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/o200/ppiamp333/AshlyFET5002002.jpg
http://i120.photobucket.com/albums/o200/ppiamp333/AshlyFET5002003.jpg
http://i120.photobucket.com/albums/o200/ppiamp333/AshlyFET5002006.jpg
http://i120.photobucket.com/albums/o200/ppiamp333/AshlyFET5002009.jpg
http://i120.photobucket.com/albums/o200/ppiamp333/AshlyFET5002010.jpg
P.S. Happy Holidays!
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/o200/ppiamp333/AshlyFET5002002.jpg
http://i120.photobucket.com/albums/o200/ppiamp333/AshlyFET5002003.jpg
http://i120.photobucket.com/albums/o200/ppiamp333/AshlyFET5002006.jpg
http://i120.photobucket.com/albums/o200/ppiamp333/AshlyFET5002009.jpg
http://i120.photobucket.com/albums/o200/ppiamp333/AshlyFET5002010.jpg
P.S. Happy Holidays!
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.
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
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
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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.
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.
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.
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.
I see no reason not to use ±80V on a Low TIM Leach.
In addition to the MJ2119X outputs:
R13, R14 need to be changed.
Q16, Q17 need to be the higher voltage MJE15032/33.
You will probably need to change the foldback curent limit.
Here is basically the Leach with three pair of outputs and 270w per channel @ 8 ohms
425w per channel @ 4 ohms :
http://www.abamps.com/pdfs/600lx-man.pdf
In addition to the MJ2119X outputs:
R13, R14 need to be changed.
Q16, Q17 need to be the higher voltage MJE15032/33.
You will probably need to change the foldback curent limit.
Here is basically the Leach with three pair of outputs and 270w per channel @ 8 ohms
425w per channel @ 4 ohms :
http://www.abamps.com/pdfs/600lx-man.pdf
Looking at the 600LX manual you posted, it's hard to read, but it looks like they use two 1K resistors going to the emitters of one pair of outputs. The Low TIM uses four 680R going to the emitter of each output as an extra precaution (?).
Should I just use 1K in place of the four 680R in the Low TIM?
Also, are the MPS8099/8599 still ok to use with their 80Vceo?
The 2N3439/2N5416 look to be rated high enough. They will definitely need some of the finned TO-5 heatsinks, right? Will the PCB mounted heatsinks be big enough for the drivers (MJE15034/35)?
Should I just use 1K in place of the four 680R in the Low TIM?
Also, are the MPS8099/8599 still ok to use with their 80Vceo?
The 2N3439/2N5416 look to be rated high enough. They will definitely need some of the finned TO-5 heatsinks, right? Will the PCB mounted heatsinks be big enough for the drivers (MJE15034/35)?
I don't know what kind of topology the Ashly is; I was just thinking about sketching a schematic, not so much to fix it but for the other Ashly's I have.
I know these old fet's are good parts, but at ~20$ each I can't afford to restore the blown channel; even more if they had to be matched.
Are the BUZ901/906 really drop-ins for the J50/K135? Or is it the BUZ901D/906D (8A vs. 16A)
I know these old fet's are good parts, but at ~20$ each I can't afford to restore the blown channel; even more if they had to be matched.
Are the BUZ901/906 really drop-ins for the J50/K135? Or is it the BUZ901D/906D (8A vs. 16A)
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Yes. They are the same type of Lateral mosfet as the Hitachis. In fact it wouldn't surprise me to learn that they started producing them as soon as Hitachi stopped manufacturing them! These things are often used in "Pro Audio" simply because they are "nearly" bomb proof with there negative temperature coefficient.
I know a chap that owns a repair shop for this kind of stuff & he uses the BUZ mosfets as replacements for the Hitachis. By the way, there are some BUZ Mosfets (sorry i can't remember the part number but it's around 900) that are again complimentary but rated at 250W per Mosfet. I guess they are double die jobbies.
They'd be the double die ones
Good to know. The 250W ones look to be the 901D/906D.
The standard 901/906 look to have the same or better specs as the J50/K135, but are 13$ ea. at Newark.com for Semelab brand. Thats 130$ to rebuild one channel (assuming the other channel is OK), much more than what it would cost me to rebuild the whole amp with Leach boards. And, the channels wouldn't match. I'd have the original hitachi's in one channel and BUZ's in the other.
I was only attempting to keep your options open by suggesting alternative Lateral Mosfets that you might not have known were available.Obviously if you can rebuild an amp but with bipolars & cheaper please don't let me stop you. Must say i prefer bipolar transistors but we aren't all the same
Happy holidays & of course, have fun
Obviously if you can rebuild an amp but with bipolars & cheaper please don't let me stop you. Must say i prefer bipolar transistors but we aren't all the same
Happy holidays & of course, have fun
I know, and I'm glad you did. I didn't now about the Magnatec parts.
I have a lot of amps with these old lateral mosfets, and they work great. This blown Ashly seemed like an ok basis for a bipolar build, thats why I've been leaning that way.
Thanks for all the help so far guys. I think all i need now is confirmation on my assumptions/calcs for the part changes in the Low TIM circuit.
Happy Holidays!
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