12AY7 in PI?

ACH91332

ACH91332

New member
Right now I have a JJ 12AT7 in PI and it's pretty cool. It's not vastly different then a 12AX7 but there is better note definition. Like I said it wasn't a day or night thing but it was a positive so I kept it.

Anyone have an experience putting a 12AY7 in the PI slot of an amp that usually has a 12AX7 or 12AT7? Just wondering what things you guys might have encountered. I'm thinking about maybe getting a 12AY7. I'm trying to get a punchier sound.
 
Re: 12AY7 in PI?

ACH91332 said:
Right now I have a JJ 12AT7 in PI and it's pretty cool. It's not vastly different then a 12AX7 but there is better note definition. Like I said it wasn't a day or night thing but it was a positive so I kept it.

Anyone have an experience putting a 12AY7 in the PI slot of an amp that usually has a 12AX7 or 12AT7? Just wondering what things you guys might have encountered. I'm thinking about maybe getting a 12AY7. I'm trying to get a punchier sound.
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Try a 5751. You can also try to get a PI tube that has both halves that match up. I put a 12AY7 in the PI of my '66 Bassman by accident and it sucked.

Here's a good article on phase inverters.
http://www.guitaramplifierblueprinting.com/files/Phaseinverter.pdf
 
Re: 12AY7 in PI?

I've used a 5751 before and it didn't really change anything at all and I would try it again but I broke my GE 5751 :(. At this point I remember it being not much of a difference so I don't find it worth it to shell out $30 on a new 5751.

And yea everyone posts that article I've read it many times awhile ago. I think even I have posted it for some people haha. It's what convinced me to try a 12AT7 and I'm thankful for that.
 
Re: 12AY7 in PI?

I kind of like the idea behind using a 12ax7 as a phase inverter. The PI starts to break up when you really push the front end of the amp, and so far that sound just seems to work. I'll have to try other tubes types some time to give it a real evaluation.
 
Re: 12AY7 in PI?

Depends on what you're looking for and the type of amp. In Marshall-style amps, the PI is where a lot of the "power tube distortion" comes from since the PI will typically clip before the actual power tubes. In Fender style amps and most high gain beasts a lower gain PI might yield better clarity since the power section is not supposed to be driven into distortion.
 
Re: 12AY7 in PI?

I think you will have to experiment with much lower gain tubes like a 12AU7 or a 12BH7 before you are going to see any dramatic differences. There is a lot of confusion as to when a phase inverted actually overdives out there. I have found that they overdrive at the same point that the power tubes do. When a power tube begins to clip, its input impedence drops significantly, causing the phase inverter to clip. On a scope, you can see this happening. If you pull the power tubes, still sampling at the phase inverter, the clipping stops...the relationship is very evident. A much lower gain PI tube will make this happen later. Will it sound good? Who knows. Anything that affects the balance of the amp will have an effect.
 
Re: 12AY7 in PI?

Just bought a AT7 not sure I care for the less gain, if you want punch AX7 is the best because the more gain it has. From Brent Jessee Recordings he suggested these
12AX7 OEM Sylvania made for amps or organs, $23 each

12AX7 GE JAN military stock, $24 each

12AX7 Lowrey Organ blackplate, Japan made 1959, $17 each

or a higher priced NOS
12AX7 grey longplate RCA made, $60

12AX7 Amperex made Holland, OEM label, $79

12AX7 GE 1950s longplate, $45.00
I tried many in mine and the newer tubes are not that great I have a Sylvania in there now thats pretty smooth. You have to try diff. tubes because they all have diff. gain and that and will sound different. Just as important as v1 to me because if you put a crappy PI tube in there it will affect the amps performance.
 
Re: 12AY7 in PI?

Well, I like the 12AT7 right now. Like I said it has more definition than the 12AX7. It tightens up the bottom end a tad and has more note separation. The dynamics of the amp are a little better as well. When I had the 12AX7 it seemed like the mids compressed and it was a more narrow sound where as the 12AT7 has a little more of an open quality to it.

I was just wondering if going even lower gain would improve that even more.
 
Re: Matched AT7... has the head room you want

Re: Matched AT7... has the head room you want

The AT7 which is usually the reverb driver seems to work great in this position. But you want it matched so both sides are putting out equally. Now I've seen folks using Electo Harmonix AX7's lately but I think its a waste of a good tube in that position.

As we've read through that one great link floating around that although the AT is as "hot" for harmonics as an AX it has 10 times the ability to handle the power thrown at it which in THAT position is more important IMO.

So a matched AT7 for the PI is a good idea. Matching the other ones is a waste of money from my readings. And that covers a lot of reading. From the best in the industry.

V! is very important for a good sound and where I'd be putting the EH AX7, V2 uses have of the tube and a good solid JJ 7025 or something along that line is a safe bet.

playign around with V1 is where you'll "color" the amps sound and the PI V3 is where you'll pass it into the Power Tubes which need to be matched as well.

Unless its a "Tweaker" By Egnater... heck, he says you don;t even need matched power tubes let alone all the other crazy things you can do with that amp. Still... I'm sticking with matched pairs. But it is odd you can drop inn 6V6's, 6L6's, EL34;s or KT88's w/0 doing anything but change the tubes.

