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post #61 of 73 Old 06-07-2013, 02:13 PM
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Steel cases being bad is a lot of audiophool folklore.
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post #62 of 73 Old 06-09-2013, 07:29 PM - Thread Starter
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Thanks
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post #63 of 73 Old 06-12-2013, 03:24 PM - Thread Starter
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This seems like a dumb question, but do I need to put insulators underneath the TO-3 transistors on my black anodized aluminum heat sink, or is it fine because the anodized aluminum won't conduct? Also, the metal outside of the transistor is the collector right? What is the best way to connect it to my PCB, just put a bolt through and solder a wire onto it?



if I do need an insulator, would these be good? http://www.ebay.ca/itm/50x-MICA-Transistor-INSULATORS-TO-3-2N3055-2N3773-/271163748180?pt=LH_DefaultDomain_0&hash=item3f229e6f54&_uhb=1
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post #64 of 73 Old 06-12-2013, 04:44 PM
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Hi WagBoss,

Those mica insulators would work, but you would need to put heat-sink compound on both sides to allow the transistor's heat to pass through. A better approach is to use insulators that are meant to conduct heat. Something like these make life simpler:

http://www.ebay.com/itm/T03-SIZE-TRANSISTOR-SIL-PAD-INSULATORS-50-pcs-/380328675862 (Don't let the price scare you yet.)

The black anodizing on the heat-sink does not work well as an insulator - a simple scratch and you smoke all of your work. You need to use either plastic screws or insulating washers to mount the transistors (I recommend plastic screws). To make your electrical connection to the collector, just connect a screw-lug with a wire attached to one of the screws, contacting the transistor's can. (so yes, the can is the collector on both the PNP and NPN transistors).

I'm sending you a private message as well.
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post #65 of 73 Old 06-12-2013, 05:16 PM - Thread Starter
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do you have a picture of how to attach to the can? All i see on a google search is stuff like this http://www.net-audio.co.uk/jpgs/303heatsink.jpg where they don't have anything connected to it?

and do you use plastic bolts underneath with the screws or just use metal?
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post #66 of 73 Old 06-12-2013, 07:25 PM
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Hi Wag,

Yeah, that picture uses metal screws (with the appropriate washers that you can't see), so the collector connection is on the other side, with a screw-lug under the nut. The connection is from the can, through one of the screws to the lug. Here is a crude example (though they seem to be missing their nuts):

If you use plastic screws, then that lug needs to be mounted on the other side, right against the tab of the can.

Notice the black washers that insulate the screws from the heatsink? That's what you need if you don't use plastic screws. It's stronger that way, but you would need to find those washers somewhere.

The MJE340 transistor, which should be mounted in the middle for the best heat-sensing, has an insulated case. So you don't need an insulator, but you do need something to help conduct the heat. Heat-sink compound or one of those same T03 heat-conducting pads would work.
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post #67 of 73 Old 06-12-2013, 07:42 PM
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best to avoid mica type insulators as they tend to become brittle and break with time and heat. insulator pads are better suited to handle heat.

have you bought the TO-3 type transistors? they can be hard to mount effectively to the circuit as they require a large space. as such, TO218/TO220 and TO247 are (usually) better choices for implementation. if it's available in TO-3 then most of the time the same transistors would also be available in said packages.

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post #68 of 73 Old 06-13-2013, 05:50 AM - Thread Starter
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Quote:
Originally Posted by paskal9 View Post

best to avoid mica type insulators as they tend to become brittle and break with time and heat. insulator pads are better suited to handle heat.

have you bought the TO-3 type transistors? they can be hard to mount effectively to the circuit as they require a large space. as such, TO218/TO220 and TO247 are (usually) better choices for implementation. if it's available in TO-3 then most of the time the same transistors would also be available in said packages.

Yeah I have all the parts already. I have a huge chassis though, an NHT power5 so there is a ton of room for my large heat sink.
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post #69 of 73 Old 06-13-2013, 05:52 AM - Thread Starter
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Does anyone know an easy/cheap way to implement a 12V trigger to this amplifier? I already have a 12V input jack on the back of my chassis, so all I need to know is what part to connect in the circuit to make it act as a switch? Or is it more complicated than that and requires a controller or something? I have the NHT control pcb board but I have not been able to find schematics or anything for it.
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post #70 of 73 Old 06-13-2013, 07:06 AM
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Quote:
Originally Posted by WagBoss View Post

Does anyone know an easy/cheap way to implement a 12V trigger to this amplifier? I already have a 12V input jack on the back of my chassis, so all I need to know is what part to connect in the circuit to make it act as a switch? Or is it more complicated than that and requires a controller or something? I have the NHT control pcb board but I have not been able to find schematics or anything for it.
you need a simple 12v relay, wired the same as you would to the AC to turn on the amp.

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post #71 of 73 Old 06-13-2013, 07:25 AM - Thread Starter
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Quote:
Originally Posted by paskal9 View Post

you need a simple 12v relay, wired the same as you would to the AC to turn on the amp.

would this work? http://www.ebay.ca/itm/2pcs-12V-DC-SONGLE-Power-Relay-SRD-12VDC-SL-C-PCB-Type-/261226717377?pt=LH_DefaultDomain_0&hash=item3cd25360c1&_uhb=1

I would just put it between SW1 and T1? And I'd just leave SW1 on all the time?
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post #72 of 73 Old 06-13-2013, 11:38 AM
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Hey Boss,

That relay should work, assuming the amp doesn't draw more than 10 amps. I prefer zero-crossing solid-state relays myself, but they're much more expensive.
Quote:
I would just put it between SW1 and T1? And I'd just leave SW1 on all the time?
I would put it in parallel with SW1 and just leave SW1 off all of the time.

That way, you would be able to turn the amp on without having the 12volts available, which would be useful for testing.
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post #73 of 73 Old 06-13-2013, 11:49 AM - Thread Starter
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Quote:
Originally Posted by MarkHotchkiss View Post

Hey Boss,

That relay should work, assuming the amp doesn't draw more than 10 amps. I prefer zero-crossing solid-state relays myself, but they're much more expensive.
I would put it in parallel with SW1 and just leave SW1 off all of the time.

That way, you would be able to turn the amp on without having the 12volts available, which would be useful for testing.

Well I have a 3 amp fuse that I will be using which is built into a switch, so I will use that as a main power switch, and then I will use the switch that came built into the NHT chassis I'm using in parallel with the 12V trigger, so then I still have a fuse, and I can bypass the trigger with the second switch if I want. Thanks.
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