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JTM45 Noob Question, Tubes?

Discussion in 'Marshall Amps' started by MacDiarmada, Sep 12, 2021.

  1. MacDiarmada

    MacDiarmada Member

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    I got my hands on an ‘89 JTM45 Reissue and a 1960BX cab. Currently, it’s got sovtek tubes but I want something better. I’m an AC/DC nut, the older Bon Scott stuff. That being said, I have 2 SGs and the Gretsch Malcolm Young model. I’m looking to emulate that vintage AC/DC sound. What tubes should I go with? I know nothing when it comes to brands of tubes. Currently, I’m playing thru a krank rev jr pro (also has sovteks). It’s decent, but it’s more of a “metal” amp. So, any experienced advice would be appreciated!



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  2. Kelia

    Kelia Well-Known Member

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    I have one and @neikeel helped me in changing a few components to make it into a 1966 specs including shared cathode and some nice KT66’s , I went Gec’s but Gold Lions will sound stellar!

    Enjoy and congrats!
     
    Last edited: Sep 12, 2021
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  3. MacDiarmada

    MacDiarmada Member

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    I’ve read about swapping out caps, removing certain parts, etc…. That is what I want!! That vintage spec! I’m handy with a soldering iron, I rewired both SGs with bumblebee caps and vintage pots, so I doubt I’d have any trouble digging into the amp.
     
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  4. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member VIP Member

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    Welcome to the forum
    Nice rig and guitars
    Cheers
    Mitch
     
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  5. Chris-in-LA

    Chris-in-LA Well-Known Member

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    If you want advice on how to mod your amp to vintage spec, post a thread in the Workbench section.
     
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  6. Kelia

    Kelia Well-Known Member

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    Good advice , changing filtering to original specs is a must imo to get that nicer spongy feel
     
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  7. scozz

    scozz Well-Known Member Gold Supporting Member

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    Best advice you’ll get today,…
     
  8. MP+

    MP+ Member

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    The Gretsch will play a big part in getting the Malcolm sound as will the SG play a big part in getting the Angus sound. Tweaking your Amp. will move you more towards one tone and further away from the other. Malcolm's tone is a touch darker, Angus's tone is brighter with more bight, put them together and you get AC/DC, but either on their own just sounds like a great guitar tone and that's it. Modding Amps. can turn into a long spiral with no definite conclusion, so a piece by piece reversible approach is the smart way to move rather than ripping into the components with a soldering iron. From the sounds of what you might be after, I would try big bottle Sovtek output tubes, or they might be Electro Harmonix these days. These will give you a touch more low mids. Preamp tubes will make some difference, but mostly, the one to work on is V1. Tung Sol 12AX7 will take out a bit of the metal style gain sound and steer it more towards a classic rock gain sound, possibly better than that is the Mullard 12AX7. Always overlooked but maybe more important than the Amp. itself - what speaker set up are you running? I would be looking at a Quadbox with 12" Vintage 30 Celestions linked to your amp at 16 ohms. 25 watt greenbacks might even be closer to the Bon era sounds but try a few options out at your local outlet.
     
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  9. neikeel

    neikeel Well-Known Member

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    The 89 RI is decent.
    The filtering on an original is 32uF 500v can next to rectifier with 32 screens/16 pi (can inside the chassis above the PT and 16uF Axial.
    Yo achieve this you need a dual 32uF can (500v) and dual 16 can. The 32/32 goes next to rectifier - half to HT and half to screens. The 16/16 goes top side.
    The RI has 100R Arcol instead of choke. I recommend a 3H or 5H 250mA rated choke with DCR around 100R or so.
    Get a good Mullard ECC83 for v1. Outputs I like are Gold Lion KT66 or later Golden Dragons (the GEC clones, not VA 6L6 dressed up to look like GECs) unless you find NOS GEC matched pair at sensible price! You may need to tweak the bias resistors to get in the right ballpark.
    Do this first and see what you think. If you want to go turretboard, mustards and Pihers (with odd cc only) post back here.
     
