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35Z5
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Post subject: Re: 12AX7 Test Modification For B&K 707  Posted: May Wed 09, 2012 4:34 pm |
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 8701
Location: Chesapeake VA
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Thanks guys...
Since this mod is so easy and users have been complaining about the issue since Noah saved the first pair of B&K tube testers on the ark, I'm surprised no one came up with this years ago...
Tom
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Uptown
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Post subject: Re: 12AX7 Test Modification For B&K 707 Posted: May Tue 15, 2012 2:44 pm |
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Joined: Apr Sat 30, 2011 2:14 am
Posts: 233
Location: Mississauga, Ontario
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Tom,
Thanks for posting this.
What a great idea! I have always been told that the 707 and 747 wasn't good for testing 12AX7's, it's nice to see a solution rather than just pointing out a problem.
Do you know if the B&K 747B is also plagued with this problem? I imagine so since it is pretty much the ss version of the 707?
I have one of those and really like it.
Thanks again,
Mauro
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35Z5
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Post subject: Re: 12AX7 Test Modification For B&K 707 Posted: May Wed 16, 2012 2:05 pm |
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 8701
Location: Chesapeake VA
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Mauro, I'm out of town and not that familair with the 747, if someone doesn't post more info, I'll see what I can find later this week...
Tom
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Jimmie Stewart
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Post subject: Re: 12AX7 Test Modification For B&K 707 Posted: May Thu 17, 2012 1:43 am |
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 498
Location: Stafford, Texas USA
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Mauro
B&K 747 or 747B is NOT plagued with this problem? Plus the747’s are not SS copy of 707’s.
The 12AX7 though tested in the Programmed section socket 29. The Tube is tested for GM,
This being one of the biggest changes in the 747 over the 707.
See manual page 22 switches 13 and 14. The book said set the 12ax7 up for low bias (0.5v)
With a 1.5 VAC signal on Switch 13 position A, GM voltage 190 VDC by set by Switch 14 position A.
By using the Programmed section sockets and some 4,5,6,7 pin adapters one can test most of the old tubes.
Jimmie
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Uptown
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Post subject: Re: 12AX7 Test Modification For B&K 707 Posted: May Thu 17, 2012 2:18 am |
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Joined: Apr Sat 30, 2011 2:14 am
Posts: 233
Location: Mississauga, Ontario
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Thanks for posting and clarifying this for me.
Glad to know!
Mauro
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bjh
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Post subject: Re: 12AX7 Test Modification For B&K 707 Posted: May Sat 26, 2012 8:02 pm |
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Joined: May Mon 07, 2012 6:13 pm
Posts: 7
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Is 22 AWG solid core hookup wire heavy enough for this mod?
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tube.hobby
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Post subject: Re: 12AX7 Test Modification For B&K 707 Posted: Dec Thu 06, 2012 12:04 pm |
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Joined: Dec Thu 06, 2012 11:47 am
Posts: 11
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I just followed the procedure and modified socket 24 on 707.
Tested some known 12AX7 that I have, for the original setting, 22 is minimum good, take it as 65%, 33 or 34 should be about 100%.
Test result on this modified socket, reading of the same tube is about 100~105%. It looks pretty compatible.
By the way, I use AWG 22 hookup wire to do this. It seems the wire used in 707 is thicker, maybe #20?
Thank you very much, Tom. I have posted my mod on my facebook. Can I post the link of this thread on it, too?
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