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RE: Mark III Premium Mod Question

If it's Ac balance the purpose is to get the SIGNAL to the control grids of the output tubes equal. Has nothing to do with BIAS. On my VTL's, I use a scope to set it perfectly! If you have a two channel scope, or Know someone that does, follow this procedure as it's much more accurate than the multimeter method.
1. Connect an 8 ohm 20 watt resistor to the output of each channel.
2. connect a probe from each channel of the scope to the grid of an output tube on one channel. On a PPP make sure you have the probe on one of the output tubes on each side of the output transformer primary.
3. Set each channel of the of the scope to AC, and to measure a 20v signal.We will set the best voltage later.
4.Place a multimeter across the 8 ohm resistor,set the meter to AC input, 10V or higher, and connect a signal generator set to 1 KHZ to the input with the output of the generator set to zero.
5.Turn on the amp, and let it warm up for 15 Min.
6. As you watch the multimeter, increase the signal level on the signal generator to five an output voltage of around 3V ( not critical). this is an output of around 1 watt.
6. Set Channel 2 of the scope to invert.
7. Measure the voltage on channel 1 of the scope, and adjust for a reasonable easily viewable waveform, then set channel 2 the same. Note:Use the selector switch, NOT the variable setting!!
8.Set the input mode to A+B.
9. Adjust the AC balance to null the trace. You AC balance for that channel







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  • RE: Mark III Premium Mod Question - truep 09:20:03 12/22/13 (0)

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