Crate V18: Mods and Conversions

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


  1. echale3

    echale3 Member

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    I prepped a list of the components needed to do the SLO coversion.

    However, being a neophyte at electronics (I can run a soldering iron just fine, rewiring a guitar is no problem, and I can solder components on a PCB w/o any problem), I have a few questions. THey are probably pretty basic, but, like I said, I'm new at this.

    What is the wattage of the resistors I'd need to do the conversions? Are carbon-film resistors OK to use? Radio Shack has a wide assortment of 1/8 watt, 1/4 watt, and 1/2 watt value packs for cheap, if any of those wattages would be suitable.

    Is there a particular type of cap needed for the ones being replaced? Are the necessary voltage ratings for the cap marked on the side of it or what? Is replacing polarized caps with non-polarized caps of the same voltage value OK or is it a bad thing?

    Thanks in advance,
    Carroll
     
  2. steeve_a

    steeve_a Member

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    Your list disappeared from the post but was on my email so I added it back in.

    If you look at the board you will find resistors of various sizes. Furthest from the controls, the two 220k and 2k2 resistors are 1 watt. For all of the other resistors I used 1/2 watt 2% metal film resistors available at all of the local electronics parts houses. If you want to use the carbon film resistors that Radio Shack uses, go for it. I would recommend 1/2 watt because they are rated for something like 350 volts (the smaller ones aren't).

    The 1uF caps I used are all poly caps, with a voltage rating of at least 50volts. I think that they sound much better than the 1uF electrolytic caps that are much easier to find. The .001uF, .002uf and .02uF caps are poly caps rated at 630v cap. For the 120pF cap I get the 1kv ceramic caps available from local electronics parts houses.

    You should be able to get all of these parts from Mouser Electronics if you can't find them locally.

    HTH

    Steve Ahola

    P.S. Just a reminder that the parts in Orange are already on the board so you don't need to buy them.
     
  3. wagdog

    wagdog Member

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    Good to hear! I'm going to give it a stab soon. I have to order some caps as my junk box doesn't have too many high voltage caps left.

    I can understand where you're coming from. I kinda like to get the most bang out of the amp as possible, and the mods I have in mine really do make the amp sound good. I liked your clips though, so I figured I'd try that out. I don't really have the skills to make drastic changes like you've done. Little changes here and there I understand and can either base my work of what others have done or figure out for myself, but what you've done here is beyond my skillset at this point. I do appreciate you sharing your work though, very much so!


    Would love to see what you come up with. My v33h sounds pretty damn good now too with the changes I made (pretty much similar to what I did with the v18). I did replace the v33 reverb with an accutronics because for some reason it sounded even worse then the v18's. The v18 is actually usable as long as I don't turn it up past 1.
     
  4. echale3

    echale3 Member

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    Cool, thanks for the tips and advice, Steve.... I think I really need to find a good book on amp design and electronics, and figure out how and why this stuff works... The electronics stuff I learned in my Physics courses at the university was very basic, and didn't go much deeper than being able to calculate resistance, Henries, and step-up or step-down levels...
     
  5. steeve_a

    steeve_a Member

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    On one hand there is the Dan Torres book, with lots of tips and tricks, but many people question his grasp of electronics theory. On the other hand there are the Kevin O'Connor books which dig very deep into theory. I have found the Aspen Pittman book to be very helpful with its extensive collection of schematics.

    Unless you are going to design guitar amps, the tricks might be more helpful than the deep theory. Although I do think it is good to know enough about the theory to understand what you are doing with the tricks.

    You can learn how to set the bias for the preamp tubes (which is determined by the plate and cathode resistors) but that doesn't necessarily make the amp sound better.

    There are a lot of on-line resources available. Check out the technical reference articles at Randall Aiken's site:

    http://www.aikenamps.com/

    R.G. Keen usually provides plenty of theory along with his projects at his GeoFex site (be sure to check out his page on troubleshooting problems with guitar amps!) :

    http://www.geofex.com/

    Many posts saved from the old AMPAGE forum with tips and tricks as well as theory:

    http://www.blueguitar.org/new/text/


    And don't forget Ken Fischer's Trainwreck Pages!

    http://www.blueguitar.org/new/schem/trainwreck/the_trainwreck_pages.pdf


    Good luck in your studies- maybe when you get this all figured out you can come back and explain it to me!

