Picked up a PA amp today for next to nothing price wise its a MegaAmp 400, I bought it to repurpose the chassis into a diy amp, but which one? I know the choice would be limited by the heatsinks of which there is 4 two each side and measure singularly L140mm, H90mm and W40mm.
What would you build and why?
2021-03-03_05-42-02 by chris reddish, on Flickr
What would you build and why?
2021-03-03_05-42-02 by chris reddish, on Flickr
The heat sinks and dual output transistor pairs look good for 150 W/ch anyway. 200 W/ch is kind of stretching soa limit on 2 pairs OT.
Honey badger won't fit. boards are too big.
What transformer voltages do you have? Is there a center tap? I'm paying $60 for 7 amp 44 v EI transformers about that size. Since I bought the price went up. No center tap. CT transformers more expensive. EI suppresses pop from distant lightning better than toroid, IMHO.
If each cap goes to one channel, then no center tap.
I would not reuse transistor sockets, if that is what those are. Wires soldered to pins are more reliable.
I've built an amp with remote output transistors. I put a 5 turn coil series the sense wire back from the heat sense device on heat sink before coupling into the VAS, to avoid ultrasonic oscillation.
Apex AX6 & AX8 can protect your speakers with a $3 4700 uf cap per channel instead of a 7 part DC detect circuit and a $40 relay. With 7 A per channel transformer power, $3 relays on e-bay specials would weld their contacts shut in a fault. Read the rating, 99.99% of relays are AC rated on the contacts. The zero voltage time quenches the arc.
Either AX6 or AX8 could be hot rodded up to 150 w/ch by using MJE15028/29 as drivers, and IMHO, same as VAS. I have that in my ST120, actually 30 mhz GE D44R4 (1968, not 200? fairchild D44) and it sounds great. Sims say HD=~.06%. Speakers are much worse than that. Use heat sinks on drivers & VAS, I did. 2 pairs OT should be fine with 6 amp drivers. Dynaco used heat sinks with the 2n5320/22 they used as drivers/VAS. Use 10 ohm 1 w base stopper resistors on OT. MJL21193/4 or MJL4302/4281 as OT. I only have a single 6.75 A transformer though, and 3.5"x3.5" per side for heat sinks, so I'm limited to 70 W peak (measured for 5 seconds) and one pair OT. TIP31c/32c did NOT sound good as drivers, highs were missing on piano & tinkly bells.
Honey badger won't fit. boards are too big.
What transformer voltages do you have? Is there a center tap? I'm paying $60 for 7 amp 44 v EI transformers about that size. Since I bought the price went up. No center tap. CT transformers more expensive. EI suppresses pop from distant lightning better than toroid, IMHO.
If each cap goes to one channel, then no center tap.
I would not reuse transistor sockets, if that is what those are. Wires soldered to pins are more reliable.
I've built an amp with remote output transistors. I put a 5 turn coil series the sense wire back from the heat sense device on heat sink before coupling into the VAS, to avoid ultrasonic oscillation.
Apex AX6 & AX8 can protect your speakers with a $3 4700 uf cap per channel instead of a 7 part DC detect circuit and a $40 relay. With 7 A per channel transformer power, $3 relays on e-bay specials would weld their contacts shut in a fault. Read the rating, 99.99% of relays are AC rated on the contacts. The zero voltage time quenches the arc.
Either AX6 or AX8 could be hot rodded up to 150 w/ch by using MJE15028/29 as drivers, and IMHO, same as VAS. I have that in my ST120, actually 30 mhz GE D44R4 (1968, not 200? fairchild D44) and it sounds great. Sims say HD=~.06%. Speakers are much worse than that. Use heat sinks on drivers & VAS, I did. 2 pairs OT should be fine with 6 amp drivers. Dynaco used heat sinks with the 2n5320/22 they used as drivers/VAS. Use 10 ohm 1 w base stopper resistors on OT. MJL21193/4 or MJL4302/4281 as OT. I only have a single 6.75 A transformer though, and 3.5"x3.5" per side for heat sinks, so I'm limited to 70 W peak (measured for 5 seconds) and one pair OT. TIP31c/32c did NOT sound good as drivers, highs were missing on piano & tinkly bells.
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