12at7

[zeppman]

Hey guys-

Anyone try subbing in 12at7s over 12ax7s in their mark iv? Just curious how they will sound, I got some mullards today.

 

[Boogiebabies]

Some of those old Mullards 12AT7's have more gain than a modern 12AX7. Figure that one out. The only place I sub is in the PI to tame down too much preamp gain and bottom end.

 

[palomino]

I bought a used Mark IV back in March and it had a Mesa 12AT7 in V2.
I think the previous owner did this to bring the gain down for channel 2
for a bluesier vibe. I had a few old RCA 12AX7's and stuck those in instead and to me it sounds warmer.

I did get a couple of those Mullard 12AT7's. I put one in V4 and it really
seems to bring out the reverb much better now. There was a Mesa SP
in there, but that made the reverb very harsh sounding. With the Mullard
the harshness is gone, unless I turn it all the way up.

Let us know what you did with it and the results!

 

[RR]

Some of those old Mullards 12AT7's have more gain than a modern 12AX7. Figure that one out. The only place I sub is in the PI to tame down too much preamp gain and bottom end.

Quite interesting, like you said "Figure that one out".

Of all the preamp tubes, 12AX7 (with the exception of above) has the highest gain followed by 7025, and I think 12AT7. So basically substituding a preamp tube 12AX7 with a 12AT7 you will lose alot of gain.

Try a 7025, this will lessen the gain but won't drop it as much as a 12AT7. Matter of preference substituding preamp tubes.

 

[zeppman]

Well I have the mullard CV4024. Received them today while I was at work, so I can't try them for a few hours. They were recommended to me, but I'm not sure what position to put them in. I don't use the reverb on the amp, so I think it would be pointless to stick it in v4. I was thinking either v1 and v2. I purchased two of them.

 

[zeppman]

On a sidenote, are the JAN Philips 6L6WGB the same as the JAN Philips 7581A?

 

[RussB]

Them Mullard CV4024's are very "toneful" as far as 12AT7's go. Try it all ovewr the place, and leave 'em where YOU like 'em, not where someone else tells you to!

and to answer your "sidenote", NO!

Look at them at the KCA website!

 

[RussB]

Some of those old Mullards 12AT7's have more gain than a modern 12AX7. Figure that one out. The only place I sub is in the PI to tame down too much preamp gain and bottom end.

Quite interesting, like you said "Figure that one out".

Of all the preamp tubes, 12AX7 (with the exception of above) has the highest gain followed by 7025, and I think 12AT7. So basically substituding a preamp tube 12AX7 with a 12AT7 you will lose alot of gain.

Try a 7025, this will lessen the gain but won't drop it as much as a 12AT7. Matter of preference substituding preamp tubes.

RR, you need to to do a little "Tube Research"

Compare a Sovtek 12AX7WA/WB to any old 12AX7 or 12AT7/6201/CV4024...and what's that about a 7025?

 

[RR]

RR, you need to to do a little "Tube Research"

Compare a Sovtek 12AX7WA/WB to any old 12AX7 or 12AT7/6201/CV4024...and what's that about a 7025?

You are probably up todate on on brands and models ... I'm not sure what you are getting at.

All things equal (sure, some brand has more gain that other and I would even say some brand 12AT7 will match up with another brand's 12A7X)

but my point was preamp tube gain are list below most to least as following:
12AX7
5751 (not 7025 I mentioned)
12AT7
12AU7
12AY7

the last two might be not in the right order.

As far as how buch gain 'this' brand or 'that' brand I'm not familiar with.

 

[Boogiebabies]

On a sidenote, are the JAN Philips 6L6WGB the same as the JAN Philips 7581A?

No. The Phillips 7581A is a 35 watt tube based off the Phillips 30 watt 6L6GC. The WGB is more similar to a 5881, but some have the exact internal structure as the 6L6GC and 7581A. I would only run it as a 25 watt tube.

 

[Boogiebabies]

Call Doug at Doug't tubes. He has some Mullard 12AT7's CV4024 that have a ton of gain.

 

[zeppman]

Well I tried them out lastnight. Really a different sound, I'd say a little rounded out, and I can really notice the drop in gain. I think one tube is microphonic though. I ordered two, and I started by placing one in V1. It was fine on ch1, but ch2 and ch3 would start to squeal...quietly at first, but shortly increasing where it would get out of control. The other tube didn't do this. So right now, I've kept the good one in v1. Gives it more of a bluesy sound I'd say. This is just my description, but "hallow" maybe? I was only able to play a couple minutes yesterday, but I'll have more time tonight, and will give you a further update. Has anyone tried them in other positions? Thanks!

