I saw someone mentioned st151 amp. It looks like cheap amp to build with any kind of material. Maybe is still to complicated and too expensive, I don't know. Jaycee has made good point mentioned good old 2N3055. What about an amp using only NPN transistors. It will be easier to find something really cheap. Even something pulled from computer psu should work....Yea yea I know that it has nothing to do with good amplification but these transistors can handle(some of them) enough of power and can handle high voltage....Just an idea. Once i use some of these and if I remember correct they come from such psu......don't kill me I know they are not some thermal track 
http://www.datasheetcatalog.org/datasheet/mospec/2SC3306.pdf
http://www.datasheetcatalog.org/datasheet/mospec/2SC3306.pdf
If it's a simple 100 watt circuit your after try this one, it can be used with supply rails up to 55 volts... It's Dave Goodmans mosfet amp very easy to build and will give 100w at 8 ohm and 150w at 4 ohm use... there's so many circuits out there on the net to choose from and will work just nice...
A Mistake there . Corrected for those who don't get inception .
If i remember closely MJ21193 is able to output 400W @ 4 ohm .
( And it might be able to do 2ohm safely ) not sure about that , but 4 ohm is safest for me , don't wanna go any lower or boundaries would just dissapear .
-separate topic-
Are there any 100W 2Ohm stable FET's / BJT's out there ?
I would like to have one , as bridging them means 200W 4 ohm -yum-
Hi blindmole,
May be I know how circuits sound in relation with anything else in the audio chains, and I know what I like. But how the hell I know what you like???
If you consider the P3A, consider also the Baby Aksa and DX amps (whichever is easier for you).
But I'm sorry that I have to question your "must be above 100W" requirement. Don't you know that we are not using 100W from a 100W amp? Just make sure you have big transformer as if your amp is 300W (because you may make a mistake by choosing 100W++ design but using inferior power supply)
May be I know how circuits sound in relation with anything else in the audio chains, and I know what I like. But how the hell I know what you like???
If you consider the P3A, consider also the Baby Aksa and DX amps (whichever is easier for you).
But I'm sorry that I have to question your "must be above 100W" requirement. Don't you know that we are not using 100W from a 100W amp? Just make sure you have big transformer as if your amp is 300W
(because you may make a mistake by choosing 100W++ design but using inferior power supply)And which amp is that? This site is full of talents that offer (for free) very good amp designs. All amps are cheap. The expensive one is the power supply. You want power, you need to have money
Yes, darlingtons (such as TIP142/147) offer high gain at low voltage, but they sound horrible. TIP41/42 on the other hand is a classics like the 3055/2955, with less possibility for counterfeit issue (fake transistor).
I don't know how you will get your PCB. In my country, 150W OCL is very popular (best selling circuit). If you can get similar PCB, you can build a variety of Baby AKSA and DX amps.
Hi DJ
I should have said of course "using a lower supply voltage". You are right if the power rails stay at +/- 35V but for a bridged amp the transistor dissipation is still an important factor. If we assume that two pairs of 2N3055/MJ2955 per channel are used they will have to dissipate something around 100W for 100W output. I recommend that blindmole uses a bridge running from +/-27..30V using two pairs of 3055/2955 per channel in a bridge configuration. The heatsinks needed would not be so great.
Thanks for the correction, but I did mean 100W into 8 ohms.
John
I should have said of course "using a lower supply voltage". You are right if the power rails stay at +/- 35V but for a bridged amp the transistor dissipation is still an important factor. If we assume that two pairs of 2N3055/MJ2955 per channel are used they will have to dissipate something around 100W for 100W output. I recommend that blindmole uses a bridge running from +/-27..30V using two pairs of 3055/2955 per channel in a bridge configuration. The heatsinks needed would not be so great.
Thanks for the correction, but I did mean 100W into 8 ohms.
John
this amplifier. pcb i will make by self. I will do it because I have already made the acquaintance who is this Amplifier so it helps me solve problems. and things which I do not understand.
On looking at the 100w amplifier link it's a basic amp and will do the job, the only draw back is there is no short circuit built in nor is there any bias trim for the o/p transistors and the amp may/will go in to thermal run way with out fan cooling..as any one built this unit and recorded test report? I've seen lots of amps with this design using diode set mmm not really a great fan of it... but hay it's ok for a cheap amp...
This one may be tricky - it is an old Elektor "current dumping" amplifier, styled after the Quad 405 but much simplified. Stability may be an issue, depending on implementation, because of the feedforward error correction it uses (L1 C3 R10 R11).
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