Rich,
what resistor value gives the low CCS current?
From that value and the voltage you worked out the CCS current.
Now, how much current is missing? 60mA maybe?
What resistor value would give you 60mA at the voltage you measured?
Temporarily add that extra resistor in parallel to the existing R1.
What is the new voltage across R1?
Calculate the current through R1 and through the extra resistor.
Add these two currents.
How close is the sum to your target?
Leave as is or calculate the next resistor to add in parallel to make up the shortfall.
what resistor value gives the low CCS current?
From that value and the voltage you worked out the CCS current.
Now, how much current is missing? 60mA maybe?
What resistor value would give you 60mA at the voltage you measured?
Temporarily add that extra resistor in parallel to the existing R1.
What is the new voltage across R1?
Calculate the current through R1 and through the extra resistor.
Add these two currents.
How close is the sum to your target?
Leave as is or calculate the next resistor to add in parallel to make up the shortfall.
Thank you Salas, I'll get some resistors ordered.
And thanks Andrew, I'll have a play with some values, I'll consider keeping the current around 200mA each rail and get better heatsinks.
@Marra - Cheers mate. I got them from this guy on ebay. If you get them, contact him and specify the high quality windings which have better copper and sleeving. He will customise any winding you like, just give him your required specs (the black one is an old spare 50VA 2 x 0-15 / 2 x 0-9 powering the DCB1 and volume control) :
220V 30W high quality R Core Transformer 9V+9V 24V+24V on eBay (end time 04-Jan-11 16:58:43 GMT)
And thanks Andrew, I'll have a play with some values, I'll consider keeping the current around 200mA each rail and get better heatsinks.
@Marra - Cheers mate. I got them from this guy on ebay. If you get them, contact him and specify the high quality windings which have better copper and sleeving. He will customise any winding you like, just give him your required specs (the black one is an old spare 50VA 2 x 0-15 / 2 x 0-9 powering the DCB1 and volume control) :
220V 30W high quality R Core Transformer 9V+9V 24V+24V on eBay (end time 04-Jan-11 16:58:43 GMT)
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180mA will be OK for your sinks with those resistors I recommended and build remains as it is. Don't buy new sinks just to run 200mA IMHO. You will not perceive a difference.
Fair point Salas. I shall follow your recommendations.
As it happens I'm finding it hard to locate some 17R / 2W or even 8.5R in a higher wattage. Farnell have 18R and 22R in 2W values so could play around with these doing what Andrew suggested with small increments.
Andrew - thats interesting about the ebay listing, must be a very recent thing. I only bought them a month ago. I actually have a custom winding lined up to buy soon from him so will contact him to find out. I'm sure he would do a deal outside ebay with a disclaimer. He is a very genuine chap and would be keen for the business.
Marra - get in touch with him and see if he is willing to do a deal. They are very good transformers.
I wouldn't say "necessary", just very very beneficial. Especially if the heatsink's contact surface isn't the smoothest. The idea is that you increase the contact area between two solid surfaces that are not perfectly flat. You only need very little, I usually apply it to the semiconductor and spread it with a toothpick, and once you tighten the mounting screw you can remove the excess goop. Locally you might find some in a computer store (for CPUs).
The reply from "Along"
Hello,sir
Due to the bad weather recently,The air mail are very very slow,most of our package sent to UK on early November still on the way,many buyers impatient to wait so long delivery time and open disputes to ask full refund,so,we only can except some countrys temporary.
We appreciate your understanding.
Best regards
Merry Christmas!
Hello,sir
Due to the bad weather recently,The air mail are very very slow,most of our package sent to UK on early November still on the way,many buyers impatient to wait so long delivery time and open disputes to ask full refund,so,we only can except some countrys temporary.
We appreciate your understanding.
Best regards
Merry Christmas!
I've got them powered up. 
I forget what I should test for voltage wise. Anyone have references voltages I should look for?
Folding the mosfets over was the only way I was going to mount these heat sinks. I'm wondering if I should drill another hole in these mosfets and secure them to the chassis.
Merry Christmas,
JG
I forget what I should test for voltage wise. Anyone have references voltages I should look for?
Folding the mosfets over was the only way I was going to mount these heat sinks. I'm wondering if I should drill another hole in these mosfets and secure them to the chassis.
Merry Christmas,
JG
Drilling another hole in the Mosfets? You're joking, right? Don't do it.
Are the Mosfets electrically insulated from the heatsinks? Otherwise your setup is prone to shorts.
Look for my build a couple of posts back and you'll find some reference voltages. Easy and probably first thing to check is the buffer's output offset relative to ground, which should be smaller than 5mV in either direction.
Nice build!
Are the Mosfets electrically insulated from the heatsinks? Otherwise your setup is prone to shorts.
Look for my build a couple of posts back and you'll find some reference voltages. Easy and probably first thing to check is the buffer's output offset relative to ground, which should be smaller than 5mV in either direction.
Nice build!
Ok, I guess I'll have to pick up some of these?
AAVID THERMALLOY | 189790F00000 | TO-218/TO-247 Package 0.009" Thick No Adhesive Silicone Insulator - Future Electronics
AAVID THERMALLOY | 189790F00000 | TO-218/TO-247 Package 0.009" Thick No Adhesive Silicone Insulator - Future Electronics