5751 in PI

[joey_truelove]

Here is a quick question. Why does this happen?

I don't need a long dialogue on electronic theory and I get that the 5751 is a lower gain tube but if I am running a quad (or a pair for that matter) of 6550's in my RM's, is that one 12AX7 in the PI really creating that much breakup to push out of the power section?

I think you're confusing gain with other things like output and distortion here. What happens is the hiss in the circuit won't be amplified/ magnified as much as it would have with a 12AX7. Even if not running the PI on full some interference will be amplified 100 times.

A valve will saturate when it's approaching it's max output and the 5751 actually has less output than a 12AX7 and hence will distort earlier. The 12AT7 that is used in Fenders for instance can put out 8 times as much current than an AX7, but has only gain factor 60 and hence will be even clearer and much more dynamic.

Another funster is the AY7, with a gain of 44 and an output at 2.5 times that of an AX7. Wouldn't necessarily run it as a PI though.

 

[sweetrock]

There one thing I can not understand .

OK guys , we all like 5751 s and know how nice it works in PI position .

But I have a question for you all .

Bruce Egnater , M.Soldano , Mr.Bogner and Steven Fryette don't know that ?
Why they insist to use 12AX7s . Even in 4 , 5 K Amps .

School me please .


Hakan :?

 

[sepherus]

There aren't any quality new production 5751 tubes out there right now. They are very close to 12ax7 spec in every regard except output/gain. Considering the other common pre tubes, I guess you could say that that isn't too far off either being rated at 100 for 12ax7 and 70 for the 5751.

 

[sweetrock]

As far as I know ,

NOS 5751 s are still not very expensive and can be found in large quantities .

There must be something that we are missing ?


Hakan :?

 

[Mattfig]

My JAN GE and JAN Sylvania 5751s sound awesome...They weren't THAT expensive...

 

[sepherus]

They might be for now, but just imagine how much they would sky rocket if manufactures started using them. I've never seen any new production amp come with nos tubes that wasn't a boutique low quantity, made to order type deal. They want to use something in CURRENT production that is readily available, with some level of quality behind it. Sovtek does make a 5751, but I've heard little good about them.

 

[sweetrock]

Yesterday , I tried a USA 5751 from the 1960s in PI position in my RM100.

I was hoping a less distortion on sound but it was something like having more power tube breaking .

I feel it like turning on the precense knob a little bit more .
It was nice .
Some excessive low bass gone and some tight bass has come , so I have to turn on the bass module knobs a little bit more and lower the treble ones .

That's what I experienced.


Hakan :wink: