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Valve (tube) amplifier schematic help

Discussion in 'General Electronics Discussion' started by Solidus, Aug 22, 2012.

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  1. Solidus

    Solidus

    349
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    Jun 19, 2011
    update - I just destroyed a 6VDC/200mA power supply's enclosure with a hammer.

    Will that work at centre tap on the filament?

    Will check data sheet and post revised schematic in a little bit for review.
     
  2. Solidus

    Solidus

    349
    4
    Jun 19, 2011
    [​IMG]

    For convenience I inserted a screencap of the valve pinout into the schematic.

    Does this work?
     
  3. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    You can run this on 12V but it will require a bit more input drive (about 5mV increase) to make it clip when you want it too. With VR1 set to minimum she starts to clip @ 20mVpp input. Increasing B+ to 12V required an input of 25mVpp to produce the same amount of clipping. Actually, not significant enough to mention.

    Chris
     
    Last edited: Aug 25, 2012
  4. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Heater @ 12V: Heater wired in series. Heater current = 150mA
    Heater @ 6V: Heater wired in parallel. Heater current = 300mA

    What do you think?
     
  5. Solidus

    Solidus

    349
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    Jun 19, 2011
    Would it not be enough current?
     
  6. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Yes it would work but so would the 12V @ 450mA model this topic is about. If you power the heater directly off the transformer secondary you'll be able to get by with a 100uF filter cap for the B+. On the other hand, if you power the heater off the DC B+ you'll need about 2000uF filter cap.

    Chris
     
  7. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    No, it wouldn't. Use your original (450mA) transformer or the 1A model.
     
  8. Solidus

    Solidus

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    Jun 19, 2011
    Okay I'll go and find one in that spec.

    I just ordered the components so I should be able to construct in a few days.

    How would I rig an assembly of 8-9 LEDs for backlighting to the transformer?
     
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
  10. Solidus

    Solidus

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    Jun 19, 2011
    I've looked at that, but I haven't bothered to go into the detail of it yet.

    Generally what I'm looking at is that because I want to wire 9 LEDs in 3 parallel chains, I need each set of 3 LEDs to be below 12V and 150mA?

    Let me know if I'm on the right track.
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    If you are using a transformer, you can use AC or unfiltered DC for your heater.

    That will be more friendly to your transformer and ease the requirements for filtering the DC.
     
  12. Solidus

    Solidus

    349
    4
    Jun 19, 2011
    But would it cause audible noise considering that both plates are tied to the AC line circuit, as Chris was contending?
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The cathodes are indirectly heated. It was the big advance in tube technology which allowed AC to be used for the heaters.

    The cathode potential is floating with respect to the heaters.
     
  14. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    To power the heater directly from the transformer none of the heater pins can be referenced to ground. You must lift pin 4 off ground. I just wanted to make sure you understood this.

    Also, a 12V transformer when rectified and filtered will produce B+ of about 16V.
     
    Last edited: Aug 25, 2012
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Here's the power supply schematic
     

    Attached Files:

  16. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Here's an update to the PSU with an RC PI filter. It should provide ripple free B+ and decoupling between the stages. Back in the my day 100uF caps were physically very large because we were working with much higher voltages. You could probably get by with much smaller filter caps, like 25uF to 35uF but since a 100uF/25V or even 100uF/35V electro's aren't large these days I chose them for super ripple free filtering.
     

    Attached Files:

  17. Solidus

    Solidus

    349
    4
    Jun 19, 2011
    Now what would the B+ line be coupled to?

    Also, could I still go the route of using a 12VDC wall supply? I'm not so sure I'd feel confident building that, but we'll see when I go to buy the next round of components.
     
  18. Solidus

    Solidus

    349
    4
    Jun 19, 2011
    Would the B+ line be coupled to the 1,6 plate lines?

    Does that circuit for the supply require a detour of the original circuit to an extent?

    Just took a few hours' nap and rethought the diagram.
     
  19. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Yeah, sure. Get a switchmode supply rated at 1A or more and you'll be able to drive the heaters and the rest from the same output.

    You may get a little hash from the power supply on the B+ rail, and considering the very low current, I'd just use an RC filter to reduce it (you could go LC if you wanted to at little additional expense due to the very low current). I understand you may want distortion, but you almost certainly don't want noise :)
     
  20. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    As indicated on the schematic B+ is the Plate Supply. It gets connected to the 9V supply line on the amplifier schematic.

    Earlier I suggested a wallwart but you wanted to build your own power supply. Well, this is it and it's quite basic. If it's too complicated how do you intend to build the amplifier?

    On second thought disregard that. Working with Mains power is not a recommended novice endeavor. Use a wallwart.

    Chris
     
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