Bluesbreaker Reissue

Discussion in 'The Workbench' started by TwinCamBlues, Oct 29, 2020.

  1. TwinCamBlues

    TwinCamBlues New Member

    Joined:
    Dec 29, 2011
    Messages:
    7
    Likes Received:
    5
    Hi Group,

    First time posting on the board and looking for some help and advise for the bluesbreaker. I purchased this amp used from Guitar Center back in 2007. Played it a few times and thought it sounded to bassy and lifeless. It became a piece of furniture or art work over the years before I started to get serious about working on amps. After watching many hours of tube amp troubleshooting, I finally got the itch to open it up. My first issue of many is the tremolo does not work and I figured the previous own removed it from the circuit. After looking at the board I found a .22u capacitor and a 1K resistor on R36. Any ideas why? R36 should be a 560ohm. Also R30 measured 8.2 ohms instead of 2.2K.

    Many resistors on the schematic that were out of tolerance. Is there any hope for this amp?

    Thanks for your input.
    TCB
     

    Attached Files:

  2. 2L man

    2L man Member

    Joined:
    Sep 30, 2020
    Messages:
    34
    Likes Received:
    12
    I can't say much certain but measuring resistance in actual circuit can be orher than individual resistor. Also capacitors can be what ever... Obviously thats what you have measured on on 68k input resistors when they are paralled when no plug is inserted. Is on/off pedal connected? It could explain that 8.2 ohms?

    Also R1, R16 and R17 see each others resistance.

    Esa
     
  3. neikeel

    neikeel Well-Known Member

    Joined:
    Feb 12, 2014
    Messages:
    4,884
    Likes Received:
    3,275
    The board looks pretty stock to me. That cap is 22uF I believe.
    As has been pointed out measuring resistors and caps in circuit is not very helpful unless they have shorted or gone open circuit.
    The basic amp in good order is bassy. Most people will dial the bass off, crank the mids, treble and presence and use the hi treble input. My BB is a 68 and only the channel 2 input works with the trem. (To use the trem without switching jacks invokes the patch cable trick between lo channel 1 and high channel 2 then you get a blend of both. Presume tubes are all in good working order?
     
    tce63 likes this.
  4. TwinCamBlues

    TwinCamBlues New Member

    Joined:
    Dec 29, 2011
    Messages:
    7
    Likes Received:
    5
    Tubes are all new and bias was set around 35. I'm planning to remove the .22uf and replace with proper 560 ohm resistor. I will post some audio clips soon.

    Appreciate the input!
     
    tce63 likes this.
  5. neikeel

    neikeel Well-Known Member

    Joined:
    Feb 12, 2014
    Messages:
    4,884
    Likes Received:
    3,275
    Is channel 2 working with trem?
     
    tce63 likes this.
  6. TwinCamBlues

    TwinCamBlues New Member

    Joined:
    Dec 29, 2011
    Messages:
    7
    Likes Received:
    5
    No
     
    tce63 likes this.
  7. neikeel

    neikeel Well-Known Member

    Joined:
    Feb 12, 2014
    Messages:
    4,884
    Likes Received:
    3,275
    Looking at this properly (on my screen, not phone!) the screened grey wire is dropped in to bypass the trace on the board that takes the signal from the voltage divider (100k/470k) on the board, near the inputs, to the input of the intensity pot, bypassing the 0.22uF cap that is on the schem (acting as a filter). It looks to be ex-factory by the fact that I cannot see evidence of the cap ever being there so no necessity to reverse this IMO.
    The mods with a cap bypassing a 1k on the cathode is just adjusting the bias of the trem triode V6a. It may be simpler just to replace that pair with a 560k as per the schem. The trem is switched off and on by the pedal which is simple latching ground switch. You might try playing with the 22k trim pot on the board (cathode of V6b) to see if you can get the trem to work.
    Presume you have the correct type of footswitch and decent working tube in the trem slot?
     
    tce63 likes this.
  8. TwinCamBlues

    TwinCamBlues New Member

    Joined:
    Dec 29, 2011
    Messages:
    7
    Likes Received:
    5
    neikeel,

    I've removed the cap and replaced R36 with a 560k resistor. Plugged in a Marshall Pedal model PEDL-90003 and was able to get a weird "tick" by tapping and rotating the VR7 Pot. When I bought the amp I noticed the knob on VR7 would not stay on the pot shaft. Thinking the knob was stripped I purchased a whole new set of knobs but that did not solve the problem. VR7 has a black shaft while all the other pots are silver. Maybe they replaced this pot and it's bad? A newbie question is why is this pot a "double stacker", meaning why 6 tabs instead of 3?




    As far as tone of the amp, it very sensitive...I mean very very sensitive. I can palm mute the strings and strum my thumb down the strings and the intensity is 10. Like no compression on the speakers.
     

    Attached Files:

    tce63 likes this.
  9. TwinCamBlues

    TwinCamBlues New Member

    Joined:
    Dec 29, 2011
    Messages:
    7
    Likes Received:
    5
    Here is my thumb lightly touching the strings and barely playing a chord.


    Input on Channel 2 bottom jack, volume at 4
     
    tce63 and Travis398 like this.
  10. Chris-in-LA

    Chris-in-LA Well-Known Member

    Joined:
    Jul 19, 2018
    Messages:
    1,756
    Likes Received:
    1,432
    Location:
    Los Angeles
    No idea about a double-stacked pot, my clone doesn’t have one. Also, the pot next to that one is loose in the video and flopping around. The tone in your video sounds great, almost too good to be playing through the low input on the regular channel. You might need a BB expert to go through that amp and tell you if anything is no longer stock. That ticking sound was troubling, something’s not right with your baby. FWIW, the tremolo on my clone works on both channels.
     
    Last edited: Nov 2, 2020
    tce63 likes this.
  11. neikeel

    neikeel Well-Known Member

    Joined:
    Feb 12, 2014
    Messages:
    4,884
    Likes Received:
    3,275
    The pot is probably not original if that is VR7 it is the intensity pot. Suggest you buy a replacement single pot of the correct value (linear 220k -250k). Also tighten the other pot ideally with lock washer behind. What happens if you adjust the VR2 on the board to adjust the threshold? (bias of the trem) nb not the output tube bias pot.

    Having said that looking at the schem again the VR8 appears to be a dual 1meg pot and is the speed pot.

    What values are the pots on your amp? Are they all set screw or push-on knob type?
     
    Last edited: Nov 2, 2020
    tce63 likes this.
  12. TwinCamBlues

    TwinCamBlues New Member

    Joined:
    Dec 29, 2011
    Messages:
    7
    Likes Received:
    5
    Neikeel,

    Sorry for the delay, I was away for work. Here are the pot listing.
    VR1 Volume II = A1M
    VR2 Volume I = A1M
    VR3 Treble = B220K
    VR4 Middle = SHB22K
    VR5 Bass = A1M
    VR6 Presence = B4.7K
    VR7 Intensity =B220K
    VR8 Speed = LOGB IMEG UK97

    Push knobs on the pots

    I will post more videos this weekend. Tube 1 and 2 have terrible microphonics. I've switched tubes out with multiple one and still have excessive microphonics. Touching the tube pins wires from inside the amp is also microphonic. Very strange. I will take some voltage measures too.

    Adjusting VR2 counter clockwise removes presence and strange tick/tremolo.
     
  13. TwinCamBlues

    TwinCamBlues New Member

    Joined:
    Dec 29, 2011
    Messages:
    7
    Likes Received:
    5
    Quick question, should the bias move this much when playing? Volume is at 2, 4, 6, 8.

     

Share This Page