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Electro Harmonix Valves ??

Discussion in 'Electronic Repair' started by Phil Allison, Aug 24, 2013.

  1. Phil Allison

    Phil Allison Guest

    **Hi to the amp techs,

    there is something odd about the HEATERS in current production EH branded
    valves.

    If you check a 12AX7EH, 12AT7EH or 12AU7EH, you get 32 ohms between pins 4
    and 5.

    Check any other brand and the reading is 10 to 14 ohms.

    The EH ones still draw 160mA at 12.6 volts like the others.

    Similar but smaller differences exist with EL34EHs and 6V6EHs too.

    That Bugera I posted about a few days back would NOT have developed the
    nasty AC fuse blowing fault it did if EH brand 12AX7s were fitted - as the
    start up heater current would be 3 times less.



    .... Phil
     
  2. Phil Allison

    Phil Allison Guest

    "Arfa Daily"

    ** I thought it was obvious.

    The filament wire is not made from tungsten, as in all the others.

    ** Been there, done that.

    12.6 volts at 160 mA = 79 ohms.

    Duhhh ..............

    ** Same valves previously sold a "Sovtek " far as I know.


    BTW: Ever see a " Sovtek " amplifier ?

    Like the MIG100 or MIG 60.

    The couple I've seen were amazing pieces of work - no PCB, laced wiring,
    ceramic sockets, heavy as hell and full of MIL high parts.

    Like something built for the Russian military.



    .... Phil
     
  3. N_Cook

    N_Cook Guest

    Have you ever come across EH EL34 with suspicious inward dimples on the
    dome end.? The retainers are ring and spring so probably heat-sink the
    outer part of the dome , leaving the central area, which could perhaps
    overheat and melt inwards. The dimples are not all the same so unlikely
    an imprint from a production jig. I find it highly unlikely that 4
    valves should have ended up with much the same dimple.
    If the getter is activated with the valves dome down , could there have
    been localised glass contact heating , causing small remelts?
    All 4 test in normal range. No other signs of the valves overheating in
    use, chalky print , green and black is still green and black and readable
     
  4. Phil Allison

    Phil Allison Guest

    "Arfa Daily"


    ** What are pins 4 and 5 ??

    ** FFS read my post before you reply with such nonsense !!!!!!!!!!!!!


    ** What are pins 4 and 5 ??

    FFS read my post before you reply with such nonsense.

    The resistance goes UP from 32 to 79 ohms when power is applied.

    Shakes head, over and over............


    ..... Phil
     
  5. Phil Allison

    Phil Allison Guest

    "Gareth Magennis" >
    ** I have a few Sovtek branded 7025s with small, silver anodes - pulled
    from an amp.

    Heaters all read 32 ohms.

    Despite a long search this morning, no pic of one quite the same is on the
    net.

    Seems incredible that Russians have found a new ( and suitable ) high
    conductance heater wire to use in the last few years that is cheaper than
    tungsten.



    ..... Phil
     
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