Bluesbreaker RI - need to fix its tone

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by pfflam, Feb 13, 2018.


  1. pfflam

    pfflam Silver Supporting Member

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    I have a Bluesbreaker that I think needs to have changes in tone

    The problems:
    - it has no attack, it sounds like it's compressed, every note is round sounding, squashing the crispness of the mid and upper range
    - its distortion is flabby and fuzzy when cranked
    - the knobs are all maxed and it has actually no change on the actual spectrum, even the presence is maxed and the crispness never arrives -it has no jangle, no jingle, just highs and other tones, no definition

    What i have:
    A bluesbreaker RI
    running nos Peavey STR 6L6gc, assorted good NOS pre-amp tubes
    and a Mullard GZ34 rectifier

    all 32uf can caps

    It has these Modifications:
    -Dragnall Transformer TXMA
    -Radiospares 045rs-l Transformer
    -MM choke

    -Zo So caps in C4, C5 -223k & C8, C9, C10
    -C11, C12, C13 Zo Sos are 104k
    -104k Zo So on the Presence knob

    -R1 has a 100k ohm Ressister
    -R17 has a 470k ohm

    and C3 has a 4.7uf 50v cap (all the mods say to put something else in there, and the original should be something else too)

    I am running it into two closed back 1x12" Victor Film cabs, and into it is a Fender fr1000 Reverb unit.
    also
    In its own BluesBreaker open back case through a Tone Tubby Alnico and a Webber Legacy with similar results

    I think maybe something has drained its crispness, its high end.


    What i wonder:
    My first thought is to get proper 5881 tubes, then try a solid state rectifier.

    But I am also wondering about the C3 capacitor - the schematic seems to say it should be 330uf.
    I wonder how this effects the tone?

    schematic: http://raw-sewage.net/images/bb62ri-schm1.jpg
     
  2. wilto

    wilto Member

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    So many variables. Could be something simple like a solder joint. Have you tried different speakers.
     
  3. pdf64

    pdf64 Member

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    Did it used to sound good?

    If so then something has changed.
    Being a consumable, bad tube/s are the most likely suspect; have you swapped in a 'known good' 12AX7 into each 9 pin socket in turn, and, if no improvement from any of them, a 'known good' pair of power tubes, and, if no improvement from those, a 'known good' rectifier?
    What is the plate or cathode idle current of the power tubes?

    Really need further info regarding the spec of those parts (or how they differ from the stock parts).

    So all the above are still the stock values?

    Have all the changes mentioned been undertaken, and the amp subsequently tested, by a competent person?
     
  4. wallaceSnr

    wallaceSnr Member

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    "Mullard GZ34 rectifier"
    Check this along with your other tubes before altering the circuit.:beer
     
  5. pfflam

    pfflam Silver Supporting Member

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    Hi folks, thanks for looking at this.

    The amp has been this way since I bought it.

    I have repeatedly changed tubes out in order to address these sonic inadequacies, so i kinda don't think it's the tubes.

    I will do some more rolling in the next few hours - (I literally have more good old tubes laying around than I know what to do with)

    The Cap and Resister changes are all evident from looking at the circuit board, but the values (at least of R1 and R17) are the same as the schematic, with the C3 cap seeming to have a different value - though I am not sure it was changed - it visibly looks like it was factory
    And from my looking at the schematic the Zo So caps are schematic values.

    I don't see a 'bright cap' - tough I am not sure what i would be looking for, but it sounds like it could use one.

    I have tried it through different speakers.

    To re-iterate - the main problem seems to be a lack of high end clarity along with a flabby crunch when driven hard, and the knobs seem to need to be cranked all the way to get close to the right highs and/or mids.
    It's overall too spongy and without clarity
     
  6. pfflam

    pfflam Silver Supporting Member

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    ok ok - it actually sounds very very Great!

    I tell you, some of y'all would kill for this tone - but me, I am used to Fender Clean Crispies and just sorta want to get a little bit more of that in it. I have checked out tubes, even tried a 5U4 in the Rectifier (sounded good but I was scared to leave it in - it had red-hot plate parts and looked a bit frightening)

    I guess I will leave it alone unless someone has any ideas in terms of a bright cap, possible bright cap switch, or any of those sorts of mods
     
  7. pfflam

    pfflam Silver Supporting Member

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    Ok, here is something I noticed - people say to change the pre-amp Can-cap filter to a 16ufX16uf, the one in there now is a 32ufx32uf.
    I don't know how it is soldered, from what I gather from my online perusalizings, it can be soldered so as to be read by the circuit as a 16uf - I am not sure if it is soldered this way, I would need to move the circuit board to find out.

    Should I just drop 10$ and get a 16uf - would that get it more Fendery if the other cap is 32uf?
     
  8. pdf64

    pdf64 Member

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    I think that JTM45 sound dull without bright caps; stock, both channels of the RI are fitted with them.
    They're mounted on the volume controls.
    Personally I prefer bright cap values higher than stock in there, eg 220pF.
    But I'm not keen on the peaking cap C6.
     
  9. MKB

    MKB Silver Supporting Member

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    The Marshall is indeed a much different animal than a Fender; are you comparing your amp's tone to another Marshall or just Fenders? It may make for diminishing returns to try to get Fender tones out of an amp not designed to do so. Also, what pickups are in the guitar that doesn't jangle with the amp?

    As far as possible problems with the amp, make sure the output transformer is set to properly match your speaker's impedance to the power tubes you are using. Some early Marshalls had a comparatively high reflected plate impedance, and that can muddy up the tone.

