Schu Posted June 20, 2014 Share Posted June 20, 2014 (edited) Can someone please teach me about tube bias?... why it is needed, when do you do it and what tools (if any) are needed to do it correctly? I am very curious as I have begun looking at some tubes as an alternative and I am just trying to get me feet wet slowly here so I don't make multiple redundant purchases. How does auto biasing work and what are the compromises associated with it? Edited June 20, 2014 by Schu Quote Link to comment Share on other sites More sharing options...
minermark Posted June 20, 2014 Share Posted June 20, 2014 I see KT88s there, great tube, did you get a manual with your amp, if not can you look up the company online and get the exact voltage's they should be balanced for ? Every amp is different as far as "Perfect Balance" goes. Quote Link to comment Share on other sites More sharing options...
Schu Posted June 20, 2014 Author Share Posted June 20, 2014 (edited) I don't have an amp... I am trying learn as much as possible BEFORE purchasing. I've always felt that it was more important to know prior to than to have and wish otherwise. Edited June 20, 2014 by Schu 1 Quote Link to comment Share on other sites More sharing options...
minermark Posted June 20, 2014 Share Posted June 20, 2014 I'll take a pic of my Bias equip, it, or a simple volt meter is all that is needed in tuning/matching Bias voltage. Quote Link to comment Share on other sites More sharing options...
Schu Posted June 20, 2014 Author Share Posted June 20, 2014 cool... later on if you happen to have time. Craig helped me understand it a bit more already. Quote Link to comment Share on other sites More sharing options...
minermark Posted June 20, 2014 Share Posted June 20, 2014 (edited) When I got the wifes amps and then mine, I ask Primeamp (China) just what he uses to keep his aligned, this is the set up, I really did not need all of these tube test/sockets, it's just they were offered with the meter for $30 each extra, meter was $100, I told him I wanted every socket test set up that went with the meter, I figured the rest of my life there will be nothing I run into that I cannot balance. He said check once or twice a year if you notice one tube glowing more than the other. Edited June 20, 2014 by minermark Quote Link to comment Share on other sites More sharing options...
Schu Posted June 20, 2014 Author Share Posted June 20, 2014 hmmm... I have no idea how to use that Quote Link to comment Share on other sites More sharing options...
joessportster Posted June 20, 2014 Share Posted June 20, 2014 get a decent digital multimeter, and typically a small screw driver, attach the leads as indicated by the manufacturer, and adjust the screw till you get the recommended reading, repeat per tube, let amp warm up for 30 minutes or so and Re-Bias..................check frequently till you know how reliably the amp / tubes holds bias. Then if the amps tend to maintain Bias set a schedule to keep an eye on them (I have had good luck with most and could get away with checking monthly) If a tube is constantly going out of Bias its a good bet the tube is worn and about ready for replacement I have seen no dis-advantage to auto Bias, I guess one could say auto Bias does not allow you to keep track of tube performance as well, I find either is pretty easy to deal with, Quote Link to comment Share on other sites More sharing options...
joessportster Posted June 20, 2014 Share Posted June 20, 2014 When I got the wifes amps and then mine, I ask Primeamp (China) just what he uses to keep his aligned, this is the set up, I really did not need all of these tube test/sockets, it's just they were offered with the meter for $30 each extra, meter was $100, I told him I wanted every socket test set up that went with the meter, I figured the rest of my life there will be nothing I run into that I cannot balance. He said check once or twice a year if you notice one tube glowing more than the other. Check once or twice a year ? Yea I am not sure I would follow that advice I have no idea why you should need all this to check Bias, every amp I have ever had required either a standard multi meter, or (rarely) a guage wired to a 1/4 plug that the amp builder decided made the task easier.....................Some amps even come with the meters onboard Why would you change or need the tube socket unless you were getting into building ?? Quote Link to comment Share on other sites More sharing options...
Fjd Posted June 20, 2014 Share Posted June 20, 2014 Why would you change or need the tube socket unless you were getting into building ?? Given the very high lethal voltages that can run through a tube amp, if a person does not have much experience in dealing with these types of high voltage circuitry, I suspect the use of sockets may be a lot safer than trying to use aligator clips underneath a chasis then trying to screw a bias pot all while watching a meter. Although I know people that have broken the guide pin from these sockets too and almost created problems not knowing where to guide pins. Quote Link to comment Share on other sites More sharing options...
Schu Posted June 20, 2014 Author Share Posted June 20, 2014 looks like Craigs designs are accessed from the tops anyway... but I agree, I dont want to die. Quote Link to comment Share on other sites More sharing options...
Fjd Posted June 20, 2014 Share Posted June 20, 2014 looks like Craigs designs are accessed from the tops anyway... but I agree, I dont want to die. Since you have been in contact with Craig, I'm sure you are aware that all of the access is from the top and that a regular meter can be used with regular probes. I have experience with the stereo version of the VRD, which works the same way and is a very easy and straight forward process. Quote Link to comment Share on other sites More sharing options...
joessportster Posted June 20, 2014 Share Posted June 20, 2014 I dont know of any fairly modern consumer amp that requires one to bias from under the chassis....................if they exist I would certainly stay away from that type design Quote Link to comment Share on other sites More sharing options...
jimmytamp Posted June 20, 2014 Share Posted June 20, 2014 (edited) Hi Schu, I think it depends on your equipment's manual but basically setting the bias is is a similar procedure. I have Bob Latino's VTA ST120, which has 2 bias set-port on the front panel. You can use a normal voltmeter and set it to DCV which has value of .000. Then you need to gorund the black color cable to any part of the chasis (or maybe some amp has dedicated GRND port) & the red to the Bias-set point (in my case, it has 2 bias-set point per channel). Then you will see the value on the voltmeter (the values depend on your equipment/refer to your manual). In my case, to set the bias, it needs to be set in Linear/apentode mode. For me, I check & adjust the bias once in a month as per instruction in the manual. I hope this help. Cheers, Jimmy Edited June 20, 2014 by jimmytamp 2 Quote Link to comment Share on other sites More sharing options...
Schu Posted June 20, 2014 Author Share Posted June 20, 2014 Hmmm. All very interesing posts above. Thank you Quote Link to comment Share on other sites More sharing options...
Schu Posted June 20, 2014 Author Share Posted June 20, 2014 Another quick question.... when you see rust on a transformer is than an indication of something bad... like excess heat? Quote Link to comment Share on other sites More sharing options...
jimmytamp Posted June 20, 2014 Share Posted June 20, 2014 As far as I know, what you're looking is only the outer case of the transformer..but I'm not sure, maybe somebody here who has more knowledge about this can chime in. Oh by the way, until I received my tube amp, I have never had expereince with them at all...and it's just less than a year ago. Cheers, Jimmy Quote Link to comment Share on other sites More sharing options...
jimmytamp Posted June 20, 2014 Share Posted June 20, 2014 Oh...and if you have to do manual bias... Don't take any alcohol prior you do the bias setting...alcohol+small screw driver+some small holes+high current = are not good combination... 1 Quote Link to comment Share on other sites More sharing options...
Schu Posted June 20, 2014 Author Share Posted June 20, 2014 Oh...and if you have to do manual bias... Don't take any alcohol prior you do the bias setting...alcohol+small screw driver+some small holes+high current = are not good combination... Quote Link to comment Share on other sites More sharing options...
wvu80 Posted June 20, 2014 Share Posted June 20, 2014 Oh...and if you have to do manual bias... Don't take any alcohol prior you do the bias setting...alcohol+small screw driver+some small holes+high current = are not good combination... And how exactly, did you discover this fact? 1 Quote Link to comment Share on other sites More sharing options...
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