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FDP Forum / Fender Amps: 1985 - Current / Weber Bias-Rite newbie HELP?!?!

dlilly69 USA	Dec 28th, 2005 02:12 PM   Edit   Profile   Print Topic   Search Topic Hi Folks, I just got a Weber Bias-Rite for Xmas. I am a newbie and really could use some help on how to use this. I am biasing 2 amps with it: - A 65 Twin RI - A DRRI The questions I have: 1. After plugging the tubes and bias rite into TWIN (6l6) amp, am I looking to set the bias of EACH TUBE to 30-35ma EACH? So each tube should read the same 30-35ma setting when I am clicking the dial on the meter from A-B-C-D? Same thing with the DRRI (6v6)? Would the DRRI be 20-25ma EACH TUBE when clicking the dial from A-B? 2. My Bias Rite has the VI option which measures plate voltage. What exactly is this used for, and how do I use this measurement to bias my amps? Is there a formula I plug the reading into to figure out the best biasing ma spec? PLEASE- any and all help would be greatly appreciated! Cheers, Dan
glrogers Contributing Member Georgia, US first time caller, long time listener	Dec 28th, 2005 02:23 PM   Edit   Profile   Print Topic   Search Topic This is best answered in reverse. Plate voltage is the voltage at pin #3 of your power tubes. You need that and your cathode current to properly bias. Current x Plate Voltage = wattage. The wattage is the number you are really biasing to. Different tubes have different tolerances. So, you need to take your current reading and voltage reading, calculate the wattage, then decide if you are too hot or too cold. A typical 6L6 shouldn't see more than 21 watts. It will vary depending on your tube. A typical 6V6 should be close to half that; but some 6V6s made today are very stout, able to handle similar plate voltages to a 6L6. You really need to know the specs of your particular tube(s). And don't get hung up on the tubes having the -exact- same reading. Unless they are PERFECTLY matched tubes, they will vary. Variances by 5ma or less are fine, and usually to be expected.
dlilly69 USA	Dec 28th, 2005 02:55 PM   Edit   Profile   Print Topic   Search Topic Thanks for the reply. I am still somewhat confused. More dumb questions- 1. Can someone give me a quick step by step walkthrough on how to use this Bias-rite properly? 2. How do I find the "Current Reading" to plug into the Current x Plate Voltage = wattage equation? How do i find the correct wattage to bias for my Twin with 6l6's and the DRRI with 6v6's? 3. I thought I saw posts all over this forum stating that 6l6's on a Fender Twin should be biased to 30-35ma each. Is this incorrect? Thanks! Dan (This message was last edited by dlilly69 at 02:56 PM, Dec 28th, 2005)
CheapGuitars Mpls, MN, US Plug in, turn on, play	Dec 28th, 2005 03:41 PM   Edit   Profile   Print Topic   Search Topic I found this calculator very handy when using my Bias-Rite to setup my JTM45 clone. Weber Bias Calculator
dlilly69 USA	Dec 28th, 2005 04:20 PM   Edit   Profile   Print Topic   Search Topic Thanks much for the calculator. Can anyone help me with some of my other questions above? Also, is a 65 Twin RI and a DRRI a class A or Class AB amp? The Bias calculator Cheapguitars posted above asked for this. Any other info would still be appreciated. I'm still not sure how to use this Bias Rite correctly! Thanks for your time and help, Dan
sponbatoc USA/Maryland	Dec 28th, 2005 04:22 PM   Edit   Profile   Print Topic   Search Topic Take the wattage of the tube, 6V6 is 12 watts (JJ6v6 is 14), divide that by the plate voltage reading, then multiply that result by .7 (70 %). The result is the current in mA at 70% of max. Example from my recent re-tube on my DRRI with JJ 6V6’s ….. 14 / 418 = .033 x .7 = 23.1 mA Jeff
sponbatoc USA/Maryland	Dec 28th, 2005 04:45 PM   Edit   Profile   Print Topic   Search Topic Dan, They are both Class AB and should be biased at no more than 70% of max power dissipation. From example above...... .033 (33 mA) is max dissipation, so 70 % of that is 23.1 mA Jeff
