"NOS" JAn Philips 5751's and 12AX7AW's

[Guest " "]

My brother is coming over this weekend to pick up some tubes from me for his large array of fender and marshall band grear. I have a small assortment of 40 mixed 12ax7's, 12at7's, 12au7's, and 12av7's that i won't be needing. Amount the bunch, there was a quad of JAn philips 5751's and a pair of jan philips 12ax7's. I remember buying them, but I couldn't use them due to the MU issue. The 5751's have a MU of 70, and most of my geat uses 12AT7's with a MU of 60 or 12AX7s with a MU of 100. I know you can use a 5751 in place of a 12AX&, but i never used a 5751 in place of a 12at7.

But I decided, what the heck...going to give them away anyway...might as well try them. So I put the 5751's (MU 70) in place of the 12AT7's (MU 60) in my power amp. Was expecting to get ocean wave back ground noise, or other issues, but actually did not. I'm not getting any indication of problems using 5751's in place of 12AT7's. I'd imagine that the results would vary across amp manufactures.

Just wanted to post that i tried it, and it seems to work.

[jcmusic]

Hey Fritz what amp did you put them in? I use 5751's in my Scott 299 in place of the 12AX7's, I have a pair of real nice Mullards 12AT7's I'd like to try if I were sure they would do no harm.

Jay

[Guest " "]

Sure that will work.

You started with 12ax7's which have a mU of 100.

You put in the 5751's which have a MU of 70.

You can certianly put in 12AT7's which have a MU of 60.

I put the tubes in a Mcintosh MC-2000. No issues. My concern was putting in a higher MU tube than what was called for. You won't have the problem since you are putting in lower MU tubes.

[jcmusic]

Sounds good can't wait to try it.

Jay

[Cut-Throat]

I would not try this. The 5751 is interchangeable with a 12AX7, with indeed lower gain.- But the 12AT7 is not interchangeable with an 12AX7 or a 5751.

[Guest " "]

" But the 12AT7 is not interchangeable with an 12AX7 or a 5751."

Why would you say that.

The 12AX7 has a MU of 100. A 12AT7 with a MU of 60, and a 5751 with a MU of 70 will work in its place but at a lower gain

Here's a small list of groupings. Any lower MU tube can be used in place of any higher MU tube. Issue will be less gain. The tube will run quieter, with less microphonic's.

My issue was running a tube with a MU of 70, in place of a tube with a Mu of 60. It operated just fine.

12AU7 17 *
12AU7A
ECC82
6189
5814
5963
7730
6680
ECC802
ECC802S
7316

4003 19
5963 19
5815 19
6189 19
ECC82 17 *
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12AV7 41
5965 41
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12AT7 60 *
12AZ7 60
CV4024 60
6201
6679
ECC81 60 *
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5751 70*
CV4017 70
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12AX7 100 *
CV4004 100
7025 100
6681 100
ECC83 100 *
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[Cut-Throat]

" But the 12AT7 is not interchangeable with an 12AX7 or a 5751."

Why would you say that.

The 12AX7 has a MU of 100. A 12AT7 with a MU of 60, and a 5751 with a MU of 70 will work in its place but at a lower gain

I did some more research and I stand corrected. It is a valid substitute.

[jcmusic]

I am glad to hear that, I have a real nice pair of NOS Mullard 12AT7's I want to put in my Scott 299 amp.

Jay