• Re: MV Rectifiers - OK-OK-OK! - Dave-A 16:33:50 02/23/03 (3)
  In Reply to: Re: MV Rectifiers - OK-OK-OK! posted by Lance on February 21, 2003 at 22:16:01:

  I wonder if using these big industrial rectifiers in a much lower power application makes them better [and safer] to use.

  I have experienced something like flashover when I powered up the amps too quickly, but I simply turned off the B+ and let the filimants heat up a little more. I have had no problems since. It seems like 30 sec. will take care of that.

  Later
  D
  
  

  ---

  • Seriously consider the 3B28 - Lance 17:50:30 02/23/03 (1)
    In Reply to: Re: MV Rectifiers - OK-OK-OK! posted by Dave-A on February 23, 2003 at 16:33:50:

    I know that many DIY amp builders like MV rectifiers. Please consider using the 3B28 in place of the 816 or 866. This tube has all of the benefits of MV but with much greater safety and less hassle. This tube was developed SPECIFICALLY to overcome many of the MV problems. The 3B28 is filled with Xenon gas. The problem with MV is the transition state between the liquid state of condensed Hg and the formation of Hg vapor. Most of the problems are related to maintaining the correct vapor concentration since the natural state of Hg is a liquid. This is not a problem with Xenon since its natural state is a gas.

    The 3B28 still needs adequate warm-up time for its filament but it is much shorter, normally on the order of 15 sec. There is another similar rectifier called the 3B25 but it is a little harder to find.

    I would also look at the 836. This is a high vaccum rectifier and thus will have greater voltage drop but it has twin cathodes (the tube is half-wave)so voltage drop is at a minimum and internal impedance is very low. This may also be a possible replacement.
    
    

    ---

    • Re: Seriously consider the 3B28 - Dave-A 06:30:02 02/24/03 (0)
      In Reply to: Seriously consider the 3B28 posted by Lance on February 23, 2003 at 17:50:30:

      Thanks Lance. I will look into these.

      Later
      D
      
      

      ---
  • More MV rectifier info. - Lance 17:18:11 02/23/03 (0)
    In Reply to: Re: MV Rectifiers - OK-OK-OK! posted by Dave-A on February 23, 2003 at 16:33:50:

    What you saw was not a flash-over. A flash-over occurs with HV applied and is essentially an internal short. What you saw was an effect caused by insufficiently developed gas plasma caused by not allowing the tube to heat up long enough. Formation of the gas plasma is important as it protects the filament from back bombardment from high-velocity positive ions. This back bombardment will eventually destroy the oxide coating on the filament. These tubes are also sensitive to over and under filament voltage. In commercial use most are operated with some type of a constant-volatge transformer that incorporates both over and under voltage relays which will open the HV supply primary if an out of range filament voltage is detected.

    Undoubtedly, running MVR at lower ratings will help but all the issues with filament voltage,warmup and temperature range are still present.

    One last thing. MV rectifiers can have breakdown efects in the MV plasma if subjected to strong magnetic fields. They should be located a reasonable distance from chokes, power tansformers and OPT's. If subjected continually to these fields tube life will be shortened.

    Check the particular tube specs. for the recommended warm-up time.
    
    

    ---

This post is made possible by the generous support of people like you and our sponsors:

Schiit Audio

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---