Tube amp 'mods'- Are there any that are worth it?

Discussion in 'Amps and Cabs' started by StevoDOD, May 27, 2008.

  1. StevoDOD

    StevoDOD Member

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    I stumbled across this mod for my Carvin amp: http://trujeque.com/x_mod.html

    and was wondering if amp mods are worth it. I don't want to compromise reliability but would like a distortion with less mud and more 'bite' or sustain/punch.

    Are 'modded' amps worth less? Are they less reliable?

    Thanks,

    Stevo
     
  2. mooreamps

    mooreamps Senior Member

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    I think it's going to depend on what the amp is, and what the mod is. It's no secret I've done about a dozen valve junior mods over the last couple years, and I'm not talking about anything from "Bitmo" or the like. On the other hand, I've talked with my friend Maurice about upgrading his Laney combo amp, and he would rather keep it stock. He is concerned that any mod's would devalue the amp. However, instead of modding his Laney, he has signed a contract with me to design and build him a 10 watt Jazz combo amp loosely based on my model-10 guitar amp.

    In this area, you may need to do some more research and determine which mod's are worth while, and there are many upgrades that are worth while, and distingush from the mod's that are just not worth having.

    -g
     
  3. mbetter

    mbetter Member

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    Mods by "names" can be sold by reputation. Mods by no-names usually can only be sold by what they sound like, e.g. locally.
     
  4. StevoDOD

    StevoDOD Member

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    Anyone try to do the mod in my initial post?

    Stevo
     
  5. mbetter

    mbetter Member

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    First, the name "Dan Torres" doesn't do anything for me. I have no personal experience but I've heard horror stories.

    Second, the first mod is just a resistor swap. My first thought was to stick a trim pot in there.
     
  6. StevoDOD

    StevoDOD Member

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    Mbetter,

    Can you tell me what you meant by 'stick a trim pot in there?'- I'm electronically challenged!

    And would a resistor swap do anything?

    Thanks,

    Steve
     
  7. mbetter

    mbetter Member

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    First off, I don't really know anything about the insides of tube amps. Well, I know that there are quite a few ways to get killed if you don't know what you're doing. I mainly mess around with pedals and stuff like that.

    A trim pot is pretty much just a variable resistor. There's a little slot where you can stick a screwdriver in and turn to change the resistance of the pot. So if you get a 2k trim pot in series with a 1.5k resistor and wire the whole thing in in place of the 3k3 resistor in R2 currently, you'd have 1.5k ohms (the mod value) at one end of the pot's range and 3.5k ohms (pretty close to the stock value) at the other end. You could get any value between the two then and see what sounds best.

    Another, simpler idea is to get a (if my calculations are right) 2750 ohm (or thereabouts) resistor and wire it in parallel with the resistor in there now. That would work out to a total resistance of around 1.5k ohms. You could do that with alligator clips probably so you wouldn't have to commit to it at all.

    Again, you should find someone who knows what they're doing in these matters because there can possibly be lethal voltages in a tube amp even when it's turned off.


    Oh and I don't know how this mod is supposed to work so I have no idea if it would do anything.
     
  8. edward

    edward Supporting Member

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    These types of mods are in the ears of the beholder: some love them (maybe the guy who "discovered" it). to others, it is dubious at best. If you feel comfortable trying it yourself, go for it ...only you could decide whether the tonal change is worth it. But if I were to pay to have it done, I wouldn't. Just not enough there to drastically change its voice, IMHO. You're better off experimenting with speakers if you're looking to change how she sounds (but still wanting to keep it).

    Edward
     
  9. StevoDOD

    StevoDOD Member

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    Gents,

    Thanks so much, I appreciate all the info. I'm learning a bunch, just sorry I got into dialing in my sound so late in the game.

    Blessings,

    Stevo
     
  10. Janglin_Jack

    Janglin_Jack Member

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    I am not familiar with that amp design, but it appears the changes are to the cathode resistors and one of the plate resistors. This changes how the preamp tube stage is biased and how much gain/distortion there is.

    All the changes noted will yeild more gain. I am not familiar enough with the schematic to determine if these changes are good or not. If you are careful and know how to solder, you can try them one at a time and see what you like.

