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    tube rectifier question on an ST-120

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    kevinmi

    Posts : 54
    Join date : 2009-11-17

    tube rectifier question on an ST-120

    Post by kevinmi on Sun Apr 07, 2013 12:35 pm

    I'm thinking of trying a GZ-33 or 37 rectifier tube on my ST-120 amp. I was wondering if the extra filament voltage draw would hurt the transformer? I know that some say there is no difference in sound between a tube rectifier and a Weber SS copper cap, but I still think a tube rectifier looks cool all lit up. The taller GZ 33 and 37's should look that much cooler!
    I'm currently running GL KT88 tubes, but plan on switching to KT-120 tubes in the near future. I am running a trio of vintage RCA clear top 12au7's in the driver board with good results. I have a few other vintage 12ua7 tubes I'm going to try after my PIO caps break in. I am a tube rolling junkie, always looking for that perfect combination!

    erlingt

    Posts : 15
    Join date : 2010-06-23
    Location : Denmark

    Re: tube rectifier question on an ST-120

    Post by erlingt on Sun Apr 07, 2013 4:43 pm

    I am running my VTA ST-70 with a GZ33. It works well, looks good and sounds good. And it is reliable, mine has now served about 1.500 hours, and is still doing fine.

    Bob Latino
    Admin

    Posts : 2376
    Join date : 2008-11-26
    Location : Massachusetts

    Re: tube rectifier question on an ST-120

    Post by Bob Latino on Sun Apr 07, 2013 5:54 pm

    Hi Kevin,

    You can run a GZ33 or a GZ37 tube rectifier in place of either a GZ34 or a Weber WZ68 SS rectifier in a VTA ST-120. The extra filament draw will not hurt the power transformer of the VTA ST-120. The only down side of using a GZ33 or GZ37 is that they are not made anymore and they tend to be expensive to purchase.

    Also remember to REBIAS the amp whenever you make a rectifier change ..

    Bob

    peterh

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

    Re: tube rectifier question on an ST-120

    Post by peterh on Mon Apr 08, 2013 2:03 am

    5U4G is available from JJ
    But it's a direct heated and will start faster. Bob , is this a problem ?


    Bob Latino
    Admin

    Posts : 2376
    Join date : 2008-11-26
    Location : Massachusetts

    Re: tube rectifier question on an ST-120

    Post by Bob Latino on Mon Apr 08, 2013 5:01 am

    peterh wrote:5U4G is available from JJ
    But it's a direct heated and will start faster. Bob , is this a problem ?


    No ... You can use a 5U4 as a rectifier in a VTA ST-120. The only minor issue is that a 5U4 has a higher voltage drop than a GZ34 and power of the amp will be very slightly lower .. The slight drop in power, though, may not even be noticeable if your speakers are fairly efficient. The advantage to using a 5U4 is that there are still many well made USA 5U4's floating around at reasonable prices. A 5U4 was used as the rectifier in many of the earlier tube color TV's of the 1960's so many of these tubes were made and many are still in circulation. Personally, I would consider a USED RCA, Sylvania or GE 5U4 (provided it tests as new) over the modern JJ version.

    If you do switch to a 5U4 after having a GZ34 or a Weber WZ68 in there, you will have to rebias your amp.

    Bob

    kevinmi

    Posts : 54
    Join date : 2009-11-17

    Re: tube rectifier question on an ST-120

    Post by kevinmi on Sun Apr 14, 2013 2:58 pm

    I just pulled the trigger on a pair of NOS/NIB Mullard GZ33 rectifier tubes. I'll report comparisons between my Mullard GZ34 and the GZ33 when I get them and have time to play with them. Maybe I'll throw in the Weber WZ68 and do a 3-way shoot out!

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