Need help with resistors

EdgE

Fractal Fanatic
Maybe some one can help me ,I have a carvin legacy vl-100 and I’ve blow the grid resistors a few times (my own fault ,test speakers ,not having it plug in etc) brought it to a place to be repaired . Any way I want to fix it myself (I am aware of high voltages)
got a schematic of the amp ,found out where the grid resistors are, figure how to test them and there no signs of life on the meter

The question I have is, it calls for a 100ohm 1/4 watt resistor ,the parts list for the amp calls for 100ohm 1/4 watt with a 1% tolerance ,which is only in metal film ,the ceramic is 5% tolerance , there ceramic in there now . Can I use a metal film resistor with the same specs.
 
if the parts list calls for metal, I would say yes. the last time it was repaired the shop must have put in the ceramic.
 
It doesn’t call for metal film , parts list calls for 100 ohm 1% , metal film is only 1% ,ceramic 5%
 
So that tells me ceramic is not good enough, and you have to use metal, or a ceramic that measures with in 1%.
 
Can only find the medal in 1% , just didn’t want to kill the amp . I sure the last guy that fixed it didn’t have the metal film.
Thanks paranoid😎 I had just found the right combination of tubes and I was getting some static ,move around a power tube and snap crackle and pop. pulled out the board with the tube sockets ,not your normal pin ones with . They were really loose
 
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The 1% or 5% tells how much tolerance the value will have.

A 1% 100ohm can range from 99-101% of the stated value (that is +/- 1% of 100).

A 5% 100ohm can range from 95-105%.

Going with a 1% vs a 5% just means you'll be closer to the designed circuit.
 
Hi @EdgE

Another option is to buy a few, and use your multimeter to select the ones that are within 1 percent of the specified value.
I tend to do that as a matter of course with audio stuff as being cloise to the design values can really make a difference.

Thanks
Pauly


Maybe some one can help me ,I have a carvin legacy vl-100 and I’ve blow the grid resistors a few times (my own fault ,test speakers ,not having it plug in etc) brought it to a place to be repaired . Any way I want to fix it myself (I am aware of high voltages)
got a schematic of the amp ,found out where the grid resistors are, figure how to test them and there no signs of life on the meter

The question I have is, it calls for a 100ohm 1/4 watt resistor ,the parts list for the amp calls for 100ohm 1/4 watt with a 1% tolerance ,which is only in metal film ,the ceramic is 5% tolerance , there ceramic in there now . Can I use a metal film resistor with the same specs.
 
The grid resistors? 100 ohms isn't a typical grid resistor value. Grid resistors are typically in the 220K range. Grid stoppers are in the 5K range. The schematic I have for a legacy has 220K grid resistors and 4.7K grid stoppers. Also neither of these is likely to be damaged. Screen resistors are the resistors that usually fail when abusing a tube amp but these are usually 5W or more.

The only 100 ohm 1% resistors I see on the legacy schematic are the heater balance resistors. These are used to make sure the heater voltage swings symmetrically around ground. They should be 1% for the lowest hum. They can be any composition: metal film, carbon comp. They should be at least 1/4W as, by my calculations, they are dissipating 200 mW.
 
Thanks Cliff, I'm doing this by process of elimination ,not my knowledge of electronics :oops: I did find a schematic that said all resistors are 1/4 watt unless noted .These were the only resistors that had been changed, and I did pull one and no reading. All the times this happened the amp still played ,just had a huge hum. I did order 100 ohm 1/4 watt metal film. Thanks for the great info :) Cliff could open tube amp repair, and the fractal magic black boxes. Just a thought :)
 
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