Building tube guitar amplifier

[Phil Smith]

Good stuff, I know nothing of "mesa" are they an original from the 1950's?. The circuits look like they are.

n.

Late 60's.
In 1969, Randall Smith, founder of mesa/boogie, as a joke, modified Fender Princeton amplifier. He removed the standard 10-inch speaker and modified the chassis to fit the larger heavy transformers that were needed by the 4x10 (four 10" speakers) tweed Fender Bassman, the circuit that he had added into the tiny 12 watt Princeton. Finally, Smith had created what would be the first Boogie.
Needing to test his creation, Smith took the "hot-rodded" Princeton to the front of the store, where Carlos Santana was present. Santana "wailed through that little amp until people were blocking the sidewalk". Impressed, Santana exclaimed to Smith, "Man, that little thing really boogies!" It was this statement that brought the Boogie name to fruition.

It was MARK I.
After that Mark II, IIb, IIc were born and finally IIc+. This amp became popular after Metallica's MASTER OF PUPPETS and JUSTICE FOR ALL albums and, surely, John Petrucci tone.

PS before MESA, Randall worked as a repair tech for a while.

 

[Notebook]

Wow, Mr Santana.....! good pedigree.

Noticed that two capacitors are changed for a "simul class"? The decoupling across V4A anode is removed, and the coupling from V1/V2 is changed. Is the "simul class" a unique power amp they built?

N.

 

[ex-orbinaut]

Thank you!

Think I might be able to get all the materials here, otherwise the next time I am in Miami for what I might not be able to get. This gives me a golden opportunity to put to practical use a skill learned as a part of a course 20 years ago and used only once since. Project on the table.

Thanks again!

 

[Phil Smith]

Wow, Mr Santana.....! good pedigree.

Noticed that two capacitors are changed for a "simul class"? The decoupling across V4A anode is removed, and the coupling from V1/V2 is changed. Is the "simul class" a unique power amp they built?

N.

Simul-class is their unique patented power amp. So what it does?
Power amp of this mark IIc+ was in two versions - 60 watts with 2x6L6 tubes (valves) at power section and SIMUL CLASS 85 watts with 2x6L6 and 2xEL34 with ability to turn off both 6L6s and play through el34 only, getting just 25 watts. There is special output trans (see schematic below) and for switching between 85/25 watts you just lift 6L6's cathodes from the ground.
So that's a key.
Original MESA/Boogie power amp schematic (MARK IV):

Thank you!

Think I might be able to get all the materials here, otherwise the next time I am in Miami for what I might not be able to get. This gives me a golden opportunity to put to practical use a skill learned as a part of a course 20 years ago and used only once since. Project on the table.

Thanks again!

You're welcome!
If you'll decide to build this amp I can give you little advice:
Here's a list of mesa key sound components that they use:
All capacitors in signal chain are Orange-Drops (225 series, but also you can install 715's).
All caps less than 1000p are ceramic.
All electrolytic caps in cathodes are tantalum KEMET.
All LDR's are VTL-5c1.

And try to copy my mistakes not - do it with original layout :lol: cause developing of your own pcbs is hard-pain work :thumbup:

Cheers!

 

[ex-orbinaut]

Thanks for that.

I will most probably be starting with the PSU, for two reasons. First, if I cannot do that, then there will be little point in doing the rest. Second, looks like it is for 220VAC input. This is okay - we have three phase AC on the grid here and I can wire up my own 220 socket specifically without bending any regulations - but I would prefer it 110VAC as houses here are wired for it. This is where I must emphasize "skill", at the moment, as in I am confident about knocking up the PCBs and obtaining the indicated components. However, much of the background knowledge and understanding is "evaporated", so to speak, through disuse. Though I have an idea what needs to be done to bump the input down, I am a bit wary of actually doing it, naturally.

In any case, as far as I am concerned, you going to get the highest praise anyone can: Imitation of your project!

 

[Phil Smith]

Thanks for that.

I will most probably be starting with the PSU, for two reasons. First, if I cannot do that, then there will be little point in doing the rest. Second, looks like it is for 220VAC input. This is okay - we have three phase AC on the grid here and I can wire up my own 220 socket specifically without bending any regulations - but I would prefer it 110VAC as houses here are wired for it. This is where I must emphasize "skill", at the moment, as in I am confident about knocking up the PCBs and obtaining the indicateed components. However, much of the background knowledge and undrstanding is "evaporated", so to speak, through disuse. Though I have an idea what needs to be done to bump the input down, I am a bit wary of actually doing it, naturally.

In any case, as far as I am concerned, you going to get the highest praise anyone can: Imitation of your project!

Thanks mate!
yeah, power supply I've drawn for European 220/240 VAC.
You can easily convert it to usual 120 V by changing transformer (It's not a problem cause you probably will buy that type you actually need and dont worry about voltages after it - they still be the same - just another voltages ratio) and replacing the 3A fuse with 4A.

 

[Notebook]

Also just noticed, that V4A and V3B may well be the same valve?(you often had double triodes inside the envelope).

As the other valves demonstrate

All this outside my experience, when I was a lad it was analogue round here...

N.

 

[Phil Smith]

Also just noticed, that V4A and V3B may well be the same valve?(you often had double triodes inside the envelope).

As the other valves demonstrate

All this outside my experience, when I was a lad it was analogue round here...

N.

Yes, I use 12ax7 (or ECC83) valves. It's a dual triode. So, for example, we have V1A and V1B - same valve but different triodes inside.
Here's a datasheet:
http://www.ampbooks.com/home/amp-technology/balanced-amp/12AX7.pdf
You can combine triodes on your pcb and call em on schematic as you want.

 

[Capt_hensley]

Sweet, I can appreciate a good VT circuit board. I used to build and etch my own solidstate power supply boards & Capacitance Discharge machines for my Model Railroad. Chemical etching is fun, getting the traces right is alot of work but well worth it in the end.

CD Machines make an electric turnout motor snap into place, Circutron makes a machine called a Super Snapper, so I gave up on mine and started buying thiers. Great work.

 

[ex-orbinaut]

You can easily convert it to usual 120 V by changing transformer (It's not a problem cause you probably will buy that type you actually need and dont worry about voltages after it - they still be the same - just another voltages ratio) and replacing the 3A fuse with 4A.

Ah, thanks. I am glad you said that. I thought you had made those coils yourself. Regarding that rectifier unit, you did make that, though? That's one component that I am pretty much up to date on, as I have been doing them with reasonable regularity over the years on car alternators overhauls.

 

[Phil Smith]

Ah, thanks. I am glad you said that. I thought you had made those coils yourself. Regarding that rectifier unit, you did make that, though? That's one component that I am pretty much up to date on, as I have been doing them with reasonable regularity over the years on car alternators overhauls.

For example, probably the best trans you can purchase are from Mercury Magnetics.
http://www.mercurymagnetics.com/pages/mainframe.htm -> choose Mesa/Boggie and there will be 2 - power trans "PT MESA-MARK-P" (with 120 V primary!) and output trans "ОТ MESA-MARK-O".
These trans are used for amp modding for best performance.
Also there you need choke (C-MESA-CH) and reverb transformer (R-MESA-RT).
Yep, they're not cheep but it's better than original MESA trans.
You can also order trans from your local guys.

The rectifier. there's usual full-wave rectifier based on four 1n4007 diods. You can put there ultra-fast diods UF4007 (like I did).

 

[Notebook]

Gosh 1N4007 diodes, 1N914, small signal diodes, 2N3819 FET, BC109...Nostalgia, I wish the Simpsons had made an episode...Maybe they have and I've forgot?

N.