Mesa Boogie D-180

[CJ]

we need to explore this Mesa creation, because somebody does not like it anymore,

 

[CJ]

six power tubes, which means we need a pwr and OPT trans, maybe a choke and an EQ with real inductors,

 

[CJ]

there is a fan switch for adjusting the noise level of the fan which is unique,

and a funky lookin 5 band>

 

[CJ]

plenty of filtering, 10 ea at 220uf/285 V-dc, 5 and 5 in series, so 2200/2=1100uf/570

large C = bass amp,

and 40-30-30uf thrown into the preamp,

somebody worked for the power company, check that buss wire job,

 

[CJ]

apples and oranges,

Sprague 715P doing the coupling around here,

looks like some silicon getting mixed into the vac circuit, makes me nervous,

and those 1/4 watt plate resistors, wtf, over?

screen resistors have been tortured up to 500 ohms,

 

[CJ]

rect and bias board,  and a crispy 470>

 

[CJ]

looky here, a transformer hidden in the back,

you can run, but you can't hide,  ;D (Efrem Zimbalist Jr.)

http://en.wikipedia.org/wiki/Efrem_Zimbalist,_Jr.

don't drop a screwdriver into this chassis when hot, you  might have sparkage,

 

[CJ]

not much schemo action online,

lack of power seems to be our dilemma,

unique is the V1/V2 input situation>
http://schems.com/manu/mesaboogie/boogie_d180.pdf

 

[Bobby Baird]

This is the amp Cliff Burton used on Master Of Puppets. Hope you get it sorted out. The fellas at Mesa Boogie were real nice to me on phone 707-789-3324 and would answer my questions on particular amps. If you need to chime in ask for Richard Duvall [email protected]. He is the manager of the service dept. He could maybe send you schematics are details on transformers.

 

[CJ]

thanks Bobby! ever been to Navasota? check out the Cornell Hurd Band there at the Western Club,

so far we got a shorted Sovtek 6L6WXT from 2004,

 

[Bobby Baird]

Your welcome CJ. I never been there, apparently it's been named the blues capital of Texas. The Western Club looks like a mighty fine honky tonk. That bands drummer Lisa is from Austin. It sounds like see likes that snare to sizzle.

 

[CJ]

yes we like the TailGators, T-Birds, Antones, Mike Buck, the Broken Spoke,  etc.

Mesa made 3 versions of this amp, this one sports the weird input situation where-by input #1 sends the signal into a 12AX, it comes back to the jack and passes thru a sw on the jack which sends it to stage 2, input jack #2 bypasses that first stage, so you get an extra gain stage with input #1,

 

[CJ]

tube #2,

 

[CJ]

unique to this amp are some constant current diodes in the cathodes of the phase inverter and buffer, this amp uses a TCR508,

a better description of this device:

"Constant-current diode is an electronic device that limits current to a maximum specified value for the device. It known as current-limiting diode (CLD), current-regulating diode (CRD), or diode-connected transistor.

These diodes consists of a n-channel JFET-transistor with the gate shorted to the source, which functions like a two-terminal current limiter or current source (analogous to a voltage-limiting Zener diode). They allow a current through them to rise to a certain value, and then level off at a specific value. Unlike Zener diodes, these diodes keep the current constant instead of the voltage constant. These devices keep the current flowing through them unchanged when the voltage changes. An example is the 1N5312. Note the negative VGS is required, as an example on the n-type junction-gate field-effect transistor 2N5457."

i am guessing that this is to prevent negative feedback,

here is the circuit>

 

[CJ]

here is the specs on the OPT, 

first time i have seen a 2x2 lace job on the lams,

turns are just a guess, most folks use about 100 turns for the sec.

 

[CJ]

here is the pwr supply and EQ from the Mesa 400, very similar to the D-180,

power tubes are just your standard config with 470-2 watt screen rrsistors and 2200 grid stoppers, -56 volts bias,

we stuck a 1.25 k 10 watt pwr resistor in series with the choke to give the tubes a bit of a break, so we have 523 plates, 515 screens, when AC is applied to the pwr tubes, there will be a bigger voltage drop across the 1.25 K which will lower keep this beast from self destructing,

 

[Bobby Baird]

yes we like the TailGators, T-Birds, Antones, Mike Buck, the Broken Spoke,  etc.

Mesa made 3 versions of this amp, this one sports the weird input situation where-by input #1 sends the signal into a 12AX, it comes back to the jack and passes thru a sw on the jack which sends it to stage 2, input jack #2 bypasses that first stage, so you get an extra gain stage with input #1,

I believe I read about this being the way they designed the amp to interface with guitar or bass. http://www.mesaboogie.com/manuals/D-180%20Power%20Amp.pdf. Input #1 being hi gain guitar, and input #2 being clean for bass. I guess this was the start of mesa foray into bass guitar territory. I currently own the mesa basis m-2000 bass amp. Their new kt88 all tube bass amp with graphic looks killer.

 

[CJ]

here is the preamp section schemo with a test tone of 50 mv @ 140 Hz (easy on the ears) applied to input 1 with vol 1 and vol 2 wide open,

voltages in red are V-ac from the signal applied,

that 15uf/10V cathode cap on V2 was bad, leaked the bias down to .44 V-dc, so we changed that,

 

[CJ]

here is the inverter circuit with V-ac test tone voltages in red and DC tube voltages in black,

of interest is the master vol control in the cathode of V4, this concept eliminates a dual pot master and 2 coupling caps which would be normally used to implement a master vol on the inverter, pretty clever, but does not have a linear increase in sound when the knob is turned, perhaps a rev log would work better, we have a linear 1 meg in there now,

not much negative feedback being applied, almost to the 'why bother' level,

 

[MatthewF]

yes we like the TailGators, T-Birds, Antones, Mike Buck, the Broken Spoke,  etc.

Mesa made 3 versions of this amp, this one sports the weird input situation where-by input #1 sends the signal into a 12AX, it comes back to the jack and passes thru a sw on the jack which sends it to stage 2, input jack #2 bypasses that first stage, so you get an extra gain stage with input #1,

I believe I read about this being the way they designed the amp to interface with guitar or bass. http://www.mesaboogie.com/manuals/D-180%20Power%20Amp.pdf. Input #1 being hi gain guitar, and input #2 being clean for bass. I guess this was the start of mesa foray into bass guitar territory. I currently own the mesa basis m-2000 bass amp. Their new kt88 all tube bass amp with graphic looks killer.

The first Marshall master volume amps use this same Hi/Lo input scheme (models 2203/2204, which later became the JCM800).

http://cdn.tonegeek.com/wp-content/uploads/2203-Preamp.gif

At that time Marshall's bass offering was the 1992 "Super Bass" so it's unlikely they'd have been encouraging bassists to plug into a 2203. I've never found much use for the "Lo" input on those master volume amps. It always struck me as odd to present the cold biased "distortion" stage as an input option; a normal electric guitar doesn't  have enough level to make it clip, and yet the clean sound is rather uninspiring. Maybe I should try plugging a bass in!