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    Driver tube flashing! ST-35

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    hrudu90

    Posts : 26
    Join date : 2011-01-02

    Driver tube flashing! ST-35

    Post by hrudu90 on Wed May 02, 2012 11:25 pm

    My driver tube on my ST-35 is flashing (only one channel)when turning on!
    The sound is still good as usual!
    Any idea? Time to replace the driver tubes?

    I would appreciate your inputs.

    Thanks


    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Driver tube flashing! ST-35

    Post by Bob Latino on Thu May 03, 2012 11:15 am

    Hi,

    The fact that the tube flashes on start up is probably an indication that that tube is "on the way out" ... You should replace the tube because when it does die it could take out a component (resistor, capacitor etc.) on the driver board for that channel. Personally if it were my ST-35, what I would do is pick up TWO NEW 7247/12DW7 driver tubes and use the one GOOD 7247/12DW7 driver tube you have as a spare.

    Bob

    plexus

    Posts : 94
    Join date : 2012-02-18
    Location : Toronto, Canada

    Re: Driver tube flashing! ST-35

    Post by plexus on Thu May 03, 2012 1:04 pm

    Bob's suggestion is a good one. I always have spare tubes around and also a set of "junkers" for testing and burn-in purposes. its a pain because you have to buy the extra tubes and store them but when a tube dies you can instantly replace it instead of waiting for one to be shipped.

    scott6058

    Posts : 37
    Join date : 2009-01-21

    Re: Driver tube flashing! ST-35

    Post by scott6058 on Thu May 03, 2012 2:49 pm

    I thought there was a post about the Mullard flash as being normal.

    hrudu90

    Posts : 26
    Join date : 2011-01-02

    Re: Driver tube flashing! ST-35

    Post by hrudu90 on Thu May 03, 2012 7:02 pm

    Thank you, Bob, for your suggestion!
    I did swap the driver tubes and the same tube is now flashing on the other board.
    So it is certainly the tube is 'on the way out'.

    Thank you.

    GP49

    Posts : 718
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: Driver tube flashing! ST-35

    Post by GP49 on Fri May 04, 2012 12:21 am

    But...is it a Mullard? MANY Mullards "flash" brightly at turn on and do so for their whole lives. There may be nothing wrong with the tube.

    I don't know who made the 12DW7s in my dad's old EICO ST-40 but they "flashed" like that the whole time he used it. Still might, but it's been in storage for more than thirty years and I would not want to just plug it in and turn it on!

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Driver tube flashing! ST-35

    Post by Bob Latino on Fri May 04, 2012 7:25 am

    I guess I read something into the poster's text and thought of the tube "flickering" rather than "flashing" when first turned on. What some of the other's have said is quite true. Mullard 12**7 and other manufacturers who had their small signal 12**7 tubes made by Mullard do exhibit a flashing when first turned on when the tube is cold. If the tube has been on for a period of time and then the amp is shut off and then turned on again while the tube is warm - then the tube WON'T FLASH. If your tube exhibits the symptoms mentioned in the previous sentence, then the tube was most likely made by Mullard and is OK. Sorry for any confusion I may have cause by my post above ...

    Bob

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