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 Post subject: Tubes
PostPosted: Sat Feb 17, 2018 2:31 pm 
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Joined: Tue Jun 26, 2012 2:04 pm
Posts: 31
Location: ottawa, ON, CA
Hi, I just bought my first tube preamp copland cts 305 ,I am completely new to tubes so I decided to change my tubes to change things up 12ax7 tong sol to a rogers 12ax7 these were tested as perfect match .My problem is that when I change them they were good but my volume was reduce by like 80% my dial on the preamp was turn up 3/4 from .Why?


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 Post subject: Re: Tubes
PostPosted: Sat Feb 17, 2018 2:58 pm 
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Joined: Wed Jul 23, 2008 5:04 pm
Posts: 2223
Location: saskatoon, SK, CA
Are you sure they are ax7 and not au7?
Not sure what else could affect gain to that extent if replacements tested good.

Googled...runs 6922s as well....don't mix em up!
12ax7 phono
6922 linestage

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 Post subject: Re: Tubes
PostPosted: Sat Feb 17, 2018 3:35 pm 
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Joined: Fri May 13, 2005 12:31 pm
Posts: 552
Location: North York, ON, CA
turehifi wrote:
Hi, I just bought my first tube preamp copland cts 305 ,I am completely new to tubes so I decided to change my tubes to change things up 12ax7 tong sol to a rogers 12ax7 these were tested as perfect match .My problem is that when I change them they were good but my volume was reduce by like 80% my dial on the preamp was turn up 3/4 from .Why?



put the original tubes you took out back in and see if that solves the problem


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 Post subject: Re: Tubes
PostPosted: Sat Feb 17, 2018 4:48 pm 
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Joined: Mon Aug 08, 2016 5:46 pm
Posts: 704
Location: Markham, ON, CA
First off, why change the tubes? If the unit worked and played well with the selection you had, then stick with it for a while to get used to the sound. Then, and only then, start changing things. New tubes often do not make for a better sound. Not to mention that brand new tubes may take a hundred hours to break in.

Go and swap back to the original tubes in their original placement. Tube rolling has to be done with consideration to what you already have, what you are trying to achieve, and then (and only then) should you give rolling a try. No guarantee of an improvement in sound by the way. That is why I have a drawer full of almost-new tubes!


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 Post subject: Re: Tubes
PostPosted: Sat Feb 17, 2018 4:54 pm 
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Joined: Fri Dec 01, 2006 2:44 pm
Posts: 364
Location: Toronto
Make sure the tubes are in their sockets all the way. Don't be afraid to gently push a little. There should be virtually no wiggle if they're properly set.


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 Post subject: Re: Tubes
PostPosted: Sat Feb 17, 2018 5:00 pm 
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Joined: Mon Jan 25, 2010 6:43 am
Posts: 112
Location: Kelowna, BC, CA
Yes to what the first 2 cammers responded. Different ax7 or au7 tubes might make up to a 10% difference in gain, but never a change like what you describe. Something is amiss with the tubes you put in.

I have seen users mix up ax7 and au7 tubes, and the amp or preamp still works but for only so long.

Leave the original tubes in the unit for a minimum of 100 hours playing time. Otherwise you will have no idea what the unit sounds like and will have nothing to compare against.

If after that, you find the highs are recessed, or too sharp, or too grainy, or bass muddy or lightweight etc, then do your research as to what tubes might rectify that. With that preamp you should achieve a very nice sound with the stock new tubes.


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 Post subject: Re: Tubes
PostPosted: Sat Feb 17, 2018 7:50 pm 
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Joined: Mon Dec 12, 2005 6:44 pm
Posts: 228
Location: Calgary, AB, CA
Tube testing is funny. What tester did you test them with? Most testers are emissions testers and not accurate for performance. You need to use a good gm tester. I agree that you need to put the original tubes back in and see if the issue remains.


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