VBIGC resistor problem

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elizard

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Joined 2003
#1
Well, I was selecting resistors for the valve buffered inverted GC, and joe's schematics are a little confusing. They don't tell you what rating the resistors should be. Now I know most should be simple 1/4watt ones, and i know the 5R6 in heater supply should be 1watt, and the 10K on the -35 rail is 1watt as well. But two resistors i'm unsure of. The two are the 0.22 on the speaker output, and the 220R in the tube power supply. Not sure if they should be 1/4watt, or 1, or 2+watts?

Thanks.
 
#2
resistors

The Tube power supply resistor must be at least as highly rated as the cathode resistor. Make it 2 Watt.

The cheap version for the output resistor: You can simply put a small inductor there. Take a 10 Ohm 1 or 2 Watt resistor and wind a thicker blank wire around (obviously coil windings should not touch each other) the resistor to make a coil and connect end of wires to resistor ends.

Gerry
 
#4
Re: resistors

elizard said:
Well, I was selecting resistors for the valve buffered inverted GC, and joe's schematics are a little confusing.... Not sure if they should be 1/4watt, or 1, or 2+watts?
Click to expand...

Hi,
simply use Ohms law:

I=V/R, P=V*I, P=I*I*R=V*V/R

If cathode resistor
CR is 10K
and voltage on it is ca
VCR=35V
(+-audio signal) chatode and anode current is
ICR=VCR/CR=35/10000=3,5mA
power consumption on
CR=VCR*ICR=35*0,0035=0,122W, standard metalfilm resistors power rating (0,6W) is OK

If PS supplays two tubes, current from it is
ICR_ALL=2*ICR=7mA, power on RPS=220ohm is
P_RPS=I*I*RPS=10mW, standard metalfilm resistors power rating (0,6W) is OK


Gerry said:
The Tube power supply resistor must be at least as highly rated as the cathode resistor. Make it 2 Watt.
Click to expand...

I don't think so.

Regards
 
#5
Re: Re: resistors

Thank you moamps, that was exactly what I was looking for 🙂

moamps said:


Hi,
simply use Ohms law:

I=V/R, P=V*I, P=I*I*R=V*V/R

If cathode resistor
CR is 10K
and voltage on it is ca
VCR=35V
(+-audio signal) chatode and anode current is
ICR=VCR/CR=35/10000=3,5mA
power consumption on
CR=VCR*ICR=35*0,0035=0,122W, standard metalfilm resistors power rating (0,6W) is OK

If PS supplays two tubes, current from it is
ICR_ALL=2*ICR=7mA, power on RPS=220ohm is
P_RPS=I*I*RPS=10mW, standard metalfilm resistors power rating (0,6W) is OK




I don't think so.

Regards
Click to expand...
 
#6
Resistors

If the designer of the Amp puts on the Cathode a 1W resistor then for sure I wouldn't put anything below 1W on the Anode.

Secondly, you have the second capacitor to charge in the power supply so there will be a large inrush current.

Gerry
 
#7
Re: Resistors

Gerry said:
If the designer of the Amp puts on the Cathode a 1W resistor then for sure I wouldn't put anything below 1W on the Anode.
Click to expand...

Hi,
"Usually", anode and cathode current are equal, than power disipation on cathode and anode resistor DEPENDS of resistors values! On resistor which has 15 times smaller resistance (10k/220) this power will be 15 times smaller. Aren't equal. Ohms law.

Secondly, you have the second capacitor to charge in the power supply so there will be a large inrush current.[/B]
Click to expand...

VBGC is low +B application with only +-35V PS. Inrush current here isn't large. I_INRUSH=35V/220ohm=160mA. Standard resistors can deal very easy with this impulse current.

Regards
 
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