# 12AU7 in V1 in my HRD?



## Verne (Dec 29, 2018)

I've been reading that placing a 12AU7 in V1 reduces volume on the HRD. I've also read where people are saying don't do it. I use mine in a smallish room and not outside the house, so dropping some volume so I can use the volume control more and work the tubes is something I'd really like. I trust the immense supply of knowledge here so I'm asking here and will believe what I read. I don't know this stuff, so is this a bad idea, or will it do what I'd like? Right now it was just serviced and retubed with 3 Sovtek 12AX7 and Sovtek power tubes.


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## oldjoat (Apr 4, 2019)

the pre amp tubes ( U/T/X) are pretty well interchangeable in amps. ( unlike power tubes )
some have less gain than others ( but work the same way) ... so less "power/ volume signal " if you will, feeding the power tubes for them to amplify.


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## KapnKrunch (Jul 13, 2016)

I found in some cases the lower gain tubes merely raise the setting on the potentiometer where you get exactly the same sound. In other cases there was a noticable difference in sound. It should be safe to try.


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## Verne (Dec 29, 2018)

Cool. Thanks guys. I was hoping the same volume level was a little further up the turn of the knob. Am I incorrect in assuming this will better utilize the tubes than having volume down around 1-2 on a knob sweep up to 12? That's kind of my idea. For my drive channel the master is at 1 at highest with drive/gain at around 2-3 o'clock.


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## GTmaker (Apr 24, 2006)

I tried an AU7 in my Super Reverb and it sucked the living tone out of my amp.
The much lower power ratings of the AU7 does not work for me.
What does work is a 5751 preamp tube. I have one on every tube amp I own.

Just use what works for you cause in the bottom lkne, you are responsible for your tone.
G.


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## oldjoat (Apr 4, 2019)

not so much better utilization of the tubes ...
just different knob positions ... 

like plugging in an electric VS a powered acoustic pickup VS a mic ... some need more or less gain to get the sound you want.


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## Verne (Dec 29, 2018)

Okay. I'd still like to try it and see. Now to source a 12AU7. Cheapest L&M has is $33. Goal is keep the $$ input down in case the result is not entirely to my liking. That way I haven't spent the $$ and now have a tube I won't likely use. Experimenting is fun.


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## oldjoat (Apr 4, 2019)

www.thetubestore.com - Your online source for audio vacuum tubes.

supposed to have a store in Hamilton 

Bellone in London still open ?


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## Verne (Dec 29, 2018)

Bellone closed down couple months back. He retired and the store was supposed to become a safe injection site. But let's not get into that discussion here. ;-)


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## JBFairthorne (Oct 11, 2014)

Verne said:


> Bellone closed down couple months back. He retired and the store was supposed to become a safe injection site. But let's not get into that discussion here. ;-)


Then why bring it up? Lol


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## Verne (Dec 29, 2018)

JBFairthorne said:


> Then why bring it up? Lol


Good point. But I figured he's ask why. Cutting corners. HAHAHA.

I also know how threads can derail quickly unintentionally. Even if it's by the hand of the OP.


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## Dorian2 (Jun 9, 2015)

Seems that 12AU7's are typically used for Reverb due to the much lower gain (20% compared to 100% 12AX7). You might be happier with a 12AY7 in there (60% to 100% of 12AX7). I've done this in both my Blackstar V1 for gain reduction on the Drive channel and in my BJ for less gain and more headroom. As long as you aren't approaching it like some kind of cheaper alternative to an attenuator you should be able to work with a lower gain preamp. I'd think the 12AU7 would be too low and would suck your Tone dry like a cheap hooker.


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## jb welder (Sep 14, 2010)

Go ahead and try, no harm will be done.
However, as @oldjoat mentioned, it won't be working the tubes any harder. Unless you are playing louder.


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## Verne (Dec 29, 2018)

Dorian2 said:


> suck your Tone dry like a cheap hooker.


That sounds dreadful. This is why I was asking. Invaluable input. The only spare I have a 12AT7 and it was put in V1 in my TM36 and I really like what it did there. I've though about an attenuator, and just find that sweet spot and leave it, but I thought it'd be a $$ pedal.


