Resistor concerns

[joesatch]

Schematic needed a large 470R resistor like 10 watts.  This is in place of a choke. Now i received this resistor and it is tiny!. I have doubts about using this.

[passaloutre]

I would guess it’s only worth 10w when thermally coupled

[Merlin]

It's a 10W rated resistor alright, but it must be bolted to 10W-worth of heatsink to acheive it. You should get away with bolting it to your chassis (especially if it's aluminium).
But do you really need 10W just to replace a choke? In a guitar amp the usual choke position won't have to supply more than 50mA say, which is barely more than a watt, no trouble for that part even without a heatsink.

[dude]

Would bolted to the chassis apply as a heat sink in cool area?

[acheld]

These are great resistors compared to the Chinesium ones you get on eBay.  Very robust.

Use some heat sink compound (just like you would when installing a CPU cooler) and bolt it to your chassis.  I've used both aluminum and steel, and both worked fine. 

Data sheet https://www.mouser.com/datasheet/2/303/acl_hs10-1890310.pdf gives minimal directions, but states to avoid surface temp more than 200C. 

[joesatch]

i did as a precaution order a regular 10W resistor and i may go with this instead.  I dont have any heatsink compound on hand. I don't trust this lil thing, i aint using it.

[glass54]

Hi Joe
Using Merlins (typical) currents figure of 50mA, dissipation in Arcol HS10 would be approx 1.175Watts!
(so you could even "free air" it  )
If I am using/or require a larger power rating than 5W, my FIRST CHOICE is an ARCOL HS10 or HS25 mounted off board in suitable chassis location as it saves Turret board/PCB degradation.
Also my first choice is an Arcol HS10/25 if i am building a non inductor supply and I have been using these for at least 3 decades.
I only use certified Heatsink compound if I'm building a Heavy Duty dummy load.
I trust this helps  Give it a go, Joe!
Regards
Mirek

[ac427v]

Great answers from people who really know electronics.

I am curious what amp would spec a 10 watt resistor in that position. Or better yet, see a schematic. Just for my general learning.

[pdf64]

Key ratings for that application is the surge voltage and current at power up.
It needs to cope momentarily with the full HT voltage and corresponding current.

A quad of EL34 in a cranked amp can draw a heap of g2 current, eg 200mA.

[tdvt]

I am curious what amp would spec a 10 watt resistor in that position. Or better yet, see a schematic. Just for my general learning.

The big, late 70s Fenders had some giant resistors on the power rail...

[SnickSound]

i did as a precaution order a regular 10W resistor and i may go with this instead.  I dont have any heatsink compound on hand. I don't trust this lil thing, i aint using it.

That's because the big one is meant to dissipate 10W through basic convection. It can get pretty darn hot in a closed environment, and without a fan to move air around.

I've used those smaller metal ones bolted to the chassis a bunch of times, never had an issue. I've seen them in use in commercial amps as well (PRS and Mesa Boogie comes to mind), again, bolted to the chassis.

Heatsink compound is cheap and you get overnight it through Amazon or get it at Best Buy. It's the stuff we use to install coolers on CPUs.

I'd have more confidence in that metal resistor than the big cement one. Would rather dissipate that heat straight to the chassis than heat up the inside of the amp.

[pdf64]

The big, late 70s Fenders had some giant resistors on the power rail...

They are a potential divider on the HT, presumably to ensure that the 500V rating of the downstream caps never got exceeded, eg at power up / when the mains was at its upper limit / no valves fitted.

[glass54]

Using pdf's example above, regarding G2's of cranked 4xEL34, G2 Pmax 18.8W dissipation at 200mA (assuming continuous current ), an ARCOL HS25 (25Watts rated) 470R should do BUT I personally would fit a HS50 (50W rated). Cost difference from RS Components in Australia A$1.00.
I would use the Heatsink compound in such application, to be sure!!
Those of you who have repaired the Fenders with 20W/30W Cement style power resistors (in PS) would understand
Kind regards
Mirek