|
|
Post by Franzen on Sept 19, 2005 12:29:05 GMT -7
Hi,
I think I once saw a post that the good DR. had made about biasing a route 66. i can´t seem to find it now. Can anyone help me ?
|
|
|
|
Post by kc on Sept 19, 2005 12:41:35 GMT -7
Franzen, Not sure about the post, but check out the Dr Z site: drzamps.com/biasnotes.htmlThe “Route 66” amp normally ships with Groove Tubes KT-66-HPs with a rating of #5 or #6. To adjust the bias we will try and set each tube’s idle current (or plate current with no input signal, Power and Standby on) into a fixed load measuring from each plate PIN3 to Center Tap of Output Transformer. This is called the Shunt Current Measurement, because you are shunting your Current Meter across high voltage. This is a dangerous setup and SHOULD ONLY BE DONE BY EXPERIENCED TECHNICIANS. I have found an easier way to dial in the Bias, and it will bring the correct operating bias point to within 97% of optimal. The safer method is to monitor the Center Tap Voltage, located on the RED and WHITE STRIPED wire that attaches to the Multi Can Capacitor. Your volt meter would be set to DC range. Ground your Common lead to the chassis and carefully measure the RED/WHITE striped wire with your highest DC Voltage range. Adjust the bias pot till the Voltage at the RED/WHITE striped wire is at 475 Volts DC. If you are using Groove Tube KT-66-HPs rated at #5 or #6 with a 5AR4/GZ-34 rectifier in the power supply then the voltage reading of 475 volts should be the optimum setting. Remember to have a fixed resistive load, or if not, a speaker will do to properly adjust the bias. |
|
|
|
Post by Franzen on Sept 19, 2005 13:10:27 GMT -7
That was JUST what I was looking for !!!!! Thank you so much !!!!
|
|
|
|
Post by DRZ on Sept 19, 2005 16:18:55 GMT -7
That was JUST what I was looking for !!!!! Thank you so much !!!! After realizing that many owners couldn't get the 475 plate volts, i realized you need at least 125 wall Volts to do it. My shop is in an industrial area and the voltage to my shop is a little on the high side. Remember the power tranny in a tube amp is a 4 to 1 step up ( in the 66 anyway). So for every volt under 125 V subtract 4 volts from that set-up, that is voltage you read AC from your wall socket. Some guys could only get about 460 V on the plates and they had 121V from the wall. The shunt meadthod or use of a bias right is better. I shoot for 28 to 32 mA per tube . Z |
|
|
|
Post by ducmike on Sept 19, 2005 17:21:44 GMT -7
I better go re-bias mine. The website sugests 33- 38ma, and I set it at 36.
|
|
|
|
Post by DRZ on Sept 20, 2005 3:25:03 GMT -7
I better go re-bias mine. The website sugests 33- 38ma, and I set it at 36. Hey if you like it leave it. KT 66's like most Beam Powered Tubes will operate between 10 and 40 mA safely. I have been setting them a touch lower to achieve a bit more clean , a touch less hair, and a longer useful life. DR.Z |
|
|
|
Post by taswegian on Sept 20, 2005 3:39:22 GMT -7
Cool, I think mine are biased at about 36. Sounds great but does break up a bit quicker than it did.
Not such a bad thing for me though. Next time I'll be looking a little lower. I think the lower biasing levels sound better pushed.
Cleveland Rocks.
|
|
|
|
Post by ducmike on Sept 20, 2005 5:10:24 GMT -7
It sounds great, so I'll leave it alone.
|
|
frank9310
Full Member
Now dig this baby...
Posts: 146
|
Post by frank9310 on May 6, 2008 8:45:54 GMT -7
Wow! Well isn't residential wiring in the U.S. 110V? So 125V - 110 = 15 x 4V = 60V
So 475 - 60 = 415V My measurement says it's around 445v so maybe my wall voltage is either slightly higher than 110v or I guess if I just stick with the mA reading I should be ok. By the way, the Shuguangs sound great at 39.5mA using a Telefunken EF86 and a Celestion G12H-30 + G12C Greenback. You want to hear rolling thunder, fat singing mids and soaring highs this is it!
I plugged a Dunlop Germanium based Fuzz Face into a Fulltone Deja 2 and with the amp on a at around 9Am I'm nailing Jimi's Star Spangled banner with the whistling bombs dropping and all! There is just no circuit like a clean circuit like the 66! Forget all those amps with the PCB multiple preamp stages. We're talking pure tone here baby! Yeah!
|
|
|
|
Post by Phil (aka Phil) on May 6, 2008 10:37:49 GMT -7
Wow! Well isn't residential wiring in the U.S. 110V? So 125V - 110 = 15 x 4V = 60V So 475 - 60 = 415V My measurement says it's around 445v so maybe my wall voltage is either slightly higher than 110v or I guess if I just stick with the mA reading I should be ok. The "wall voltage" in the U.S. used to be 110V "back in the day" but now it's 120V +/- 5% which works out to 114V-126V. 120V is the "nominal" voltage. Remember when you use things like Bias Rites and other bias tools that measure cathode current that you're reading cathode current AND screen current. They both flow back to ground through the cathode. As a fudge factor you can assume 5% of the reading is screen current, so if you're reading 40mA, 2 mA is screen current and you're really at about 38mA of cathode current. |
|
|
|
Post by zdogma on May 6, 2008 11:38:09 GMT -7
Wow! Well isn't residential wiring in the U.S. 110V? So 125V - 110 = 15 x 4V = 60V So 475 - 60 = 415V My measurement says it's around 445v so maybe my wall voltage is either slightly higher than 110v or I guess if I just stick with the mA reading I should be ok. The "wall voltage" in the U.S. used to be 110V "back in the day" but now it's 120V +/- 5% which works out to 114V-126V. 120V is the "nominal" voltage. Remember when you use things like Bias Rites and other bias tools that measure cathode current that you're reading cathode current AND screen current. They both flow back to ground through the cathode. As a fudge factor you can assume 5% of the reading is screen current, so if you're reading 40mA, 2 mA is screen current and you're really at about 38mA of cathode current. That's interesting, I wasn't aware of that. I'll keep that in mind next time I bias up. |
|
|
|
Post by dixiechicken on May 6, 2008 13:32:29 GMT -7
|
|