    Steve "Flying by the Seat of my Pants" Ahola
     
  6. echale3

    echale3 Member

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    Well, I got on Mouser's site, and was able to find everything I needed in-stock, with the exception of the 1-watt 220K resistors. They do have a 2-watt 220K resistor in stock, which should be a suitable replacement, I'd hazard a guess.

    Anyway, it looks like, for about $25 (shipping included) in parts and an hour or two worth of disassembly/soldering/reassembly, a Soldano SLO OD channel clone could be mine......

    My finger is poised over the "buy" button on the Mouser website :dude

    Thanks for the advice on amp theory and tricks, as well as the development and schematics you did!
     
  7. steeve_a

    steeve_a Member

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    Yes, the 2 watt resistors will work fine. Usually you can move up to a higher wattage but sometimes the larger physical size can be a problem. For these resistors there is plenty of room and be sure to suspend them up from the circuit board at least 1/2" like the stock parts.

    A few more notes on the Soldano mod: I tried replacing the stock 250k Volume and Gain pots with 1M and 500k but they made the amp get too loud too fast. And I think that I like the amp better without the jumper across C16 and R22. I was also thinking of cutting the overall gain through the preamp by replacing R15- maybe going down to the stock value of 100k or maybe to 220k. I may decide to put a trim pot in temporarily to figure out which value works best. (This particular V18 smells like it was stored in a barn! There seemed to be some corrosion inside the chassis and the traces seem to be flimsier than the other two V18's I've modded. So I hesitate to do too much more soldering and desoldering on it...)

    Steve Ahola

    P.S. Give yourself plenty of time to do this mod. If you rush while desoldering the resistors you can pull up the traces. So take it slow and double-check all of your solder joints with a DMM. I'd figure maybe 4 hours total for the Soldano mod- 5 or 6 hours for the other mods because there is more work and I'd replace a few of the pots (it takes me about 20 minutes to file and cut the shaft of generic pots to use in the V-18).
     
    Last edited: Dec 10, 2008
  8. scihibmxer@juno

    scihibmxer@juno Member

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    MF was down to just v18-212 and v50-112, so we picked up another v18, likely going with a rocket type mod on this one, and a v50. The v50 was quite disappointing, lack luster sound. So what do you think about a conversion of the v50 to a 6v6 power amp?
     
  9. steeve_a

    steeve_a Member

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    So does the Clean Channel have a lackluster sound, too, or just the OD channel? With Bo Diddley playing one, I figured it HAD to be good... :banana

    It looks like you have 400+ vdc going to the plates, which would be a little high for 6V6's. And the amp does use fixed bias with an adjustment pot- but I think you would have to revise the bias circuit to work with 6V6's.

    For starters you might try replacing the 12AX7's with lower gain varieties (I like the Groove Tube 5751M's but NOS 12AY7's are also nice). I think that the suggested mods for the V33 should work on the OD channel of the V50 once you figure out the reference numbers.
     
  10. scihibmxer@juno

    scihibmxer@juno Member

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    The comparison was the clean channel in the v50 to the clean channel of a v33h, using the same stock speaker. From the schematics these preamp channels look identical, whereas the v50 OD channel is missing the cap jumper on v1b (if schematics are correct!). This was at basement volume, with just one guitar. Maybe stage volume would be different.

    But we found the new v18-212 out of the box sounds better than the earlier v18-112 when it was stock. The bass tone control had little to no effect on the earlier v18, on the new one it is responsive. The stock 33k slope resistor was replaced with a 100k on it, and now it is very responsive. So maybe there was a bad solder connection on the earlier v18???

    PS: The stock speaker didn't sound too bad with the clean channel on the v33 head.
     
  11. steeve_a

    steeve_a Member

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    FWIW of the 3 V18-112's I've received so far, one actually sounded pretty good right out of the box although the circuits on all 3 looked identical. Go figure! :dunno

    At least in my experience the bass control goes from "about right" at 0 to "way too much" at 5 to "Geez Louise, get a room!" at 10 so there could have been a bad solder joint on your older V18-112. I believe that they use wave soldering techniques in the factory in China (dipping the bottom of the board into molten solder) and presumably do some sort of basic QC. The amp seemed to work so they shipped it out. (I doubt that they try adjusting the controls very much during their tests.)

