Hi there!
This is my first post, i hope this question is not so stupid!
I've been given an Ampeg V4BH for tube replacing and biasing. This a 4x6L6 amp. And I've used a 6L6GC matched quarted from TAD (Tube Amp Doctor from Germany). This is my first time adjusting the bias so I have a few questions. I hope you can help me.
This is the procedure I've follow. Values were measured after 3 hour of heating. Tubes are named 1-4 from left to right (front view)
1) I've set the bias voltage (Pin 5) to -48V (Tube1 and T2) -46V (T3 and T4)
2) Plate Votage (Pin 3) is 451V (for all tubes)
3) This amp has fuses on the cathode so I've removed each the fuse and measured the current for each tube. I've got:
Tube1 - 31.1ma
Tube2 - 31.4ma
Tube3 - 35.6ma
Tube4 - 37.1ma
4) Then I've measured the Screen Current (Pin 4) measuring the Voltage drop across the screen resistor (I've measured the screen resistor too). I've got:
Tube1 - 1.44ma
Tube2 - 2.03ma
Tube3 - 1.87ma
Tube4 - 1.74ma
5) I've calculated the static dissipation wattage as (Ic-Is)*Vplate. I've got:
13.38 0.51
13.24 0.51
15.21 0.59
15.95 0.61
Tube1 - 13.38W (51%)
Tube2 - 13.24W (51%)
Tube3 - 15.21W (59%)
Tube4 - 15.95W (61%)
Now my questions:
1- This values look right so far. Could someone confirm that I am not doing anything wrong?
2- I've noticed that tubes are matched by pairs. Is this normal?
3- I don't know if this bias is too cold/hot for this type of amp. I've been recommended to set the bias around 55% but, do you have any recommendation for this type of amp? Which would be a nice value? I am not a Bass player so I can't judge by ear!
Thank a lot for taking time to read this.
This is my first post, i hope this question is not so stupid!
I've been given an Ampeg V4BH for tube replacing and biasing. This a 4x6L6 amp. And I've used a 6L6GC matched quarted from TAD (Tube Amp Doctor from Germany). This is my first time adjusting the bias so I have a few questions. I hope you can help me.
This is the procedure I've follow. Values were measured after 3 hour of heating. Tubes are named 1-4 from left to right (front view)
1) I've set the bias voltage (Pin 5) to -48V (Tube1 and T2) -46V (T3 and T4)
2) Plate Votage (Pin 3) is 451V (for all tubes)
3) This amp has fuses on the cathode so I've removed each the fuse and measured the current for each tube. I've got:
Tube1 - 31.1ma
Tube2 - 31.4ma
Tube3 - 35.6ma
Tube4 - 37.1ma
4) Then I've measured the Screen Current (Pin 4) measuring the Voltage drop across the screen resistor (I've measured the screen resistor too). I've got:
Tube1 - 1.44ma
Tube2 - 2.03ma
Tube3 - 1.87ma
Tube4 - 1.74ma
5) I've calculated the static dissipation wattage as (Ic-Is)*Vplate. I've got:
13.38 0.51
13.24 0.51
15.21 0.59
15.95 0.61
Tube1 - 13.38W (51%)
Tube2 - 13.24W (51%)
Tube3 - 15.21W (59%)
Tube4 - 15.95W (61%)
Now my questions:
1- This values look right so far. Could someone confirm that I am not doing anything wrong?
2- I've noticed that tubes are matched by pairs. Is this normal?
3- I don't know if this bias is too cold/hot for this type of amp. I've been recommended to set the bias around 55% but, do you have any recommendation for this type of amp? Which would be a nice value? I am not a Bass player so I can't judge by ear!
Thank a lot for taking time to read this.
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