Crate V18: Mods and Conversions

Discussion in 'Amps and Cabs' started by steeve_a, Nov 15, 2008.


  1. steeve_a

    steeve_a Member

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    I've been taking my modded amps to local blues gigs and they haven't been putting out as much power as I would like. Yeah, they are only 18 watts but I think I might try undoing some of my changes in the power section.

    #1. I'd been replacing the 470k EL84 grid loads (R45 and R46) with 220k resistors since that is what is typically used in EL84 amps. It is very critical not to overdrive EL84's with too large of a signal because the sound can get very ugly. (6L6's and 6V6's are much more forgiving!) However it just occurred to me that the signal going into the phase inverter is being limited by IC1-B which is powered by a + and - 14.7vdc supply, which would limit the swing of the output signal significantly.

    Solution #1A: revert the output section to stock (including the 10k grid loads R43 and R44)

    Solution #1B: remove IC1-B and the surrounding circuitry. This could be done by removing R19 and R26 and jumpering the signal around IC1-B. (I'll have to study the board to figure out which copper pads to jumper). I believe that the reverb would still work just fine, although it may be necessary to further attenuate the signal going into the reverb driver chip if the dwell is excessive. That upside to this mod is that the audio signal path would be all-tube, having removed the one solid state buffer stage. And if it doesn't work resistors R19 and R26 could be put back.

    #2. Less is more! In my latest conversion (V33 into Soldano) I am going to be skipping a lot of the parts replacements that I did in my V18, just to see how it works in a stripped-down version of the mods. Rather than try to get everything done in one fell swoop... So I color coded some of the optional steps and will take them only if there is a specific need (like more gain or less gain). The traces on these circuit boards can be reworked only so many times and then you are reconstructing them with jumper wires on the bottom of the board.

    Well, Happy New Year everyone!

    Steve Ahola
     
    Last edited: Jan 14, 2009
  2. Bentheemo

    Bentheemo Member

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    Hey all I have a completely stock V18 and was looking to curb the overwhelming bass with a new speaker, a Green Beret (Greenback clone). Around page two somebody mentioned messing with the electrical aspect to curb the bass. Has anyone else done this? Any other mods recommended to do to a completely stock V18?
     
  3. steeve_a

    steeve_a Member

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    Several people have been pleased with just changing the 33k slope resistor R18 to 100k. That will lessen the lows and mids while boosting the highs a bit. Another simple mod is to replace the first preamp tube (the one closed to the input jack) with a lower gain 12A_7 tube, like a 5751, a 12AY7, a 12AZ7 or for an even bigger reduction in gain, a 12AU7. But that does not specifically curb the bass but rather just lower the gain which many people (like me!) think is excessive.

    HTH

    Steve Ahola
     
  4. Bentheemo

    Bentheemo Member

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    Well what about the reverb is there a must have mod for the V18? I think I get lost in all the options ha
     
  5. steeve_a

    steeve_a Member

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    For all of my V18's (5 of 'em now- I'm hoping that the IRS will let me list them as dependents!) I've been changing out these 3 resistors:

    R37: from 1M stock to 470k
    R38: from 220k stock to 100k
    R40: from 100k stock to 27k

    With those mods (and the stock reverb tank) I like the reverb better than the one on the Peavey Classic 30/50/Delta Blues. But not as much as the reverb on a BF/SF Fender... :(

    In any case, those mods make the reverb usable for me.

    Steve Ahola

    P.S. Here is a technical description of what those parts do in case you want to experiment more:

    R37*** sets the level of the signal driving the reverb springs

    R38 sets the gain of the reverb recovery IC stage (V33/50 already use the correct 100k value here- I suspect that Crate screwed up in using the 220k resistor for the V18)

    R40 sets the input level going into the reverb recovery stage

    *** In my first V18 I thought I would get fancy and replace the 1M resistor with a 1M "Dwell" control (as on the 3 knob Fender Reverbs). It worked great (I put a 120k resistor on the tail to ground so that you could not kill the reverb signal completely) but I usually just kept it set to the 470k position so I skipped the Dwell control on my other V18's and hardwired in a 470k resistor, which you can adjust for your own tastes560k for more drive or 390k for less drive.
     
