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Post subject: 12AX7 vs 12AT7 in V1
Posted: Mon May 02, 2016 1:10 pm
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Aspiring Musician
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I've had my HRD for just over four years now and for the last two or so I've been using the following tube configuration:
V1: U.S. Made JAN 5751
V2: U.S. Made JAN 5751
V3: 12AT7 / ECC81 Mullard
Power Tubes: GT-6L6

Recently the preamp tubes went and shortly afterwards the power tubes followed so after replacing and biasing the amp (done by a qualified tech) I have this tube configuration.
V1: GT-12AX7
V2: GT-12AX7
V3: 12AT7 / ECC81 Mullard
Power Tubes: Ruby 6L6

I was going to return to the 5751s in V1 and V2 but decided to give the GT-12AT7 a try. I popped a 12AT7 into V1 and the amp did get quieter but there was a rattle. I thought the tube was bad. Put the 12AX7 back in V1 and the brand new 12AT7 in V2. No rattle but no noticeable change in tone/volume either. I repeated the process with another brand new right out of the box 12AT7 and got the same rattle. When the 12AT7s are in V2 the rattle is gone.

Is it the tubes or the fact that they're in V1?

Right now I have the 12AT7 in V2 which has made the dirty channel a little smoother but no noticeable change on the clean channel.
V1: GT-12AX7
V2: GT-12AT7
V3: 12AT7 / ECC81 Mullard
Power Tubes: Ruby 6L6

Thanks and Cheers!
BM

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Post subject: Re: 12AX7 vs 12AT7 in V1
Posted: Mon May 02, 2016 4:04 pm
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12AT7 have a less gain than 12AX7 that why amp is less louder .

Rattle ; a bad 12AT7 tube. No good tube should rattle


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Post subject: Re: 12AX7 vs 12AT7 in V1
Posted: Mon May 02, 2016 4:28 pm
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The new 12AT7 tubes both rattled in V1 but not in V2. It's possible both are defective but unlikely and the fact that there's no rattle when they're in V2 seems to suggest something else. Not sure.

edit: V2 not V3

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Last edited by Bluer Monkey on Tue May 03, 2016 6:50 am, edited 1 time in total.

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Post subject: Re: 12AX7 vs 12AT7 in V1
Posted: Mon May 02, 2016 5:10 pm
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Short answer;

V1 is amplified by V2 which is amplified by V3...

A small defect / rattle / noise in V1 is amplified 2 times more if the same tube is in V2.
Same tube in V2 may not have enough amplification to be hear rattle / noise.

Which are the brand name of yours 12AT7 ?


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Post subject: Re: 12AX7 vs 12AT7 in V1
Posted: Mon May 02, 2016 7:49 pm
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After changing out the stock speakers which were 'Fender special designs' to Jensen C12-K 100watts in both my Deville 212 and Blues Tweed Deluxe, I really like the preamp tube lineup of a 12aY7 in the V1 slot and a 12aT7 in the V3 slot which is the phase inverter... Using groove tubes. These few changes have yielded a fantastic sounding amp in my opinion of course.

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Post subject: Re: 12AX7 vs 12AT7 in V1
Posted: Tue May 03, 2016 5:26 am
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I am no electronics expert but my understanding is that 12AT7 and 12AX7 may not be interchangeable in a particular circuit.

The 12AX7 is all about voltage gain whereas a 12AT7 is about current. You may have to consider making other changes in the circuit if you really want to use a 12AT7 in V1. You might be better off sticking with a 5751 if you want less gain than a 12AX7.


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Post subject: Re: 12AX7 vs 12AT7 in V1
Posted: Tue May 03, 2016 6:38 am
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fifty4 wrote:
I am no electronics expert but my understanding is that 12AT7 and 12AX7 may not be interchangeable in a particular circuit.


.


I often do that in many amps , like others people, without any rattle or noise issue


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Post subject: Re: 12AX7 vs 12AT7 in V1
Posted: Tue May 03, 2016 8:35 am
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Thanks for the replies. As always they're much appreciated.

fifty4 wrote:
I am no electronics expert but my understanding is that 12AT7 and 12AX7 may not be interchangeable in a particular circuit. ...
I'm no electronics expert either, fifty4, and this too was my first thought but luckily for guys like us we have stratele52 and a bunch of others who know their stuff and are always willing to help.

I decided to try the brand new 12AT7 tubes in V1 in my Blues Jr. and bingo it was shake-rattle-and-roll. Sounds like bad tubes. I called the store and they said no problem for an exchange.

Cheers!
BM

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Post subject: Re: 12AX7 vs 12AT7 in V1
Posted: Wed May 04, 2016 6:34 am
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Follow up: Stratele you were right about the tubes. Brought back the two Groove Tube 12AT7 and exchanged them for two Ruby 12AT7. Popped one into V1 and all is smooth ...

Thanks
BM

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Post subject: Re: 12AX7 vs 12AT7 in V1
Posted: Wed May 04, 2016 7:23 am
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Bluer Monkey wrote:
Follow up: Stratele you were right about the tubes. Brought back the two Groove Tube 12AT7 and exchanged them for two Ruby 12AT7. Popped one into V1 and all is smooth ...

