Difference between JMI AC30 and AC30TB

Discussion in 'Amps and Cabs' started by drbob1, May 10, 2005.

  1. drbob1

    drbob1 Silver Supporting Member

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    I'm going to have to thin down the herd for a move. I have an AC30TB combo with blues coming, and an AC30 non-TB with silver Bulldogs that's not super healthy, so I'm not sure a direct comparison will be helpful. What is the difference in sound between the two (besides the obvious increased EQ choices with the TB)?
     
  2. QuickDraw

    QuickDraw Member

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    does the non topboost ac30 have ef86's in the preamp?
     
  3. drbob1

    drbob1 Silver Supporting Member

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    I don't think so, it's a grey panel (so 64-65) so it should be 12AX7s, right? Didn't the EF86s go out with the AC30/4s?
     
  4. Kiwi

    Kiwi Silver Supporting Member

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  5. drbob1

    drbob1 Silver Supporting Member

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    Well, no answer from the guys at PP. Anybody?

    On another note, there's a guy over there who'll mod any JMI AC30 to AC30/4 specs. For the combo with the wrong speakers or the head with the replaced PT, that's very tempting!
     
  6. QuickDraw

    QuickDraw Member

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    i got a book at home with some info, i'll try to post some tonight, but if it was me i wouldn't mod it, i believe the silver speakers are the same as the blues, what is not healthy about the amp?
     
  7. QuickDraw

    QuickDraw Member

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    ok, this is from "the tube amp book 4.1th edition" by aspen pittman, which i strongly advise anyone to buy, great book!

    "the top boost is definatly the best sounding of the bunch because it had 2 extra ECC83 preamp tubes and a complex tone boost section that gave it extra punch compared to the standard ac30"

    "the ac30 was also available with reverb or extra gain in the tone section-- they were either labled ac30 rev or ac30 top boost."


    hope that helps, btw i run a home for sick ac-30s if it needs a home

    :D

    you may also want to try a dallas rangemaster with the non top boost, as they sound great on the normal channel of the ac30
     
  8. guitarman_1

    guitarman_1 Silver Supporting Member

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    The ac30/4 was the one with the ef 86. After they went to the ac30/6 it became a 12ax7. Im sure there maybe some rare exceptions, but that is the rule. Now on the ac15 you get a ef 86 preamp tube up into the mid 60's. Hope this helps, as I have a 1961 ac30/4.
    Thanks.
    O
    :)
     
  9. drbob1

    drbob1 Silver Supporting Member

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    Now that's an amp I'd like to play. Actually there's a guy who'll rebuild a JMI AC30 to AC30/4 specs. Would it be worth sending one of the non-original ones to him? Is it different/better enough to be worth further modding a JMI?
     
  10. guitarman_1

    guitarman_1 Silver Supporting Member

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    I cant say which is better, They all have their strong points. I like the chime of the 65 tb model with a strat. The ac30/4 is darker more marshall voiced than the 12ax7 model. It also has more gain. Mind you it has chime, just in a different vein,but witha Lester the ef 86 front end is a killer.. I will say, The ac30/4 is very special.I dont know how the reworked ones would sound, but i would probaly try the mod on a re issue first.
    Hope this helps.
    O
     
  11. Sir EL84

    Sir EL84 Member

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    Hi,

    I don't have his name, but there's at least one person who builds the EF86 channel into a rear mounted unit much like the early Top Boost retrofit add on. This can be added to any AC30 w/o losing what you already have.
     
  12. drbob1

    drbob1 Silver Supporting Member

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    Now this would be VERY useful. Any idea how one might find him?
     
  13. Roe

    Roe Member

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  14. µ¿ z3®ø™

    µ¿ z3®ø™ Member

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    having both the EF86 and top boost is really nice in one amp.
     
  15. hamfist

    hamfist Member

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    Ah, new Heritage AC30H !!!

    and you're right, it's a cracker.
     
  16. µ¿ z3®ø™

    µ¿ z3®ø™ Member

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    actually, i was referring to the matt romasco built and fairly rare JMJ30.
    sadly, there is no tremolo circuit, but that is more than made up for w/ absolutely stunning recreation of three different JMI era AC30s. brilliant, normal and top boost. well worth looking out fro on the 'used' market if one is looking for that type of amp.
     
  17. starfish

    starfish Supporting Member

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    What year is the AC-30TB? What model chassis is the non-TB (treble/normal/bass)?

    If you're trying to make a decision on which to buy, it's going to come down to your ears and personal prefs. With old JMI amps, they can sound quite different from amp to amp, regardless of circuit type. Some of this may be due to requisite maintenance, component drift, tubes, etc. Not to mention that the earlier amps used different transformers from the gray panel era amps. Some overlap along the way.

    Generally, a non-TB amp, assuming it is normal model chassis (not treble or bass), will sound somewhat darker. There is one less gain stage in the brilliant channel and no bass/treble eq. If it were my decision to make, I'd go with the TB version with blues. I doubt you will be unhappy with the tone. Otherwise, if the non-TB version is a treble model chassis and it is a lower cost, then it may be a wiser choice.

    The treble model can sound really great and you can always add an aftermarket TB unit. If the amp is a 64-65 and not currently TB'd, then it already has the cut out in the rear panel, located behind the serial plate. If you end up top boosting it, you get the best of all worlds - a TB brilliant channel and treble version of the normal and vibrato channels. It really opens up the amp, less dark, more chimey on every channel. In contrast a normal model with top boost and a normal model without top boost only differ in the brilliant channel, the one that is top boosted.

    I highly recommend the aftermarket TB built by Don Butler. He is in the States too so it is generally easy to get in touch and get one. They sound great and are pretty easy to install if you can solder and read pretty straightforward instructions and locate points on a circuit (i.e. wiper of a pot, pin 9 of a tube, etc.) There are only 5 wires - B+, heater, ground, and in/out wires of the TB circuit.
     
  18. soldano16

    soldano16 Member

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    I'm playing a 63 non TB that was set to treble model spec by Todd Sharp.

    All I can say is that it's a wonderful sounding amp that I play on the brilliant channel.

    I use a Lovepedal BBB07 as a Rangemaster clone and WOW!!!!!!
     
  19. drbob1

    drbob1 Silver Supporting Member

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    Wow, talk about an old thread coming back! Let's see, since this thread was started, I traded a decent 59 Basssman for a REALLY nice candy panel AC30TB (probably not the smartest trade, but I never played the Bassman and I do play the Vox). The grey panel AC30TB combo lives next to it in the basement and both sound brilliant. The combo with the bulldogs has been upgraded to a MM OT (since the original had been replaced with some wierd thing that just sounded WRONG) and lives at church where it gets played every week. It sounds killer, and may be the quietest of the bunch (Ed from Edtronics in Madison installed the OT and worked on it, it's been reliable for 3 years now, IIRC, with just a retube (Tung Sols and some Russian NOS EL84s from Lord Valve). The head with the replace PT is long gone, to a home where I hope it gets played a lot. There's also an AC30HW living down there, another great sounding amp (retubed with Mullards). I tried the AC30CC and the AC30HH, but neither bumped any of the 4 off their perches. I'd consider an AC15H for the EF86 channel and lower output, but the older AC30s just have something the newer ones don't to my ears...
     

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