Marshall valvestate 100r bias problem

[Demian2020]

Hi! I need some help with an marshall amp. The output trasistors blewup and I put tip141 and tip146 instead bdv65 and bdv64. I check all the other components of the power output and checks all ok, but the bias is set to 1.2v at the base of the transistors. I nedd to now how I can adjust the bias voltaje in this circuit. Help I'm lost PD: I use tip142 and tip147 but they blewup much faster.

[Helmholtz]

A base-emitter voltage slightly above 1V is normal for Darlingtons at idle.

How much do R19,21,24,25 drop?

[Demian2020]

A base-emitter voltage of about 1.2V is normal for Darlingtons at idle.

Hi but they run so hot at 8 ohm impedance. Only two transistors run hot the other two run cold.

[Helmholtz]

Please see my edit above and post all 4 emitter resistor voltage drops.

You should use identical darlingtons on each side.
Bias can be adjusted by the values of R18/R20. Higher resistance should lower bias.

[Demian2020]

A base-emitter voltage slightly above 1V is normal for Darlingtons at idle.

How much do R19,21,24,25 drop?

Ok R19 0.02V R21 0.03V R24 0.13 and climbing R25 also climbing 0.6v then I ear a little pop an goes to 0v

[Demian2020]

A base-emitter voltage slightly above 1V is normal for Darlingtons at idle.

How much do R19,21,24,25 drop?

T10 and T11 got hot the rest cold

[Demian2020]

Now in the npn transistors I have 0.4v between B E and in the PNP transistors I have 0.7v I'm so lost

[Jazz P Bass]

"T10 and T11 got hot the rest cold"

Well, seeing as the T 9 /10 and T 11 /12 are each in parallel, that does not make any sense.
I would check that the ballast resistors are o/k & connected properly. R 19 /21 & R 24 /25.

Check T7 & T8 as they may have shorted in the failure

A word of note: please do not connect the 8 ohm load until you figure out what is wrong.

[Helmholtz]

Ok R19 0.02V R21 0.03V R24 0.13 and climbing R25 also climbing 0.6v then I ear a little pop an goes to 0v

Looks much too high.
In absense of better information, I would adjust to 0.01V = 10mV each or even lower. This assumes good 0.33R emitter resistors.
But you need to use identical darlingtons each side.

[Demian2020]

I change T4 in the schematic calls for tip 29 but in circuit its have an tip 31 now I have 1.2v again between B E in all 4 output transistors. But the drop in R24 an R25 still 0.10v T7 and T8 checks fine. I have some brand new for change

[Demian2020]

Looks much too high.
In absense of better information, I would adjust to 0.01V = 10mV each or even lower. This assumes good 0.33R emitter resistors.
But you need to use identical darlingtons each side.

All four ballast resistors checks 0.33 ohms

[Demian2020]

"T10 and T11 got hot the rest cold"

Well, seeing as the T 9 /10 and T 11 /12 are each in parallel, that does not make any sense.
I would check that the ballast resistors are o/k & connected properly. R 19 /21 & R 24 /25.

Check T7 & T8 as they may have shorted in the failure

A word of note: please do not connect the 8 ohm load until you figure out what is wrong.

I just replace T7 & T8 but no change

[Demian2020]

Looks much too high.
In absense of better information, I would adjust to 0.01V = 10mV each or even lower. This assumes good 0.33R emitter resistors.
But you need to use identical darlingtons each side.

What resistors do you suggest to replace with R18 and R19?

[Dave H]

Bias can be adjusted by the values of R18/R20

Don't R18, R20 set the output current limit?
R12, R13, TR6 set the bias

[Helmholtz]

What resistors do you suggest to replace with R18 and R19?

Optimal value requires trial and error. Start with 120R and increase to 150R or 180R if necessary. Or wire 100R trimmers in series with existing resistors. All emitter resistor voltage drops should be equal.