6BM8 Volatge regulator

Discussion in 'Tube Audio' started by jaymanaa, May 30, 2010.

  1. jaymanaa

    jaymanaa AK Subscriber Subscriber

    Anyone ever use the 6BM8 as a voltage regulator?:scratch2:
  2. Squidward

    Squidward Scrappy Mod Moderator

    I've seen it used in some PS arrangements, but I can not recall which ones, and how/what they actually regulated. Neat concepts, but nothing I've built/played with (yet).

    My only problem with using 6BM8 in a PS is that I don't have many of them, and I can't find them cheap ever as they're a semi-popular output tube. Would be nice to find some PS schematic with more obscure tubes.

    What'cha building? This for the preamp?
  3. jaymanaa

    jaymanaa AK Subscriber Subscriber

    Yep, the preamp PS. I saw a design somewhere that used feedback to the triode grid to regulate. I thought it would be neat to do a different type of tube regualtion, and I think I will only need two.:yes:
  4. soundmotor

    soundmotor super modified Subscriber

    This one?

  5. jaymanaa

    jaymanaa AK Subscriber Subscriber

    That's it I think! What is the heater bias terminal all about??:scratch2:
  6. soundmotor

    soundmotor super modified Subscriber

    That is a question for Eric Barbour as I sure as hell don't know.
  7. golana

    golana analog Subscriber

    Whatwould the second valve be?

    Oh, never mind. I see iot's the 2nd half.

    Looks interresting!
  8. Scuzzer

    Scuzzer Fixed Bias

    I had an answer but wasn't sure it was right so I deleted it.
  9. Bob91343

    Bob91343 Super Member

    The heater bias allows you to keep the heater-cathode voltage within ratings.

    Where can one buy some of these tubes without paying top dollar?
  10. electroking

    electroking a- v- karma member

    A pass-tube! Looks like a pass transistor in a solid-state regulator...
  11. Scuzzer

    Scuzzer Fixed Bias

    Russian 6F3P. About $4 or so each.
  12. vinylkid58

    vinylkid58 Super Member

    Here's one based on the 6GV8. Scroll down the page for the schem.


  13. Bob91343

    Bob91343 Super Member

    Well you can buy those tubes at about $4.50 but shipping cost puts it out of the running.

    Those regulator circuits have a major flaw. The zener diode is a high voltage unit and its temperature coefficient of voltage is high. So the output voltage will climb considerably as it warms up. If I remember correctly, the coefficient runs around .12% per degree C so if there is a 40 degree rise the voltage will climb about 5%. For 250 Volts that will be 12 or 13 Volts drift.

    A more stable solution would be to use a VR tube. Their coefficient is very small and they are available in several voltages from 75 to 150 Volts.
    Last edited: May 31, 2010
  14. soundmotor

    soundmotor super modified Subscriber

    On an audio circuit is that an issue? The supply would be stable once it reaches the final voltage, yes?

    But where in the circuit does it connect?
  15. soundmotor

    soundmotor super modified Subscriber

    You left out the best part, some like the OD3 glow purple -


  16. battradio

    battradio AK Subscriber Subscriber

    To the center tap of the filament transformer , if you look in a tube manual it will give the voltage rating for heater cathode,it is 100 volts for a 6BM8
  17. wa2ise

    wa2ise AK Subscriber Subscriber

    Do you really need a tube to do this? I wouldn't think you'd hear any "tube magic" with a tube regulator.

    I've used high voltage power transistors (the sort that were used for the horizontal output in older TVs and computer monitors) to do this.
    Just connect a regulated source to the transistor base, like a VR tube or a stack of neon bulbs.

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