ohms, so just plug a speaker in and see where
>you're at tone-wise. If you have a combo amp, just make an RCA-to-speaker
>cable adaptor and plug a speaker in. Who knows, it might not sound as bad
>as you think. And with some tweaking...
>Food for thought..

This could combine well with an effects unit before and afterwards. Using 2 MIDI effects units and a foot controller, you can simultaneously switch level and eq settings before *and* after the amp, as well as pre and post effects, forming a programmable power-tube-based tube amp emulator.

I think of the power tube and speaker (or load) as a tone engine. The brains to put around this tone engine are the pre and post multieffects units.

We are *seriously* in need of some tuned, scaled-down cabinets and guitar speakers. It stands to reason that a 4x12 cabinet won't respond richly to a 1-watt tube amp. It's likely that a 6" 5 watt speaker in a tuned cabinet would be a better match. Also, a compact speaker isolation cabinet such as the Micro Room generates less boominess or thumping -- less room noise.
tube convertor sockets

I want to buy and try things like the Black Jack tube convertors which enable plugging a certain spec'd preamp tube into a power-tube socket.

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