    BE SURE YOU KNOW WHAT YOU ARE DOING INSIDE AN AMP SO YOU DON'T KILL YOURSELF!!!!:munch

    Jack
     
  11. case4bass

    case4bass Member

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    Read Dan Torres and Gerald Webber's books. They have lots of tips about modding
    old fenders. Ignore all hearsay.....Dan's books are easy to understand and you can find many articles By Gerald in old vintage guitar issues.
     
  12. epluribus

    epluribus Member

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    Tube amp mods...worth it? Yeah, tons, presuming you know enough about the mod to dial it in for your ear and your hands. Trouble is, it's a rather dark art at best. Neither difficult nor insurmountable, but it'll take some learning.

    Does it depress the value of the amp? IMHO, generally yes. A prospective buyer has no idea if the mod was done well or not, or what it means to the longevity of the amp. Besides, the more you mod, the less the original schematic means--uncharted waters for a tech. All that said, all you gotta do is un-mod the mod before you put it up for sale--provided you un-mod correctly.

    How to learn this stuff...read the Amp Tech forums here a lot. Learn to read schematics as well, and find some amps similar to yours--then you can read what those owners did to their amps. If you've not done so, get some basic electronics under your belt so you have an intuitive idea of what the juice is doing--Navy NEETS is a comprehensive training course that's free online. And definitely above all, don't even pull that chassis till you're dead sure you know how to work safely--big volts even unplugged!

    Sounds like a lot, and it is, but that's what'll get you from the sound in your head to a circuit that sings it. Caution: addictive hobby. :)

    --Ray
     
  13. Austinrocks

    Austinrocks Member

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    really depends on who does the mod, and if the buyer sees that mod as desirable, the omega mod is one I got for my fender hot rod deluxe, Jim Price only mods hot rods. The mod has greatly improved the amp, especially with drive channels tone, which went from harsh to great tone. One issue you need to be aware of the mod will void the warrant, Fender has a 5 year warranty, so if I have problems with the amp probably have to send it Jim Price for repairs, but for $250 for the basic mod, and $125 for the pedal mid and preamp boost, its a reasonable price on a very easy to get amp.

    http://www.omegaamps.com/mods2.html

    there are mods you can do that wont effect the warranty

    1) power tubes, my mark iv and hot rod deluxe use 6v6s, the JJs 6v6s handle the higher plate voltages that the other 6v6s wont, this does cut the power in 1/2 and you need to use a lower impedance tap, 4 ohms for the stock 8 ohm speaker in both my amps, a dummy plug in my hot rod deluxes external speaker jack gets that, so its really easy to go back and forth, the bias was right when I did that. The 6v6s have a sweet bubbly tone, that gets very addictive.

    2) preamp tubes these can really change the tone of the amp, just remember to get a balanced tube for the drive, want both power tubes to be equally driven. I tryed different tubes in my hot rod deluxe, the 12AT7 and 12DW7 are lower gain tubes than the 12AX7, which does get the volume down and the amp cleaner, however the hot rods have a 6 dB attenuator on input 2, which does the same thing, perfect for bedroom and practicing and I really hate giving up range in an amp, the gold pin JJs ECC83S got me a marshall like tone when I put them in V1, V2 and V3, really suprising that would do that, and my DSL401 really became reduntant. The standard pin ECC83S are the fender tone tubes put those in V1 and V3, clean channel and driver of the hot rod, also have those in my mesa mark iv, left the gold pin version in the driver channel since its so perfect there. Played with other combinations generally found that long plate preamp tubes have microphonic problems in the amp, so would avoid them, mine were the JJs EC803S, both standard and gold pin versions,

    3) reverse the polarity of the speaker, usually gets much better bass and better tone, done this on all my amps with great results, its easy to reverse in most cases, I do check with a 9volt battery, I want the speaker to go backwards when the 9 volts is applied, most go forwards. Such a simple thing not sure why most amp builders don't do this, I have noticed some JBL speakers have the polarity reversed at the pins.

    4) bias a simple cheap multimeter can really help with the tone of the amp, my hot rod deluxe's factory bias point, 60mV really was the worst tone point on the amp, slightly underbiased the amp really cleaned up and the headroom increased. Over bias the amp got a great distorted tone, left mine a round 75mV, about the highest I really want to go, not all tubes can handle much higher, but its an easy way to get the tone you want in the amp, just get a multimeter so you know what your doing, biasing while blind not a good idea.

    eurotubes is a good resourse, tubes and biasing videos.

    http://www.eurotubes.com/index.htm

    the JJs tubes work well for me, can not say that for a lot of the other tubes.
     

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