BBZink Posted April 9, 2017 Share Posted April 9, 2017 Good Day all, i have purchased a 2a3 Bowei integrated amp on ebay, and it plays well. Now i want to upgrade chinese tube on it. there is 2 potentiometer (behind the tube), i could access with a screwdriver. Does anyone knows what is the purpose of those potentiometer? Could not find anything on it, so my guess was to ask you all? Also tube on this amp are weird, could i replace them with something more standard or NOS? exemple 2a3C=?; GZ3=? and 6h8c=? regards Quote Link to comment Share on other sites More sharing options...
Schu Posted April 9, 2017 Share Posted April 9, 2017 You didn't think about asking the seller about the bias? 2 Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted April 9, 2017 Share Posted April 9, 2017 30 minutes ago, tapajeurs said: 2 potentiometer (behind the tube), i could access with a screwdriver. Does anyone knows what is the purpose of those potentiometer? Those are most likely the bias adjustment pots for the amp. There may be a bias ranged printed near the two adjustment pots. 33 minutes ago, tapajeurs said: Also tube on this amp are weird, could i replace them with something more standard or NOS? exemple 2a3C=?; GZ3=? and 6h8c=? Until you find out the bias adjustment range I would keep the tubes that came with the amp. A lot of people want to quickly get rid of the Chinese tube. They just assume that they are not good. Actually, they make some pretty good tubes. China and Russia never stopped using tubes when the US went thru the transistor age. A lot of tubes made in China and Russia are re-branded for overseas sale. Try and find a manual for the amp. Let us know how you like it. 1 Quote Link to comment Share on other sites More sharing options...
Schu Posted April 9, 2017 Share Posted April 9, 2017 pictures would be cool to... enjoy Quote Link to comment Share on other sites More sharing options...
BBZink Posted April 9, 2017 Author Share Posted April 9, 2017 54 minutes ago, Schu said: You didn't think about asking the seller about the bias? So far, it is for the noise... Quote Link to comment Share on other sites More sharing options...
BBZink Posted April 9, 2017 Author Share Posted April 9, 2017 Could not resist that candy red look! it work flawless. And banzai, i have put the tube on, sound amazing! but not sure i have the proper "noise" adjustment? only downsize, no phone socket. ps i found back the seller, send a question, will wait and see! Sometimes i am to much in the problem to think outside the box... Thanks Quote Link to comment Share on other sites More sharing options...
BBZink Posted April 9, 2017 Author Share Posted April 9, 2017 57 minutes ago, derrickdj1 said: Those are most likely the bias adjustment pots for the amp. There may be a bias ranged printed near the two adjustment pots. Until you find out the bias adjustment range I would keep the tubes that came with the amp. A lot of people want to quickly get rid of the Chinese tube. They just assume that they are not good. Actually, they make some pretty good tubes. China and Russia never stopped using tubes when the US went thru the transistor age. A lot of tubes made in China and Russia are re-branded for overseas sale. Try and find a manual for the amp. Let us know how you like it. no ranged print. NOS Marconi are on, couldn't wait, but will keep china as backup and no manual, but found seller contact and send my question, so far the only thing i learn it is for the noise floor. it is suggested to play with them until there's no noise? not sure if i understand this and why? Quote Link to comment Share on other sites More sharing options...
BBZink Posted April 9, 2017 Author Share Posted April 9, 2017 here what was written in original ad: (sorry for bold text, it is cut and paste) "2A3C is compatible with 2A3 and 2A3B . Direct heating cathode and low power consumption. Two triodes can be used for class A and AB amplification". What does that mean? regards Quote Link to comment Share on other sites More sharing options...
avguytx Posted April 10, 2017 Share Posted April 10, 2017 These are just some of the reasons I chose to stay away from those...as much as I liked how they looked. Definitely good looking amps. But pop the covers off those OPT's and have a look. Quote Link to comment Share on other sites More sharing options...
BBZink Posted April 10, 2017 Author Share Posted April 10, 2017 OPT's?? what is it? Quote Link to comment Share on other sites More sharing options...
mike stehr Posted April 10, 2017 Share Posted April 10, 2017 7 hours ago, tapajeurs said: So far, it is for the noise... They are more than likely hum/null pots for AC heating of the output tubes. (2A3) Just adjust the pots with no signal for the least amount of hum through the speakers. 1 Quote Link to comment Share on other sites More sharing options...
Marvel Posted April 10, 2017 Share Posted April 10, 2017 ^^^ My Welborne Labs Moondogs 2A3 amps have this one adjustment only. Bruce Quote Link to comment Share on other sites More sharing options...
BBZink Posted April 10, 2017 Author Share Posted April 10, 2017 So far, the seller told me, it is auto bias, so your infos is correct, btw, there on sale on amazon to! Quote Link to comment Share on other sites More sharing options...
BBZink Posted April 10, 2017 Author Share Posted April 10, 2017 3 hours ago, wdecho said: Mike Stehr is most likely correct. Most 300B/2A3 SE amplifiers have a noise adjustment pot. Bias adjustment pots are mainly for push pull amps. As long as you stick with the same kind of tubes you should be good for different brands of the same tube. OPT is an abbreviation for output transformers. Nice looking amplifier and I bet it sounds great. I have heard the difference between a 2A3 and 300B is "not much." I just looked on Ebay for a price, great deal. I do not exactly know what the seller is saying about being used as Class A or A/B. To my knowledge all single ended tube amplifiers are class A. Probably just a sales pitch for those that do not know the difference. As much as I like buying American there are great deals coming from China on tube amplifiers vs American prices. You can expect the prices to go up soon due to tariffs. So my NOS Marconi are in good hand, the amps is long to break-in almost 6 month/12 hours a day, but after that smooth sound, and voicing is incredible. NOS ad a little something on the warm side and this amp is dead quiet (i mean noise floor), one of the quietest i had so far. As far as i could afford it, i'll go with north american product, but here, it was a steal deal and most likely "tweakable" if needed by my 80years old technician that help me in the past bring back to life old tube amp and tube receiver. Quote Link to comment Share on other sites More sharing options...
avguytx Posted April 10, 2017 Share Posted April 10, 2017 12 hours ago, tapajeurs said: OPT's?? what is it? OutPut Transformers. Quote Link to comment Share on other sites More sharing options...
BBZink Posted April 19, 2017 Author Share Posted April 19, 2017 Sorry, wrong post, i tought i was in right this minute Quote Link to comment Share on other sites More sharing options...
BBZink Posted July 22, 2017 Author Share Posted July 22, 2017 Just to let you know, lately i have a hum, after few research myself and with the help of the cable guy, he discover that the cable company installation has forgot to ground there cable before going in the house, so when i was hooking tv on computer, there was a hum in the system, took me two week to find the source and then cable guy work 2 hours, checking cable from the house to the pole. Still enjoy my amp, great bargain, lovely sound. One upgrade i want to do, is to replace the potentiometer for volume, any clue to what i should put in? regards ps, i am looking maybe for my other hifi room to buy a cav45 from CJ, is it a good choice? any comment? maybe i should star a new post for this one? 1 Quote Link to comment Share on other sites More sharing options...
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