New 12AY7 vs 5751, can't hear the difference...!

[Aldo]

Hi,
I've been swapping tubes in V1 looking for some more headroom. I can tell the difference between 12AX7 and 5751, but I'm unable to hear any difference between 5751 (JAN phillips... NOS?) and 12AY7 (gold pins EH), same headroom, same tone... I was even thinking about recording some tests in case my hearing memory was failing and see if that way I can notice someting! Has anybody experienced this? maybe this one 12AY7 I have has more gain than normal...

[stokes]

Its all very subjective,but I think the difference between a 12AY7 and a 5751 is wider than between a 12AX7 and 5751.I never A/B'd a current production tube,tho.I have always thought the current production 5751's sound like a weak chinese AX7,perhaps the AY7's are the same?

[Aldo]

"I have always thought the current production 5751's sound like a weak chinese AX7,perhaps the AY7's are the same?"

At least in my case they sound very similar.... but neither of them sound bad! the 5751 I have may be NOS (not sure, I think it's JAN Phillips), the 12y7 is EH, the only problem is that I was expecting some decrease in gain and a bit more headroom with the latter, but they sound the same at the same settings

[stokes]

Tha JAN Phillips is an "old stock" tube,if its new old stock is questionable.I dont know this to be a fact,but the current production 5751's sound to me like they just labeled some "weaker" AX7's as 5751's.I have many NOS 5751's and 12AY7's and can tell you I do see a big difference between these tubes.It is possible that you have a weak 5751,unfortunately I dont have any current production AY7's,but I can tell you that in my experience,the 12AX7 is closer to the 5751 than the 12AY7 is to the 5751.It is kind of hard to realize "more headroom" as the 12AY7 decreases drive,it also gives you less overall volume.I never recommend using a lower gain tube like the AY7 to get more headroom,in order to percieve an appreciable gain in headroom it is usually necessary to alter the power stage.I use a 5751 in the V1 of just about all my amps,but only to "smooth" out the preamp distortion.To me it makes it more creamy sounding than the AX7.What amp are you talking about here,and what exactly are you trying to accomplish?

[Aldo]

Hey, thanks for the input! The amp is a Bassman 59ltd. I'm trying to invoke "Max headroom" without compromising too much the character of the amp. I'm trying the 12AY7 because I see people recommends it for this amp and thought it could give me more clean range.

The amp is loaded with new production tubes (apart from the 5751); TAD 12AT7 in V3, stock 12AX7 in V2, stock GT 6L6GC and 5AR4 rectifier. I have a spare diode rect. to plug for a bit more headroom. Long ago I biased the amp somewhere around 31 mA/tube, but mind you I didn't make any calculations... I just went a bit hotter than stock (26 mA it was). I'm getting the same results with the 5751 and 12AY7: Single coils, 4 on the volume knob is mainly clean; 4.5 starts to saturate, both tubes with a similar perceived loudness and character. If the 12AY7 doesn't stretch that range I suppose the diode rectifier could help...

[stokes]

I'm not sure what kind of plate volts you have there,but if it is in the 400v range you can go quite a bit higher with that plate current.You want to be in the 21 idle watt range for those 6L6GC's.Obviously you have a current meter and adjustable bias.I would go with the solid state rectifier,although the 5AR4 is pretty close,and bias so you idle at about 21 watts.Just multiply your current times the plate volts, .031X400v's would only be 12 watts idle,pretty weak for a pair of 6L6GC's.Shoot for closer to 21 watts idle and with that 5751 you will be quite happy,I think.

[Aldo]

Yeah, when I tried the diode rect some time back I didn't notice much difference, however I felt it sounded a bit nicer with the 5AR4 and left it there. The amp stock bias was about 26 mA/tube (52 mA both) and I went up to about 31 mA (62 total), but I don't know the plate voltage. Next week I'll try to make readings, calculations and aim for for these 21 idle watt you recommend. I think now it's sounding right but I'm interested in seeing the effects of biasing. Thanks !

[stokes]

Since you have a 2X6L6GC push-pull out put you dont add the current draw of the 2 sides as you did in your last reply."26ma/tube (52ma both)".You are interested in only what is being drawn on either "side" of the OT.I imagine the plate volts are in the 400v zone,so that 31ma's is only idling at about 12 watts,kind of cold for a pair of 6L6GC's.Like I say,dont add the 2 tubes current draw,you are only concerned with the "per tube" draw.

[Pedro Vecino]

I can tell the difference between 12AX7 and 5751, but I'm unable to hear any difference between 5751 (JAN phillips... NOS?) and 12AY7 (gold pins EH), same headroom, same tone...

5751 Philips has a unique sound. They have a distinctive bass profile, more discreet, great frequency extension
(sounds crystal clear) and almost as importantly: very little compression. I use in CAE OD100 to outline the lows, Carvin Legacy for the same (and to control his excessive compression), Hot Rod Deluxe/Deville to use Les Pauls/335..., and other amps. A useful tube.
Russian 12AY7 have their typical (russian) compression and narrow frequency extension. Can offer a more rounded ("vintage") sound at first glance but with less detail and dynamic touch.
I´ve not compared the differences in gain but I get the feeling of having more gain than the classic American 12Ay7. Closer to a typical american 5751.

[MWJB]

Plate volts for RI Ltd Bassman will be well in excess of 400v, lowest that I have personally seen is 461v with a GZ34/5AR4, the most is over 520vdc. 31mA is not by any means "cold" (some harp players run 7-8mA per tube, that's cold - for guitar late 20's up is OK), you shouldn't need to increase plate current by more than a few mA per tube, bear in mind that increasing plate current significantly may not improve headroom...it'll probably bring on earlier break up.

It's safer to assume that most 6L6GC on the market today are 25W, rather than 30W (an exception is the JJ6L6GC)...the Reflector 5881WXT that come stock in the amp (GT are just a reseller, not a manufacturer) can take quite a pounding though.

Aldo, how hard are you running the mids?

The EH 12AY7 runs less plate voltage that a 5751 (more in line with a 12AT7), but can have more gain than many NOS 12AY7 types, I'm not totally surprised that differences are subtle at low volume settings with a 12AT7 in V3 and the weak 12AX7WA in V2, however, you may hear a more pronounced difference as you drive the amp harder.