Resistors

AL1

Member
Messages
84
Can anyone tell me if a 100 ohm 10 watt wirewound resistor can be used to discharge capacitors?
 

aleclee

TGP Tech Wrangler
Staff member
Messages
12,573
The resistor's value is way too low. More typical would be a 100K resistor.
 

Fuchsaudio

Member
Messages
7,742
It should be fine for discharging caps. 100-K would take way too long to discharge a typical power supply.
 

AL1

Member
Messages
84
Does it matter which way it is soldered to the alligator clips? Is there a positive or negative end?
 

John Phillips

Member
Messages
13,040
With all respect to Andy, I think 100 ohms is way too low - that will risk internal damage to the caps. Not quite as bad as shorting them with a screwdriver, but close.

I'd go for 100K and a little patience.
 

Fuchsaudio

Member
Messages
7,742
I'll concede to maybe 1 to 5K 5-W, but who has the time for a 100-K ? I use 1.5K 5-W's , since I use them in amps elsewhere anyway.
 

AL1

Member
Messages
84
Andy, this 100 OHM 10 watt resistor was all radio shack had. Where can I get a1.5K 5 watt resistor?
 

John Phillips

Member
Messages
13,040
Originally posted by Fuchsaudio
I'll concede to maybe 1 to 5K 5-W, but who has the time for a 100-K ?
I charge by the hour! :p.

No, actually it doesn't bother me to spend a couple of minutes waiting. Gives the soldering iron time to warm up, have a think about what I'm doing etc... then again, I'm semi-retired as an amp tech now and I'm not exactly rushed off my feet (except by my two-year-old daughter!).

I'd agree with anything over 1K. That limits the initial current to 0.5A from a 500V power supply (and it drops below that immediately of course), which is OK.
 

THLH

Member
Messages
163
Actually, the best way to discharge the caps is to run a straight jumper wire from the #1 pin on the first preamp tube to the chassis ground, then switch the amp on (after unplugging it of course). The uses the full resistance of the amp to drain the caps nice and slow.
 




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