Where to get a 30K power resistor? &

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JayB
Senior tube assistant
Posts: 115
(5/26/05 8:35 pm)
Reply  Where to get a 30K power resistor?
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 Where can one find these things? Wirewound 30K
 
Tiny Daddy
I only work on Fender's
Posts: 1235
(5/26/05 9:51 pm)
Reply  Re: Where to get a 30K power resistor?
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 Is it more than 5 watts?
 
6G16
Junior tube assistant
Posts: 10
(5/27/05 6:04 am)
Reply  Powerresistor
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 RS electronics or Farnell (Newark)

 
EL34
Administrator
Posts: 2987
(5/27/05 7:52 am)
Reply
  Re: Powerresistor
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 If you can do with 3 watt, you can use a 27L and a 2.2K to get close enough.

I stock both in 3 watt metals.
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JayB
Senior tube assistant
Posts: 116
(5/27/05 10:55 am)
Reply  Re: Powerresistor
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 The one in the power supply, 20watt dropping resistor. These things dump some pretty good heat. I'm not sure what I could get away with here. 10 watt could do it I think. I was thinking of using the 27k 3 watt Doug has but I'm wondering how long that would last. The problem is as that resistor heats up, up goes the resistance and the plates start seeing 500V. Might not be anything to worry about?

Any check the temp of the 47ohm resistor in the bias supply? That thing can burn. I'm surprised fender used a 1/2 watt there.
 
EL34
Administrator
Posts: 2989
(5/27/05 12:23 pm)
Reply
  Re: Powerresistor
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 You can use 3-10K 3 watters in series and you end up with a 9 watt rating. Each resistor drops it's own voltage and you spread out the voltage drop 3 ways.
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ganzonimx
I only work on Fender's
Posts: 790
(5/27/05 12:40 pm)
Reply  Re: Powerresistor
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 Depends how much voltage you drop over that resistor and how much current is drawn after the resistor.

If you can detail the application it would be easier to say what wattage you should go for.

Chris


 
Tiny Daddy
I only work on Fender's
Posts: 1236
(5/27/05 12:53 pm)
Reply  Re: Powerresistor
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 Suggest you should spread the heat around some by using a pair of 15k (ohmite) or a 10K and a 15K (xicon) form Mouser.
 
JayB
Senior tube assistant
Posts: 117
(5/27/05 3:29 pm)
Reply  Re: Powerresistor
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 Take a look at the TwinII schematic. The power supply. You'll see what I'm looking at. They use 1 watt 220K's at the main filters so I don't see why 1 watt would be ok. I never checked to see what temp they get to though.
 
ganzonimx
I only work on Fender's
Posts: 791
(5/27/05 6:11 pm)
Reply  Re: Powerresistor
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 1 W is ok, These resistors re called bleeder resistors and have two function.

they distribute the charge equal over the two caps and they discharge the caps after switching off the amp.

If you want to do the math: 2x220K = 440K. They "short out" around 450V. I calculate 450V/440K = 1 mA.

They dissipate 0.45W, so a 1W resistor is sufficient, though I always put in 2 W resistors..

Chris




 
JayB
Senior tube assistant
Posts: 119
(5/27/05 7:44 pm)
Reply  Re: Powerresistor
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 ganzonimx, it's the 30k 20 watt I'm messing with. Look at the TwinII schematic and You'll see it.
 
Tiny Daddy
I only work on Fender's
Posts: 1238
(5/27/05 9:18 pm)
Reply  Re: Powerresistor
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 Where is this TwinII schematic??
 
JayB
Senior tube assistant
Posts: 120
(5/27/05 10:30 pm)
Reply  Re: Powerresistor
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 Use the concertII. I can't find the twin on the internet to post. ConcertII is exactly the same except the bias grid resistors.

www.blueguitar.org/new/sc...oncert.jpg
 
Tiny Daddy
I only work on Fender's
Posts: 1239
(5/27/05 11:30 pm)
Reply  Re: Powerresistor
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 Instead of trying to drag the voltage down with a 20 watts resistor, I think the 2700 ohms should be larger, like 12K ohms.
 
JayB
Senior tube assistant
Posts: 121
(5/28/05 9:16 am)
Reply  Re: Powerresistor
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 After tinkering with it all night, I manage to get it back down. Resoldered the joints and it quit rising so high. The cure to it all was the standby switch. I accidently wiggled it while soldering and the wire from the main B+ popped off. Looks like it was just connected there with one strand of wire. Rewired, cleaned up and soldered back on. Voltage it where it should be now. Maybe raises 5v as she warms up. That sucker bit me in the process which amazed me. Should of grounded that wire out first. Hurt like the dickens.

I should find something suitable to replace those things. Atleast something close to it. I know I'm going to at some point in time and they happen to be odd ones.

Edited by: JayB at: 5/28/05 9:26 am
 
6G6
I only work on tube amps
Posts: 421
(5/28/05 9:34 am)
Reply  Re: Powerresistor
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 Yeah, that nasty ol' B+ just has no respect.
Sometimes the shock isn't so bad, but slamming into the opposite wall hurts.
Be careful, folks!
Glad you found it.
 
ganzonimx
I only work on Fender's
Posts: 792
(5/28/05 9:40 am)
Reply  Re: Powerresistor
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 Yea thats wired, that resistor  

I see now reason to leave that resistor in. If you drop it out you would have to go up with the 2700 , like TD said, and as a bonus you woun't need anymore a 10W, 3W would be ok and you would have less heat dissipation inside the amp.

PS: maybe Fender put in the resistor to make the amp sound a little warmer. hahah

Chris
 
JayB
Senior tube assistant
Posts: 123
(5/28/05 10:07 am)
Reply  Re: Powerresistor
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 I'll measure the amps across it and see what I come up with. Increasing the 2700ohm makes better sense to me also.
 
 
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