Dual vs Triple gain structure

[sumitagarwal]

I know that the dual and the triple are supposed to be mostly identical aside from power output but I noticed something interesting: both amps have 5 12AX7 tubes, but different numbers of power tubes. Doesn't an amp need one preamp tube per pair of power amp tubes? Then the dual would be using 2 12AX7's for that, leaving 3 tubes for input and gain stages, while the triple would be using 3 12AX7's for that, leaving only 2 tubes for input and gain stages.

Does this sound accurate? Does the Triple effectively have one less preamp tube for input and gain stages than the Dual?

 

[fluff191]

The amount of preamp tubes in the Recto's are not related to the power tubes (i.e. output) of the amp. The main difference between the 2 amps is the additional 50 watts the Triple is rated for. Same preamp section. Because of the additional power, the trannys are a bit bigger as well.

 

[cradlefish]

I know that the dual and the triple are supposed to be mostly identical aside from power output but I noticed something interesting: both amps have 5 12AX7 tubes, but different numbers of power tubes. Doesn't an amp need one preamp tube per pair of power amp tubes? Then the dual would be using 2 12AX7's for that, leaving 3 tubes for input and gain stages, while the triple would be using 3 12AX7's for that, leaving only 2 tubes for input and gain stages.

Does this sound accurate? Does the Triple effectively have one less preamp tube for input and gain stages than the Dual?

it's true plus the additional 50 watts calls for one extra rectifier tube as well.

 

[sumitagarwal]

This is what I'm suggesting:

DUAL (5x 12AX7; 4x 6L6):

preamp 12AX7 12AX7 12AX7
\ | /
----------------
| |
12AX7 12AX7
/ \ / \
power 6L6 6L6 6L6 6L6


TRIPLE (5x 12AX7; 6x 6L6):

preamp 12AX7 12AX7
| |
----------------
/ | \
12AX7 12AX7 12AX7
/ \ / \ / \
power 6L6 6L6 6L6 6L6 6L6 6L6


Terrible diagram, but does it make sense?
(argh! It's removing all my spaces!)

 

[94Tremoverb]

No, sorry, this is completely wrong - the number of preamp tubes is unrelated to the number of power tubes.

Each pair of power tubes does not require one preamp tube. There is *one* preamp tube - called the phase inverter - that supplies signal to all the power tubes, which are arranged in two sets. It makes no difference whether these sets are one, two, three (or more) power tubes each, they are simply operated in parallel as if they were one large tube with more power capability.

The only difference between the Dual and Triple Rectifier is the number of power and rectifier tubes and the size of the transformers - it's the same amp but simply with a 150W power section instead of 100W. There is no difference whatever in the preamp or gain structure.

(Edit: typo)

 

[domct203]

94Tremoverb is correct. If you download both manuals from Mesa Boogie there is a tube task chart that lists all the preamp tube functions.

Dom

 

[sumitagarwal]

Thanks for the clarification, guys... you learn something new every day!