Thanks
BM



**********************************************

One thing I have learned about tubes and it doesn't matter what brand, is that at least 50% of the time ..they have either been bad or have a short life . I am certainly not speaking for everyone who owns a tube amp but this is been my experience when purchasing new tubes regardless of the brand . Fortunately, solid-state amps have come a long ways in recent years with technology and can render fantastic tones with excellent effects.

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Post subject: Re: 12AX7 vs 12AT7 in V1
Posted: Wed May 04, 2016 11:26 am
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musicmatty wrote:



**********************************************

One thing I have learned about tubes and it doesn't matter what brand, is that at least 50% of the time ..they have either been bad or have a short life .

It is not my expérience with lots of customers and friend who use modern tubes in their amps.
Probably you talk about people who never bias their power tubes.


Fortunately, solid-state amps have come a long ways in recent years with technology and can render fantastic tones with excellent effects.

Do some A/B test and chance you change your mind or you listen cheap tubes's amp or good tubes amps not in a good shape.



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Post subject: Re: 12AX7 vs 12AT7 in V1
Posted: Wed May 04, 2016 12:03 pm
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stratele52 wrote:
12AT7 have a less gain than 12AX7 that why amp is less louder.

I play harp (harmonica) as well as guitar, and harp mics are notoriously finicky about high gain circuits--whether they're tube, solid state or digital...stand in the wrong place or play at the wrong volume, and it's Squeal City with a high gain tube (like the usual 12AX7).

Because of that, I put a (lower-gain) 12AY7 tube in the "Normal" Channel of my '63-reissue Vibroverb. Lowered the gain, lost the squeals, fattened up the bottom end, made me smile. It also made for a significant difference if I plug my guitar into that channel.

I have read (but not personally experienced) that using a 12AT7 (lower gain factor than a 12AX7) as a pre-amp tube (V1 or V2 on my amp; I'm not sure about yours) will not only lower the gain and volume, but can sometimes tend toward a colder, more sterile tone...have you found this to be the case?

It would be interesting if you were able to do an A/B comparison of a 12AT7 vs. a 12AY7 vs. a 12AX7 in the same slot, and hear your impressions of the three different tubes...

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Post subject: Re: 12AX7 vs 12AT7 in V1
Posted: Wed May 04, 2016 1:07 pm
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Screamin Armadillo wrote:
...I have read (but not personally experienced) that using a 12AT7 (lower gain factor than a 12AX7) as a pre-amp tube (V1 or V2 on my amp; I'm not sure about yours) will not only lower the gain and volume, but can sometimes tend toward a colder, more sterile tone...have you found this to be the case?

It would be interesting if you were able to do an A/B comparison of a 12AT7 vs. a 12AY7 vs. a 12AX7 in the same slot, and hear your impressions of the three different tubes...

This is totally subjective, of course, but I'd tend towards the opposite: a warmer, smoother, sound. I've tried 5751s in V1/V2 and liked the results. The 12AT7 in V1 really brings down the volume. On the clean channel I can dime the amp and get just a nice OD at a comfortable level that does not require hearing protection. I suspect a 12AY7 in V1 would be too low and bring the amp down to bedroom level.

Cheers!
BM

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Post subject: Re: 12AX7 vs 12AT7 in V1
Posted: Wed May 04, 2016 2:12 pm
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Bluer Monkey wrote:
Screamin Armadillo wrote:
...I have read (but not personally experienced) that using a 12AT7 (lower gain factor than a 12AX7) as a pre-amp tube (V1 or V2 on my amp; I'm not sure about yours) will not only lower the gain and volume, but can sometimes tend toward a colder, more sterile tone...have you found this to be the case?

It would be interesting if you were able to do an A/B comparison of a 12AT7 vs. a 12AY7 vs. a 12AX7 in the same slot, and hear your impressions of the three different tubes...

This is totally subjective, of course, but I'd tend towards the opposite: a warmer, smoother, sound. I've tried 5751s in V1/V2 and liked the results. The 12AT7 in V1 really brings down the volume. On the clean channel I can dime the amp and get just a nice OD at a comfortable level that does not require hearing protection. I suspect a 12AY7 in V1 would be too low and bring the amp down to bedroom level.

Cheers!
BM


The original 59 Bassman amps came with the 12aY7 in the V1slot. If your second channel on your amp is a gain Channel , there's no need to change out the 12ax7 for a lower gain tube...as you would like to have the extra gain because it's a gain stage. The 12ax7 tube is a 100% distortion tube. The 12ay7 tube is somewhere around 60% I believe however, it certainly will not bring your amp down to bedroom level ..a 12au7 tube would bring your amp close to that level :shock: A 12aT7 tube in the V3 slot phase inverter is a nice fit as well... This is what delivers it to the power tubes with a bit more smoothness rather than 100% distorted tube.

You should experiment around with different gain stage tubes and draw your own conclusions :wink:

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Post subject: Re: 12AX7 vs 12AT7 in V1
Posted: Wed May 04, 2016 2:53 pm
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musicmatty wrote:
... You should experiment around with different gain stage tubes and draw your own conclusions :wink:
Good idea, musicmatty. I'll give it a go. I have two 12AT7 tubes, two 12AX7 tubes, and the 12AT7 / ECC81 Mullard in V3.

Cheers!
BM

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