  6. Bentheemo

    Bentheemo Member

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    Oh wow thanks a lot
     
  7. Bentheemo

    Bentheemo Member

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    Wait what wattage for the resistors?
     
  8. steeve_a

    steeve_a Member

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    I believe that the stock resistors are 1/4 watt carbon film. What I keep around in all values for guitar amps are 1/2 watt metal film resistors which tend to be a bit stronger physically and less noisy. Sometimes it does take a bit of "persuading" to get them to fit in where you removed the physically smaller 1/4 watt resistors...

    Good luck!

    Steve Ahola
     
  9. Bentheemo

    Bentheemo Member

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    Ha thanks a lot. After listening to the sound slips on previous pages I'm highly considering the SLO mod but am afraid it might not be versatile enough. It had amazing bluesy vintage qualities, but can it reach Nirvana distortion? Does it take pedals well?
     
  10. steeve_a

    steeve_a Member

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    The bluesier clips are with lower gain preamp tubes (like the 5751 or 12AY7). For more gain you can use 12AX7's. And it works great with the pedals I've used- you might need to fiddle with the tone controls depending on the pedals you are using. Its like a real tube amp- the stock Crate is kinda like a toy amp... :crazyguy

    Well, that is my experience with the amp mod- your smileage may vary! Omigawd I can't believe I just said that- it sounds like a *******ed Hallmark greeting card! ;)

    Steve Ahola
     
    Last edited: Jan 16, 2009
  11. Bentheemo

    Bentheemo Member

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    Haha. What are the preamp tubes in there now? I'm sorry for being such a bother but I've never done something like this and want to be 200% sure with everything. Does this mod address the stock bass issue or would I have to replace R18 anyway?
     
  12. steeve_a

    steeve_a Member

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    For the clips that I posted I used GT5751M's for all 3 positions, with JJ EL84's. Since then I have replaced V3 (the tube farthest from the input jack) with a GT12AX7M. For more gain you could just use the tubes that came with your amp. I would use the Sovtek 12AX7WB for V1 (the tube closest to the input jack).

    Your choice of speaker will effect your bass response. I do think that the stock speaker is a piece of crap and you ought to replace it with anything you have around that is 8 ohms and can handle at least 25 watts...

    Hope that helps

    Steve Ahola

    With this circuit you really have an entirely different amp
     
  13. Bentheemo

    Bentheemo Member

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    Thanks you've been soo helpful. Your original post with all the editing done is the way you personally found it to sound and work best right? I lost track youve added and taken away so many things haah
     
  14. steeve_a

    steeve_a Member

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    It would be easiest to just follow the drawing:

    http://www.blueguitar.org/new/schem/misc_mod/crate_v18_soldano_conversion-layout.gif

    Most people are skipping the output section mods, the resistors numbered R43 to R46.

    Yes, I did edit the initial post here since that is what someone might see first.

    Good luck!

    Steve Ahola
     
  15. Bentheemo

    Bentheemo Member

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    I have a question although it may seem stupid yet again- I'm confused on the component replaced with jumper( Is that just as it sounds? Component removed then a jumper put in place?) and Im confused with the component highlighted for special attention, what do you do with those components exactly? sorry for being such a bother but I am rather new at this. Thanks in advance
     
