• RE: MQ OPTs for Tubelab SE 300b - Paul Joppa 15:04:55 07/26/15 (4)
  In Reply to: RE: MQ OPTs for Tubelab SE 300b posted by jdrouin on July 23, 2015 at 10:46:42

  At 400 volts plate to filament (the filament is grounded in the circuit shown), a current of 55-60mA is plenty when using a 5000 ohm transformer. So an EXO-003 would do the job in parafeed into the EXO-050.
  
  At Bottlehead, long ago we used the EXO-003 at 70mA with 300Bs with no problems - it is rated very conservatively. We ran it at 3000 ohms with the TFA-2004.
  
  Don't ignore the RH-60 Robin Hood series feed transformer. It's a compromise, but Mike has a good sense of where and how to make compromises. :^)
  
  My two cents.
  
  
  

  ---

  • RE: MQ OPTs for Tubelab SE 300b - jdrouin 09:30:26 07/27/15 (3)
    In Reply to: RE: MQ OPTs for Tubelab SE 300b posted by Paul Joppa on July 26, 2015 at 15:04:55

    Thanks, Paul and braubeat. I hadn't considered parafeed before, in part because I've never read about any TSE builders using it. I did a search and came up with one person who in fact used the EXO-003 and a Robin Hood OPT, which he vastly preferred over the James OPTs he had used initially.
    
    There wasn't much info about how he did it but I will write to find out. If parafeed requires a change to the circuit topology, this could be a real issue because the circuit is embedded in a PCB. It does have some variability through the use of jumpers.
    
    Since this is my first build, I was planning to go with a more traditional SE OPT that nearly everyone uses for this project, but I'm definitely open to parafeed and am going to look into this more.
    
    Question: if I were to go with the EXO-003 and either the EXO-050 or RH-60, what kind of wattage per channel do you think I'd get with 300Bs?
    
    Jeff
    

    ---

    • RE: MQ OPTs for Tubelab SE 300b - Paul Joppa 13:04:36 07/27/15 (2)
      In Reply to: RE: MQ OPTs for Tubelab SE 300b posted by jdrouin on July 27, 2015 at 09:30:26

      The RH-60 is a series feed transformer. The same coil is available for parafeed, where it handles zero direct current but has more inductance for deeper bass - assuming the parafeed choke has more inductance than the airgapped RH-60.
      
      For parafeed, no changes to the circuit board are needed; you just have two pieces of iron and a parafeed capacitor that are mounted off the board. (A 3.3uF/630v capacitor would be a good choice.)
      
      Power is about 8 watts - see the chart at the link.

      • 300B operating point chart   (Open in New Window)

      
      

      ---

      • RE: MQ OPTs for Tubelab SE 300b - braubeat 08:28:58 07/28/15 (1)
        In Reply to: RE: MQ OPTs for Tubelab SE 300b posted by Paul Joppa on July 27, 2015 at 13:04:36

        here is one example of how the parafeed output can be hooked up.
        
        http://www.magnequest.com/diy/lessard/diy_lessard_schematic.htm
        
        michael
        

        ---

        • RE: MQ OPTs for Tubelab SE 300b - braubeat 08:35:03 07/28/15 (0)
          In Reply to: RE: MQ OPTs for Tubelab SE 300b posted by braubeat on July 28, 2015 at 08:28:58

          if you decide to go with the RH series output with a plate choke you just request the parafeed version when you order it
          
          michael
          

          ---
• RE: MQ OPTs for Tubelab SE 300b - jdrouin 10:14:36 07/24/15 (1)
  In Reply to: RE: MQ OPTs for Tubelab SE 300b posted by jsdrouin@gmail.com on July 23, 2015 at 10:46:42

  Hi Mike,
  
  Sorry to put you on the spot there. It wasn't my intention. I just suck at delayed gratification and was getting hot to trot on this project.
  
  If you have any thoughts on what might work for the project, let me know. Have a great vacation.
  
  Best,
  
  Jeff
  

  ---

  • RE: MQ OPTs for Tubelab SE 300b - braubeat 08:40:41 07/25/15 (0)
    In Reply to: RE: MQ OPTs for Tubelab SE 300b posted by jdrouin on July 24, 2015 at 10:14:36

    You can always go with the ex0-50 and bac-80. That would be 5K and 80ma. It would require only minor changes to the circuit. Lots of people think this is the best sounding unit Mike makes. I have an 845 amp running at 480 volts 80ma. into a 5K parafeed output. It is the best sounding amp I have heard.
    
    Michael
    

    ---
• RE: MQ OPTs for Tubelab SE 300b - mqracing 23:47:25 07/23/15 (0)
  In Reply to: RE: MQ OPTs for Tubelab SE 300b posted by jdrouin on July 23, 2015 at 10:46:42

  Hi Jeff:
  
  I did get your email... and read it... then scratched my head because I did not (and do not) have a quick or surefooted answer for you.
  
  Many times I'll get an email that (with the best of intentions on my part) I'll read and say to myself that (at a minimum) I'll need some time to think it through or I'll need to do some research or that I need to contact one of my audio bud designers who might have a better answer than I have...
  
  so what happens is.... the email does not get answered right away... because I don't have an answer to offer...
  
  and I'm thinking that I will get back to it...
  
  and before I know it the email gets buried...
  
  what I probably should do is advise the email sender to post their questions\queries on the MQ forum here at Audio Asylum if I cannot readily reply.
  
  So apologies... and I'll try harder to be more decisive in the future in directing difficult to answer emails to post to the forum.
  
  Please bare in mind... that I am NOT a circuit designer or EE or etc. I'm reasonably good a designing and building magnetics... but many of the applications specific inquiries that I get... really fall outside of my area of expertise.
  
  best of,
  
  I hope one or more of our readers can help you out,
  
  MSL
  
  
  
  Builder of MagneQuest & Peerless transformers since 1989
  
  
  

  ---

Post a Followup:

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

Crux Audio

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

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

---