18 Watt tone question

Discussion in 'Amps and Cabs' started by rhinocaster, Jan 21, 2008.


  1. rhinocaster

    rhinocaster Supporting Member

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    OK 18 Watt gurus I have a question. My new (used) Blockhead 18 watt combo sounds great, but I've noticed a couple of things. It seems like the 1st side (Volume and tone only) is relatively quiet. The 2nd side (Tremolo side) is twice as loud, but the tone control doesn't seem to do very much if anything. Is this the way these amps normally are or does it sound like a mod to beef up the drive on the tremolo side?

    I LOVE the sound of this amp, and I doubt I'm going to change anything, but I'm just wondering what is normal with these guys. Any help is greatly appreciated!
     
  2. phsyconoodler

    phsyconoodler Member

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    It shouldn't be that way.The normal and trem channel share a double triode.The trem has a tube for the oscillator and there is one tube for the phase inverter.They should have similar gain structures.
    Try swapping the tubes around.You may have a weak half triode in V1
    The tone controls the way they are originally are not much good for anything.They have a very limited range.You can wire up a 5E3 tone control for a more responsive sweep.
     
  3. rhinocaster

    rhinocaster Supporting Member

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    I'll try swapping the V1 tomorrow. There's no tube chart in the amp. Do these guys take 3 12ax7s? Everything looks good inside the amp and it does sound great on the Tremolo side. Just no tone control. The other side is quieter like I said, but the tone control works on that side. The amp sound fantastic on the Trem side right now. I'd hate to change that!
     
  4. 78tsubaki

    78tsubaki Member

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    Just keep track of what tubes you swap and you should not have a problem getting back to your starting point if that is where you want to go.
    My Reinhardt 18 (non Tremolo) does use 3 12ax7s. The Blockhead is probably the same but once again have a look when you remove them.
    The tone on Channel and the TMB side work well and do make a difference. There is not a noticeable difference in the volume between the channels there may be a slight difference in perceived volume due to the edge provided by the channel 2 tone stack.
    I agree with phsyconoodler's recommendation.
     
  5. rhinocaster

    rhinocaster Supporting Member

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    Thanks for the input guys. The amp uses 3 ECC83 preamp tubes. I swapped the tubes in the first two positions and the amp suddenly had a loud clicking sound. I assumer the position 1 is the preamp tube, position 2 is the Trem oscillator and position 3 is the phase inverter. It would certainly seem like something isn't right with the first preamp tube. I did change things back and put a Sovtek 12ax7 in the V1 position, and it seems like the 1st channel is now a bit louder. The tone control on the Trem side still doesn't work. I actually sounds like it's completely removed from the signal path.

    I'm a bit confused!
     
  6. Steve Dallas

    Steve Dallas Supporting Member

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    The tone control not working isn't normal. Most people like the tone control on the trem channel better than the normal channel (which seems to just sweep from "muddy" to "not muddy." That causes me to wonder if you have something wrong in there.

    If you want to post or email me some detailed photos, I can probably help you troubleshoot the amp long distance.

    Or the guys over at 18Watt.com would be willing to help.
     
  7. 78tsubaki

    78tsubaki Member

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    Did you save the tube you replaced with the sovtek. You might try putting that one or another known good spare back into V1.
    You might also check you signal chain. Are you straight in or do you have effects connected? How is your cord?
    Have you tested the tone with the tremolo turned all the way down?
     
  8. jay42

    jay42 Member

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    The trem circuit is overly sensitive to the specific tube. I think it's gain related, but it may be more complicated. As a result, it may take trying several 12ax7's in that position, before getting a keeper. All the other comments are correct. Something is wrong with the tone circuit...probably a cold solder joint or a bad cap. Someone will have to troubleshoot it.
     
  9. cugel

    cugel Member

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    yep
    i tried several tubes in this position and settled on a jan ge
    also a chopstick and playing with the leaddress from this tube worked WONDERs on my GDS build
     
  10. rhinocaster

    rhinocaster Supporting Member

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    I do think that something isn't working. It sounds like the tone control is completely removed from the circuit. I've never experienced this before with any amp. I've included a couple of photos, but I don't know if it will help. Thanks for looking, and thanks to everyone for helping with this! Now that I look at it, the solder joint at the lower W looks odd.

    [​IMG]

    [​IMG]
     
  11. phsyconoodler

    phsyconoodler Member

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    On the volume control it has a 500pf cap and a ceramic disc cap joined together and going to a white wire with a clump of solder.The 18 watt trem volume has a .005uf cap going from the right lug of the volume pot to the left side cap of the phase inverter.Those caps should not be joined together where they are.the white wire in the clump needs to be there,but the ceramic disc cap should not be there.It should be in series with the right lug or 'inline' with the wire coming off the right lug of the volume control.
    That may be the cause of your problem.
    Otherwise,the wiring is neat and tidy and he uses quality components.That's the only thing that raises an eyebrow for me.Because the board is underwired,I can't see if everthing goes to the right places.
     
  12. rhinocaster

    rhinocaster Supporting Member

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    Well, thank you! I've never spent any time playing with the inside of amps, so most of this is foreign to me. It's interesting that something looks odd in the same area where the tone control is. This is another one of those things that seems like it would be odd coming from the builder. We never really know what happens to these things when they change hands. I just picked up an RS Telecaster that had the neck shimmed to hell for no reason.

    I will be having the amp looked at by my tech, but if the tone control isn't working, does anyone see a reason that I can't play the amp at a show the way it is right now? I'd love to play it this weekend.
     
  13. Steve Dallas

    Steve Dallas Supporting Member

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    Beautiful work on that one! Several things stand out. One of which is the fact that the builder moved the PI to the proper location next to the power amp instead of the weird location in the original amp.

    If you like the tone you are getting, I don't see any reason why you shouldn't go ahead and use it this weekend. In the mean time, we can give it a good look and let you know what is amiss.

    Psycho and I are probably in agreement, but I'd like a few minutes to give it a look when I'm not so tired.
     
  14. rhinocaster

    rhinocaster Supporting Member

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    Take your time. Your help (As well as everyones input) is so greatly appreciated. You guys are great!!:BEER
     
  15. rhinocaster

    rhinocaster Supporting Member

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    Well, I played the amp at my gig last night, and I have to say that I was blown away. I didn't miss the tone control at all. I'm really wondering if the amp was moded at some point to remove the tone control from the circuit. Would this be the reason that the Trem side is louder than the non Trem side?

    I have to say that I'm reluctant to change anything. The amp sounds great at home when I plug into the non Trem side. The tone control and the lower output lets me find a cool tone at lower volume, and at a gig, the higher output and thicker driven sound is very useful. There are also a few songs that I use Trem on, so that side works great in a club.

    Last night I played my new RS Guitarworks Relic Tele into a Lovepedal Purple Plexi and then right to the amp. It was a night of great British blues tone! My clean tone was slightly overdriven and completely controlable with the volume knob on the guitar, and the Plexi pedal gave an incredibly natural sounding overdrive for solos. It kinds of sounded like a supercharged tweed deluxe. Anyway, I think that the Blockhead was a wonderful choice for my British sounding amp needs. It was a VERY authentic small Marshall sound!
     

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