  10. MP+

    MP+ Member

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    Fair call from neikeel. Those vintage specs would have been running turretboards and different value capacitors / chokes etc. Bear in mind the vintage amps were also running transformers that just aren't around these days and what we nowadays call NOS tubes which will cost a fortune, these two items alone accounting for a big slice of the tone. I'm pretty sure Malcolm was running a 100 watt super bass into an 8x12 (two cab) speaker set up and just cranking it to the distortion level that was used, no pedals. That speaker set up alone had a lot to do with his sound. I thought you might have been starting with EL34 output tubes which led to my point of going with big bottle Electo Harmonix. They would give you more of 5881 tone which might approximate the low mid boosts of 100 watt super bass. The Gold Lion KT66 are an awesome tube, I'm guessing you're swapping out 5881's?. I've swapped out my EL34 tubes with Gold Lion KT77 and they sound monster. Really made a difference, but hard to say if they pushed the amp into 1975 sounds. Then again I'm talking JCM 800 territory. Whichever way you turn, you will be heading for an approximate close replica rather than dead on vintage spec. Not sure of your technical ability, but you don't want to poke around in there without discharging the filter caps, in case that's something you might not have been up with. Definitely give the greenbacks a go, they will get you heading towards that tone.
     
  11. neikeel

    neikeel Well-Known Member

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    I think real Malcolm tones will be a 45/100?
    Closest to that at sensible volumes would be a ss rectified early Bass JMP50
     
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  12. MP+

    MP+ Member

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    I think it was the early JMP 100 Super Bass that really carried. I had the luck of once playing through one that had been stashed away in a furniture storage facility for decades, had the original "B" cabinet with it, all original factory tubes, totally untouched. Pots were all scratchy and needed some very carefully applied Electrolube. Valves were all crackling but came back after I plugged them out and back in a few times. Full on Aussie 240V in an abandoned warehouse that was converted to a single rehearsal room. Cranked it up to about 7 and it was the real deal. Nothing else in the world sounds like that and yep, not to many places in the world where you could away with that these days. To really throw fire at it, I also plugged in a Gretsch Baritone that was lying around - brutal! The early work was around 1975 and they were just using the Marshall Amps. of the day in Australia. Angus would have been doing the same with a JMP 100 Super Lead, plugging in the SG and cranking it to 7 or 8. It was all just before my time but I heard a few descriptions from friends who caught them live in suburban gigs at town halls and outdoor public parks around Sydney. Lots of loud bands back then, no such thing as a distortion pedal, it all came from the master volume knob.
     
  13. dro

    dro Well-Known Member

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    Here we go again.
    You are chasing a demon that can't be caught with a question like that.
    There is allot more to the angus (studio) tone than an SG and an Amp.
    Don't chase his tone. CHASE YOURS.
    But if you are relentless. Your first purchase should be a KIKUSUI PCR 4000M power regulator, set your amp to 240volt set regulator to 236.1v
    Buy all the tubes you can afford.
    And ......... CRANK IT DUDE
    :headbanger:
     
  14. MP+

    MP+ Member

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    No questioning that, everything is rearranged in the studio. Mic. placements, mic. types, the mix desk itself, the room - and the list goes on and on. The common theme I can hear is that their sound relies on output stage distortion both live and recorded, so yes some sort output attenuator, or a large empty warehouse in the middle of nowhere with ear protectors on, or maybe just half on.
     
  15. MacDiarmada

    MacDiarmada Member

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    Good info from most. Needless to say I will be building my own clone early next year.

    @dro I get what you’re saying, but….
    I’m 48, went to my first AC/DC concert when I was 5 (1978). I play by ear, I know NOTHING about music. I don’t care to write my own stuff, or anything else like that. I’ve been “playing” for a little over 30 years and I know pretty much every song of theirs that Bon sings on. I’m content with my band of other “old guys” and getting together in each other’s garages and putting on little impromptu shows for our neighborhoods, that’s really it. I have no need or interest in my own sound.
     
  16. dro

    dro Well-Known Member

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    I was in Highschool when AC/DC came out. The first show they did in Fresno. They were Booooed.
    They were different. People have trouble adjusting to different.
    I too am a much bigger fan of Bon Scott than Brian Jonson.
    I figured when Bon Dies AC/DC was done. Like Zeppelin when they lost John Bonham later that same year. Then Lennon the day before my 20th birthday.
    1980 was a bad year for Rock&Roll.
    If you can play loud. All you gotta do in crank that JTM45.
    If not either get an attenuator (don't really recommend) or a nice O/D pedal.
    I chose the latter. Went with the 120volt Carl Martin Hot Drive-N-Boost.
    Couldn't find what sounded good to me with the 9v stuff.
     

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