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Tek scope question

Discussion in 'Electronic Equipment' started by Chris Young, Jan 2, 2004.

  1. Chris Young

    Chris Young Guest

    I finally got around to buying a scope yesterday (Tek 465B), and in
    looking thru the specs in the manual, it states that the max input
    voltage (for either DC or AC coupled) is 250Vp plus the peak AC voltage,
    or 500Vpp.

    I intend to use this in some upgrades to my tube preamp; I would like to
    take a look at AC ripple off the filter caps in the PS sections, one
    portion which is at 425Vdc, the other which is at 250-260Vdc or
    thereabouts. I know the second one should be OK, but what about the
    first?

    When I was a tech, I didn't worry much about it, since it wasn't my
    scope <g>. Now that it is, uhhh...

    Thanks,

    Chris

    (remove the obvious to reply)
     
  2. Robert Baer

    Robert Baer Guest

    As long as there is no ground loop (chassis of the preamp and chassis
    of the scope), then the ground of a X10 probe is connected to the ground
    of the PS (presume at chassis ground), and the probe tip goes to the
    monitor point.
    The probe rating, as i remember, is 500V; since it is dividing by 10,
    that gives a maximum of 50V to the signal input connector - which has
    its own rating.
    There are special high voltage probes for monitoring signals in the KV
    region, which may be useful on rare occasion.
     
  3. BFoelsch

    BFoelsch Guest

    My 465B book interprets it differently, it say 250V for the TOTAL of the DC
    plus the peak AC, or 500 v P-P below 1kHz.

    Don't be cheap, buy yourself some 10X probes and then all will be legal. You
    can get decent probes new for about $35. Look at the Velleman or Pomona or
    Probemaster probes, a step up would be PMK. If you work on tube stuff you
    may want to consider getting a few 100X probes as well. The minimum
    sensitivity of the 465B (without probes) is 5V/division, so, without probes,
    you can display only 40 volts P-P on the screen. That is only about 12
    VRMS, and you may well exceed that in some preamp and many power supply
    situations.

    However, for audio frequency work, you could just hook up an external series
    capacitor to block the DC component. Likewise, for low frequency work, you
    could improvise a 10X probe by putting a 9M resistor in series with the
    input. Don't expect much accuracy above 5 kHz or so, however.
     
  4. Chris Young

    Chris Young Guest

    Hi,

    Thanks for the response. The scope came with two probes, P6105 and P6109 (I
    believe). They are both x10 probes.
     
  5. If you have x10 probes, the probe is likely the limiting factor. There is a
    website somewhere which has a table of the tech details of all Tek probes.
    Unfortenately I lost the URL, I seem to recall it was dedicated to old Tek
    equipment.

    Mat Nieuwenhoven
     
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