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Post subject: 12AX7 preamp valve options
Posted: Tue Jan 21, 2014 9:41 am
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Amp experts here: I'm hoping to reduce the noise on the clean channel without affecting the timbre, and wondered if replacing the 12AX7 phase inverter with a 5751 would help.
I changed the clean channel 12AX7 to a Mullard and the EL34 power tubes to red Svetlanas, which really helped opening up the treble, but it didn't do anything for the noise.

So, do I risk anything by trying a 5751 for the phase inverter valve? It's the same voltage and load as a 12AX7, right - just lower gain (and hopefully noise)?


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Post subject: Re: 12AX7 preamp valve options
Posted: Tue Jan 21, 2014 10:16 am
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If you're only getting noise on one channel then the PI tube isn't where the problem lies, that tube is on all the time your amp's running. It's more likely that the noisy tube is the first in the signal chain, the one furthest away from the power tubes.

Having said that, some amps are noisy for other reasons. Low quality capacitors and resistors can contribute to noise, as can poor wiring layout.

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Post subject: Re: 12AX7 preamp valve options
Posted: Tue Jan 21, 2014 10:38 am
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What Amp are we talking about here..??

cheers!

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Post subject: Re: 12AX7 preamp valve options
Posted: Tue Jan 21, 2014 11:37 am
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It's an Orange Rocker 30.
V1: 12AX7, half used for clean channel, half used for 1st stage dirty
V2: 12AX7, 2nd and 3rd stage dirty
V3: 12AX7, Phase inverter
P1 & P2: EL34, self-biasing (cathode bias)

And I do get the noise on both channels, but I only see it as a problem on the clean channel.
I changed a Ruby to a Mullard (reissue) for V1, and the power tubes to matched Svetlanas, which opened up the upper midrange and treble, but did nothing (bad or good) for the ambient noise.
Currently, there's a Sovtek 12AX7-WA in the phase inverter position.


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Post subject: Re: 12AX7 preamp valve options
Posted: Tue Jan 21, 2014 3:27 pm
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Have you tried plugging the amp into a different outlet? Sometimes the noise from light fixtures, cell phones, etc transfer over to the amp via power or even the pickups on the guitar. Does it make noise with nothing plugged in? How old is the amp? I think someone mentioned bad/old caps, resistors, etc. that could also be a problem.

Hope this helps.

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Post subject: Re: 12AX7 preamp valve options
Posted: Tue Jan 21, 2014 7:29 pm
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socal323 wrote:
Have you tried plugging the amp into a different outlet? Sometimes the noise from light fixtures, cell phones, etc transfer over to the amp via power or even the pickups on the guitar. Does it make noise with nothing plugged in? How old is the amp? I think someone mentioned bad/old caps, resistors, etc. that could also be a problem.

Hope this helps.


No, it's not ground hum, it's persistent and random white noise, even if run from an unplugged UPS without a guitar plugged in. It's actually more quiet than my other three amps, so I'm not trying to solve a bad or new noise problem as such - I want to get it even less noisy on the clean channel.
Preferably to the point that I can keep it on a medium loud setting without having to turn it off or down if I record something else with a mic.


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Post subject: Re: 12AX7 preamp valve options
Posted: Thu Jan 23, 2014 10:02 pm
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I don't see any risk in trying one. I would describe a GE triple mica 5751 as quiet. You could also try something in the 7025 realm as well. No risk to anything but your funds, and not really much of one at that.

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Post subject: Re: 12AX7 preamp valve options
Posted: Thu Jan 23, 2014 10:11 pm
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arth1 wrote:
So, do I risk anything by trying a 5751 for the phase inverter valve? It's the same voltage and load as a 12AX7, right - just lower gain (and hopefully noise)?


Regardless of the real cause of your problem, a 5751 is a direct replacement for a 12AX7 (as is a 12AY7). It will drop the overall gain on the amp slightly though.

