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Anybody here into vacuum tube amps?

Discussion in 'Fred's House of Pancakes' started by bredekamp, Jul 1, 2010.

  1. bredekamp

    bredekamp Member

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    Hi.

    This is a picture of a tube amp kit I bought a while back. It's a great kit, but it has a crummy power supply so I've been messing with it trying to get the ripple down. The anode voltage is 200V!

    I'm too scared to leave the thing on when I'm not in the room in case my cat comes sniffing.

    I just love tubes. They're so much more fun than transistors. I recently ordered some tubes on e-bay to build this:

    Hybrid Headamp

    I'm gonna etch two boards and give the one away to friend for his birthday. It only uses 24V so it's "safe" to stick your fingers into.
     

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  2. KK6PD

    KK6PD _ . _ . / _ _ . _

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    If you have a Hummmmm or AC Ripple problem you need to either replace or add bigger power supply filter capacitors. Caps will dry out from the heat of the tubes. If you have the schmatic drawing, look for the caps that are connected to the output of the AC rectifier. 200 volts B+ is typical. I would use a cap rated at least 300 volts plus, and 30,000 mfd or more. If you want PM me, I fix complicated electonics for a living, tube amps are easy! This is a simple fix!!

    Also, make sure the humm is not a gound loop problem. To test this, unlug ALL inputs, and turn volume up. If it's quiet, it's not the Caps, but a bad ground from something connected to the amp. If however you hear the humm with nothing plugged into the amp, caps are bad!!
     
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  3. bredekamp

    bredekamp Member

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    Thanks. I'll try the LARGE value cap and check out the ground. It came with a measly 220uF which I swapped for a 1000uF and there was an improvement according to my oscilloscope view. On 200V there is now 800mV peak to peak of ripple. It's not audible on speakers, but on headphones during quiet passages it's there.
     
  4. KK6PD

    KK6PD _ . _ . / _ _ . _

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    OK your on the right track, if you want a quick service tip, take a pair of insulated jumper clips, I made up a set, Red & Black about 18" long, and get your new test cap, and just jumper it across the existing cap in question. I do this trick with the power ON, I first connect the cap ground to cap in question ground, turn on the amp, set the volume, pick up the INSULATED + lead and simply touch it to the cap in question + connection.
    WARNING, you will see a slight spark, that's the start of the test cap charging up, it lasts a mini fraction of a second, after the first time, I got over it.....however this test will immediatly let you hear how much of a difference the cap you picked has on the hummmm your trying to eliminate, you could just connect both leads with power OFF, but then you have to remember how loud it was...I am assumng you are using an AC coupled O'scope to monitor the B+ line?
    There will ALWAYS be some small AC component on the output, it's part of the tube thing, but you sure can take steps like you are trying to minimize it. When done with his test, DO NOT touch the test Cap's + and - leads. The cap is now charged to B+ potential, and you will get an annoying shock if you touch them!!! Use the jumper clip to short the caps + to - leads, again small spark, but the cap is now safely discharged!!!

    I too love Headphones, and YES, humm is annoying!!! That's why I too went the route of a seperate headphone exclusive amp. SWEET!!! Good Luck
     
  5. usbseawolf2000

    usbseawolf2000 HSD PhD

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    Yes, Woo Audio make the best bang for the buck amps. I listened to WES at a show and it blew me away.
     
  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    How much power does that amp produce?

    Is the amplifier working in Class A, to minimize distortion?

    Where can you buy replacement tubes (eBay, or ??)

    <Regarding your headphone amp project> I don't understand how a low voltage tube works. The spacing between the filament and the anode must be really tiny to allow 24V on the anode to attract the electrons produced by the filament. I would suspect that such a tube doesn't offer much dynamic range.

    I'm more familiar with mobile tube radios that use a vibrator to produce high voltage for the tube anodes.
     
  7. qbee42

    qbee42 My other car is a boat

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    I was always a big fan of the 12AU7.

