'nuther Rockytop JTM45 demo

Discussion in 'Member Video and Sound Clips' started by jzucker, Mar 24, 2008.

  1. jzucker

    jzucker Supporting Member

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  2. leodiditright

    leodiditright Supporting Member

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    Sounds great again ! where the dirt is coming from?? I have an original 1965 JTM45 and with the channels jumpered with both volumes on 2, the sound remains dead clean + if I put my treble on zero like you did, it will sound totally muddy, so either my JTM45 is a weirdo or those Rockytop are a lot different than the originals ?
     
  3. JMarck

    JMarck Member

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    Jack, that sounds amazing! Really great tone, IMO!

    --Josh
     
  4. 57special

    57special Silver Supporting Member

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    Yeah, my 65 JTM45 has a lot of cleans in it.
     
  5. jzucker

    jzucker Supporting Member

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    I think this amp has the plexi preamp circuit in it which has much more highs and mids than a true jtm-45 (which I happen to prefer). This amp uses the output transformer and tube rectifier so it's lower powered then a plexi-50 but with the hotter preamp it's got a lot more gain. It's basically like having a 35-40 watt plexi amp.
     
  6. leodiditright

    leodiditright Supporting Member

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    Do you have KT66 in it?
     
  7. jzucker

    jzucker Supporting Member

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    EL34
     
  8. deeval

    deeval Supporting Member

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    I like that so much better as a more purer tone,Thanks:dude
     
  9. jzucker

    jzucker Supporting Member

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    By the way, when this amp is on 2 is INCREDIBLY loud. Maybe it's the taper on the pots that is contributing to the difference between this and the older ones but this one is a hybrid, bridgeing the gap between jtm and plexi. I'm considering getting another one with the 100 watt output transformer to get that huge/big bottom that the superleads are known for. I'm not sure of the plate voltage on this one but I'm guessing it's low 400s. I'd probably want upper 400s if i get a 2nd one. Maybe power scaling too. I bought a power scaling kit for this amp but it sounds so good I hate to touch it...
     
  10. 57special

    57special Silver Supporting Member

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    The taper sounds like the volume control on the early 70's 50 watters. The taper on the old JTM45's is pretty even.
     
  11. leodiditright

    leodiditright Supporting Member

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    So it's an hybrid, EL34-tube rectifier, those are features borowed from both JTM45 and plexi. My JTM45 on 2 is not loud, but with single-coils, it's getting dirty only from 6-7 up and at that time it is LOUD.
     
  12. jzucker

    jzucker Supporting Member

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    I bought it used but my understanding it that it's more of a plexi with a tube rectifier but it can take KT66 or 6L6 tubes. The EL34 tubes are louder but the amp's dirtier with the tube rectifier. Anyway, it sounds killer for cream and hendrix tones and it's not flabby/farty in the low end like some marshalls can be.
     
  13. ToneZappa

    ToneZappa Member

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    Wow Jack that sounds very cool (playing & sound) some good righthand pick and fingers going on there. You are holding the pick in a more standard way than when you play your jazz stuff !........... always enjoy these vids. :AOK
     
  14. Woodyworld

    Woodyworld Member

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    Lovely tones and Playin as always Jack. Beautifully warm

    Hell man you've got some gear!
     
  15. jzucker

    jzucker Supporting Member

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    Really? I've been fooling around with some benson picking for a while but on this video I switched back to my old way. Not sure if i'm ever going to get the benson picking down.
     
  16. Crikey

    Crikey Member

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    Wow, nice playing and tone! I enjoyed both demos. Thanks for sharing, Jack!



    Crikey
     
  17. mrmojorisin

    mrmojorisin Member

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    Jack my Rockytop 45/50 runs at 450 v on the plate in tube rectifier mode and 465 v in ss rectifier mode.

    I think amp you have is his straight 45. He makes a 45/50 that has three switches on the back: 45 vs 50 (preamp change), tube vs. ss rectifier, negative feedback run off 16 ohm vs. 8 ohm OT tap.

    The negative feedback switch is very interesting: The 45's run it on the 16 ohm tap. The 50's run it on the 8 ohm tap. I like setting it to 50 and running with teh 16 ohm NFB tap...tightens the bottom up a bit. Conversely, its nice to be able to run it as a 45 and go with teh 8 ohm tap so it sounds a bit more agressive and loose.

    The 45/50 is an amazingly versatile amp. Mine also has power scaling, which adds further to the versatility. Its amazing to me these amps can be had for between 800-900 in the used market. Vintage Marshall tones for days.

    Only thing I dont like about mine is that teh builder is impossible to get hold of...
     
  18. jzucker

    jzucker Supporting Member

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    Thanks for the info. I need to take mine apart and measure the plate current but based on the size of the OT I think you're right about it being a 45. In that case, the bigger OT would likely be wasted but it might be interesting to run it with a plexi 50 OT since that would work better with the EL34s I'm using...

     
  19. mrmojorisin

    mrmojorisin Member

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    Jack I think he uses the same Heyboer OT for both the 45 and the 45/50.

    Its this one I believe (from Weber VST):

    HYOT45$58.004545 watt Marshall output transformer
    3400(6800) : 2(4), 4(8), 8(16), 16(32). Headroom, punchy, dynamic.


    This is definitely the tranny thats in my RT 45/50.
     
  20. jzucker

    jzucker Supporting Member

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    Mine says JTM45 2-4-8-16 HTS-8113. Looks like it's universal OT for bassman/plexi/jtm

    It's pretty small. Looks more like a 40 watt OT than a 50. My original plan was to put the 100W OT in there and then run it at 1/2 the rated output impedance since I'd be only using 2 tubes. I've done that before and it sounds *HUGE*. However, I'd have to move the choke over since it's very close to the OT as it is. I emailed jesse to ask him he'd do that along with installing the power scaling but haven't heard back from him yet.

    EDIT - Just heard back from him. He confirmed that it should have 460v on the tubes and that he thought power scaling and the 100W ot would work great in there so I emailed him to find out how much...
     

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