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

Here ya go!

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

• Posted by Ludwig6 (A) on November 8, 2013 at 19:18:44

  In Reply to: RE: 5751 or 12AX7 tubes in a CJ Premier 11A Power Amp? posted by JNS on November 8, 2013 at 15:52:41:

   

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

Thanks for the replies!   (Especially yogiboy).

I had tried to contact CJ but didn't get an answer yet.   If they get back to me I'll post their answer here as well.

@prof 

A 12AX7 is a poor substitute. The 12AT7 has similar amplification factor but vastly different plate resistance (much lower).

Whenever a tube circuit is designed, hopefully the circuit is optimized for the tube in mind. When you put something else in there that has different characteristics, distortion will be increased, gain will be affected (which will mess with the feedback) and bandwidth will be affected.

Because of its increased gain, its entirely possible that the amp might oscillate under certain conditions with a 12AX7 installed as a sub.

You're stuck with the 5751.

Very helpful atmosphere!   Thank you!

Ah well, that's fine.  I can still get 5751 tubes.