Very informative Hifigeek as usual. I have a pair of CL120's (modded by Steve Huntley in 2005) with balanced inputs. In addition to what was discussed thus far in this thread, the best place to start is to obtain tubes from ARC. That way you will know that they are well matched. Money well spend IMO. I have always taken a bias reading within the first 10 minutes. If you have a reading above 65mvdc (.065 VDC) you must drop it by turning the pot down. As the amp warm up the bias will increase and you do not want this to go to 75mv (or higher) as the amp warm up. Some techs will turn the pot to minimum before turning it on which is a good idea actually. Then you let the amp for at least an hour and you take a reading. Then you ramp up the bias to 65mvdc using the pots. Continue to observe your meter as the reading may go past 65mvdc ever so slightly. Bring it down to 65mvdc. ARC recommends doing a final read and setting after a full hour of thermal operation.
For the Servo, ARC suggests the amp to be left on 2-3hrs after the bias has been set so that it can reach full thermal operation. Resist the urge to fiddle with the Servo adjustment unless you are sure that it is out of range. You need to connect your positive probe to TP3 and negative one to TP2 (Classic 120) WARNING: HIGH VOLTAGE. You MUST use isolated alligator clips. The last thing you want is slip your probe onto chassi ground. You should get a reading of +/- .2mv or less. If it's above that you need to bring it down and as Hifigeek points out it can be a difficult task. Patience is of the essence here. Turn the pot ever so slightly (CW to make more positive and CCW to make more negative) and wait 5 minutes for the reading to stabilize. It's easy to over/under adjust so be gentle with the pot. It is normal for the reading to "float" somewhat as the Servo works. If you observe a reading that is within the range mentioned above when you connect your DVM then you need NOT touch the pot.
Hope this helps. Information above come from Leonard Gustafson and Chris Ossanna RE: Bias and Servo adjustment for a CL120's.
The best thing for you is to give Calvin a call and he will be more than happy to send/fax you the Bias/Servo adjustment procedure for your CL60. The procedure applies for both the CL60 and V70.
Good luck.
For the Servo, ARC suggests the amp to be left on 2-3hrs after the bias has been set so that it can reach full thermal operation. Resist the urge to fiddle with the Servo adjustment unless you are sure that it is out of range. You need to connect your positive probe to TP3 and negative one to TP2 (Classic 120) WARNING: HIGH VOLTAGE. You MUST use isolated alligator clips. The last thing you want is slip your probe onto chassi ground. You should get a reading of +/- .2mv or less. If it's above that you need to bring it down and as Hifigeek points out it can be a difficult task. Patience is of the essence here. Turn the pot ever so slightly (CW to make more positive and CCW to make more negative) and wait 5 minutes for the reading to stabilize. It's easy to over/under adjust so be gentle with the pot. It is normal for the reading to "float" somewhat as the Servo works. If you observe a reading that is within the range mentioned above when you connect your DVM then you need NOT touch the pot.
Hope this helps. Information above come from Leonard Gustafson and Chris Ossanna RE: Bias and Servo adjustment for a CL120's.
The best thing for you is to give Calvin a call and he will be more than happy to send/fax you the Bias/Servo adjustment procedure for your CL60. The procedure applies for both the CL60 and V70.
Good luck.