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  1. #1

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    Hey all,

    I am thinking about swapping out the V1 12AX7 in my Hot Rod Deville for a 12AY7 in order to get a bit more play on the volume knob. I mainly use this 65 watt tube monstrosity for home playing, and can barely get the volume to 2 before the neighbour's giraffe starts to panic.

    1) Will the swap have the desired result? (More usable volume range)

    2) Are there any downsides to doing this?

    Thanks!
    Jay

    'boobadoobadoobaooababop!'

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  3. #2

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    yes

    no


    cheers

  4. #3

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    Here's a gain chart for the 12a?7 type tubes. Other options are a 5751 and 12AU7. Start with a 5751 or 12AY7, if you need more gain reduction try the 12AU7. These tubes won't turn you're 65 watt amp into a low power bedroom amp, but it will help tame it a bit.

    Another option is to put a volume control in the effects loop (preamp out & power amp in). If you have a graphic EQ pedal give it a try in the loop to reduce the volume and tweak the tone a bit to compensate for any tonal changes (i.e. boost the mids or upper mids for a 'loudness' effect).
    Last edited by MaxTwang; 07-07-2016 at 01:00 AM.

  5. #4

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    I put both an AY7 and an AU7 in the V1 of my old silverface Bassman, not to reduce distortion -- because the damned thing wouldn't distort -- but because both tubes, to my ear, seemed "rounder". I settled on the AY7, a VOS Sylvania, to help tame the amp's sharpness. The stock AX7 was just too crispy in that amp.

  6. #5

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    Thanks, guys... I'll start a-swappin'!
    Jay

    'boobadoobadoobaooababop!'

  7. #6

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    You can't hurt anything, just try and see if you like it!

    I tried with my Blues Deluxe and yes, it does give you more play on the volume knob but you will also loose overall volume.
    Jazz, Funk, Soul & Boogaloo: My group | Listen to Hip Jazz a Go Go! | Jazz, Soul, Blues: Eva La Voix

  8. #7

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    12AX7 Family Tube Substitution

    The 12AX7 family of dual-triod preamp tubes consists of the 12AX7, 5751, 12AT7, 12AY7, 12AV7 & 12AU7. These are all pin compatable with one another, the only differences being the gain factor of each tube. A common substitution is to replace a 12AX7 with a 5751 or a 12AT7 to tame a preamp that tends to overdrive too easily, allowing you to get a better 'clean' sound out of your amp.
    Tube Gain Acceptable Substitutes
    12AX7 100 5751 12AT7 12AY7
    5751 70 12AX7 12AT7 12AY7
    12AT7 60 5751 12AY7
    12AY7 45 5751 12AT7 12AV7
    12AV7 41 12AY7 12AU7
    12AU7 19 12AV7
    It is important to note that the above is not carved in stone and basically any of these tubes can be substituted for any other. You can always replacing a higher-gain tube with a lower-gain tube, using your ears to tell you whether this was good idea or not. As example of this, my Fender Pro Junior amp came stock with two 12AX7 tubes - one for the preamp and one for the inverter. I have since re-tubed it with a 12AU7 in the preamp stage and a 12AT7 for the inverter. The 12AU7 in the preamp gives a nice clean sound, and the 12AT7 inverter helps prevent overdriving the power amp.

  9. #8

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    You will like the results of the swap to a 12AY7 in terms of tone, but realistically, that amp will still be a beast for home use and you will still wake up the neighbors giraffe at a volume of 2. I made the same change on a 40 watt Blues Deluxe, and 2 was still plenty loud, it just sounded better.

  10. #9

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    I have built bunches and bunches of amps. Many of them were Fender circuits. The substitutions noted above all work well.

    The 12AY7 is a particularly good V1 sub for the 12AX7. It is a great taming device that also yields a very sweet result.

    The chief differences you will likely notice will be in the 4-7 range of your volume control, where the distortion will be less and the overall volume will be noticeably lower. At the lower, cleaner volume levels, you will notice a sweeter, rounder tone...things will get more "Fender-y."

    One of the things I like is amps that use linear taper volume pots. The volume isn't all squished down into the 1-5 range. Half-way on a linear pot is half power, etc. Amps like Polytone use linear taper pots. In Fender amps, only the Showman, IIRC, employed a linear taper volume pot. That's why the Showman seemed, unlike most other Fender amps, to not convert into distortion by a volume setting of 4-5.

    Unfortunately, with the Hot Rod DeVille you have to exercise skill with soldering in order to swap potentiometers without putting enough heat to the circuit to lift the copper traces from the circuit board. If you have done board-level work on computers, you have skill enough to do this.

  11. #10

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    Quote Originally Posted by 999369 View Post
    ...It is important to note that the above is not carved in stone and basically any of these tubes can be substituted for any other. You can always replacing a higher-gain tube with a lower-gain tube, using your ears to tell you whether this was good idea or not. As example of this, my Fender Pro Junior amp came stock with two 12AX7 tubes - one for the preamp and one for the inverter. I have since re-tubed it with a 12AU7 in the preamp stage and a 12AT7 for the inverter. The 12AU7 in the preamp gives a nice clean sound, and the 12AT7 inverter helps prevent overdriving the power amp.
    I did this as well. The only issue that I have is that there is volume bleed with the volume pot turned all the way down. I don't think that the tube swap made that happen as I have changed the output transformer and had Fromel do their mods - it could be a whole host of other things I suppose. Very quiet, clean, and expansive amp now. I assume that the volume bleed is nothing to worry about.

