Power amps for tri amp system

[DerekVa]

May I humbly suggest a trio of Fisher 30A mono amps? This is what I'm using in my home theater (driving a trio of Klipsch KP250 industrial Heresys) and they work extremely well in this application. I've actually mounted two of the amps (using the stock console mounting points) to the backs of the left & right speakers so that my speaker cables are ~ 6". While stuff on eBay is usually quite overpriced, if you ask around, you can usually find ones in desperate need of work for not much money (I paid $90 and $45 for two of mine, and built the third out of spare parts in a Hammond box).

-D

[coolhandjjl]

Lots of great suggestions here, I wish to thank everyone for their input.

With my initial emphasis being midrange, it seems that either an SE amp, or an amp with a UL/Triode mode switch is what I am after. (SE the same as Strapped Triode?) Regarding power supply, I'm guessing ss with a choke is more economical that tube based rectification? Which has less noise?

Seems that the kits that fit my needs are either 4 wpc, or jump up to 17 wpc like the ST35, and its associated clones. The ST35's seem like complicated builds, and expensive as well. Add to that, all the discussion about cathode bias vs EFB mods, power supply mods, makes it seem like an ST35 will also requite some careful thought and planning to integrate these mods.

I looked at Tom McNally's page and he has some SE amps in the 8 wpc range. If I wanted SE in the 8~12 wpc range, is he the go-to-guy?

[kheper]

Lots of great suggestions here, I wish to thank everyone for their input.

With my initial emphasis being midrange, it seems that either an SE amp, or an amp with a UL/Triode mode switch is what I am after. (SE the same as Strapped Triode?) Regarding power supply, I'm guessing ss with a choke is more economical that tube based rectification? Which has less noise?

SS diodes are thought to produce more noise than tube rectifiers, but most people do not notice the noise.

Any tube (a triode, a tetrode or a pentode) can be run in SE. Pentodes and tetrodes are operated in UL mode, providing that the output transformer has UL taps. The UL/Triode switch just switches the output tube between UL and triode mode.

Seems that the kits that fit my needs are either 4 wpc, or jump up to 17 wpc like the ST35, and its associated clones. The ST35's seem like complicated builds, and expensive as well. Add to that, all the discussion about cathode bias vs EFB mods, power supply mods, makes it seem like an ST35 will also requite some careful thought and planning to integrate these mods.

I looked at Tom McNally's page and he has some SE amps in the 8 wpc range. If I wanted SE in the 8~12 wpc range, is he the go-to-guy?

Tom McNally has made MANY amps. The JE labs SE el34 will hit ~8W in UL mode. A KT88 can do 8-12W in SE UL mode.

http://diyaudioprojects.com/Tubes/KT88/

[msmpe]

My "dream" system is bi-amped, and most of my breadboard experiments have leaned to that end. If you have a good sized listening room, then you can go with lotsa watts. For the bass - SS is OK, but PP tube amp in UL mode with god damping is way better in my opinion. Shoot for 50W/ch. For the mid section, 5 to 20 W/ch will work, shoot for 10 or more. The tweeter does not need much but still need to have plenty of head room, try for no less than 3W/ch.

Harmonics is an important consideration. 2nd harmonics on the mids and tweeter is essential in my opinion, and bi/tri-amping lets you take advantage of that. SE-UL for the mids is a good choice. The JE Labs EL34 is perfect, although in UL you lose some of the 2nds and pick up some 3rds. I'm building one similar myself, but mine will be an ambiance amp for small full range side speakers. Mo-beta is 300B SET and crank it. Shoot for 10-12W/ch with top of the line OPT. The mid is actually the most important octave ranges for conveying the essence of the music, so don't scrimp there. And you need plenty of headroom, so more watts is better. The 300B is the quintessential SET, my bi-amp system will use 300B SET for the mid/highs.

For your tweeters, just about any tube run in SE triode strapped mode will give you those oh-so-sweet 2nd harmonics. I've had success with 6BM8, EL84, 6V6, 6AV5, 1626, but I'd lean toward an EL34 SE triode strapped. Look for the "sweet spot" as you'll get all the watts you need regardless.

Sounds like you have your drivers, so pick the frequency ranges/crossovers to suit the drivers. If you have a clean sheet, I'd suggest the bass run the first 3 octaves, the mids carry the middle 4, and the tweeters blow the top 3.

If you google around, you can find some info on how many watts are required for good balance depending on where the crossovers are. Try Elliot, Mapletree....

You've got a great project ahead of you