dlilly69 USA	Dec 28th, 2005 05:00 PM   Edit   Profile   Print Topic   Search Topic Thanks Jeff. How would I find out the wattage of my tubes? What is the wattage for 6L6 stock Fender tubes for the Twin RI and stock 6v6 for the DRRI? Is there a way to find out the wattage for any type of tube? Thanks! Dan (This message was last edited by dlilly69 at 05:39 AM, Dec 29th, 2005)
sponbatoc USA/Maryland	Dec 28th, 2005 05:05 PM   Edit   Profile   Print Topic   Search Topic If you want to reverse things and determine the percentage of max that you are biased at before you make any adjustments........ Bias reading is 21, volts are 418 and you have a JJ 6v6 (capable of handling 14 watts) .021 x 418 = 8.778 8.778 / 14 = .627 (round to 63%) ... meaning that you are currently biased at 63% of max plate dissipation. Jeff
ajbergren Contributing Member * USA/IA Transcend Time	Dec 28th, 2005 05:08 PM   Edit   Profile   Print Topic   Search Topic I have a bais rite and the DRRI, so I can walk you through biasing this amp. Plug the 6V6s into the bias rite head, and then plug the assembly into the DRRI. Flip the amp to standby and let it warm up for a few minutes (5-10 should be fine). Set the meter to read plate volts, and note the plate voltage for both tubes (it should be ~410 V) for both. Write down these values. Flip the VI switch to cathode current. Note these values (should be ~20 mA for each). Write these values down. Now, multiply the plate voltage by the cathode current for each tube independently. For example, 410 V x 0.02 A = 8.2 W. Now, a typical 6V6 in a class AB amp should be biased no higher than 70% max at idle (i.e., with no input). Typcial 6V6s are rated at 12 W (some are 14 W) maximum dissipation. 12 W x 0.7 = 8.4 W! Looks like you are good to go! If, however, you encounter higher ratings (like 30 mA and 410 V), you will want to turn the bias adjustment pot counterclockwise. This will allow you to decrease the plate dissipation to a safe level. Likewise, you could increase the bias, if needed. Now, if you get drastically different readings for the two power tubes, you *may* want to think about replacing the set. Hope this is clear, AJB.
ajbergren Contributing Member * USA/IA Transcend Time	Dec 28th, 2005 05:10 PM   Edit   Profile   Print Topic   Search Topic Stock tubes on new DRRI are EH, and are rated at 12 W.
sponbatoc USA/Maryland	Dec 28th, 2005 05:18 PM   Edit   Profile   Print Topic   Search Topic A stock 6v6 is 12 watts, and I believe a 6L6 is 23, but I'm not positive. I'm trying to remember some website address's, not having much luck. ahhh , here's one..... Duncan Amps Bias FAQ
dlilly69 USA	Dec 29th, 2005 05:44 AM   Edit   Profile   Print Topic   Search Topic One more question: The weber bias calculator gives 2 options for 6L6's- 6L6 and 6L6 GC'S. What kind of tubes are in the 65 Twin RI- 6L6 or 6L6GC? What's the difference? It seems to make a big difference on the calculator. This is great info! Thanks for all the help guys. Much appreciated!! :) Cheers, Dan
ajbergren Contributing Member * USA/IA Transcend Time	Dec 29th, 2005 08:11 AM   Edit   Profile   Print Topic   Search Topic Should be 6L6GCs in the Twin, but this can vary. There is a lot of confusion surrounding the specific tube names these days, as each manufacturer seems to call their 6L6s something different. True 6L6s have metal cans, and are not generally used in guitar amps. 6L6GCs are the ones of interest (GC stands for Glass Container). There is also 6L6GBB (Glass Bottle) that are rated slightly differently, I think. Then there is the 6L6EH, which is Electroharmonix's version of the 6L6GC, and so on. To check what kind of tubes are currently in your twin, look for markings (under the Groove Tubes stamp if they are GT). AJB.
rfrakes331K USA RonHalen Jokingly He Says	Dec 31st, 2005 08:48 AM   Edit   Profile   Print Topic   Search Topic Different tubes are described on the Tube Store's website: http://www.thetubestore.com/powertubesonly.html I am curious, did any directions come with your Weber Bias Rite?
dlilly69 USA	Jan 1st, 2006 10:09 AM   Edit   Profile   Print Topic   Search Topic Actuallly, no directions came with the bias-rite. There are some basic directions on the weber site, but not enough for a newbie, imo.

FDP Forum / Fender Amps: 1985 - Current / Weber Bias-Rite newbie HELP?!?!

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