Quiet 12at7 for reverb send?

Sean B

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Looking for recommendations for a quiet 12at7 for reverb send slot in a 68 CVR. Being picky as I have been recording recently and am able to play at home for the first time in a while. The reverb starts to get pretty noisy around 3-4 which is where I like it to be. I have a few about the house, some EH, some JJ, some Mullard CV4024 (which I have in the PI), among others old and new. Most start to get noisy around 2. The quietest is a no name made in China tube I have, but I'm still wanting less hiss. Am I nitpicking? Yes I am. Played live with this amp for 5 years and it's never bothered me, but in this context it's starting to. Just wondered if anyone has a 'go to' 12at7 for low noise. Tone and country of manufacture not important. Just want low noise. Could be just chasing my tail, but I tried quite a few 12ax7 in the trem slot on this amp for the same reason. I ended up with a Mesa 'select', which is a JJ. That particular tube is noticably quieter than any of the dozen or so I tried. It's the only tube I have put in the first gain stage of my Red Knob Twin set to approaching silly volume and not made much noise. I ended up buying a couple more of the Mesa 'select' rebranded JJ's and they were nowhere near as quiet. Selected consistency I guess. Just buy a ton of 12at7s and try them out? Luck of the draw, or is there a preferably cheap 12at7 which is known for low noise?
 

slider313

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The 6679 is a communication grade 12AT7. These were used in police, coast guard and fire truck radios. The RCA version is a good choice.
 

archetype

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Looking for recommendations for a quiet 12at7 for reverb send slot in a 68 CVR. Being picky as I have been recording recently and am able to play at home for the first time in a while. The reverb starts to get pretty noisy around 3-4 which is where I like it to be. I have a few about the house, some EH, some JJ, some Mullard CV4024 (which I have in the PI), among others old and new. Most start to get noisy around 2. The quietest is a no name made in China tube I have, but I'm still wanting less hiss. Am I nitpicking? Yes I am. Played live with this amp for 5 years and it's never bothered me, but in this context it's starting to. Just wondered if anyone has a 'go to' 12at7 for low noise. Tone and country of manufacture not important. Just want low noise. Could be just chasing my tail, but I tried quite a few 12ax7 in the trem slot on this amp for the same reason. I ended up with a Mesa 'select', which is a JJ. That particular tube is noticably quieter than any of the dozen or so I tried. It's the only tube I have put in the first gain stage of my Red Knob Twin set to approaching silly volume and not made much noise. I ended up buying a couple more of the Mesa 'select' rebranded JJ's and they were nowhere near as quiet. Selected consistency I guess. Just buy a ton of 12at7s and try them out? Luck of the draw, or is there a preferably cheap 12at7 which is known for low noise?

There may not be a 12AT7/ECC81 that's known for low noise, as it's not typically used in audio stages where low noise is critical.

There are plenty of NOS possibilities and they are far cheaper than 12AX7s. 2022 pricing is wacky high due to current events, with the high-priced sellers asking $40-50 for average tubes. I think that's stupid high and not worth it. You should be able to get a NOS tube from $15-25 if you look diligently. You'll likely pay a premium above that if you ask the seller to select for low noise.

Note that "low noise" is not the same thing as "low microphonics." A triple-spacer, built like a truck 12AT7 may have low microphonics, but not low noise.

Just keep in mind that you don't need a specific manufacturer or internal design: you just need low noise. Any US/EU/UK/JP-made 12AT7 is going to be a durable tube for your application.

Your best bet is to get a tube that's been rebranded for a hi-fi, stereo, or organ manufacturer, as these are often ordered with a spec for low noise. Hammond, Wurlitzer, Baldwin, Fisher, McIntosh, Dynaco, Eico, etc. On top of that, you can sometimes pay an upcharge and ask to have one selected specifically for low noise.

I've done trouble-free business multiple times with the following folks.

Brent Jessee has lots. Breeze past the $350 audiophile ones and you'll see the $15-25 ones. Remember, you're not looking for a manufacturer or internal design. He even sells 'ugly' tubes at a discount.

Tube Depot will charge you an average of $40 for the privilege, plus $4 to select for low noise.

KCA NOS seems to be out of stock on most all 12AT7, but is worth keeping an eye on.

Doug's Tubes has some.

Good luck. My thought is that the issue isn't likely the tube itself, but the gain of the tube magnifying another source of noise. Using a low-noise tube may do nothing but reveal that the tube isn't the root cause of the noise. Some '68 Custom series amps could be used on the bench as white noise generators for troubleshooting other amps.
 

schmee

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I think you will find it's not the tube and it sounds like you have tried the usual things to improve the reverb noise floor. I wonder if there are any wire routing or other hints regarding this on line?
 

Sean B

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The Custom 68 have a rep of being noisy due to lead dress and other design things. A 12AU7 could maybe help maybe not. Many people seem to prefer a 12AU7 in that position in Fenders.
Will give this a try. I still have an old RCA cleartop somewhere I think. If not a new one won't break the bank.
 




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