A Look at Preamp Tube Gain Factors

[@bluesbondsman]

I just swapped a 12AY7 Sylvania into my 5F1 build that previously had a 5751 GE in it, I was surprised at how little volume I lost and that I can now get full 6V6GT power tube saturation without all of the Bees in a box sound from the 5751. My 5E3 build has always used the 12AY7 in V-1 and I love that sound so I thought the 12AY7 should help its little brother the Champ and indeed it did !!!

[@wseeback]

Perfect, scientific demonstration, that gets right down to the bottom line. This is definately the best comparison ever done. The type of demo that I would want see see rather than any "playing" demo. Thank you SO much, John!!!

[@gheumann]

Excellent. So glad to see someone deal with actual DATA as opposed to "Facebook Knowledge". As a harmonica microphone/ amp expert - (and everyone should recognize that microphones are most definitely NOT the same as guitar pickups and strings in both output level AND sensitivity to sound waves) - I want to point out that as long as you can turn the amp up enough to get into the feedback zone, you're STILL getting the maximum available power from the amp in the real world. Lowering gain isn't so much about reducing power as it is changing the characteristics of feedback, from "razor's edge" to "controllable swell". I use the following analogy: Imagine you have a Mazda Miata with a 500hp V8 motor - and the gas pedal only moves 1/2”. THAT is what trying to “drive” an amp with too much gain is like. Reducing the gain considerably is like adding 5” of throttle pedal travel. Idle is still idle, and full throttle is still full throttle. But you can much more easily control the car in the corners, and you can much more easily control the amp - which allows you to use more of its useful power. That gets you A LITTLE louder but sure helps you manage feedback while playing. Again - thanks for this clear and well done video!

[@AcadAFB]

I change my preamp EnGL tube to a JJ 12AU7 / ECC82 and something amazing just happend! AMAZING. Love the amp now :)

[@MercAudio99]

Nicely done video. I'm taking this from a slightly different perspective by starting to incorporate tube pre's on select inputs to bring back the warm sound to the Digital world for live show production.

[@terryare]

This is great, but I would still like to hear the differences...

[@joanburgin6304]

Some of the amps out there, especially higher gain amps, may not react well to having a misc. 9A pinout twin triodes plugged into a sockets where a 12AX7 or other tubes belong. One builder (I won't mention names) made a change mid production, or possibly made the amp as a one off. The tube chart showed a 12AT7 was supposed to occupy that socket, but the amp arrived in the shop with a 12AX7 in that position. It worked and it sounded okay, but not like other examples of that model amplifier. We put a 12AT7 in and it arced violently, so we powered down the amp and tried another 12AT7 with the same exact result. Some more research showed the circuit had been altered and was set to run a 12AX7 with the lower Rp than the 12AT7. Eventually we settled on using a real 5751 made by GE with a plate resistance in the 5800 @ 250 Vp range rather than over 10K ohms plate resistance with the 12AT7. Whomever made the changes to this amp was "sailing way too close to the wind", when he plotted across the curves to select the components for that gain stage. Compared to NOS 5751s modern 5751s seem more like 12AX7s that failed to make the grade. The GE 5751's gain was closer to a GE 12AT7WA. Thankfully most designers opt for amp designs that are markedly more stable, and not running right on the edge of catastrophic failures. This amp was made by a very famous name, and one almost everyone would recognize immediately. Not knowing what, why or how it got the way it did, I will keep the name to myself out of respect.

[@Luna25174]

Escuse me do you know if I are any difference between use a tubes with different gain than ones with the same gain??? I bought separately two tubos, But I don’t know if can I use them like this or maybe those can affect my sound quality one is gain A: 94.7 gain B 97.5 and the other is gain A: 104.4 GainB 94.1.

[@hadleymanmusic]

Do I find brightness in the preamp tubes or do I go for different power tubes? I need more brightness.

[@lorencing]

Thanks for the video, very informative and just what I was looking for as I was wondering if I can replace the 12ax7 with the 5751 and it looks like I can :)

[@uptopmikep7065]

Very interesting objective comparison. Thanks! It really helps.

[@gringopig]

Where did you find that signal generator? That must be pre 1970's. Nice touch but good grief, its a museum piece! And it that a Tectronix 475? Good God - those all died on us 10 years ago and the screens became so dim we had to use hoods to see anything lolol

[@HammerToneAmps]

Very interesting video & nicely done. One thing I take from this is that the JJ 5751 is likely just a relabeled 12AX7. I think the 5751 results should be closer to the 12AT7 than the 12AX7.

[@shakeAbooty88]

+HammerToneAmps Agreed.

[@bucyruserie1211]

Hi HTA, I know this is a reply you made a couple of yrs ago, but the 5751 tube is not, or should not be a relabeled 12ax7. The tube started out in 1952 by G.E. and was for industrial applications. Having a slightly higher heater current of .350 amps in parallel or .175 amps in series. It was designed to withstand vibration and intermittent operation. As you stated, it's MU factor is 70 closer to a 12at7. I only know because I got a bunch of em from a powerhouse in Texas slated for demolition. I didn't know what they were at the time, but they are great tubes... I gather you know this though, and were probably talking about the JJ's only (they probably are just relabeled). I have seen your video's of the Guitar amps you have made ( I thought they sounded and looked great), and have made a few of my own from Hammond ao-43 and 39 chassis. I hope you are still making amplifiers, as I have not seen any new one's posted. Take care, Tom

[@hadleymanmusic]

Does the clip come from the power tube???

