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Old 21st May 2004, 11:55 PM   #1
Wagener is offline Wagener  South Africa
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Default do I need to heatsink these?

the silver transistors (2N3440 and 2N5416)

also the output filter resistor is a (2W) as specified by Dr. Leach. Is this big enough?

What would the difference be in using a wirewounded 5W resistor in place of the 2W ceramic resistor.
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Old 22nd May 2004, 06:23 PM   #2
lucpes is offline lucpes  Europe
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ouch!

your inductor is a tad bit flimsy. Wind a larger one using larger gauge wire (use a pencil or whatever), then use the 2W resistor soldered AFTER you solder the coil in-place (maybe under the board). The whole output passes through the coil, the resistor is just for damping. Don't 'attach' the inductor to the resistor, make it the other way round.

No need to use a 5W resistor IMO.

It's best to heatsink the trannies, just for the sake of it.

You also should've left some space between the white 5w (emitter?) resistors and the board to allow some cooling in case it is needed.

Maybe the one in the pic is overkill, but why not?
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Old 22nd May 2004, 06:30 PM   #3
lucpes is offline lucpes  Europe
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image didn't come up upon edit:
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Old 22nd May 2004, 06:47 PM   #4
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Have any one tried replace those white ceramic resistors with thick film power resistors and listen for the sonic differences. I have replaced my passive crossover 5W white ceramic resistors with 20W Ohmite thick film power resistors same values with very positive result.

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Chris
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Old 22nd May 2004, 08:02 PM   #5
Wagener is offline Wagener  South Africa
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Dr. Leach had these instructions :

L1 - 10 to 12 turns #22 solid insulated wire wound tightly around R49 and soldered to the leads of R49 where they emerge from the resistor body. Click here to see an illustration. Solder one end of a piece of #22 solid wire to one end of R49. Wind the wire tightly around R49 to form L1. Clamp the windings to R49 with a small bench vise. Strip and solder the other end of L1 to R49.

What is the effect of using a thicker wire and also using more turns?

Thanks for reply
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Old 22nd May 2004, 08:27 PM   #6
jdoorn is offline jdoorn  Netherlands
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I agree with lucpes regarding the heatsinks. But I don't see why you should't follow the directions for the coil. I would use larger gauge wire though, to minimize the resistance of the coil !

Regards, Jan
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Old 22nd May 2004, 08:47 PM   #7
lucpes is offline lucpes  Europe
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Quote:
Originally posted by Wagener

What is the effect of using a thicker wire and also using more turns?
Sorry, did not mean to imply that you need more turns than specified.

More turns will increase inductance - thus a decrease the amplifier's bandwith, this is generally not what you'd want to do, the pic was attached to give you an idea of how it's generally done.

Using larger magnet wire will allow for better power handling; the one you currently have should be enough for this kind of power output (<100W).
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Old 23rd May 2004, 12:49 PM   #8
djk is offline djk
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Q12 and Q13 are running class A at 4.2mA, if you run no more than 70V then they will be running about 300mW, no sink required.

Q14 and Q15 are running in class A at 4mA and go into class AB above there. Considering the gain of the drivers and outputs, the shift to AB is probably above 100W/8R, I wouldn't worry about it.

The 2N3440/5415 will handle about 1W in 25*C ambient, up to 10W on a sink.
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Old 23rd May 2004, 03:05 PM   #9
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Default As we learned with lawyers and Judges

When we have some doubts, if the man is guilty or not...do not arrest him.
About heat...if you have some doubt, put a heatsink on it.... always be better, and good looking too.
regards,
Carlos
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Old 23rd May 2004, 11:37 PM   #10
djk is offline djk
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"if you have some doubt, put a heatsink on it"

Not much point on a 10W transistor running at 300mW.

Matter of fact, if the pairs that are close touch, BANG!!!

Be careful here.
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