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Rectifier Hum

Posted on March 13, 2017 at 19:24:08

Posts: 442
Location: South Central
Joined: May 27, 2002
September 12, 2002
I recently tried an experiment with my amp. I substituted a NOS Mullard GZ34 for a 5U4GB. Where there was NO noise or hum with the 5U4GB, the GZ34 hums. I have two of them and substituted one GZ34 for the other GZ34. The hum decreased but did not go away. I Thought full wave rectifiers are interchangeable as long as the voltage differences are accounted for.

My problem is that while it hums, I like the sound of the GZ34. Any ideas what might be causing this?


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RE: Rectifier Hum, posted on March 13, 2017 at 19:32:33
Bored Member

Posts: 12349
Joined: July 31, 2007
May 17, 2009
The GZ34 will make more B+. You may need to reduce the idle bias of your output tube ---> to have idle wattage in nominal range.


RE: Rectifier Hum, posted on March 14, 2017 at 13:08:07
Alpha Al
Industry Professional

Posts: 2430
Location: N. Carolina
Joined: February 16, 2004
December 3, 2015
You might want to verify that the B+ is taken off pin 8. That is the cathode terminal of a GZ34.

With a 5U4, the B+ can be taken from either pin 8 or pin 2, it does not matter because there is no cathode

You can get hum taking B+ from pin 2 of a GZ34.


RE: Rectifier Hum, posted on March 14, 2017 at 17:40:31

Posts: 1757
Location: PACIFIC
Joined: August 8, 2010
December 0, 0000
Yes, the increased voltage will also make more power and increase the gain of the drive stage and could also make a low level hum more evident.


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