 

[Ken j]

12AX7 dual triode is just one member of a family of tubes that have different amounts of gain. The 12AX7 has the most, and is rated at 100. Here are the ratings of its siblings:

12AX7=100 12AT7=60 12AY7=45 12AV7=41 12AU7=20



If my memory serves me right 7025 is the industrial number for a 12AX7.

 

[RR]

12AX7 dual triode is just one member of a family of tubes that have different amounts of gain. The 12AX7 has the most, and is rated at 100. Here are the ratings of its siblings:

12AX7=100 12AT7=60 12AY7=45 12AV7=41 12AU7=20



If my memory serves me right 7025 is the industrial number for a 12AX7.

Thanks Ken j, that's what I mean.

Did you check on 5751? Its gain is supposedly between 12AX7 and 12AT7. IT supposedly what SVR used on his Fenders.

 

[RussB]

12AX7A/7025/ECC83/CV4004 (100)
5751WI (71)
5751 (70)
CV4024/12AT7WA/6201 (61)
12AT7/ECC81/6679 (60)
6072/6072A (45)
12AY7/ECC82 (44)
12AV7/5965 (41)
5814A/12AU7A (21)
12AU7/ECC82/6189/5963 (20)

 

[Timbre Wolf]

Well I have the mullard CV4024. Received them today while I was at work, so I can't try them for a few hours. They were recommended to me, but I'm not sure what position to put them in. I don't use the reverb on the amp, so I think it would be pointless to stick it in v4. I was thinking either v1 and v2. I purchased two of them.

Heya Zeppman -

It was me who recommended the Mullard CV4024. I prefer it for fat cleans, when put in the first input position (V1). It definitely lowers gain, but provides a ringing clarity that I have found to be unmatched by any of the nearly 40 preamp tubes I've experimented with (including 12AX7, 5751, 6201, 12AT7, E180CC, 12BZ7, 12BH7A, and 12AU7 types). You'll find you have to re-dial your sounds (increase the gain setting, set tone to taste), but I'll bet you'll like what you come up with. Fatter, more well-defined lows, articulate mids, and highs that are airy and available, but which won't hurt you. The CV4024 is my number one recommendation, in V1, for stellar cleans and slight dirt (just-breaking-up).

I have often heard folks cite the voodoo spirit of SRV, having used a 5751 for V1 as a "secret weapon." I love SRV's tone, and I have tried a number of 5751s, and have concluded that they're all too "dry" for my taste - emphasizing upper mids and high frequencies, and lacking the "juicy" low-mids and tight lows that I treasure in the CV4024. SRV sounded great, indeed, but I think the impact of the 5751 was small compared to the fact that he mixed down many amp tracks in his recordings.

I have also found that the CV4024 is wonderful in higher-gain applications (lead settings), but in this case, a high-gain 12AX7 should be the first input tube, and the CV4024 should be the next gain stage. Check your manual for which tube position this would be. My favorite high-gain combo is a Raytheon black-plate/halo-getter 12AX7A in V1, with the Mullard CV4024 following. The CV4024 really carries the harmonic overtones of the driven 12AX7, yielding complex highs that shimmer, but are never harsh.

I'm sorry to see that you've gotten a microphonic CV4024. I have a dozen of these, and have never encountered a microphonic one yet. Perhaps you should have a talk with your supplier about getting a replacement. If that falls through, try putting the microphonic tube in your phase inverter position (closest to the power tubes). By the way, I like your description as "hollow!" I agree, and this is what I mean when I say the mids are very clear and articulate, and the highs are airy and available, but not assertive - just the potential empty space to hold the treble as it flows through. Cosmic, maaan!

Hope you dig 'em as much as me! Cheers!

 

[zeppman]

Timbre Wolf, glad to hear from you again. I remember that you were the one who recommended these Yeah, I really enjoy the tube. V1 affects channel one, v2 affects ch2 and v3 has the biggest influence on ch 3. Due to the multiple gain stage design of the mark iv, I realized that putting the mullard in V1 affects the gains of ch2 and ch3, i have to really crank the gains on those.... that is the only problem I really see. Anyways, I'm enjoying my new "secret weapon" as you put it, it really changed my overall tone, in a good way. I'm working on obtaining other obscure tubes to try out!

 

[Ken j]

Did you check on 5751? Its gain is supposedly between 12AX7 and 12AT7. IT supposedly what SVR used on his Fenders.

According to The Tube Amp Book By Aspen Pitt (deluxe revised edition, 2003) pg.108, you are correct.

Russ's numbers are correct 5751=70.