• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

#26 pre amp

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#3,441
Vinylsavor said:
Hi!



Seems your linestage is not out of balance.
Also your test with reversing the channels shows that it is not the line stage.
Most likely a bad wiring as Cheah already suggested.



This is the big disadvantage of filament bias, if the tubes differ in emission they draw different currents. This causes a different voltage drop across the primary. In your case it means the difference between the two tubes is about 3mA which is a lot.

When using filament bias the tubes should be tested and the current should be verified in circuit since there is no self adjustment mechanism any more as in cathode bias

Best regards

Thomas
Click to expand...

How do you calculate the 3mA, TIA for teaching me.
 
#3,446
Hi!

merlin el mago said:
No, I fixed these when the TVCs.
Click to expand...

So you still have the channel imbalance?

merlin el mago said:
Now I resoldered again & checked all input-outputs at Right channel also I'm rolling new tubes to see what's happen because the measurements are OK
Click to expand...

Instead of just rolling tubes, maybe try a more structured approach.

Your measurements indicated identical gain. Try at different frequencies also to make sure

When you switched the left and right inputs at the TVC, it was still the same channel which appeared louder?

Again this would indicate that the problem is not in the line stage.

Best approach:

With everything connected, measure the signals at both channels:

At linestage input
linestage output
TVC input (inside your TVC box right at the TVCs)
TVC output

That will tell you where exactly the problem occurs

It would also be helpful if you report back more clearly what you have done and where you measured to help further

best regards

Thomas
 
#3,449
Vinylsavor said:
Hi!



So you still have the channel imbalance?



Instead of just rolling tubes, maybe try a more structured approach.

Your measurements indicated identical gain. Try at different frequencies also to make sure

When you switched the left and right inputs at the TVC, it was still the same channel which appeared louder?

Again this would indicate that the problem is not in the line stage.

Best approach:

With everything connected, measure the signals at both channels:

At linestage input
linestage output
TVC input (inside your TVC box right at the TVCs)
TVC output

That will tell you where exactly the problem occurs

It would also be helpful if you report back more clearly what you have done and where you measured to help further

best regards

Thomas
Click to expand...

Yes I have channel imbalance.

I have the TVCs in a separate box, I used without the lineamp and NO difference of gain between channels🙂

So last measurements done without TVCs

Thanks for help
 
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