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    Is my rectifier tube bad?

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    MV213

    Posts : 10
    Join date : 2017-11-04

    Is my rectifier tube bad?

    Post by MV213 on Sat Mar 24, 2018 4:27 pm

    I just finished my ST-120 this morning. Just before lunch I got the first 6550 biased with no problems following the initial startup instructions from Bob. I then shut the amp down to have lunch. Starting back up, I now have no bias and no B+. I still have 430 vac at the rectifier tube. Seems likely to be the rectifier tube but I wanted to run it by the experts here. I think I’ll switch to a Weber copper cap if that’s the issue, I do have the TDR.

    Thanks for any help!

    J.P. Mears
    Dallas, OR—the OTHER Big D

    MV213

    Posts : 10
    Join date : 2017-11-04

    Re: Is my rectifier tube bad?

    Post by MV213 on Sat Mar 24, 2018 7:36 pm

    Well, I was anxious to try the amp out so I bypassed the rectifier tube with a couple of 1N4007 diodes. Success! My amp biased up beautifully and fired up and sounds great! I have some modifications to do, so no pictures yet. I’m glad I opted for the TDR even though I planned to use a tube rectifier.

    A quick conversation with Bob prompted me to look at my line voltage which is kind of high, almost 124 VAC. I will be picking up a variac. I’ve also ordered a new rectifier tube of a different brand and will do the diode backup mod on it.
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    j beede

    Posts : 435
    Join date : 2011-02-07
    Location : California

    Re: Is my rectifier tube bad?

    Post by j beede on Sun Mar 25, 2018 12:27 am

    Well done. 1n4007 diodes are your friend and every DIY tube audio fan should keep a supply on hand. Also, if you don't already have them, add a couple 22uF, 450V electrolytics to your tool kit. These are the easiest way to confirm/bypass a bad segment in a quad cap.
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    Bob Latino
    Admin

    Posts : 2634
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Is my rectifier tube bad?

    Post by Bob Latino on Sun Mar 25, 2018 9:57 am

    MV213 wrote:A quick conversation with Bob prompted me to look at my line voltage which is kind of high, almost 124 VAC.  I will be picking up a variac.   I’ve also ordered a new rectifier tube of a different brand and will do the diode backup mod on it.

    On the back of the parts list sheet on every VTA amp kit is a warning about running your VTA amp at voltages of 122 VAC or higher. Your addition of diodes in place of a rectifier tube will make the B+ DC voltage even higher than with a tube rectifier. My advice is to not run the amp until your variac arrives.

    Bob

    MV213

    Posts : 10
    Join date : 2017-11-04

    Re: Is my rectifier tube bad?

    Post by MV213 on Sun Mar 25, 2018 11:58 am

    Thanks Bob! I should have it soon. In the meantime I’ll work on my mods. Thanks again for your help.

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    bluemeanies

    Posts : 221
    Join date : 2015-02-09
    Age : 67
    Location : Folsom Pa.

    Is my rectifier tube bad

    Post by bluemeanies on Sun Mar 25, 2018 2:14 pm

    Thank God I purchase a Variac!
    My in house voltage level varies as low as 117 and as high as 125 on a daily basis. Since the addition of the Variac it takes the guesswork out of the equation and knowing my m125's are operating safely.
    A worthwhile investment.

    MV213

    Posts : 10
    Join date : 2017-11-04

    Re: Is my rectifier tube bad?

    Post by MV213 on Sun Mar 25, 2018 11:59 pm

    I didn’t realize my voltage was so high. My variac is on the way. Mods continue, hopefully will wrap them up in a day or so.

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