[@GavinSteiner]

How do you know what tubes WILL and WONT work in your amp? For example, my Traynor YCV40WB has: Preamp Tube - 3x 12AX7WA Dual Triodes Power Amp Tube - 2x 6L6GB Beam Power Tubes I want to lower the output so that I can reach that "sweet spot" at a lower volume, but have no idea what tubes are or aren't compatible.

[@thetubestoretv]

You can use any 12AX7 type, the "WA" is not critical. For the power tubes you can use any 6L6 or 5881 type, the suffixes do not matter. Regarding lowering the power, it's not really possible with tubes alone, unless you're very close now. An attenuator would be the best for a dramatic reduction.

[@bucyruserie1211]

Hi, I am kind of shocked that you told Gavin S the suffixes do not matter?? The 6L6, 6L6G and 6L6GB have a Max plate dissipation of 19Watts. The 5881 is 23Watts PD, and the 6L6GC is a whopping 30Watts! Simply swapping tubes with a different suffix would require re-biasing the amplifier.. At best using the wrong tubes would produce lackluster performance, in other cases the tubes could red-plate causing plates being warped and ruined tubes

[@purplepeanuts8027]

Don't be shocked. His question wasn't asking if he could swap power tubes and not rebias. It was what 6L6 types work in a Traynor YCV40, and any and all versions work in that amp. Of course the difference you point out between the types are accurate can will affect how the amp will be biased, etc.

[@bucyruserie1211]

You may be correct, however considering he didn't even know what tubes could be swapped in the pre-amp, I kinda doubt he understood biasing output tubes. The Tubestore telling him to get an attenuator was a good idea, but I think they should have also recommended maybe trying a 5751, 12ay7 or even a 12au7 in V-1 to lower overall output..Just my opinion. Take care

[@rickmilam413]

Two thoughts - One is I wish the power with the 12AX7 had been mentioned (I don't think I missed it). The second is I wonder how many are surprised that with the factory standard 12AX7 the amp is hitting full rated power at a setting of 3.

[@EpicWinz]

I have a channel strip that has a 12AX7 on the preamp and 2 12AX7's on the EQ. Can I change the 2 12AX7's on the EQ with 12AT7's and leave the 12AX7 on the preamp? Just don't want to damage the channel strip... Great vid btw Thanks

[@thetubestoretv]

Although damage is very unlikely, I don't imagine the sound will improve at all, and likely will suffer rather. However this is really a question better answered by the channel strip manufacturer.

[@EpicWinz]

www.thetubestore.com Thanks for taking the time answering. Sadly the manufacturer went out of business, but I'll heed your advice and stick with 12AX7 (just a shame I can't easily get NOS Mullards in this type!) Thanks again.

[@83draconian]

Question: Are the preamp tubes that are being changed in the Phase Inverter position? The reason for the question is that the power (wattage) becomes lower as the gain factor in the Preamp tubes decreases.

[@thetubestoretv]

He uses V1 in a Deluxe Reverb.

[@hadleymanmusic]

I want smoothe not harsh, a 12 aw7 or a 12 ay7?

[@hadleymanmusic]

I may be wrong but what is a???? 6350?? I barely remember my tubes stash got stole

[@lincland3867]

This whole subject is something I've been reading up on, and experimenting with, and I still don't fully understand the results of swapping tubes. I know about the lesser gain factors, etc. I know that if you put a 5751 in the V1 position, it doesn't drive quite as hard as the AX7. But none of this speaks to the effect on the tone. Is that just random? An AT7 might be bright or dark depending on the manufacturer? Or an AY7? I've tried AY7s, AT7s, 5751s, and various brands of AX7s, and all I can figure out so far is that they all sound different. It depends on the level you drive them too. If anyone has any more sources on this I'd appreciate it.

[@IPushHard]

I like my amp generally speaking. It has a habit of getting fizzy with the gain cranked high and the clean is a little too bright. I want a warmer clean, and a bigger dirt channel with less compression fizz and more punch. It has the usual 12AX7's in the pre-amp and some EL34's power tubes. My plan...and believe me when I say that I dont know what the hell I'm doing... is to change out the the EL-34's for 6v6 power tubes. Yes, I know I'll lose some volume. I dont care. It's only a 50 watt amp and its self biasing. I checked with tech support to make sure that the swap was OK/safe, and they said that it was fine, and noted the volume loss that I'd see. Again... I dont care. The 2nd part of my plan is to swap pre-amp tubes to something with a little less heat. I dont even use the gain channel very often because I get my dirt from pedals... usually a Deluxe Big Muff...but I have a crap ton of dirt pedals to choose from. So my main focus on that channel is to get a tone that is usable in some way and add that to my tone arsenal. I'm thinking that some 12AT7's or even 12AX7b's would get me there. I think the key factor for me is to have a usable gain knob all the way across its range. Currently, the gain will change nicely to maybe 6 or 7 and then its just gets more compressed and fizzy anywhere above that. But again, I dont know what the hell I'm doing. Anyone have thoughts or advice? I could sure use it. ... Oh by the way. I play heavier rock. Not metal. I dont care about the chug factor. I care most about dynamics and tone. Thanks

[@hadleymanmusic]

What dont compress?