Converting to 12sn7gt

crackuser · 4913

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Offline crackuser

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on: September 15, 2011, 10:39:11 AM
Hello, I am new to the forum and have ordered my first Bottlehead kit. The reason for this post is I have several 12sn7gt tubes and would like to try them in the Crack amp.  I acquired these about a decade ago and liked the sound out of them enough that I bought 9 of them. The code on the tubes is OKN-UE.  From looking at a Phillips Tube Manual(if I read it correctly anyway) they were made by Thorn A.E.I Valve Company. Because Phillips reused date codes every 3 years till 1955 there either 1948-51-54. I read also that Thorn A.E.I is tied to Mullard Supply. From my research I think Thorn A.E.I made Brimers, but I don't know if these are re-branded Brimers, Mullards,or none of them.  Is there someone here on the forums that could identify them? Its had me curious for years if I have had them correctly identified. Here is a picture:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fimg4.imageshack.us%2Fimg4%2F4558%2Fp1000256q.jpg&hash=1b3c4e1370f05301859580e0bcf029f92ea2edf2)
Another:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fimg849.imageshack.us%2Fimg849%2F8847%2Fp1000257f.jpg&hash=e1080997b5efac3bf8ee32b161866c378e19b4ab)
  I found out that I can have the top plate drilled for the larger octal socket from the factory so I am going to go ahead and try them in the crack amp. They sounded good when I had them paired with the Russian 6H13C so I thought I would try to pair them up again.
 I hope hum doesn't become in issue with what I am doing. I read in a post by "Doc" that changing these tubes this way may. I have a DC regulator kit coming in case I need it. I hope I don't and I am OK with 12.6 volt A.C. from a transformer. I guess I will find out.
  
 
 
  
« Last Edit: September 15, 2011, 02:22:38 PM by crackuser »


Offline crackuser

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Reply #1 on: September 15, 2011, 02:02:34 PM


Offline Grainger49

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Reply #2 on: September 15, 2011, 02:24:00 PM
If no one here knows these you might post on Audio Aslyum Tubes/DIY forum:

http://www.audioasylum.com/forums/tubediy/bbs.html


Offline crackuser

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Reply #3 on: September 15, 2011, 02:45:28 PM
O.K. thanks for the web address. I will let this float here for a couple days to see if someone has seen them before and then I will try the other forum.


Offline Paul Joppa

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Reply #4 on: September 15, 2011, 05:45:10 PM
The Crack has 6.3 volt filament power, not 12.6 volt. Your easiest option would be to add a 12.6 volt, 0.3 amp (or greater) transformer to supply the heaters. You might consider a 12 volt DC supply as well. Be sure to ground one leg, or the center tap if one is available.

Paul Joppa

Offline crackuser

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Reply #5 on: September 16, 2011, 12:07:45 AM
   I have a 12.6 volt 2 amp transformer that looks like it will fit in the back and I ordered a regulator circuit board . I have received communications from them that indicates that the regulator will be able to output 12.4 volts D.C. with the 12.6 volts A.C. input and the load of the 12sn7 tube on it.
  Specs on the board are:
Input voltage:DC 4 - 35V, or AC 4 - 26V.
Output adjustable range: 1.5 - 32V DC.
Maximum continuous output current: 5 Amps.
  I do have a question before I start the kit, should I go with a higher voltage rated transformer? Will 12.4 volts be O.K for the filaments? Also the company has a chart for the regulator showing that at 12.6 volts the board will do 2 amps(it matches the output of the transformer) so there is plenty of headroom there for amp draw of the tube.
  
  
« Last Edit: September 16, 2011, 01:03:59 AM by crackuser »


Offline Grainger49

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Reply #6 on: September 16, 2011, 01:12:55 AM
The regulator board will produce more DC than the RMS AC input.  There is some voltage wasted in the regulation process but you should have more than 12.6V available with the transformer and regulator board. 

The tube is probably rated for 12.1-13.2V or something like that.  With slightly lower voltage on the heater you get longer tube life.


Offline crackuser

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Reply #7 on: September 16, 2011, 04:08:44 AM
You are correct at higher voltages. The specs on the board showed more D.C. output than A.C. input but higher output starts at about 13 volts. Lower than 13 volts it shows slightly lower D.C. output than A.C. input.
Here they are:
Input VS Output Range:
Input Voltage Output range adjustable
DC 12V --1.5 to 9V DC
DC 18V-- 1.5 to 15V DC
DC 25V --1.5 to 22V DC
DC 35V-- 1.5 to 32V DC
AC 9V-- 1.5 to 8V DC
AC 15V-- 1.5 to 16.4V DC
AC 21V-- 1.5 to 25V DC
AC 26V-- 1.5 to 32V DC


Offline crackuser

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Reply #8 on: September 16, 2011, 04:36:17 AM
Quote from: Paul Joppa on September 15, 2011, 05:45:10 PM
The Crack has 6.3 volt filament power, not 12.6 volt. Your easiest option would be to add a 12.6 volt, 0.3 amp (or greater) transformer to supply the heaters. You might consider a 12 volt DC supply as well. Be sure to ground one leg, or the center tap if one is available.

Thanks for answering one of my questions. Its center taped and I was wondering if the center tap would be to ground. I know some about electronics but still learning.


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