Higher Power Low TIM Leach

Stormrider · 23rd December 2009, 11:35 PM

I picked up a dead Ashly FET500 today, pretty cheaply. It's a 400W/4R per channel, fan cooled, mosfet (2SJ50/2SK135), pro-amp. It uses four pairs of the Hitachi lateral fets per channel.

Upon disassembly, in one channel, I found one J50 and one K135 had a hole blown in them, and another K135 severely discolored. Also, the board has a small burn on it next to a diode. Unless someone has a source for these outputs, cheaply (haha), I'm thinking this amp is a lost cause as is. The 2nd channel looks OK, visually.

So, I'm trying to think of a project to build into the chassis using the existing power supply. IIRC, from my other FET500, the rails are +/-80Vdc. Looks like a ~1KVA transformer. I am not really set up to print my own PCB's, so I was leaning towards the Low TIM Leach, using four pairs of MJ21193/94 per channel on the +/-80Vdc.

Does the professor still sell boards? Would I be able to use his boards for a project like this?

http://i120.photobucket.com/albums/o...FET5002002.jpg

http://i120.photobucket.com/albums/o...FET5002003.jpg

http://i120.photobucket.com/albums/o...FET5002006.jpg

http://i120.photobucket.com/albums/o...FET5002009.jpg

http://i120.photobucket.com/albums/o...FET5002010.jpg

P.S. Happy Holidays!

wahab · 23rd December 2009, 11:42 PM

you can use top3 2SJ162/2SK1058....they have exactly the same caracteristics but you ll have to change the whole sets...16 fets...

Stormrider · 24th December 2009, 01:13 AM

Interesting solution. But, I think converting the amp to use the TO3P packages would be as much work as retrofitting it with the Leach PCB's and, I already have the MJ21193/94's. I still don't understand why Hitachi discontinued the TO3 lateral. Seems like every mosfet amp from the 70's and 80's used it.

mlloyd1 · 24th December 2009, 02:31 AM

wow, i've never seen hitachi mosfets blown up like that!
speaking of letting out the magic smoke ....

mlloyd1

taj · 03:58 AM

The 80v rail voltage is WAY too high for a stock Leach amp. He uses protection circuitry that is nailed to the rail voltage, and the input and VAS section may not be able to handle that voltage. But you could make it work with Jen Rasmussen's Leach boards maybe (a thread here). Other alternatives for that rail voltage and TO3 output devices that come to mind, are Quasi's NBIP amplifier (a thread here), and Destroyer X's DHR Turbo (a thread here). Those last two need you to etch some boards (which isn't too big a deal really.)

It may be simple enough to piggyback (securely and with grease) another thick strip of aluminum onto the heatsink ledge to provide a mounting surface for TO-3P, TO-247 or TO-264 devices. Then you've got lots of choice for devices.

..Todd

Damon Hill · 24th December 2009, 03:57 AM

Geez... I've never seen a TO-3 device blown like that. (boggles)

You'd have to use Marshall Leach's Superamp to use those rail voltages; he doesn't sell the boards for that version.

Leach SuperAmp Plans

This is a "totem pole" design that uses two pairs of 'stacked' output devices and drivers.
As you can see, there's a lot of power in that much rail voltage but the MJ21193-96 family of devices should handle it well.

Stormrider · 24th December 2009, 04:20 AM

OK, no go on the Leach boards. Looks like this project will have to hold off until I can get the tools/materials for making my own boards. Thanks for the help guys.

As for these TO3's, I think they deserve a place in the Magic Smoke Hall of Fame. I really don't know how the original owners did it.

taj · 24th December 2009, 03:50 PM

That's a nice chassis. Because of its single large power supply, my first thought would be to make a nice gutsy subwoofer amplifier with it.

Yes, get yourself a PCB making set-up, your options expand by an order of magnitude.

..Todd

megajocke · 24th December 2009, 08:21 PM

Actually, the Leach circuit is usable on +-80V with some part changes. The high voltage SOA of the MJ2119x devices is good so there isn't really any benefeit in the cascoded connection of the SuperAmp with such output transistors.

Stormrider · 24th December 2009, 09:46 PM

Quote:

Originally Posted by megajocke

Actually, the Leach circuit is usable on +-80V with some part changes. The high voltage SOA of the MJ2119x devices is good so there isn't really any benefeit in the cascoded connection of the SuperAmp with such output transistors.

Good to hear some hope for this. Can you elaborate?

