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    Rectifier Testing Question

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    Drugolf

    Posts : 25
    Join date : 2014-12-29

    Rectifier Testing Question

    Post by Drugolf on Mon Jan 12, 2015 1:54 am

    So after doing some restoration work on my ST70 and replacing the rectifier tube, the new one seems to be glowing very bright. Down at bottom area of the heater I guess is where I would say it is from. I have not worked with tubes enough to say better.

    I want to test things before I run it as it is. What are some specific tests I should make sure I do related to the rectifier? Some tests I may do with my multimeter. Other test requiring additional equipment I will leave to my tech. I did just do the Diode mod. I read a little about filament voltage?

    Thanks guys.

    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: Rectifier Testing Question

    Post by MontanaWay on Mon Jan 12, 2015 1:59 am

    Drugolf wrote:So after doing some restoration work on my ST70 and replacing the rectifier tube, the new one seems to be glowing very bright.  Down at bottom area of the heater I guess is where I would say it is from.  I have not worked with tubes enough to say better.

    I want to test things before I run it as it is.  What are some specific tests I should make sure I do related to the rectifier?  Some tests I may do with my multimeter.  Other test requiring additional equipment I will leave to my tech.  I did just do the Diode mod.  I read a little about filament voltage?

    Thanks guys.  

    what model rectifier tube are you using? Different manufacturers of the same model tube can 'look' different....even 'act' different...some are a little brighter than others, quite normal. Apart from the brightness, everything else is working OK?, sound is good, no hum etc.?
    All voltages meter out OK?

    Drugolf

    Posts : 25
    Join date : 2014-12-29

    Re: Rectifier Testing Question

    Post by Drugolf on Mon Jan 12, 2015 2:36 am

    Japanese mullard.
    I recall everything testing okay but I want to go back and check with a focus on that area. It was working when tested but the tube seemed bright throughout that process. It was just bench test speakers so I have not got to quality of sound. I want to test more before running this tube much.

    eickmewg

    Posts : 38
    Join date : 2014-08-29

    Re: Rectifier Testing Question

    Post by eickmewg on Mon Jan 12, 2015 7:41 am

    I am using a JJ GZ34 in my VTA ST-120. The heaters in this tube are considerably brighter than either the KT-120 power tubes or the JJ ECC82 drivers. I wouldn't worry if things sound good.

    Drugolf

    Posts : 25
    Join date : 2014-12-29

    Re: Rectifier Testing Question

    Post by Drugolf on Mon Jan 12, 2015 11:24 am

    Can someone describe for me how to correctly test/check the filament voltage?

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Rectifier Testing Question

    Post by Bob Latino on Mon Jan 12, 2015 11:58 am

    Drugolf wrote:Can someone describe for me how to correctly test/check the filament voltage?

    Just check the AC voltage across pins 2 and 7 of any output tube. You should get about 6.3 volts AC. With today's higher voltages, however, it could be anywhere between 6 and 7 volts AC ..

    For the rectifier tube, you should get about 5 volts AC across pins 2 and 8. It will probably be a little higher than that ..

    Bob

    peterh

    Posts : 641
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Rectifier Testing Question

    Post by peterh on Mon Jan 12, 2015 12:04 pm

    Drugolf wrote:Can someone describe for me how to correctly test/check the filament voltage?
    Any decent voltmeter with an AC range.

    Note that the filaments on the GZ34 is elevated to +500V DC be very careful!
    You could connect the voltmeter ( on pin 2 and 8 on the GZ34 ) in advance before powering up.
    When powered up it should have 5VAC +-10%

    Filaments on other tubes (in a st70) should be at 6.3VAC , these are located on pin 2 and 7
    on the octals and 4,5 to 9 on the novals ( see tube data for the specific tube).
    There is two 6.3 V windings on ST70, one for each side. On the original st70
    those were connected in the octal sockets on the front, thus it was very easy to measure.
    ( from another post )
    I have found no layout of the front octal sockets however,this is extracted from the build instructions
    ( it might be in error )
    1 and 2 _might_ be 6.3V
    3 is ground
    5 B+
    8 bias test

    Drugolf

    Posts : 25
    Join date : 2014-12-29

    Re: Rectifier Testing Question

    Post by Drugolf on Mon Jan 12, 2015 4:30 pm

    Thanks guys! Right on at 5.
    Tube burned out. I went out of teh room for 2 minutes, came back in and the heater was no longer aglow. Must have been bad. Put in a new one (Groove tube) works fine.

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