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## Verne (Dec 29, 2018)

jb welder said:


> Go ahead and try, no harm will be done.
> However, as @oldjoat mentioned, it won't be working the tubes any harder. Unless you are playing louder.


I may source an inexpensive tube to try it still just for curiosity sake, but as @Dorian2 mentioned, I may look into an attenuator. It'd likely be my better option, I just hadn't thought of it. This way my TM36 also reaps the same benefit.


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## oldjoat (Apr 4, 2019)

nuttin stopping u from swapping in the 12at7 for a test


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## Verne (Dec 29, 2018)

I may, but it involves taking apart the TM36. I have stumbled across an idea based on @Dorian2 idea of an attenuator. I have an old Hosa one button channel switcher as an attenuator base. I have the original 1/4" jack from it, and the little white Strat that was given to me has a donor 1/4" jack. I have enough wire from when I created a test jack for speakers. I found a video online showing a way of building it without the need for power. I am now about to do this pedal and hope it turns out. I'll post back. @Dorian2 ............ if it weren't for your post, I'd be sitting in the water waiting. Here's goes nothing. Cheers.


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## High/Deaf (Aug 19, 2009)

Verne said:


> Cool. Thanks guys. I was hoping the same volume level was a little further up the turn of the knob. Am I incorrect in assuming this will better utilize the tubes than having volume down around 1-2 on a knob sweep up to 12? That's kind of my idea. For my drive channel the master is at 1 at highest with drive/gain at around 2-3 o'clock.


By the looks of your settings (drive/gain @ 2-3 o'clock), you are using quite a bit of preamp drive to get a distorted sound at low levels (master @1). Putting in a lower gain 12A?7 (or 5751) will reduce the amount of gain, meaning you will have to run the preamp gain control up around 3-4 o'clock to get the same amount of gain/distortion. The change in master volume position (or sensitivity) will be minimal.

But trying different preamps tubes is easy. And having some spare tubes around is never a bad thing.

An attenuator is probably going to more what you're looking for. Sounds like you are going ahead with a fixed resistive load/attenuator?


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## Verne (Dec 29, 2018)

I am and I'm loving the chance to try. My stumbling block is not having the proper pot on hand. I am sooooooo close to success. I do have another thread where I explain more, and getting great responses as well in the pedal forum. I love the wealth of knowledge and advice GC. I still will try another tube as I want to learn all that I can about how things can change, or how they don't.


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## Dorian2 (Jun 9, 2015)

I spent a good amount of time messing with tubes in my amps after joining this forum as well Verne. Well worth the effort and minimal time it takes to feel and hear the different response from other tubes.


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## jb welder (Sep 14, 2010)

I'm getting worried about possible misunderstanding about this attenuator. If it's not the right type you could damage your amp.
Are you talking about something between amp and speaker? If so, it will not be using a regular pot.
Or is this just a 'volume control' that goes in the effects loop?


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## Verne (Dec 29, 2018)

I officially gave up on the volume control. I want one between my pedal board and the amp. That way I can control the volume of any guitar to any amp. I could not get this to work so I scrapped it for now. I'll play with tubes, it's far more straight forward than building something when I am just learning to build. I don't want to run it through FX loop because I want to run it before the amp.


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## jb welder (Sep 14, 2010)

For that kind of application I'd recommend a volume pedal.
If you want to build, keep your eye out for junk/broken wah type pedals. Fairly easy to convert.


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## Verne (Dec 29, 2018)

@jb welder This is pretty much what I was after minus the switch to turn it off. Mine was going to be placed after my board and be on at all times when the board was powered on. This is $33 on Amazon. May go with this instead of mucking around more. I'll do my tube mucking, less work and mess.  (At least until I take a workshop on pedal building)


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## mhammer (Nov 30, 2007)

Verne,

I think one of the notions you need to factor into your thinking is that gain is multiplicative. Huh? If I have a gain stage that amplifies the input 10x, followed by another that amplifies 10x, followed another that does the 10x thing, then I have a total final gain of 10 * 10 * 10 = 1000. So, reducing or increasing the gain of any one of those stages changes the final product. but can also yield the same product. 
6 * 10 * 10 = 10 * 6 * 10 = 5 * 12 * 10 and so on.
Of course, many amps provide attenuation between stages. If my first stage is 20x, then that's clearly hotter than 10x, and 20 * 10 * 10 would get me 2000x, which is a LOT more gain than 10 * 10 * 10. But if I have a volume control after that first stage, then I could turn down the output of that stage before it hits the next one, such that the final product might be not much different than 10 * 10 * 10, or even 5 * 10 * 10.