  16. eDDyHaTe

    eDDyHaTe Member

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    Hi this is my first post on the gear page forum
    i'm here because i bought a v18 and was wondering what to do to make it better i've noticed that most of you did extreme mods to yours (by extreme i mean messing around with the internal components)
    i would like to try a few myself but i'm just no good with electronic devices
    well anyways i did do some modifications to my v18
    first I put in some new tubes
    V1 = PM 12at7 (made a big difference a huge lost of that bassy sound)
    V2 = Tung Sol 12ax7 (also did some good)
    V3 = at first i left the stock tubes there but after trying a few things i went with another Tung Sol 12ax7

    and the amp sounded pretty balanced
    so i tried putting some mesa boogie el84 to replace the power tubes
    made a huge diffrence it opened up the sound made it more focus
    and i added a celestion seventy 80 speaker i had left from another amp

    got rid of the muddyness i had left
    and now it's a pretty damn good sounding amp
    but i would love to have a more focused overdrive when the gain is cranked up
    i wish i could do something real easy

    well that's about it

    ED
     
  17. zombiwoof

    zombiwoof Supporting Member

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    Well, we're right in the middle of a big thread about extensive mods, but I'll say that other than tube/speaker/reverb tank upgrades, I don't think you have to do any other modding to the amp to make it sound good. All of these mods are fine, but I think they are all aimed at making the amp into something different. Right now, I've got a made-in-England Celestion V12-60 Silver Series speaker in mine, and have done tube swaps, and I think it sounds great now. I probably will still try some more tube swaps to try out different tubes I have, but at this point I have a nice old Raytheon long black plate 12AX7 in V1, a Groove Tubes 5751M in V2, and a vintage 12AT7 in V3. If I were you, I'd get that 12AT7 out of V1, a 12AT7 is not meant to be used in a gain position, you already found out that it sounds a bit thin. Try a 5751 instead, it has about the same gain but is great in the V1 position. The GT one is excellent, or try to get a couple of different vintage ones, I got a bunch of NOS and ANOS preamp tubes from Ebay for very little money. Actually, I would try that Tungsol in V1 and put a 5751 or 12AY7 in V2. I tried an EH 12AY7 in V1 (it was all I had), and it also thinned out the sound too much for me, but it sounded better in the V2 position. My recommendation is to try each of the following combos:

    V1 12AX7 - V2 5751- V3 12AT7, or...
    V1 5751- V2 5751 - V3 12AX7 or 12AT7, or...
    V1 5751 - V2 12AY7 - V3 12AX7 or 12AT7

    I have found that having a lower gain tube in V2 works better than in V1.

    With the combo I used, I can run the bass control up around 4 no problem. I also would get any Sovtek 12AX7WA or WB out of there (that's what came in the amp) they are just mediocre sounding tubes. I pulled mine and sold them on Ebay for $15 for all three in one day.

    I ended up using a 12AX7 in V1 for the simple reason that there are a lot more choices in AX7's out there to choose from then 5751's, and the Raytheon and a black plate RCA I also had sounded too damn good to leave out! Putting the lower gain tube in V2 brings the humongous gain down to a reasonable level, and V1 has more effect on the tone.

    I'm just going to get the Accutronics reverb tank and be done with it, I think this is a great amp with a few tweaks like this, it isn't going to sound like a Fender or something else but it sounds really good!

    No offense meant to Steve A. or the others who are doing extensive mods, I would just like to offer the opinion that it isn't really necessary to make this amp sound good.

    Sorry for the long post,
    Al
     
  18. zombiwoof

    zombiwoof Supporting Member

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    I guess I made a mistake about the 12AT7 you put in V1, you actually said you liked it, but I'll stand by my opinion that you are better off putting a good 12AX7 or 5751 in that position, and adjusting the other two tubes to taste. It might get you closer to what you're looking for. 12AT7's are by design driver tubes, they are different than other 12*** types and will usually not sound the best in gain positions.

    Al
     
  19. steeve_a

    steeve_a Member

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    "Component is replaced with jumper" means exactly what it sounds like. The "special attention" is left over from a different drawing and doesn't mean much here. For the R11 100k plate resistor you do add a 0.001uF in parallel. R29 and R32 are highlighted in orange just in case I decide to replace them later so you can ignore that.

    Steve Ahola
     
  20. turtleheadblues

    turtleheadblues Supporting Member

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    Ive got a new v18 2x12 combo if anyone needs one.
     

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