'97 LM6100 bias

marshalltsl

marshalltsl

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Hi
I have a bias issue on my LM6100. I installed a 6L6 GC quad. I have 432 vcc on plate and 59mv per tube with trim pot on the minimum value. It's a hot bias. Withoutpower tubes I have 489 vcc on plate and the bias it's -40,7 -28,6.

Some days ago R253(470R 5W) was open, no bias on v10. I replaced it and test some bias components. All seems fine.
On my '97 LM6100 the power board it's a 6100-63-00 issue 4 (have the 5881 sticker on it) On my amp R212 it's 33K and C220 it's 22n 630v.
I'll apreciated your help.
Thanks.
 
marshalltsl said:
I fixed. I change R212 value. Now it's 43K.
Click to expand...

5881 and 6L6 is the same type of tube. 5881 is the military version of 6L6.

I don't understand what you are telling us.
Take out the power tubes.
Turn the power on.
Turn the standby to "warm-up."
Do not turn the standby to "operate."
Check DC voltage on pin 5 of each output tube.
What DC voltage is on Pin 5 of each output tube?

Usually the bias must adjust to -42 volts DC for each output socket.

If the 470 screen grid resistor is bad, the tube is probably defective.
You cannot use the old output tube.
You will need to buy a new pair of tubes, but do not install the tubes until we check every thing else.

Do not put the tubes in.
Do not play the amplifier.
We need to do more testing before the amp is operated.

Plate volts:
The plate volts will be high if there is no tubes installed, this is normal.

No entenc el que ens està dient. Treu els tubs d’energia. Encendre l’alimentació. Gireu el mode d'espera al "escalfament". No gireu la reserva per "funcionar". Comproveu la tensió de corrent continu en el pin 5 de cada tub de sortida. Quina tensió de corrent continu es troba al pin 5 de cada tub de sortida? Si el resistor de la quadrícula de la pantalla 470 és dolent, probablement el tub sigui defectuós. No podeu utilitzar el tub de sortida antic. Haureu de comprar un parell de tubs nou, però no instal·leu els tubs fins que no revisem la resta. No introduïu els tubs. No reproduïu l'amplificador. Hem de fer més proves abans que l’amplificador funcioni. Volts de placa: Els volts de la placa seran elevats si no hi ha tubs instal·lats, això és normal.
 
Last edited:
Ok, I blowed a grid resistor because I installed a bad quad of power tubes. Days ago I check my amp before I blow a grid resistor. I noticed that the amplifier had a very high bias current setting. I have a bunch of coin base 6L6/5881 tubes. But I don't have a tube tester. Then I tryed 4 other tubes. One was bad. That is because I burned a grid resistor.

I installed a new 6L6GC quad(30w Max disipation). But I still had a hot bias. Then I connected a 10K resistors in to R212. Serial conection.

Thanks AMS. I will report the values.
I hope you andestand my explanation.
 
marshalltsl said:
Ok, I blowed a grid resistor because I installed a bad quad of power tubes. Days ago I check my amp before I blow a grid resistor. I noticed that the amplifier had a very high bias current setting. I have a bunch of coin base 6L6/5881 tubes. But I don't have a tube tester. Then I tryed 4 other tubes. One was bad. That is because I burned a grid resistor.

I installed a new 6L6GC quad(30w Max disipation). But I still had a hot bias. Then I connected a 10K resistors in to R212. Serial conection.

Thanks AMS. I will report the values.
I hope you andestand my explanation.
Click to expand...
Treu els tubs.
No utilitzeu l’amplificador.
Feu més proves primer.
Poseu els tubs a ÚLTIMA.
 
marshalltsl said:
Ok, I blowed a grid resistor because I installed a bad quad of power tubes. Days ago I check my amp before I blow a grid resistor. I noticed that the amplifier had a very high bias current setting. I have a bunch of coin base 6L6/5881 tubes. But I don't have a tube tester. Then I tryed 4 other tubes. One was bad. That is because I burned a grid resistor.

I installed a new 6L6GC quad(30w Max disipation). But I still had a hot bias. Then I connected a 10K resistors in to R212. Serial conection.

Thanks AMS. I will report the values.
I hope you andestand my explanation.
Click to expand...

Do not turn the standby switch to "operate."
Keep the standby switch in "warm up" position.

The high voltage will remain OFF, for all the testing.

L’alta tensió romandrà desactivada, per a totes les proves.
 
Last edited:
marshalltsl said:
Without power tubes.
-32,36 (bias trim pot ar min. value position)each tube. Power switch on.
-45,15 (bias trim pot ar min. value position) each tube. Power switch and stand-by switch working.
482 Vcc on plate.
Click to expand...

You need to fix the bias before you put the tubes in.

Heu d’arreglar el biaix abans d’entrar els tubs.
 
Turn Power Off
Disconnect Mains Voltage
UN-plug Mains power

1. Test R232 5.6K
2. Test R 233 5.6K
3. Test R237 5.6K
4. Test R 238 5.6K
5. Test R 234 150K
6. Test R235 150K
7. Test R213 22K
8. Install R212 33K
9. Test R251 470 ohm
10. Test R252 470 ohm
11. Test R 253 470 ohm
12. Test R 254 470 ohm


1. Prova R232 5.6K
2. Prova R 233 5.6K
3. Prova R237 5.6K
4. Prova R 238 5.6K
5. Prova R 234 150K
6. Prova R235 150K
7. Prova R213 22K
8. Instal·leu R212 33K
9. Prova R251 470 ohm
10. Prova R252 470 ohm
11. Prova R 253.470 ohm
12. Prova R 254 470 ohm


Marshall LM6100 Biastest.png
 
Last edited:
Amp Mad Scientist said:
Turn Power Off
Disconnect Mains Voltage
UN-plug Mains power

1. Test R232 5.6K
2. Test R 233 5.6K
3. Test R237 5.6K
4. Test R 238 5.6K
5. Test R 234 150K
6. Test R235 150K
7. Test R213 22K
8. Install R212 33K
9. Test R251 470 ohm
10. Test R252 470 ohm
11. Test R 253 470 ohm
12. Test R 254 470 ohm


1. Prova R232 5.6K
2. Prova R 233 5.6K
3. Prova R237 5.6K
4. Prova R 238 5.6K
5. Prova R 234 150K
6. Prova R235 150K
7. Prova R213 22K
8. Instal·leu R212 33K
9. Prova R251 470 ohm
10. Prova R252 470 ohm
11. Prova R 253.470 ohm
12. Prova R 254 470 ohm


View attachment 45373
Click to expand...
Thanks you! I tested many components of this list. But you know I'm not an amp tech. I trust in you. I will do it.
Again thanks AMS!
 
I test all parts of the list. All are ok. Are all this parts tolerance 5%? I remember have -40 v dc when I tested. Do I need remove this parts to test It properly?
Thanks.
 
marshalltsl said:
I test all parts of the list. All are ok. Are all this parts tolerance 5%? I remember have -40 v dc when I tested. Do I need remove this parts to test It properly?
Thanks.
Click to expand...

Remove the output tubes.
Turn on the power.
Turn the standby to "operate."
adjust the bias pot.
What is the most voltage that you can adjust for pin 5 of the output socket?
What is the lowest voltage you can adjust?
What is the highest voltage you can adjust?

Traieu els tubs de sortida. Encendre l’alimentació. Gireu el mode d'espera per "funcionar". ajusteu l'olla de biaix. Quin és el màxim voltatge que podeu ajustar al pin 5 de la presa de sortida? Quin és el voltatge més baix que podeu ajustar? Quin és el voltatge més alt que podeu ajustar?
 
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