6V6 line preamp

[6L6]

Does it run that hot? Yeouch.

[Salas]

Owes to run Vout times 20mA spare on the output sink. Thus 7W constantly.

[buzzforb]

Idid my own boards and used cut down heatsink USA profile, 6" wide. It had both channels main heat producers on it. Got too hot.

[6L6]

Salas, it the 7W on the board mount sink or the bigger, outboard one?

[Salas]

The outboard one. Its easy, listen: IRF840 has 1.0C/W thermal resistance core to case. If you have 45C in a box like with this preamp with all the radiators from heaters PSUs, tubes near, regs sinks contributing, load resistors hot etc. and using say a single 1C/W sink for two regs, it will go up 18.2C (14W*1.3C/W) from ambient because I derate the sink by 30% due to hot spot mounted semis uneven surface heat spreading. And that is when fins are perpendicular to air flow by natural convection. 45+18.2C=63.2C on sink's fins to touch. Now a normal Silpad can give additional 1.2C/W. 7W on each IRF840 times 1.2=8.2. Add it to 63.2=71.6C on each 840's body (case). Its hot nucleus gets 1C per W more thermal resistance trying to dissipate to its case's body, thus reaches 71.6+7=78.6C. Those silicone chips inside 840s are 125C rated before meltdown. Using the above points discussed, you may project the spec of any common sink or individual ones flanking the box for two regs, factor in box ambient correctly, how much spare current ups how much temp, everything. In any case isolate well. The Mosfet tab carries B+. !!!!

[Salas]

P.S. Consider that electronics live 4 times longer each time we halve their operating temperature. Use a contact K-Type thermocouple to have a temp picture of everything I mentioned. Flukes have that brown one, some others have the yellow end one, and there are cheap IR thermometer guns but good only for black surfaces and it takes some confirmation of the IR cone aim and distance to get the knack using them to report truly. If you have a cheap DMM get an Amprobe AM-270 since you are in US where you can get it easily, has proper input protection and all the modes, honors its CAT rating, $90. Be careful with cheap or simply unsafe DMMs when messing with HV especially if to measure inline current. That is why I put TP ItoV reading on the SSHV2 board, to save incidents. Best of luck for finishing it in one go, and be careful.

[zgondouin]

Hi all,

I wish everyone a Good day. My name is zach, I am new to the forum and this is my first post. I am new to diy and electronics but have built a couple tube amps from kits before and now I feel confident enough to build salas 6v6 from scratch. I have most parts to complete the preamp and have procured the power supply components to be used. I'd like to make a separate supply for each channel hence i bought 2 power transformer and 2 supply chokes. As i feel the preamp is worth the effort and cost. I modeled the power supply at PSUD designer but do not know how to attach the simulation results. this is what i did.

this is only for 1 channel!
power transformer is a hammond 272fx- 600vct@ 173ma with sec. dcr of 143ohm and hammond 193j- 10H@200ma with dcr 82 ohm. rectifier will be type 83MV.

thank you!

[tubo]

hi!

what is the total current draw of the circuit including 2 salas regulator? thanks

[zgondouin]

Will this psu simulation be good enough? this is only for one channel! thank you

the rectifier is an 83MV.

[zgondouin]

Originally Posted by tubo

hi!

what is the total current draw of the circuit including 2 salas regulator? thanks

I believe it is about 44ma for both channel! i haven't built the salas high voltage regulator yet, but i don't think it needs to be accounted for when summing up the the current draw of the circuit. Im basing this only from my limited understanding( I really don't know anything) and I might be wrong., So we need the inputs of those who know.