NOSValves Posted October 4, 2005 Share Posted October 4, 2005 Thebes, Nope you have it wrong. Biasing has nothing to do with the B+ voltage applied to the plate of the tube. Biasing adjusted and sets the current that is drawn through the plate of the tube. The bias is controlled by applying a negative voltage the control grid in a fixed adjustable bias amp like your 8B or 299. Craig Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted October 4, 2005 Share Posted October 4, 2005 Thebes: "So B+ is effectively refering to positive. So biasing an amp is essentially adjusting the amount of voltage going to the tubes so that all tubes have the same voltage running through them? Which to my understanding and confusion means actually applying a negative bias (B-) when biasing the amp." Craig: He is actually partly correct with this. You are right, Thebes, B+ does refer to positive voltages (these are the high voltage supplies for the plates of the tubes) and your description of bias adjustment is not completely off base. There is a negative voltage invloved, so you were close. Some types of transformers have bias tap available of maybe 50 volts or so, but not all amps are biased the same way. Some amplifiers use cathode bias, for example, where a 'fixed' cathode resistor is used rather than the way Craig mentioned above. Erik Erik Quote Link to comment Share on other sites More sharing options...
thebes Posted October 4, 2005 Share Posted October 4, 2005 Thanks guys I kinda figured I'd get it wrong but it's nice to know I was in the neighborhood. How about my question about properly aligning the plug though? Any advice? Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted October 4, 2005 Share Posted October 4, 2005 Yup, you were in the neighborhood, which is just about there! Good! Quote Link to comment Share on other sites More sharing options...
hwatkins Posted October 6, 2005 Share Posted October 6, 2005 Thanks guys I kinda figured I'd get it wrong but it's nice to know I was in the neighborhood. How about my question about properly aligning the plug though? Any advice? Bump - This is a question I wish I had asked. I had assumed that in various forms the power is being conditioned before it hits the real meat of the matter (the transformer) and that most caution was taken to defeat any sort of polarity issue that may arise from a two prong plug. Much like our Mommies - they were doing it for our own good. Regardless of my uninformed thoughts - there would still be a correct polarity solution for the plug if I read it right. Help please - 7 of me have a headache over this issue.... Quote Link to comment Share on other sites More sharing options...
DRBILL Posted October 6, 2005 Share Posted October 6, 2005 Thebes: "How about my question about properly aligning the plug though? Any advice?" Nobody wants to touch this because we don't want to be responsible for an electrocution! Seriously, a lot of old gear had non-polarized power plugs. And yes, it CAN matter which way they are inserted in the recepticle. It is a matter of hum reduction and "ground loops" rather than safety. (I wont even get into AC-DC equipment.) Here is a safe and fool-proof way of determining which way the plug should go. You will need to test each piece of equipment seperately. Nothing must be attached to the device (except speakers, in the case of amplifiers). Plug it in. Turn it on. With a neon circuit tester, hold one test tip between your fingers and touch the other tip to the chassis of the device. If it glows faintly, turn the plug over. There should be no glow. That is the proper plug position. Mark the plug for future reference. Repeat for all devices. If you get a faint glow in both positions or no glow in both positions, you will have to resort to trial and error, listening for a faint hum when all the equipment is connected in its usual configuration. I hope this helps. Did you know that many "zip cords" (power cords) are marked? Feel for a ridge on one lead and a smooth surface on the other. DRBILL Quote Link to comment Share on other sites More sharing options...
thebes Posted October 6, 2005 Share Posted October 6, 2005 It sure is great to have a doctor on the premises. That is just a fantastic answer and really helps a lot. I've seen threads here where people have metnioned flipping the plug around and getting better sound, correcting a hum prblem etc, but nobody until now, has given the proper guidance on how to figure out correct polarity. I actually have one of those glowing cirucit testers and can do this without hurting myself or others. Since I can do this without an electrifying experience I thank you very much, but I'm not sure how my putative heirs will react to the news that I will be around a bit longer. Quote Link to comment Share on other sites More sharing options...
hwatkins Posted October 6, 2005 Share Posted October 6, 2005 It sure is great to have a doctor on the premises. I actually have one of those glowing cirucit testers and can do this without hurting myself or others. Yo Marty - don't get too cocky....If damage can be done I am sure you will find a way. I too send my thanks Doc. Quote Link to comment Share on other sites More sharing options...
DRBILL Posted October 6, 2005 Share Posted October 6, 2005 I may be a doctor, but it ain't the kind that does you no good! You know what BS is. MS is "More of the Same". PhD is Piled High and Deep! I have no illusions any more. DRBILL Quote Link to comment Share on other sites More sharing options...
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