Amplifiers also differ in terms of where they stick the tone stack. So, if I use a 12AX7 at the input stage, and there are two gain stages before the signal reaches the tonestack, then stage 1 might overdrive stage 2, making more work for the treble control to dial down the harshness.

Going at it from the other direction, tubes amps will often use something from the 12A-7 series for the driver/phase-splitter that pushes the output tubes. Reducing (or upping) the gain of that stage changes how hard the power tubes are pushed, and ultimately how much the power-tube saturation contributes to the sound.

A number of classic amps start with a 12AY7. For instance, the first stage in a 59 Bassman is a 12AY7, followed by two more gain stages from a 12AX7 before hitting the tonestack and then phase-splitter.


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## Verne (Dec 29, 2018)

Awesome. Thanks for such a great explanation and the time it would have taken to write. I will be watching for tubes when I can. I will look for at least one of each 12a-7 and play with what sounds beat to me. If looking at the amp from behind, is V1 the first beside the power tubes, or furthest away? Soooooo much learning.


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## jb welder (Sep 14, 2010)

V1 (circuit wise) is traditionally placed furthest from the power tubes. But it is not a set rule and you may find exceptions.
In your case furthest from the power tubes is V1.


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## PTO (12 mo ago)

Random bump to say I tried this in my Traynor after reading some threads about it on various forums. It definitely reduced gain but didn’t really give me more usable tone. I was wondering if by raising the acceptable volume threshold from say 3 to 6 on the gain knob, I would unlock some more tones, but it wasn’t the case.

In fact, I find that the amp gets too hissy with the master at 5+ with either tube, so the using the 12AU7 gave me _less_ flexibility. It was fun to try it out though. I might consider a 12AY7 at some point, which is a bit less of a departure.


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## Latole (Aug 11, 2020)

I alway use 12AY7, this tube work better than 12AU7 or other.
12AY7 is the best replacement for a 12AX7 / ECC83 .


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## diyfabtone (Mar 9, 2016)

5751's work for me. Any other 12A_7 type is worth a go too. I have a Real Tube 12AX7 OD pedal that I never really liked until I dropped in a 12AU7.


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## Latole (Aug 11, 2020)

diyfabtone said:


> 5751's work for me. Any other 12A_7 type is worth a go too. I have a Real Tube 12AX7 OD pedal that I never really liked until I dropped in a 12AU7.


12AX7 = 100% gain
5751 = 70% 
12AY7 = 45% and it is not too low


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## Paul Running (Apr 12, 2020)

PTO said:


> Random bump to say I tried this in my Traynor after reading some threads about it on various forums. It definitely reduced gain but didn’t really give me more usable tone. I was wondering if by raising the acceptable volume threshold from say 3 to 6 on the gain knob, I would unlock some more tones, but it wasn’t the case.
> 
> In fact, I find that the amp gets too hissy with the master at 5+ with either tube, so the using the 12AU7 gave me _less_ flexibility. It was fun to try it out though. I might consider a 12AY7 at some point, which is a bit less of a departure.


For the 12AU7, try increasing the resistance of the cathode resistor to 2.2K -2.7KΩ for each section; that will bias the tube in the center of the linear region...it may sound more to your liking at 5+ on the MV.


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## loudtubeamps (Feb 2, 2012)

@Verne
In my experience subbing a lower gain tube in the pre amp does indeed suck the life, however.... using at the Phase Inverter can work wonders.
For best results,I would recommend an AU or AY.
The audible difference with subbing an AT in place of the AX anywhere will be minimal.


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