Issues on Selmer T&B Reverb

Discussion in 'Ampage Area' started by j.s.c, Dec 22, 2008.

  1. j.s.c

    j.s.c Country Gent

    Aug 19, 2008
    france
    I got a Electronic issue on my christmas gift which is a Selmer Treble & Bass Reverb Head made in 1968 Serial°56718... I received it few days ago and there are few major issues.

    I buy this amp because a friend of mine has a killer selmer treble & bass without reverb from 1969 (same BLACK/SILVER - Late 1967 to 1969). My friend's amp works well and will be used as Reference for the following tests...

    I ask santa Claus to find a same one with REverb option.
    Hereafter the description find on the refernce web page (http://www.vintagehofner.co.uk/selmer/black/sel4b.html) for THE TREBLE N' BASS 50 & the REVERBERATION evolution...

    A version of the above T'n'B 50 in a larger cab featuring footswitchable reverb on the normal channel, hence one extra control knob. Cabinet size 20.3/4" x 9.1/4" x 11.1/4". Valve complement EL34 (2), ECC83 (3 actually seems to be 4), 6BR8 (1) and 2 silicon rectifiers.


    THE ISSUES WITH THIS AMP :
    The amp works nice clean sound, but...
    1...reverb doesn't work.
    2...the amp work volume is divided by 2 compare to my friend's amp.
    3...there is no tone difference between the two channels.

    -EL34 seems to work well
    -All the others 5 are 4xECC83 and one exception which is a ...6BR8 (in slot 2)
    -The valves in position 2 & 3 don't shine, but seems to work well when we put them in my friend amp.
    -Moving the reverb pot make the amp crakle a lot but without any "spring effect".
    -All in the reverb tank seems to be good.

    Hereafter pic of the valves and schematics i found on internet...but there is no 6BR8 value on this one. Moreover, the standby is linked to the "bass" channel and should be linked to earth instead of THT?? strange to have 390V to earth by the stand by????. but I'm an amp newbie. Could this schematic be full of mistakes ?

    Thanks to those who can help !
    Joss
     

    Attached Files:

  2. j.s.c

    j.s.c Country Gent

    Aug 19, 2008
    france
    valves details

    is green those who shines. The red one don't shine.
     

    Attached Files:

  3. Jukebox

    Jukebox Gretschified

    Age:
    64
    Jun 2, 2008
    Foreston,MN
    I'm the wrong person to ask,but If they don't light up pull them and have them check . The tubes might be bad. It's a place to start.
     
  4. JohnnyCrash

    JohnnyCrash Gretschie

    336
    Nov 22, 2008
    Fullerton, CA
    If you are 100% sure that the schematic is for your amp, then there should be NO 6BR8 tube. It should instead be a 12AX7/ECC83.

    If you can, take close up photos of the amp's inside. Especially the preamp and it's components (resistors/caps)... in particular the 6BR8's stuff.

    We first need to verify the circuit is the same as the schematic. If so, we need to replace the 6BR8 for a ECC83/12AX7 to start.
     
  5. j.s.c

    j.s.c Country Gent

    Aug 19, 2008
    france
    schematics 100% sure but without reverb

    One of my friend told me that the schematics for the t&b50w reverb is full of little mistake and that we should have a look on the t&b50w without reverb, because this one has been checked... Please look at it...
     

    Attached Files:

  6. JohnnyCrash

    JohnnyCrash Gretschie

    336
    Nov 22, 2008
    Fullerton, CA
    OK, schematics with mistakes. We still can NOT look at a "verified" schematic for a different circuit/amp.

    We're going to have to take photos of the insides.

    Those circuits are all simple, so photos should be the best way to do this. Take a lot of up close photos. Try to get the color bands on the resistors in the photos too.

    It should be pretty basic and easy. The reverb circuit isn't working and that is a small/basic part of the circuit. After that we'll attack the volume issues and then maintenace (elecrolytic cap replacement).
     
  7. j.s.c

    j.s.c Country Gent

    Aug 19, 2008
    france
    pics

    Here is the circuit. List of the pots from left to right :
    - - - TREBLE CHANNEL - - -
    REVERB POT | BASS | TREBLE | VOL

    - - - BASS CHANNEL - - -
    BASS | TREBLE | VOL
     

    Attached Files:

  8. j.s.c

    j.s.c Country Gent

    Aug 19, 2008
    france
    with few comments

    list of issues : 1/2 power, no tone difference between both channels, reverb out of order.
     

    Attached Files:

  9. JohnnyCrash

    JohnnyCrash Gretschie

    336
    Nov 22, 2008
    Fullerton, CA
    1. The schematic posted above is not correct for this amp.

    2. The 3rd socket (from right to left) appears that it MAY be wired for a 6BR8 tube. Notice the 6.3v heater wires (twisted yellow and brown) go yellow to pins 4 and 5 and brown to pin 9 for the other tubes. This socket on the other hand has a brown to pin 4 and a yellow to pin 5.

    Is this correct? If so, put the 6BR8 in the 3rd socket.

    I cannot see how the second tube socket is wired at all. It appears the brown 6.3v heater wire goes to pin 9, IF SO, preamp tube #2 should be a ECC83 instead of a 6BR8. Double check it.

    3. In fact, it doesn't look like preamp tube #2 has many wires soldered to it at all. Can you tell me where the inputs for each channel go (tube socket and pin number)?

    4. Those are not the silicon rectifiers, those are multisection filter capacitor cans.

    5. Changing V2 and V3 to the correct tubes may resolve the Reverb and the volume issues... then again...

    6. V5 is your Phase Inverter tube and the 0.02uF input capacitor does NOT look original. It looks like channel #1's output goes directly to the PI tube instead of through that 0.02uF coupling cap (the green wire from the far right side). Which may be OK.
     
  10. j.s.c

    j.s.c Country Gent

    Aug 19, 2008
    france
    V2/3

    Changing V2 and V3 ...

    Dosen't change anything (no tonality difference between both channels, half headroom, no reverb) ! But now all values are shinning...
    I have to visit an amp tech, i think :cool:

    Anyway thanks for your advises.
    Joss
     
  11. JohnnyCrash

    JohnnyCrash Gretschie

    336
    Nov 22, 2008
    Fullerton, CA


    This indicates the heaters are wired correctly for the tube types you now have in place.

    I'd order all new tubes and set them aside for a bit.

    Now we can move to the next step(s). The volume issues could be due to old/bad tubes and the reverb not working could also be due to a old/bad tube. The wrong tube was in the wrong socket for probably a long time. This could have been bad for the other tubes.

    Most importantly though, the filter capacitor cans and other electrolytic caps need to be replaced. This might be best left to a repair man, since high voltages will still be in the caps even when off and unplugged.

    Eventually, you should read up on safety and build/repair your own amps. It'll save you a ton of money. I've built over a dozen amps for myself at a fraction of the cost to buy them new or even used.

    1. It may only need a re-cap job and new tubes.

    2. While he's in there replacing the caps, have him add a bias trim pot, since your Selmer appears to be fixed bias (but not fixed adjustable bias). This will allow you to use a few different types of power tubes similar to EL34's and fine tune bias for new tubes or tube swaps. It'll also get you more power/volume out of it.
     
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