Project in mind.

[XQtioner]

So I'm new to amp building and have a question to go along with my introducing myself.
My plan/vision is to build a high(ish) watt bass amp (500w) and custom 4-10" bass cab from scratch.
My bass amp start point is the new Boogie Strategy Eight:88, to whit, variable output, 1/4, 1/2 and full power but I want to use 6 KT88's (all 8 tubes at full and 4 KT88's at 1/2) and 2 6L6GC's for the 1/4 output.

Thoughts???

[XQtioner]

To add further to this project, I would ask pro's and con's for the following:
Tube rectifier vs. MOSFET
12AX7 vs. 12AU7
EI power tranny vs. Toroidal vs. SMPS
I do not yet have a schematic or block diagram and am gratefully accepting input and will post once drawn.
I look forward to any and all input a/o critique/criticism 

[eleventeen]

So I'm new to amp building <<------->> My plan/vision is to build a variable output, 1/4, 1/2 and full power, 6 KT88's (all 8 tubes at full and 4 KT88's at 1/2) and 2 6L6GC's for the 1/4 output.


Those phrases ought not be used in the same sentence. There is no way that is a project suitable for a beginner, not in the same galaxy.

[HotBluePlates]

Said a different way:

I've been tinkering amps a long while (since about the late-90's); I wouldn't want to build a 500w amp for any amount of money. The biggest off-the-shelf output transformer I'm aware of is the Hammond 1650W rated for 280w down to 30Hz, which weigh 28lbs! And you need 2 of them for a 500w bass amp... (scratch that, looks like Plitron has a 400w OT that weighs ~23.5lbs, but it costs ~$500 before shipping and, since it's probably a toroid, will be viciously intolerant of unbalanced d.c.) The chassis is gonna need some major engineering to support the weight of the power and output transformers of such a beast.

By the time you're up to the 400-500w range, you really should be looking at solid state amps on the market. On the tube side, it would be much less heartache to simply buy a 300w+ SVT than to build one. I repaired an original SVT with 6146 output tubes once for a friend, and it's a feat just disassembling and reassembling that amp.

I don't mean to be discouraging, but this is a big dream, not unlike saying, "I want to learn to modify cars. My first project will be a Ferrari scratch-build."

[HotBluePlates]

Answering other questions:

Tube rectifier vs. MOSFET

Big power = big power supply. And LOTS of current. That rules out tube rectifiers for any sensible plan, pretty much dictating solid state rectifiers.

The power supply will also be complex. For 6146, 6550 or KT88's and high power, you're probably looking at a B+ of 600v+, with a screen supply roughly half that. Most often, the path taken is 2x 300v power supplies (2 high voltage windings, 2x sets of rectifiers, one supply stacked on top of the other) to give 300v and 600v outputs. 600v goes to the OT and output tube plates, while the 300v supply powers output tube screens and the preamp.

EI power tranny vs. Toroidal vs. SMPS

I'd think you wouldn't consider a switch-mode power supply (SMPS) in an amp at all; they are generally big noise problems waiting to happen, and you likely can't find them off-the-shelf in the voltages/currents/VAs you'd need for such a big amp.

Toroids are great for saving space & weight, and radiate less hum due to their construction. But it may be harder to find what you want in a single toroid power transformer, if you're going for massive power supplies to build a beast.

That pretty much leaves EI transformers, and probably a mix of several for a very high-power amp.

12AX7 vs. 12AU7

The smart moves for tube bass amplification were pretty much already figured out by Ampeg & Sunn. You'd be best copying one of their preamps/phase inverter/output stage verbatim.

[uki]

Hi there and welcome !

Listen to those guys they know what they are saying, I'm also new to amp building stuff, I did build one amp without much experience and knowledge and I'm having some problems to get the amp to work properly, Start with something simpler, what about a Fender Bassman , or even a smaller amp to get some experience, then you'll get a very good notion and experience about what to build an amp is, don't get discourage, small steps would be much wiser move.

[PRR]

> Plitron has a 400w OT

This (or even their little 300W job) could easily be pushed 500 Watts as a bass stage amp. (Their nominal power bandwidth is far below what even drop-tuned bass will ring at; their bass distortion is far below any loudspeaker smaller than a semi-truck.)

I used to tour with 750 Watts of tube. (5 channels on 3 chassis.) This is part of why I've gimped in pain for decades.

I recall that the least mistake in 150+ Watt tube amps is major drama and expense.

There is a lot of detail in even a small amp, and nobody is born knowing this stuff. I've repaired heaps of gear and scratch-built quite a lot, but building a complete Champ from chassis and iron was challenging.

Either commit the next few years to NOTHING but working on amps, or go buy a kilo-Watt shoebox amp.

The speaker is perhaps less challenging and less dangerous.

However four Tens is not really enough for 500 Watts of guitar, and way under-size for 500 Watts of bass. Eight Tens may take the power, but Tens are usually not designed for large excursion and won't move the vast amounts of air needed to boom the bottom octave. You'll slap the snot out of them.

Note also that, up to a point, doubling the speaker total cone area doubles the efficiency and output, and narrows the pattern (more throw). It can make good system-sense to upsize the speaker and downsize the amplifier. That leads to less-insane 300W or even 150W amp. Of course the speaker may not fit in the van.