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OK, so I messed up one resistor on a huge Mouser order and now I need some help. On the quad cap, the 6.8K dropping resistor I ordered was a two watt resistor instead of a three watt. I messed up the BOM & I did not realize it until I got my order. The part I ordered was 282-6.8K-RC instead of a 283-6.8K-RC. The 22K is a three watt.

I am trying to do the math to see if I can use the two watt safely. Otherwise I have to reorder and pay 16 times the price of the resistor for shipping ($.49 x 16 = $8.00 shipping). This math I can do!

Any thoughts?

Thanks,

Dave

Dave -

The original Dynaco ST-70 manual doesn't mention resistor wattage,
but I am pretty sure they used a 6.8K 2 watt part. Put yours in,
if it gets really really hot, or smokes, get a bigger one.

I think it will work just fine.

Is this on a stock ST70, between cap lugs B & C? The manual shows only a 40 volt drop across that part (415V -> 375V).

V=I*R and P=I*V. Rearranging, I get I=V/R, so P=(V/R)*V. Therefore, P=(40/6800)*40=0.24, or less than a quarter watt. I guess it really boils down to the initial inrush current (charging the empty cap) but I'd imagine you'll be fine with the two watt part.

Thanks Ty. Yes, you have the resistor location correct. I thought I was way off in my math. This high wattage must be for inrush???

Tom, The original part is a two or three watt carbon. I did check the manual and you are correct--no specification on wattage.

I'll check the temp after some use (when it is off).

Thanks,

Dave

skidave wrote:OK, so I messed up one resistor on a huge Mouser order and now I need some help. On the quad cap, the 6.8K dropping resistor I ordered was a two watt resistor instead of a three watt. I messed up the BOM & I did not realize it until I got my order. The part I ordered was 282-6.8K-RC instead of a 283-6.8K-RC. The 22K is a three watt.

I am trying to do the math to see if I can use the two watt safely. Otherwise I have to reorder and pay 16 times the price of the resistor for shipping ($.49 x 16 = $8.00 shipping). This math I can do!

Any thoughts?

Thanks,

Dave

I am using a 2W as a dropping resistor on the can cap in my st70, but I do not know which one it is.

The 2W should be ok. Carefully check it for signs of heat after it has been on for an hour or so.

I use 1 or 2W in power supplies weather they need them or not for voltage rating safety factor.

Cheers!