MIKE.D79 Posted December 15, 2016 Share Posted December 15, 2016 (edited) Nearly merry Christmas to all! I have a somewhat newbie question, although hopefully simply answered. I recently purchased some new tubes for my cary ae3 tube pre amp (the shuguang cv181z [is actually a 6sn7 type]) and just wanted to find out how hot the amplifier can safely get? I have been told by grant fidelity that there should be no issue with these tubes in this amp. these tubes have replaced the tung-sol GTB reissue and have noticed that the tubes themselves along with the amplifier are certainly running hotter then before. The amplifier chassis (right near the tubes) itself is certainly NOT to hot to touch and the tubes are hotter still but i can hold my fingers on for a few of seconds before it begins to get uncomfortable. with the tung-sols I would consider that it ran really very cool for a tube amp, the chassis was pretty Much completely cool and i could hold a finger on the tube without any real discomfort. Obviously there has to be some absorbed heat from the tubes them selves, but just wanted to find out if there was any kind of test or tell tale signs? Am I being overly cautious? seeing as I have just had the tube amp serviced and bought new tubes that were not cheap, I clearly want to avoid any damage. Thanks again and merry christmas to all. Mike [EDIT] I should add that i have had the amp running for good number of hours and the temperature remains stable after a while, and there is nothing to indicate any issues as far as the music being played is concerned. "seems" to happily go about its business playing music. Edited December 15, 2016 by MIKE.D79 Link to comment Share on other sites More sharing options...
Guest BobbyD Posted December 15, 2016 Share Posted December 15, 2016 Someone experienced in valve amps like @ehtcom or @guru and some others may shine some light (pardon the pun). My experience is to confirm the tube spec's are 100% compatible before substituting, and I always check with some of my learned buddies before changing anything. I am sure some one will solve this puzzle for you. Link to comment Share on other sites More sharing options...
ehtcom Posted December 15, 2016 Share Posted December 15, 2016 (edited) Hi Mike A Tung-sol 6SN7 heater draws 0.6 amp current, dissipating ~3.8 watts of heat. A CV181 heater draws 0.95 amp current, dissipation ~6.0 watts of heat. So it will get hotter. As long as the heater supply can handle the extra current. there shouldn't be any issues. Cheers, Earle. Edited December 15, 2016 by ehtcom 1 Link to comment Share on other sites More sharing options...
MIKE.D79 Posted December 15, 2016 Author Share Posted December 15, 2016 thank you, In regards to the heater, I downloaded the specs sheet for the cv181 z from grant fidelity. It specs this: filament heating: UH 6.3v IH 0.6a ???????????????????????????????????? I've seen this come up before with the heaters and this tube? part of the confusion. Or am looking at the wrong thing? Link to comment Share on other sites More sharing options...
VanArn Posted December 15, 2016 Share Posted December 15, 2016 Earle is on the right track with the heaters drawing higher current than the original 6SN7GT valves, although the CV181-Z version is specified at 0.9 A. There are other departures from the 6SN7 specifications in that Mu is higher and the correct bias point should be lower. Ideally alterations to the circuitry should be made to suit the Shuguang valve. 1 Link to comment Share on other sites More sharing options...
ehtcom Posted December 15, 2016 Share Posted December 15, 2016 Well I guess it will depend on whether the manufacturer has just put a 6SN7 internal into a pretty glass envelope, or they have made a true CV181 replica. Datasheet for the CV181 says 0.95 amp. cv181[1].pdf Link to comment Share on other sites More sharing options...
MIKE.D79 Posted December 15, 2016 Author Share Posted December 15, 2016 AAAhhh yes, The black treasure cv181 z is labeled as 6sn7 replacement. I don't now why they name it as a cv181. the Z on the end is supposed to indicate it is something different to a true a cv181. they also spec it is not to replace a true cv 181. I guess it is all to do with marketing and some other crap. 1 Link to comment Share on other sites More sharing options...
ehtcom Posted December 15, 2016 Share Posted December 15, 2016 1 minute ago, MIKE.D79 said: AAAhhh yes, The black treasure cv181 z is labeled as 6sn7 replacement. I don't now why they name it as a cv181. the Z on the end is supposed to indicate it is something different to a true a cv181. they also spec it is not to replace a true cv 181. I guess it is all to do with marketing and some other crap. Do you want the truth? Because calling it a CV181 means they can charge more $$ for it. 1 Link to comment Share on other sites More sharing options...
Guest BobbyD Posted December 15, 2016 Share Posted December 15, 2016 2 minutes ago, ehtcom said: Do you want the truth? Because calling it a CV181 means they can charge more $$ for it. That old chestnut............ Link to comment Share on other sites More sharing options...
MIKE.D79 Posted December 15, 2016 Author Share Posted December 15, 2016 1 minute ago, ehtcom said: Do you want the truth? Because calling it a CV181 means they can charge more $$ for it. Yep i figured that. But this new production tube i've been told from grant fidelity, who seem to have a very good reputation and is a major dealer of the shuguang cv181z, is supposed to be designed for and work with 6sn7 circuits. it is starting to get concerning if there has been misinformation thrown my way by grant fidelity. again they assured me that this tube will work without issue in my amp? Sorry to sound like I'm discrediting advice here, I'm really not, it's just a hard pill to swallow if i've been given bad advice from what is supposed to be a very reputable distributor with a good reputation. Thanks again, mike. Link to comment Share on other sites More sharing options...
Guest Posted December 15, 2016 Share Posted December 15, 2016 From what I have gleaned, and in my limited experience, these CV181s can be used quite safely as a 6SN7 substitute in any well designed amp. I'd suggest your Cary falls into the well designed category. Link to comment Share on other sites More sharing options...
VanArn Posted December 15, 2016 Share Posted December 15, 2016 Perhaps the solution to the heat problem is by way of actual measurements and given the manner in which the characteristics can vary from valve to valve, several items may need to be tested. There has to be a reason for the apparent temperature difference ( other than very low emission original 6SN7,s ). The larger surface area of the CV181-Z envelope should result in it being slightly cooler . Link to comment Share on other sites More sharing options...
MIKE.D79 Posted December 15, 2016 Author Share Posted December 15, 2016 Thanks all for your responses. I think i might have to try and find someone in Perth experienced enough to have a look. I don't think i would have the tools to take any sort reliable measurement. I have also emailed cary with the spec sheet to get there opinion. All I want to do is listen to music, is that to much to ask?? Again thanks to all and have a merry christmas. Link to comment Share on other sites More sharing options...
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