Post by Paul (TRANE) on Sept 22, 2008 8:02:25 GMT -7
Observations on Biasing:
On Friday I put in a new set of GT-KT66C (#6) in my amp. I used my Weber Bias Rite to do the actual biasing observations. I plugged the Bias Rite into the tube sockets on the head and the KT66 tubes in the Bias Rite sockets. Same as always. I let the amp warm up and then turned the amp on. The head was in an amp cradle. Actually, the amp cradle is one of the best pieces I have found for holding the chassis for this type of work. But I digress, anyway, using the Bias Rite I measured a Plate Voltage of 440V on tube A and 470V on tube B. Now I found this to be quite an odd occurrence. The Plate Voltage should be at least close to one another. So, I took out my multi-meter and checked the voltage on Pin 3. Using the DMM I found both tubes to have a plate voltage of 456V to 460V (probably due to wall voltage fluctuations) but the voltage on A was always the same as the voltage on B. So knowing that the Plate Voltage readings were inaccurate how do I trust the mA numbers on the Bias Rite? Basically, I wound up getting using the Bias Rite to get me into the ballpark of what I was looking for and did the “fine tuning” of the bias based on the tone I was hearing from the amp.
I am considering one of these to see if there is any difference in the readings. www.amp-head.com/product_info.php?cPath=21&products_id=70
So what do you guys do here when you find such discrepancies? Are there any other easy, “safe”, ways to make sure that you have the correct readings on the Voltage & mA side? I just want to make sure I am doing the job accurately and not putting the tubes at too high of a bias for safe operation.
Right now the amp sounds better than it ever has. Great thick defined sound with great clean to lead sounds at the turn of the guitar’s volume knob.
Thanks, any inputs would be greatly appreciated.
Paul G.
On Friday I put in a new set of GT-KT66C (#6) in my amp. I used my Weber Bias Rite to do the actual biasing observations. I plugged the Bias Rite into the tube sockets on the head and the KT66 tubes in the Bias Rite sockets. Same as always. I let the amp warm up and then turned the amp on. The head was in an amp cradle. Actually, the amp cradle is one of the best pieces I have found for holding the chassis for this type of work. But I digress, anyway, using the Bias Rite I measured a Plate Voltage of 440V on tube A and 470V on tube B. Now I found this to be quite an odd occurrence. The Plate Voltage should be at least close to one another. So, I took out my multi-meter and checked the voltage on Pin 3. Using the DMM I found both tubes to have a plate voltage of 456V to 460V (probably due to wall voltage fluctuations) but the voltage on A was always the same as the voltage on B. So knowing that the Plate Voltage readings were inaccurate how do I trust the mA numbers on the Bias Rite? Basically, I wound up getting using the Bias Rite to get me into the ballpark of what I was looking for and did the “fine tuning” of the bias based on the tone I was hearing from the amp.
I am considering one of these to see if there is any difference in the readings. www.amp-head.com/product_info.php?cPath=21&products_id=70
So what do you guys do here when you find such discrepancies? Are there any other easy, “safe”, ways to make sure that you have the correct readings on the Voltage & mA side? I just want to make sure I am doing the job accurately and not putting the tubes at too high of a bias for safe operation.
Right now the amp sounds better than it ever has. Great thick defined sound with great clean to lead sounds at the turn of the guitar’s volume knob.
Thanks, any inputs would be greatly appreciated.
Paul G.