Blues Deluxe + 12AT7 = ?

NomadNomad Frets: 549

On going through some boxes, I found a 12AT7 / ECC81. It's branded Sylvania on the box, and marked as made in USA on the box and on the valve. Looks unused.

If I were to stick this in my Blues Deluxe RI, what effect would it have in which valve position? Would I need to change any of the circuit elements around the valve?

The amp's used at home only, low volume, no attenuator.


Nomad
Nobody loves me but my mother... and she could be jivin' too...

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Comments

  • earwighoneyearwighoney Frets: 3491
    edited June 2018
    The 12AT7 can be used in a FBD, and it's usually used in the Phase Inverter position which is the V3 slot. 

    I myself have one in my FBD and I prefer it to the stock 12AX7 tube.  
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  • NomadNomad Frets: 549
    What difference would you say it makes?

    Nomad
    Nobody loves me but my mother... and she could be jivin' too...

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  • ZoolooterZoolooter Frets: 886
    Less gain
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  • NomadNomad Frets: 549
    Zoolooter said:
    Less gain


    Which, unless I'm missing something, would mean that the output valves don't get driven as hard, which would amount to no real difference in a home-use amp that's nowhere near driving the output valves anyway. I guess that would mean the volume controls would have to go up a bit more to get to the same volume, which is potentially a plus.

    So, no 'opening up of the tone'? No 'sounds like a Twin'? No snorting pixie dust off of corks? :)

    Nomad
    Nobody loves me but my mother... and she could be jivin' too...

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  • ICBMICBM Frets: 71960
    V1 - lower gain, brighter clearer tone (some can find it a little 'cold') and a slightly more useful range on the clean channel volume control.

    V2 - not very useful in my opinion, but won't do any harm to try it. Lower gain, but a 'thinner' sound.

    V3 (phase inverter) - clearer, more 'open' tone, slightly more bottom-end depth.

    Personally, I prefer it in V3, a 12AY7 in V1, and a 12AX7 in V2.

    There shouldn't be any issue with surrounding components, although it will load the plate resistors a little more heavily - it's not impossible that one could fail earlier than it would otherwise, but it's rare. Fender did have a batch problem with the PI plate resistors in these and early Hotrod amps, but I haven't seen a dead one for some time now.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • jpfampsjpfamps Frets: 2723
    ICBM said:
    V1 - lower gain, brighter clearer tone (some can find it a little 'cold') and a slightly more useful range on the clean channel volume control.

    V2 - not very useful in my opinion, but won't do any harm to try it. Lower gain, but a 'thinner' sound.

    V3 (phase inverter) - clearer, more 'open' tone, slightly more bottom-end depth.

    Personally, I prefer it in V3, a 12AY7 in V1, and a 12AX7 in V2.

    There shouldn't be any issue with surrounding components, although it will load the plate resistors a little more heavily - it's not impossible that one could fail earlier than it would otherwise, but it's rare. Fender did have a batch problem with the PI plate resistors in these and early Hotrod amps, but I haven't seen a dead one for some time now.
    I think the problem with PI anode resistors was more to do with the voltage compliance only being 350 VDC rather than a batch problem.

    The Deville had more problems with this, and higher voltages (made worse by the 230 / 240 V wiring issue yawn..........).

    Fender now use a higher rated resistor.

    I've found 12AT7s to be prone to microphony in V1.
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  • ChuckManualChuckManual Frets: 692
    ICBM said:
    V1 - lower gain, brighter clearer tone (some can find it a little 'cold') and a slightly more useful range on the clean channel volume control.

    V2 - not very useful in my opinion, but won't do any harm to try it. Lower gain, but a 'thinner' sound.

    V3 (phase inverter) - clearer, more 'open' tone, slightly more bottom-end depth.

    Personally, I prefer it in V3, a 12AY7 in V1, and a 12AX7 in V2.


    This is exactly how I've set up my Blues Jr.  Sounds great.
    Not much of the gear, even less idea.
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  • ICBMICBM Frets: 71960
    jpfamps said:

    I think the problem with PI anode resistors was more to do with the voltage compliance only being 350 VDC rather than a batch problem.

    The Deville had more problems with this, and higher voltages (made worse by the 230 / 240 V wiring issue yawn..........).

    Fender now use a higher rated resistor.
    Oddly enough I don't think I've ever seen it on a Deville. Small sample randomness probably...

    Whatever it was, they've fixed it now anyway - something Fender have been pretty good at with this series, unlike many other companies who seem to just rip up a design and start again, rather than fixing it.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • ZoolooterZoolooter Frets: 886
    Nomad said:
    Zoolooter said:
    Less gain


    Which, unless I'm missing something, would mean that the output valves don't get driven as hard, which would amount to no real difference in a home-use amp that's nowhere near driving the output valves anyway. I guess that would mean the volume controls would have to go up a bit more to get to the same volume, which is potentially a plus.

    So, no 'opening up of the tone'? No 'sounds like a Twin'? No snorting pixie dust off of corks? :)

    I changed to a 12AY7 and 12AT7 in V1 and V2 in a 12w 6V6 amp, and it made a big difference for playing at home. Perfect in fact, coupled with an inefficient speaker. It previously had 2 12AX7.
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  • NomadNomad Frets: 549

    Sounds like V3 is the way to go (can't think of a reason to reduce the preamp gain, or make the sound thinner).

    Regarding the anode resistors on the PI, the amp is from 2013, and my 2004 schematic shows them as 0.5W. Don't know if they have been upgraded since the schematic.

    Am I right in thinking that they need to dissipate about 0.25W with a 12AX7, and more like 1W with a 12AT7? Do they dissipate this/whatever all the time (ie, not signal dependent)?


    Nomad
    Nobody loves me but my mother... and she could be jivin' too...

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  • NomadNomad Frets: 549
    Nomad said:

    Am I right in thinking that they need to dissipate about 0.25W with a 12AX7, and more like 1W with a 12AT7? Do they dissipate this/whatever all the time (ie, not signal dependent)?

    No, 0.025W (and 0.9W for the 12AT7). Does it really change that much?


    Nomad
    Nobody loves me but my mother... and she could be jivin' too...

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  • DJH83004DJH83004 Frets: 196
    I wouldn't get overly hung up about the maximum values from the datasheet, it is the in-circuit design that counts, and basically 1/2 watt anode resistors are generally fine for any of the range of valves you are considering, it is when manufacturers drop down to 1/4 watt that there can be issues. FWIW,  I struggle to hear any tonal difference when swapping valves in the PI position, but then again my hearing is pretty shot after all these years in this game  :)      
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