I have a new Fender Bassbreaker 007 amp with a single ended EL84 power section. The first stage was designed around a 12AX7 with a 330K plate load resistor, 3.3k cathode resistor and 285V on the plate.
This arrangement was too "hot" for my taste; I got much more satisfactory results by putting a 12AY7 there and turning the amp's "Gain" pot up more (it comes after the first triode). This seemed to allow the other stages in the amp to contribute more to the tone. I feel that the tremendous gain of the 12AX7 was swamping whatever the other tubes were contributing.
My question is -- can I return to using a 12AX7 but change the operating conditions so it behaves more like the AY in this position? If so, what might you suggest? Although I have tinkered with amps for 50 years, I am just getting my feet wet with load lines and design matters of that nature.
And...it may seem silly, but this would be the only amp I own that has a 12AY7 in it and I would rather not have to remember that fact.
This arrangement was too "hot" for my taste; I got much more satisfactory results by putting a 12AY7 there and turning the amp's "Gain" pot up more (it comes after the first triode). This seemed to allow the other stages in the amp to contribute more to the tone. I feel that the tremendous gain of the 12AX7 was swamping whatever the other tubes were contributing.
My question is -- can I return to using a 12AX7 but change the operating conditions so it behaves more like the AY in this position? If so, what might you suggest? Although I have tinkered with amps for 50 years, I am just getting my feet wet with load lines and design matters of that nature.
And...it may seem silly, but this would be the only amp I own that has a 12AY7 in it and I would rather not have to remember that fact.
If swapping the tube type gets you where you want to be, then what is the point of trying to apter the circuit in hopes a different tube will sound that way? By swapping the tube you can restore stock operation in a few seconds by swapping the tube back. if you alter the circuit, you have to go in and unalter it to return to stock.
By the way, just my opinion, but I don't buy your rationale for the other tubes having space to contribute more. Your different tube altered the gain structure of the amp, that caused the difference right there. NO need to rationalize further.
If you liked the 12AY7, I suggest a 5751 might also be an interesting tube to try. It also has a lower gain than a 12AX7, and plugs right in.
By the way, just my opinion, but I don't buy your rationale for the other tubes having space to contribute more. Your different tube altered the gain structure of the amp, that caused the difference right there. NO need to rationalize further.
If you liked the 12AY7, I suggest a 5751 might also be an interesting tube to try. It also has a lower gain than a 12AX7, and plugs right in.
The point is to stick to the same tube type I use in every other amp, something I can buy on a Saturday at a Guitar Center and doesn't require me to single out this amp for special treatment and remember what's in there which fades from memory fairly quickly.
I did actually start with a 5751 since I had one on hand. I liked it and thought I'd take it further with the 12AY7 which I liked even more.
I'm hearing something that's different about the tone whether my description passes scientific muster or not... Maybe there is sufficient difference in other parameters like in/out impedance that's inherent to the two tubes that creates a different result due to different loading or something. It wouldn't be the first time that musicians who hear a difference, are told we are imagining things, and then are later declared right, when the missing parameter is measured!
I did actually start with a 5751 since I had one on hand. I liked it and thought I'd take it further with the 12AY7 which I liked even more.
I'm hearing something that's different about the tone whether my description passes scientific muster or not... Maybe there is sufficient difference in other parameters like in/out impedance that's inherent to the two tubes that creates a different result due to different loading or something. It wouldn't be the first time that musicians who hear a difference, are told we are imagining things, and then are later declared right, when the missing parameter is measured!
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you hear a difference, I would too. I was just suggesting one need not look any farther than the tube swap itself for an explanation of the tonal difference.
ANother illuminating experiment is to try several brands or models of the same type tube. You like 12AY7? Try NOS RCA, GE, SYlvania, whoever. For that matter among current production 12AX7 there is a wide range of tube performance available. They are not generic.
ANother illuminating experiment is to try several brands or models of the same type tube. You like 12AY7? Try NOS RCA, GE, SYlvania, whoever. For that matter among current production 12AX7 there is a wide range of tube performance available. They are not generic.
From what I read of recent Fender amps, it is unlikely you can modify the circuit without major trouble.
I understand "not remembering", but it seems simple enough to buy two spare 12AY7 and keep them in your kit.
Preamp tubes "should" last "forever". I routinely saw 20-30 year old preamp tubes working fine. And with 330K(!!) plate resistor, Fender sure is not cooking this stage. I have less experience with recent-made tubes, but frequent failures do not seem to be common.
If there is a cathode cap, snip one end and try 12AX7.
You can probably get a 12AT7 at Banjo Mall on a rainy Saturday night and get through the gig.
I understand "not remembering", but it seems simple enough to buy two spare 12AY7 and keep them in your kit.
Preamp tubes "should" last "forever". I routinely saw 20-30 year old preamp tubes working fine. And with 330K(!!) plate resistor, Fender sure is not cooking this stage. I have less experience with recent-made tubes, but frequent failures do not seem to be common.
If there is a cathode cap, snip one end and try 12AX7.
You can probably get a 12AT7 at Banjo Mall on a rainy Saturday night and get through the gig.
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Oh it's a journey opening up one of these and getting the boards spread out so you can work on them. And yes, I surely can tuck a couple 12AY7 inside the cabinet in a pouch - it does close up completely. But I want to pursue the 12AX7 idea. I do have a highly experienced amp designer friend who rolls his eyes when I come to him with questions like this but if I buy him lunch he will indulge me... We'll see where this goes.
You answered yourself
So you want to mod your amp to be protected from the very very very unlikely event that the 12AY7 dies , it´s a Saturday afternoon, you *do* have a gig that very night, and you forgot to buy a backup?