I dropped in a matched set of Old Meas Boogie 6L6 matched tubes I've had stashed for 20 years or so. Next is thwe Mecury Magnetics "drop in" iron and knock that 15 watter into a 40 watt amp. Be a small Super Reverb! w/o the reverb. :)
 
Re: 12AY7 in PI?

aleclee said:
Depends on what you're looking for and the type of amp. In Marshall-style amps, the PI is where a lot of the "power tube distortion" comes from since the PI will typically clip before the actual power tubes. In Fender style amps and most high gain beasts a lower gain PI might yield better clarity since the power section is not supposed to be driven into distortion.
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Wow. That's good to know. Since the PI tube is technically a part of the power amp, and not the preamp, amp builders could fudge the "power tube" distortion angle, without the actual power tubes doing the heavy lifting every really getting distorted.
 
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Re: 12AY7 in PI?

Gets fun and interesting in the "Egnater Tweaker" where you have Fender, Vov and Marshall all at your finger tips. I opted for the most room to flex them muscles. I also put 6L6's in it. Next is the 40 watt Mercury Iron. That's one crazy amp! and it doesn't need the new iron but I'm sick. :naughty:
 
Re: 12AY7 in PI?

I'm fairly sure that the PI almost never clips the signal at any point. When PI is saturated, the amplitude in the grid of the powertube is at maximum and cannot be increased further. If this occurs before the powertubes are overdriven, they never will be as the signal amplitude is not high enough. The Pi needs to be the last thing that gets overdriven or the amp will not produce full output. The clipping that does happen is more than likely the powertube grids being overdriven, not the actual Phase inverter. All of this is assuming that the powertubes are in class B or A/B where the "negative swing" from the PI makes the powertubes to go into cutoff where they don't produce output.

If the powertubes were enough overdriven to lower the input impedance, the signal would get clamped at the grid. This is the point were the powertubes start drawing significant grid current and as the output of the plate driven phase inverter is inheritly high, the signal voltage is swamped by the grid. This makes the tube to clip it's output hard for long enough, that no signal is actually produced. This is the Blocking distortion and it's never a good thing. If the tube grids were driven by a cathode follower that can source the required current, then the blockin would not happen and it would be possible to drive the amp into grid current region. Some huge bass amps(>200W) actually do this as it allows for greater signal swing from the output tubes and thus improve the efficiency of the amp by reducing the amount of needed powertubes for given output.
 
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Re: 12AY7 in PI?

So what happens when a lower µ tube is placed on the PI? In theory, little to nothing. The Phase inverter is feedback controlled, which already makes up for a flat and wide output responce and the lower µ tubes tend to make it even more so. The preamp of a basic guitar amp has little to no amplification beyond 10kHz and guitar does not produce much higher frequencies than maybe 5 or 6kHz. Even those are just the highest of high harmonics of the highest notes from the guitar and they are maybe a couple per cent of the fundamental signal in amplitude. So, with clean amps I'd guess that µ the PI tube makes no difference! With highly distorted signals that have very high harmonics, the PI might make the sound more bright and percussive as even the highest harmonics pass through. The harmonics never make it to the ear of the audience as woofers, that almost all guitar speakers are, cannot vibrate fast enough. The high harmonics do modulate the signal envelope and that does make a difference.
 
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Re: 12AY7 in PI?

ACH91332 said:
Well, I like the 12AT7 right now. Like I said it has more definition than the 12AX7. It tightens up the bottom end a tad and has more note separation. The dynamics of the amp are a little better as well. When I had the 12AX7 it seemed like the mids compressed and it was a more narrow sound where as the 12AT7 has a little more of an open quality to it.

I was just wondering if going even lower gain would improve that even more.
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what kind of amp you using? I may have missed that.

I'm guessing the EL84 based amps side with the Marshal in with the Marshall / Fender tube distortion side of things. Wish I had my own tube tester for matching tubes. that would be helpful but then it's really applicable on only A/B push/pull?

That can't be right can it?
 
Re: 12AY7 in PI?

AniML said:
Has anyone tried a JJ ECC803S as a PI?
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A brother Night Train owner! That's the only amp I haven't tried to mod yet. I love that little thing. Just so handy and toneful but I'd like to find something to sweeten up that direct thru sound. Sounds better w/ the controls than w/o.

I JUST asked my fiend about Class A's an PI's... EL84's in-particular. Will post the answer when I get it. Giving him a chance to let his Blood Pressure go downbefore I call. He'll know, he worked for Leo Fender as his chief engineer. Handy guy to have around... Bob Rissi. :approve:
 
Re: 12AY7 in PI?

psycom said:
A brother Night Train owner! That's the only amp I haven't tried to mod yet. I love that little thing. Just so handy and toneful but I'd like to find something to sweeten up that direct thru sound. Sounds better w/ the controls than w/o.

I JUST asked my fiend about Class A's an PI's... EL84's in-particular. Will post the answer when I get it. Giving him a chance to let his Blood Pressure go downbefore I call. He'll know, he worked for Leo Fender as his chief engineer. Handy guy to have around... Bob Rissi. :approve:
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Well...

As of earlier today I am a former Night Train owner. I just sold it to another forum member. It is a great amp. The Voxy chime is killer, and I agree the bright mode is where it's at. I am looking for something a little darker; a bit more Marshallier. I have a Tweaker or maybe an 18w clone on the top of my want list.

I was actually asking about the ECC803 for my SCXD
 
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