    In one of my V18-112's two of the large resistors mounted off the board were bent close enough together for them to arc and damage the associated output tube. This was in a factory sealed box. It's probably a good idea to remove the back cover and do a quick visual inspection before firing these amps up for the first time. A short circuit like that could burn out a resistor or IC and it might not be that easy to track it down.

    Steve Ahola

    P.S. The 47pF cap from the plate to the grid of V1b on the V18 and V33 schematics would cut the highs a bit and possibly help with oscillations (although I would usually put it from the plate to the cathode for that). I don't think it would be a big difference in the sound. You might want to see how the 6L6 tubes on your V50 are biased- if it is set very low ("cold") that could make it sound duller. Cathode biased EL84's are going to sound different from fixed biased 6L6's so that might be the difference.
     
  12. JPenn

    JPenn Member

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    Mine seems to actually add high end fizzyness instead of doing anything to the lowend:eek:

    I've read different posts about folks just removing parts from the board and I also notice alot of the components are removed for your Wreck mods Steve. Are there things that can be removed to make this amp sound better without getting into tech territory? It's not too hard to use snips[​IMG]
     
  13. steeve_a

    steeve_a Member

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    Having played the stock amp just an hour or two, I will defer to your judgment on that (I do recall that the amp was way too deep and bassy, and that the bass control had some effect on that but that's about it). If you have the gain set high enough for overdrive and distortion turning up the bass control can produce the symptoms that you describe.

    In the conversion mods that posted here many of the components are removed to reconfigure the architecture of the printed circuit board to recreate other designs. So as parts are removed, jumpers are added to get the signal from Point A to Point B. Some parts can be removed without interrupting the flow of the signal so there is no need for a jumper.

    There is an older thread here at The Gear Page with a whole sh*tload of simpler mods:

    http://www.thegearpage.net/board/showthread.php?t=448629&goto=newpost

    Steve Ahola
     
  14. sak

    sak Member

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    Hey Steve, I'm most of the way through adapting your clean channel conversion, and the character of the amp has changed pretty drastically. I've changed everything but R53, R15, R16, and C12, and the amp is sounding very ridiculously bright. Before, it was a pile of mud, now, there's nothing but chime. Also, even my smoothest OD pedals sound grainy and cheap through the amp now... being somewhat of a novice to amp modding, I gotta ask: am I missing something? Or do the remaining component swaps make a huge difference?

    I've checked my joints with a DMM, and it everything seems to check out. I appreciate any help!
     
  15. steeve_a

    steeve_a Member

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    Take a look at the link below for a preliminary layout drawing for the Clean Channel mod. Some of the jumpers were tricky in bypassing V1b. I've been using an Eminence Red, White and Blues speaker with this amp- right now my only complaint is that there is too much bass! (I usually need to turn the bass control down to 1). So I was thinking of upping the slope resistor from 56k now to maybe 82k but I need to run it through Duncan's Tone Stack Calculator.

    I've been playing my Clean Channel V18 every day and I love it! It's a lot like a Deluxe Reverb Reissue but much lighter. And it works great with my pedals (although I may set the tone on my Tube Screamer lower than I would on an amp that wasn't as bright and chime-y). For a darker sound I recommend the MJ mod very highly...

    Steve Ahola

    EDIT Here is a preliminary layout drawing for the Clean Channel mod. For a thicker sound you can optionally leave the jumper off R22 (on the tail of the tone stack). The color codes are the same as the MJ Conversion *but* I used Yellow to indicate components which were not removed and with the values being the same as the stock amp.


    http://www.blueguitar.org/new/schem...ean_channel_conversion_layout-preliminary.jpg

    For the bass control you can tack solder a 470k or 510k resistor between the two outside terminals on the bottom side of the board instead of replacing the 1M pot with a 250k audio taper pot. Or leave it stock if you think that the amp doesn't have too much bass (that can depend on the speaker that you are using).

