RT-707 Help Request

Discussion in 'Tape' started by anonyme-x22, Dec 6, 2017.

  1. anonyme-x22

    anonyme-x22 New Member

    Messages:
    19
    Hi,

    I have rt-707 on which i cannot set 0DB on the vumeter at 470mv Imput.
    One can be close, the second is at his maximum -1DB, but in these case the -20db, is not good.
    If i set the -20db Correctly, i got something like -2db/-1db. Could it be a failure of one of the vumeter, or it is definitively my imput signal which is out of balance, and not at 0db ?

    Thanks in advance,
    Rgds,
     
  2. GPS16

    GPS16 Well-Known Member

    Messages:
    664
    Location:
    UK Manchester
    Hi,

    the 0dB set point is for an input signal to give 450mV OUTPUT. The reference point is the Millivolmeter and not the generator.

    We are also back at the test tape as there is also the adjustment for 450mV with a 250 nWb/m magnetic reference from the reference tape.

    Try the line level check again any way. As long as the playback levels have not been moved. You should be OK.

    Also I recall that the output pots on the rear panel need to be at the click position.

    Cheers.

    GPS16
     
    smurfer77 likes this.
  3. anonyme-x22

    anonyme-x22 New Member

    Messages:
    19
    Hi,

    That's what i've done:
    Adjusted the line imput to have 450mv to the output.
    In fact i need 470mv to have one at 0Db, at 450mv, the most i can get is -1db.
    The playback level does not import because the monitor is set to source.
    The output pot were at the click point!

    Thanks in advance,
    Rgds,
     
  4. GPS16

    GPS16 Well-Known Member

    Messages:
    664
    Location:
    UK Manchester
    Hi,

    as you have the same problem on both channels, that is throwing me a bit.

    Are you doing the calibration with Headphones plugged in? The output for those is taken just before the Meter Amp. They may be an additional load which is dropping the feed to the Mater Amp.

    Just a thought!!!

    Other than that there may be electrolytics required to rule them out. The age of the machine generally dictates that they be ruled out first. If they clear the fault a full electrolytic replacement may be advisable.

    Cheers.

    GPS16
     
  5. anonyme-x22

    anonyme-x22 New Member

    Messages:
    19
    Hi,

    In fact, the right one can go at 0db with 450mv imput but after this, the -20db is not good, if i set the -20db good, the most i get is -1db/-0.5db. This is acceptable.
    The second goes from -20db to -2db/-1..5db.
    No Headphones plugged in.
    But just thought about something:
    The left and the right are separated in the line in potentiometer.
    I have mesured 450mv on the left channel, but don't have verified the right one.
    Perhaps the potentiometer has some wear so the left and the right position need to be adjusted separately in order to have 450mv on both channel output!

    Every electrolytics capacitor have been replaced except the three 0.1ùf of the servo control board, but i don't think they will change something.
    Also, when cleaning the relay of the command control board, one has broken. I have lost the auto-reverse...
    Does anyone has good references for replacing these two one.
    I'm in contact with oaktreevintage.com but, they are very slow, and the relay they have seems to come from other machines...

    Also for those who's have low output, in rec mode, don't clean the command control relay, you will end with a broken one try returning the tape :)

    i've noticed that the issue is the contact metal in the relay which is going out with years of switching. So after 40 years change them...

    Rgds,
     
    Last edited: Dec 9, 2017
  6. GPS16

    GPS16 Well-Known Member

    Messages:
    664
    Location:
    UK Manchester
    Hi,

    you should be adjusting the Input Level to get 450mV on the OUTPUT before any adjustments are made to the Cal Pot for the meters. This applies to both channels. The 0dB point should be concentrated on. The meters in the machine and the electronics driving them are not really accurate enough to give a good reading at -20dB. An external Millivoltmeter is required for that.

    Also, when setting levels for recording, the 0db level will be the one of interest.

    Cheers.

    GPS16
     
    smurfer77 likes this.

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