    Tom
     
  8. Patrick Wong

    Patrick Wong DIY Enthusiast

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    My preferences had been more towards transmitting tubes: 6146B, 3-500Z, etc.
     
  9. qbee42

    qbee42 My other car is a boat

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    Like to run things at a bit higher frequency I see. Perhaps some sort of Klystron would suit your fancy.

    Tom
     
  10. Patrick Wong

    Patrick Wong DIY Enthusiast

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    No, I was never into making my own radar or trying to communicate at UHF frequencies, at the power levels implied with the use of that power tube type. I guess the closest that I got to that is using my kitchen microwave with its magnetron tube... ;)
     
  11. bredekamp

    bredekamp Member

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    Class A, 8 Watt into 8 ohm

    Look at Oatley Electronics
    Oatley Electronics

    or

    DIY Audioprojects
    DIY Vacuum Tube (Valve) Amplifier Projects - Hi-Fi Audio

    Replacement tubes are readily availble on ebay and also from:

    http://www.tubedepot.com

    The low voltage tubes are called "Space Charge Tubes" They often employ an internal grid at a slight positive potential to throw the electrons towards the much more positive anode. They cannot produce much power and is therefore used in so called hybrid designs where the tube provides the voltage gain and a germanium transistor would provide the current to the load.

    look at:

    http://www.junkbox.com/electronics/lowvoltagetubes.shtml
     
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  12. bredekamp

    bredekamp Member

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  13. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Yes, I recall the main consumer purpose for those tubes was to serve as RF amps within television receiver tuners.


    Thanks, I had not previously heard of this tube design, nor the idea of putting a small positive voltage bias on the grid.
     
  14. qbee42

    qbee42 My other car is a boat

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    Small acorn tubes have been used since WWII. They were used in anti-aircraft VT shells, where Doppler radar was used as a proximity fuse.

    Tom
     
  15. Classic Car Guy

    Classic Car Guy Active Member

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    Hi there,
    This might be a too late follow-up. Have known anyone install a tube amp lets say in a regular car or a Prius?
     
  16. audiodave

    audiodave Active Member

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    I've seen fairly modern tube amps in the 12 volt market but pretty pricey. I wouldn't bother.

    Posted via the PriusChat mobile app.
     
  17. Classic Car Guy

    Classic Car Guy Active Member

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    Just finished working on the Prius today. Trans fluid, Lube, oil and filter. lower motor mount, idler bearing, blow out the air cleaner...
    Part 2:
    Just finished working on my Yaqin. Changed the bias resistor, check the anode, cathode voltage, bias the amp, change new quads of KT-88. Check all the preamp tubes. Hopefully I can get atleast 2000 hours on this set. I might try a different output tube setup.
    Price of good tubes are totally out of control now too. Unless I can find a newer generation/modern tube that has the sound and quality.

    Joe_Stereo_May2017.jpg
    SAM_6967.JPG
     
    #17 Classic Car Guy, Feb 17, 2019
    Last edited: Feb 17, 2019
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  18. a_gray_prius

    a_gray_prius Rare Non-Old-Blowhard Priuschat Member

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    Are you familiar with the Fallout series of video games? I imagine it would be a lot like that.

    There are a few companies that apparently make mobile tube amps:

    Milbert, the Most Musical Amplifiers

    Butler Audio
     
  19. Classic Car Guy

    Classic Car Guy Active Member

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    Have you ever used a Genalex gold lion KT-88? I ordered a brand new set of 8 and I saw the readings are way too lower than the standard ones I use. New one is normally 4750. The set I got is only 4000 micro ohms. Maybe I should return this?
     
  20. Classic Car Guy

    Classic Car Guy Active Member

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    Sounds sweet. I don't think I can afford that. Lol... Anyways I got my setup don't. I kept the original JBL's But in the back side... Whallaa!
    Joe_Rockford_Subwoofer_Setup.JPG