1K/25W

[sagitt]

would it be OK if I put 1K/12.5W resistor instead of 1K/25W for 2xEL84 liverpool?the only thing that worries me is max.voltage rating for this resistor...btw it is chassis mount.

[sliberty]

I have an alternate schematic (not the one we typically use here) for the Liverpool which actually references that resistor in a 2 tube system. It suggests using 1.7K instead of 1K. I can only assume that this is because with fewer power tubes, the load on this resistor will be lower, resulting in higher voltages or screens and preamp tubes. I am not sure if this is correct, but it seems logical.

As for the max voltage, I would probably stick with the 25W resistor spec, but if you have something smaller on hand, it should be OK down to about 15W (not calculated - just ball parked). I wouldn't go fully in half though.

[katopan]

My reply is going to be unconventional, so take it for whatever you want.

In my Express build with EL34s and standard voltages I used two standard 5W wire wound resistors to make up the 1K at 10W. They are mounted with a bit of aluminium channel I bent up holding them against the aluminium chassis. No heatsink compound or anything. When I was doing all that waveform testing I had the amp running between full load clean to fully cranked for over 3 hours and those resistors got only warm to the finger touch. I know there has been so much discussion about the 25W rating of that resistor and I've written my views before. Rating vs actual power dissipation all depends on heat transfer.

[Littlewyan]

I vouch for the 25W resistor. Mine gets slightly too hot to touch after 30minutes of use. Depends on what power valves you use a bit. I don't think 6V6s will draw as much current as EL34s but I'd still stick with the 25W.

[keewee]

yea, they run hot those rockets heat sinking is good idea !!

[guitarmike2107]

would it be OK if I put 1K/12.5W resistor instead of 1K/25W for 2xEL84 liverpool?the only thing that worries me is max.voltage rating for this resistor...btw it is chassis mount.

What is the voltage rating of your resistor?
What Primary impedance are you going to use?
1k/12.5w will be overkill for a 2 x EL84 liverpool amp, assuming you are using 18w/Vox AC15 iron.
Most 18w amps only need 2 - 3w resistors in this position and are pushed pretty hard.
I think Ken just had a stash of 1K/25w resistors that he liked to use, or maybe he like the wirewound properties.

[sagitt]

not sure about voltage rating,this is what I have http://eu.mouser.com/ProductDetail/Vish ... TzQLimc%3d .OT is 8K,2xEL84.find this formula from datasheet for maximum working voltag but it is a bit confusing...

[pdf64]

I hate it when the manufacturer's info doesn't put a spec or even a guideline as to such a key limiting parameter.

[guitarmike2107]

Its a 12.5w resistor, so maximum voltage it can handle is 111v, otherwise you will overheat the resistor. - when heat sinked correctly.

Using Ohm law maximum current is .111A - when heat sinked correctly.

This resistor will not see a 111v voltage drop across it unless there is a fault condition. i.e. a dead short after the resistor, and that is the reason commercial amps would use a flame proof resistor in this position. I don't know if these types of resistor are flame proof.

[pdf64]

Its a 12.5w resistor, so maximum voltage it can handle is 111v, otherwise you will overheat the resistor. - when heat sinked correctly.

Using Ohm law maximum current is .111A - when heat sinked correctly.

This resistor will not see a 111v voltage drop across it unless there is a fault condition. i.e. a dead short after the resistor, and that is the reason commercial amps would use a flame proof resistor in this position.

At power up, there may be a momentary voltage across the resistor that is greater than that.
My experience is that resistors, whose steady state power dissipation rating is well in excess of that which it may be exposed to in normal operation in such an application, may fail.
On investigation, I concluded that their limiting element voltage rating of 200V may be the reason for that failure, as it may be exceeded at power up.