1) that tube, as mentioned above, will likely last at least 20 or 30 years.
Just curious, how old are you?
Yes, it´s relevant to the answer.
2) in the very very very unlikely case all those planets align , you might simply pop a 12AX7 there and play.
It will definitely work, and quite well, it will carry you through the night.
Will people notice the "changed sound", complain and ask for their ticket money back?
Think again.
3) even if it were possible, how could *we* know what to do to your amplifier so it behaves (using a 12AX7) as if it had a 12AY7?
From your own words, "it is not a gain difference problem but something unexplainable"
- OK, I'm 66. Of course a 12AX7 will work, that's what it came with. Preamp tubes have never actually gone dead on me so I don't anticipate that tube 'dying' on me but they do get microphonic, hum and whistle when they go bad.
- People barely notice if my amp is even on, so no they won't even notice, but it's not about them, it's about what gets me off when I plug in.
- Being that this place is plausibly populated with some people who know their way around a load line (I do not), I thought it was a reasonable question to ask here.
I seem to have stumped the band with this one, so either I am trying to make gold out of lead, or this just isn't the right place for the question!
- People barely notice if my amp is even on, so no they won't even notice, but it's not about them, it's about what gets me off when I plug in.
- Being that this place is plausibly populated with some people who know their way around a load line (I do not), I thought it was a reasonable question to ask here.
I seem to have stumped the band with this one, so either I am trying to make gold out of lead, or this just isn't the right place for the question!
Tube amps are for playing with, as well as playing through
You could (as suggested) remove cathode cap(s), or
Use a split load resistor, or
Increase the related PSU resistor to reduce supply voltage to that tube.
Go ahead and play, but we can't predict what you will hear. Just have fun trying.
You could (as suggested) remove cathode cap(s), or
Use a split load resistor, or
Increase the related PSU resistor to reduce supply voltage to that tube.
Go ahead and play, but we can't predict what you will hear
. Just have fun trying.Buy a better 12ax7 tube. Gold pins etc.
I recomend 6n4 because comparison to gold lion ecc83
6n4 sounds better,
I recomend shuguang 12ax7-T as a more expensive alternative
I'd read a article where western people reviewd a full music 12ax7 from china. They say the sound its up with the best, mullard siems etc.
Shuguang 12ax7-t is markted as the best from china on a chinese online store (it is the best tube I own)
TJ Full Music 12AX7 Gold Pin Box Plate Tube (pair) - MSRP US$110.00/pair | Grant Fidelity Home Audio
TJ Music Full Music Vacuum Tubes – Reviews | TONEAudio MAGAZINE
they question life of chinese tubes on the review, I had 6n4 running for 5000+ hours running hot and black with heaters at 6.3V, still going
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SMY14INCH Thank you for the reply and suggestions. It appears that you are suggesting additional types of 12AX7 tubes. I am looking for a suggestion about how to suitably modify the operating conditions in the amp so that a 12AX7 can be used, in a low-gain arrangement, to resemble the results I am getting using a 12AY7.
A lot of us were wondering why you're asking the question!
Given you want to keep only 12AX7s then you're going to have to do the hard yards of working out what is making the 12AT7 sound better - is it the gain profile? Is it the change in F3 points? is it the different capacitance? is it the lower plate resistance?
In theory you can just work out where on the AT curves you are sitting and pick Rk,Rp and Ck to get similar operation. However it's never that simple in guitar amps as what you do here affects stuff there
Definitly going to take some experimenting. Load lines won't tell how the sound in your amp is going change, what with all the other stages involved.
You can do this two ways. Make a change and listen or put the amp on a scope before and after.
If you want to tinker, see if the cathode is bypassed by a capacitor and remove it. Or, find the 330k resistor and parallel another one. This will cut its value in half, and is easy to remove if you don't like it.
That tube is running so lean now, that the extra voltage and current won't hurt it.
You can do this two ways. Make a change and listen or put the amp on a scope before and after.
If you want to tinker, see if the cathode is bypassed by a capacitor and remove it. Or, find the 330k resistor and parallel another one. This will cut its value in half, and is easy to remove if you don't like it.
That tube is running so lean now, that the extra voltage and current won't hurt it.
Well thank you everybody. thoglette is right, looks like I'm going to have to get down & dirty and do the hard work. I was hoping for an easy answer but alas... thanks audiopro for the tip on doing it the easy way. nigelwright7557, I was thinking much the same thing. My original post is on Page 1 so you probably didn't see it.
Thanks, and as I said, it is relevant.
Being blunt and for a good cause, that 12AY7 will outlive you.
For the remote possibility it fails as you fear, a backup one will be more than enough.
All questions are reasonable and merit an answer .... and you got a few
Maybe not what you expected though.
No, the place is fine, just that the bare question is hard to answer:
1) the main point: *you* are using that amp, clearly it sounds different (nobody doubts that) but :
a) we don´t know exactly what it is you are liking now
Say sound is slightly brighter and less distorted (just a made up example)
Even being there right besides you , listening the same you do, even liking it better than before , maybe you like it because it´s brighter and we like it because it´s cleaner.
Then we suggest a mod so 12AX7 sounds cleaner .... and after you finish you test it, get dissappointed and say "no, that was not what I was expecting".
b) to boot, we are not even there !!!!!
So how can we answer your question?
There is only an obvious difference: gain, and you already discarded it.
Many of us can design a gain stage (including 12AY7) from the ground up, starting with a blank sheet of paper and a datasheet .... extrapolating that to answer questions based on *taste* is a bit too much
As a side note: if any tube could be made to sound like any other just by changing components around it .... then why so many types were successfully made and marketed by the 100´s of Millions, when only a handful types woud have been enough?
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