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Post subject: Re: 12AX7 preamp valve options
Posted: Fri Jan 24, 2014 5:19 am
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Lightnin MN wrote:
What Amp are we talking about here..??

cheers!


+100

No answer yet ! It is the first thing to know .

And better to post in Amps section , more expert there IMO


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Post subject: Re: 12AX7 preamp valve options
Posted: Fri Jan 24, 2014 5:36 am
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stratele52 wrote:
Lightnin MN wrote:
What Amp are we talking about here..??

cheers!


+100

No answer yet ! It is the first thing to know .


? It's answered in the fourth post in this thread, directly under the question.


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Post subject: Re: 12AX7 preamp valve options
Posted: Fri Jan 24, 2014 5:53 am
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Jah Soldier wrote:
I don't see any risk in trying one. I would describe a GE triple mica 5751 as quiet. You could also try something in the 7025 realm as well. No risk to anything but your funds, and not really much of one at that.

Thanks - I'll give it a go, then, I think!

It's nice that three of the most effective ways to change your sound are cheap to try - strings, tubes and picks. (I just tried out Dean Markley Helix strings, to see if they would reduce slide noise. Yes, they did, along with everything else. I have never had strings that dead before. Back to Ernie for me. But all I lost was the price of a beer.)


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Post subject: Re: 12AX7 preamp valve options
Posted: Fri Jan 24, 2014 6:09 am
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arth1 wrote:
stratele52 wrote:
Lightnin MN wrote:
What Amp are we talking about here..??

cheers!


+100

No answer yet ! It is the first thing to know .


? It's answered in the fourth post in this thread, directly under the question.


Oups ! Sorry , Orange Rocker 30

Noise ; are your input jacks have a good working shorting ground contact ?


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Post subject: Re: 12AX7 preamp valve options
Posted: Fri Jan 24, 2014 6:26 am
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stratele52 wrote:
Oups ! Sorry , Orange Rocker 30

Noise ; are your input jacks have a good working shorting ground contact ?

I haven't checked, but will.
The white noise I'm trying to get rid of is present no matter whether anything is plugged in, though - it's what most people would consider normal. But I want the clean channel to become as noiseless as possible; quiet even with the volume turned up. I know it's doable, cause class AB stereo system tube amps manage, so there's no reason why a guitar tube amp shouldn't either. Yet the norm for guitar amps seems to be somewhat hissy, even for clean channels.
I just like to improve it :D


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Post subject: Re: 12AX7 preamp valve options
Posted: Fri Jan 24, 2014 6:30 am
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Noise is normal or not ? That is a question that only a tech when studying the amp , circuits , wiring, may know . Some amp need mod to be quiet

I do it often.

Any shematic and picture inside ?


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Post subject: Re: 12AX7 preamp valve options
Posted: Fri Jan 24, 2014 8:53 am
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arth1 wrote:
The white noise I'm trying to get rid of is present no matter whether anything is plugged in, though - it's what most people would consider normal. But I want the clean channel to become as noiseless as possible; quiet even with the volume turned up. I know it's doable, cause class AB stereo system tube amps manage, so there's no reason why a guitar tube amp shouldn't either. Yet the norm for guitar amps seems to be somewhat hissy, even for clean channels.
I just like to improve it :D


It would be helpful if you could post a recording of the noise you are hearing. Truth is, you may be tilting at windmills. You can't really compare the noise performance of a tube guitar amplifier to that of a tube hi-fi amp. The purpose and design of each is different. Every component in an amplifier affects it's noise performance: tube selection, use of metal film resistors vs carbon film, circuit layout, even the location of the volume control in the gain stages. Unless you are willing to redesign your amp for minimum noise, the only option you have is tube swapping which can become a very expensive effort. If "most people" (including a good tech) would consider the noise level of your amp to be "normal", that may be as quiet as you can get it. Someone earlier mentioned using 7025s. Yes, those are low noise versions of 12AX7s. Fender used them years ago. NOS ones sell for $100 each (or more).

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