    EDIT #2 Did I forget to mention that I added a Cut control to this amp? My bad! In the V18 amps I've seen there is no cap mounted to the pads for C32 so I have been running wires from those pads to a Cut control mounted on the bottom of the chassis. That would be a 250k pot wired as a variable resistor in series with a .005uF cap.

    EDIT #3 While adding a conjunctive filter of 1500pF/1kv & 10k/5W the other day I noticed a few other modifications that I hadn't added to the drawings:

    - 56pF/1kv ceramic cap on V1 tube socket between pins 1 & 3
    - 150pF/1kv ceramic caps on V2 tube socket between pins 1 & 3 and 6 & 8
    - 150pF/1kv ceramic cap on V3 tube socket between pins 1 & 6

    I added these as a preventive measure to handle oscillations, but they also toned down the treble a little bit.
     
    Last edited: Dec 18, 2008
  16. scihibmxer@juno

    scihibmxer@juno Member

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    Thanks Steve, great information!

    What do you think about a cathode follower before the tone stack in a Soldano conversion (atomic 16), it looks like you include it in the rocket conversion?

    We have researched the v50 6L6 conversion to 6v6 some, it appears JJ 6v6 can operate up to 500 volts, so the 420 volts B+ would work with a rebias. However, this amp will likely be headed back, the v18 appears to be the gem in this series...
     
  17. steeve_a

    steeve_a Member

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    For these projects I have set the limitation of using the existing printed circuit board. To add a DC-coupled pair with cathode follower to the circuit would require another triode. Yes, the cathode followers are an important part of the SLO architecture with two of them in the FX loop immediately ahead of the tone stack. Another big difference is that the SLO runs a much higher voltage to the preamp tubes. But the overall result is very impressive. I just replaced R15 with a 120k resistor (the stock value was 100k but I upped it to 330k, a value used in the SLO). The gain structure is a lot more normal now although the real test will be during the day tomorrow (I can't crank it up too much at 3:00AM).

    I would like to see adaptors that plug into the sockets for EL84's that would allow you to use 6V6's in the V18 or V33... :dude

    It seems like the V50 could be a real workhorse- if they are still around I may eventually get one instead of a fifth V18-112... What the heck- if I have all 3 of them (the V18, the V33 and the V50) I can build houses and hotels- right? Or is that just in the game of Monopoly? :NUTS

    Steve Ahola
     
  18. scihibmxer@juno

    scihibmxer@juno Member

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    We were looking at a Pignose G40V mod (6L6 => 6v6) and noticed a similar dedication of v2 to a cathode follower, similar to the atomic 16. In the v18 you would loose the v2a gain stage, putting the 220/330 (100 stock) signal splitter after v1b and the new v2a is the old v2b. That gives you the extra triode. It seems there is more than enough gain in the preamp...:crazy
     
  19. steeve_a

    steeve_a Member

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    So you were referring to the Soldano Atomic 16 and not my Soldano SLO Conversion... I thought that was just a typo. My bad! :jo It was the SLO design that would need another preamp tube to properly implement the DC-coupled cathode follower.

    The Soldano Atomic 16 is like the Marshall 2204 master volume version of the JCM800 but with EL84 outputs instead of EL34. And the Pignose G40V is Dennis Kaeger's version of the 2204 with 6L6 outputs.

    I have been looking into using that design in the V33 to take advantage of the channel switching circuitry: the Clean Channel would be wired up like a Plexi and when you engage V1b you would have the extra gain stage of the 2204 design. The 2204 preamp by itself should work great in a V18 as you suggest. But so far it is the only design that comes to mind that would really fit in well with the V33 channel switching scheme- or the V50 for that matter...

    Steve Ahola
     
    Last edited: Dec 13, 2008
  20. wagdog

    wagdog Member

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    Did Steve's Soldano Mod last night. Couldn't really try the amp 'til today 'cause my wife was sleeping when I finished. Took just over 4 hours, and I took my time.

    Did a clip today after being outside all morning dinking with my broken snowplow (grrrrrrrrrr)...

    http://www.wagner-usa.net/wagdog-v18-soldano-mods_mixdown01.mp3

    Used a srv strat. Speakers are the stock 2x12. The amp sounds better through a 4x12 I have. Clip goes from fairly clean to full gain.

    I really like the results, much more responsive amp now.

    Thanks Steve!
     

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