    Bluesbreakers are tuned a bit more to the warm\thick side of tone, as compared to the much brighter Super Leads. If you're getting a lot of muddy tone with humbuckers, you could try some Super Lead values such as going to 0.022uF coupling caps in place of 0.1uF, and tweak the tone stack.

    I would not go to 330uF on C3 if you are using humbuckers and lots of gain, as that can mud up the tone a lot. The 4.7uF is a better value in that respect; in fact Super Leads use a 0.68uF in that position.
     
  10. pfflam

    pfflam Silver Supporting Member

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    This is intriguing, what exactly do the different values do tone-wise?

    I am playing a Telecaster that also has a middle humbucker. I would love to be able to dial in more chime.

    From what I am gathering from online searches, the BB-reissues did not have a bright-cap - how easy is it to install one?
    I'd consider doing that with an on/off switch
     
  11. lpnv59

    lpnv59 Supporting Member

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    Bluesbreaker RI are a dark amp to begin with. I had one with a bunch of mods and a set of Alniico blues. Great amp and definitely darker than any of my blackface Fender combos. Maybe its just not the amp for you!
     
  12. stratified

    stratified Member

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    Take a look at the phase inverter tail resistor/presence control arrangement in the schematic.
    Is that misdrawn or is that how these amps are actually wired?
    It looks as though the cathode is DC decoupled from ground (Except perhaps through the 27k feedback resistor and the output transformer secondary).
    What am I missing here?
     
  13. pdf64

    pdf64 Member

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    The RI schematic you linked shows a 100pF bright cap on the vol control of each channel.
    The schematic notes that they are mounted on the pot, not the board.

    Yes, there's (hopefully) an error on the schematic in that regard.
    The amp should actually work as drawn, as the phase splitter cathode current would still find its way (via the 27k feedback resistor and OT secondary) to circuit common. However, there would be a lot of negative feedback and it might not be stable / sound good.
    I've not had chance to closely examine an RI, so can't say for sure whether the schematic is wrong or if they really are built that way.
     
    Last edited: Feb 14, 2018
  14. pfflam

    pfflam Silver Supporting Member

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    Here are pictures of the circuit and the vol pots, I don't see bright caps on them, but there are wires going places - I tried following the traces and still do not find any Bright caps.

    So, I am thinking of plopping some caps on here, and maybe adding switches to them -(running wires to the back of the chassis and cutting holes for the switches.(?))

    I am assuming what I do is simply solder them to #2 and #3 lugs?

    Should I go with the original specs? If I want brighter, what size would you recommend?

    pics: the vol pots

    the circuit:
     
  15. pdf64

    pdf64 Member

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    I can't see bright caps in the photo, so it seems they may have been removed.
    Hence your amp might seem muffled.
    Some folks seems to like that, each to their own.
    To make it brighter, the best thing would probably be to try the stock values of bright cap first, but get some alternative values in if you're buying parts.
    100pF is the lowest value that has much effect, so I suggest get 2 each of 100pF, 120 or 150pF, 220pF, 470pF.
    I prefer polystyrene caps in these low values; ceramic caps may have tolerance, temperature sensitivity and microphonic issues.

    Yes

    The grid circuit fed by the volume control is extremely sensitive (high gain and high impedance), so running wires to remote switches in that circuit is a bad idea.
    Any switches should to be immediately adjacent to the volume control, as per regular Fender bright switches.
    Alternatively, replace the vol controls with ones that incorporate a pull-push switch.
    Bear in mind that as the amp is muffled without any bright cap, such switches can be used to put additional caps into circuit, eg hardwire 100pF and have 120pF on the switch.

    Also, as noted above, I suggest to remove C6, the treble peaking cap.
    It makes the hi-treble channel brighter (irrespective of the vol control setting - bright caps have progressively less effect as the vol control is advanced) but at the expense of making the normal channel more muffled.
     
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  16. pfflam

    pfflam Silver Supporting Member

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    Thanks, I'll try those out.
     
  17. 71strat

    71strat Member

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    Heres the inside of my Metro LTD ED GMP45 head. You might look into some of the specs Valvestorm uses for their kits. They are Metropoulos Spec. I also like the Heyboer Transformer.

    Mines running NOS M/O 1956 KT66s, and NOS Mullard Pre/Rectifier. I love this amp, and to my ears just totally kills my Blackfaced 69 Dual Showman rvb for cleans, though the DS is louder. To me the Metro is more harmonically rich.

    Showman is also completely gone over, NOS tubes, ODS Mod, and is a fire breather with the mod kicked on. But is tame with it off. Like a Twin Rvb.

    Though my amp doesn't have Tremolo.

    Other than a Metro JTM45/100 LTD ED, this is my desert island amp. I'm also running Pulsonic G12H T1221, and a Mather oversize TVB cab x EC Collins Pinstripe/Bluesbreaker cloth.



    [​IMG]
     
    Last edited: Feb 16, 2018
  18. pdf64

    pdf64 Member

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    Unfortunately the photo is too small to discern component values, could you try and link / upload higher resolution images?

    As you've been using those tubes, they're not NOS ;)
     
    Last edited: Feb 16, 2018
  19. MKB

    MKB Silver Supporting Member

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    In that position, in general, the larger caps tend to extend the gain boost (as a cathode bypass) more into the bass. You are basically tweaking the boost rolloff by changing that value. In the mids and trebles, you may not hear a difference between a 0.68uF and 330uF, but with a humbucker, you might get too much mushy bass boost with the larger value caps.

    The Super Leads have a lot of gain and are tweaked for brightness, but some of the part choices tame the shrillness (such as the mustard caps and carbon film resistors and ceramic small value caps). That balance between brightness and no shrillness is IMHO the essence of Marshall 70s tone.
     
  20. 71strat

    71strat Member

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