Looking for FET's and Toroid's

[Sowhat]

I have got the bug to design and build another amp, this time it's going to be a high power bass amp but I'm having some problems finding sources in the U.S. for a few of the components I have decided on using.

1. EXC10N20 (EC-10N20) and EXC10P20 (EC-10P20) lateral MOSFET's in TO3 cases.

2. The power transformer. I want to use a dual primary (117/230V) and 100V CT secondary at around 300VA. I have found a Triad VPT100-5000 toridal transformer but it's 500VA and is a bit big and heavy not to mention expensive. Would like to find a smaller one at around 300VA. I will be creating +-70 volt rails on this power sucker.

Anyone have some U.S. sources for these things?

[loudthud]

For transformers in the US you can't beat Antek: https://www.antekinc.com/index.php

For FETs the selection of TO-3s is slim. The industry is moving away from that package because there are no big orders from OEMs. Same applies to TO-92s. You should consider the TO-3P or TO-247.

[Steve Conner]

The Exicon MOSFETs are only available from Profusion, a UK-based company. Exicon is their house brand. The Magnatec BUZ901 and BUZ906 are very similar, available from MCM in the USA. (They ship from Farnell in the UK though, as far as I know.)

All of these devices are lateral MOSFETs. Pretty inefficient compared to BJTs and vertical MOS devices such as the IRFP240 and IRFP9240, which will give you more output power for the same rail voltages.

However lateral MOSFETs still have their devotees who claim they are the most tubey-sounding of all semiconductors. I won't get drawn into a debate about how true this is. I'll just say that I've built two amps with them and been satisfied with the results. They also allow the simplest power amp design, as they're very easy to drive and need no thermal compensation.

And if you already have heatsinks drilled for TO3s, you won't find any VMOS devices in TO3 packages any more, so your choice is down to lateral FETs or some hefty BJTs like the MJ15024 and MJ15025.

[Sowhat]

Thanks for your suggestions guys,

I guess I can order direct from Profusion for the FET's in TO3's, not too bad with slow boat shipping (airmail) at a little under $50 for 2 pairs. It's that tubey thing I was looking for with the laterals if indeed it actually sounds that way. The transformer on the other hand is going to be a tough nut to crack because Antek while having a good selection of transformers just don't have the specs I'm looking for. Right now unless I find something better, the Triad VPT100-5000 seems to be my only choice and will work just fine, it just seems a bit of a waste having all that power overhead in that 500VA transformer when I only will be utilizing about 300VA. I could of course use the space saved by a smaller transformer for things like the soft start circuitry and rectification/filtering... oh well, I can squeeze that stuff in somehow, there's a few square inches available here and there.

[Enzo]

SO are there any commercial amps using a toroid PT similar to your specs? Like Hartke, or Fender, or Ampeg, or any of a thousand PA power amps? Might find a better price on one of them.

[Sowhat]

Doh! ... never thought about that, great idea, I'll have to take a look see.

[loudthud]

You won't beat $36.00 for the Antek AN3450.

[Sowhat]

Wow! How did miss that one, I thought I looked through all the Antek stuff... I get my +-70 volt rails and I get my 300VA and it has dual primaries (very cool!). Not only that but it has spare 18 and 12 volt taps as well, maybe I can gin up some sort of unbalanced plus/minus supply with those for the preamp (thank god for zeners). Still it's kind of big at 4.8 x 3.1 but I think I can deal with that. Thanks loudthud. $36.00, that's incredible!

[loudthud]

The guys at the diyaudio forum use them. diyAudio Some of the stuff you can see but you may have to join. If you want to post something, the first five posts will be reviewed by a moderator before it shows up, usually only takes a couple of minutes.

The only problem they find is that the secondaries are not prefectly balanced. They suggest you use a separate bridge for each winding, then to the caps and then joint the grounds in a star with the speaker return. I think Nelson Pass uses Antek and he is out there ..... The one thing I don't like is the color coding on the leads. You have to ohm the windings out to make sure you know which wire goes to which winding.