  12. #11

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  13. #12

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    just to clarify-

    in the v1 12ax7 position..the 5751 or 12ay7 are considered to be the best substitutions...the 12at7 and 12au7 while indeed having less gain also affect other tonal parameters..the latter 2 are actually more "cousin" tubes than "brothers" to the 12ax7

    in the phase inverter tube spot, the subbing between the 12ax7 and 12at7 is far more common and far less invasive to tone

    start with 5751..which cuts gain by 1/4...if it's still not enough, then go to 12ay7 which cuts gain by a little more than 1/2


    also in regard to the overall volume of the amp with these substitutions..the difference is not that marked, in pure db..as the extra gain of the v1 will contribute more to the distortion of the amp than actual volume...ie. set an amp volume on 7 and its a certain db output..gun it to 10 and it's usually around the same db output but grindier sounding..since the power tubes are still putting out the same wattage, but you are just hitting them with a bit more

    cheers
    Last edited by neatomic; 07-07-2016 at 07:57 PM. Reason: cl-

  14. #13

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    Awesome, thanks again for all of the info, folks. I'm pretty clueless when it comes to tubey stuff, and electronics in general. I don't have much hope to turn this beast into a genuine bedroom amp, but I quite like it, so anything I can do to tame it is helpful.

    I'll give the 12AY7 a try, and it sounds like the linear taper volume mod might be something to consider down the track.
    Jay

    'boobadoobadoobaooababop!'

  15. #14

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    NOS 5751 sounds sooooooooo good

  16. #15

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    i think it very much depends on the exact tube you put in there. i used to do this sort of thing all the time because i play lower wattage amps, but ultimately against it. it shifts the point where your amp starts distorting, but in a lot of cases, it shifts the point of where your amp starts sounding interesting, or good. i would have to crank the amp up louder with a less gainy tube to get a nice sound, which, for my indoor playing, sort of defeated the purpose. it just sounded dull, flat and just kinda sat there at lower volumes, and i kept compensating with more volume or some boosts/overdrives to give it a little life.

    that aside, a great sounding tube is a great sounding tube, and i've used various random nos 5751s and such with great success. i actually use a couple of those in my 100 watt monstrosity. they transformed the clean channel from garbage to usable, and often pretty. they also extended the shades and range of gain available, but they lowered the overall amount of gain available. i'm generally ok with the trade off.

    so i'd say give it a shot. try to get a nice one and see what it does. you may like it, you may not. you may find a use for it somewhere else (some of my unliked disused tubes sound amazing in a pedal).

  17. #16

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    I've changed the 12AX7 with 12AU7 in my Micro Terror, and guess what? Seems great now even for jazz sessions!

  18. #17

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    If you attach a lot of importance to the currrent sound profile of your amp, an outside solution coudd be a Tone King Iron Man II attenuator. Not cheap, but it will allow you to push the volume knob up - giving you the usual breakup up or distortion from your tubes - whilst keeping the sound level delivered through the speakers low.

  19. #18

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    OK, this thread missed the most important thing. Your neighbor has a giraffe?
    Beauty is as close to terror as we can well endure. -Rainer Maria Rilke

  20. #19

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    Relative gain chart for 12A type tubes that you may find useful

    Tube Question: Swap 12AX7 for 12AY7?-12ax7chart-jpg
    Regards,

    Gary

  21. #20

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    Speakers can also have a great affect as well. But make sure they can handle 100 watts of power.

  22. #21

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    Quote Originally Posted by MaxTwang View Post
    Here's a gain chart for the 12a?7 type tubes. Other options are a 5751 and 12AU7. Start with a 5751 or 12AY7, if you need more gain reduction try the 12AU7. These tubes won't turn you're 65 watt amp into a low power bedroom amp, but it will help tame it a bit.

    Another option is to put a volume control in the effects loop (preamp out & power amp in). If you have a graphic EQ pedal give it a try in the loop to reduce the volume and tweak the tone a bit to compensate for any tonal changes (i.e. boost the mids or upper mids for a 'loudness' effect).



    I salute you, Sir!

  23. #22

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    The gain in any amplifier, tube or solid state, circuit is mostly determined by the circuit design.

    If a circuit is designed for a lower gain than the max, most are, subbing a lower gain device may or may not have any effect.

    The lower gain device may be pushed to or beyond it's limits.

    Without studying the circuit I would not be comfortable swapping the device, unless a swap chart indicated otherwise.

  24. #23

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    Quote Originally Posted by BBGuitar View Post
    The gain in any amplifier, tube or solid state, circuit is mostly determined by the circuit design.

    If a circuit is designed for a lower gain than the max, most are, subbing a lower gain device may or may not have any effect.

    The lower gain device may be pushed to or beyond it's limits.

    Without studying the circuit I would not be comfortable swapping the device, unless a swap chart indicated otherwise.
    In the HotRod and Blues-series amps it’s no problem, you can easily swap them out.

    Very old thread btw!
    Jazz, Funk, Soul & Boogaloo: My group | Listen to Hip Jazz a Go Go! | Jazz, Soul, Blues: Eva La Voix