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Ok to substitute 12AX7 for 5751 tubes in CJ Amp?

Hi Folks.

Despite having owned my Conrad Johnson Premier 12 tube monoblocks for over 20 years, I'm just starting to play around with tube rolling recently.  (Previously, when a tube got tired I'd just replace them with whatever CJ recommended at the time).

Playing around with the input tubes:   The CJs come with 5751s (I've been using GE), and as I understand it 12AX7 tubes are higher gain.   However, are they not interchangeable in most cases?  Just don't want to screw anything up in my amp.

Thanks.

 

prof
facten
2,969 posts
 

Under what circumstances is a 12AU7 is a substitute for a 5751?

12AU7 substitutes are ECC82, 7316, 5814, CV491, 6189, E82CC, 5963, 6350, 6680 and a few others . Have never seen 5751 as one of them

thecarpathian's avatar
thecarpathian
5,124 posts
 

Yes, I believe the 5751 is a compatible substitute for the 12ax7.

But, I’d confirm it with a call.

noromance's avatar
noromance
10,181 posts
 

12AU7 = 5751,

No. I think you mean 12AT7 with an amp factor of 60. The 12AU7 is much lower at around 17 at 250Vdc. 5751 is 70. 12AX7 is 100.

 

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yogiboy's avatar
yogiboy
5,891 posts
 

Here ya go!

RE: 5751 or 12AX7 tubes in a CJ Premier 11A Power Amp?

Before posting here I sent an email to CJ and received the following response: "The voltage amplifier tubes are 5751. This is a military/industrial tube similar (but not identical) to the 12AX7. The 12AX7 will work as a substitute. The inverter is a 6FQ7. They are getting to be hard to find, but we do have those available here."

So the 12AX7 is OK to use, but I take to heart the recommendations here that I stick to 5751 since they are still available. I have made a bid on some GTE Sylvania 5751 on Ebay: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=370935303697&ssPageName=ADME:B:BCA:0:3160

https://db.audioasylum.com/mhtml/m.html?forum=tubes&n=254681&highlight=replacing+5751+with+12ax7&r=&search_url=%2Fcgi%2Fsearch.mpl%3Fforum%3Dtubes%26searchtext%3Dpsvane%2Buk%2Bel34

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