23rd December 2009, 11:35 PM	#1
Stormrider diyAudio Member Join Date: Apr 2006 Location: Connecticut	Higher Power Low TIM Leach I picked up a dead Ashly FET500 today, pretty cheaply. It's a 400W/4R per channel, fan cooled, mosfet (2SJ50/2SK135), pro-amp. It uses four pairs of the Hitachi lateral fets per channel. Upon disassembly, in one channel, I found one J50 and one K135 had a hole blown in them, and another K135 severely discolored. Also, the board has a small burn on it next to a diode. Unless someone has a source for these outputs, cheaply (haha), I'm thinking this amp is a lost cause as is. The 2nd channel looks OK, visually. So, I'm trying to think of a project to build into the chassis using the existing power supply. IIRC, from my other FET500, the rails are +/-80Vdc. Looks like a ~1KVA transformer. I am not really set up to print my own PCB's, so I was leaning towards the Low TIM Leach, using four pairs of MJ21193/94 per channel on the +/-80Vdc. Does the professor still sell boards? Would I be able to use his boards for a project like this? http://i120.photobucket.com/albums/o...FET5002002.jpg http://i120.photobucket.com/albums/o...FET5002003.jpg http://i120.photobucket.com/albums/o...FET5002006.jpg http://i120.photobucket.com/albums/o...FET5002009.jpg http://i120.photobucket.com/albums/o...FET5002010.jpg P.S. Happy Holidays! __________________ AJ

24th December 2009, 01:13 AM	#3
Stormrider diyAudio Member Join Date: Apr 2006 Location: Connecticut	Interesting solution. But, I think converting the amp to use the TO3P packages would be as much work as retrofitting it with the Leach PCB's and, I already have the MJ21193/94's. I still don't understand why Hitachi discontinued the TO3 lateral. Seems like every mosfet amp from the 70's and 80's used it. __________________ AJ

24th December 2009, 03:44 AM	#5
taj diyAudio Member Join Date: Feb 2005	The 80v rail voltage is WAY too high for a stock Leach amp. He uses protection circuitry that is nailed to the rail voltage, and the input and VAS section may not be able to handle that voltage. But you could make it work with Jen Rasmussen's Leach boards maybe (a thread here). Other alternatives for that rail voltage and TO3 output devices that come to mind, are Quasi's NBIP amplifier (a thread here), and Destroyer X's DHR Turbo (a thread here). Those last two need you to etch some boards (which isn't too big a deal really.) It may be simple enough to piggyback (securely and with grease) another thick strip of aluminum onto the heatsink ledge to provide a mounting surface for TO-3P, TO-247 or TO-264 devices. Then you've got lots of choice for devices. ..Todd Last edited by taj; 24th December 2009 at 03:58 AM.

24th December 2009, 04:20 AM	#7
Stormrider diyAudio Member Join Date: Apr 2006 Location: Connecticut	OK, no go on the Leach boards. Looks like this project will have to hold off until I can get the tools/materials for making my own boards. Thanks for the help guys. As for these TO3's, I think they deserve a place in the Magic Smoke Hall of Fame. I really don't know how the original owners did it. __________________ AJ

24th December 2009, 08:21 PM	#9
megajocke diyAudio Member Join Date: Jan 2003 Location: Solna	Actually, the Leach circuit is usable on +-80V with some part changes. The high voltage SOA of the MJ2119x devices is good so there isn't really any benefeit in the cascoded connection of the SuperAmp with such output transistors. __________________ The bewitching snivvie is dulcet paragon.


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23rd December 2009, 11:42 PM	#2
wahab diyAudio Member Join Date: Nov 2009 Location: algeria/france	you can use top3 2SJ162/2SK1058....they have exactly the same caracteristics but you ll have to change the whole sets...16 fets...

24th December 2009, 02:31 AM	#4
mlloyd1 diyAudio Member Join Date: Feb 2001 Location: illinois	wow, i've never seen hitachi mosfets blown up like that! speaking of letting out the magic smoke .... mlloyd1

24th December 2009, 03:57 AM	#6
Damon Hill diyAudio Member Join Date: Mar 2001 Location: Auburn, WA (somewhere between Seattle and Tacoma) Blog Entries: 1	Geez... I've never seen a TO-3 device blown like that. (boggles) You'd have to use Marshall Leach's Superamp to use those rail voltages; he doesn't sell the boards for that version. Leach SuperAmp Plans This is a "totem pole" design that uses two pairs of 'stacked' output devices and drivers. As you can see, there's a lot of power in that much rail voltage but the MJ21193-96 family of devices should handle it well.

24th December 2009, 03:50 PM	#8
taj diyAudio Member Join Date: Feb 2005	That's a nice chassis. Because of its single large power supply, my first thought would be to make a nice gutsy subwoofer amplifier with it. Yes, get yourself a PCB making set-up, your options expand by an order of magnitude. ..Todd

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