Tube amp topologies

Discussion in 'Tube Audio' started by Squidward, May 8, 2008.

  1. Leland47

    Leland47 AK Subscriber Subscriber

    I'll really have to crack the books to get this.....

    Could someone post what type some of the common tubes are? And/Or what type of circuits they might be used in....

    EL34...very common

    EL37....more rare...had a Fisher Model 100 monoblock that used this tube.

    7591....also see this one in fisher equipment.

    6V6.... this one seems pretty common also.

    Thanks :music:


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  2. dnewma04

    dnewma04 The Healer Staff Member Super Mod Subscriber

    I believe all of those outside of the 6v6 are power pentodes. The 6v6 is a beam power tetrode.

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  3. Sprags

    Sprags Well-Known Member

    Elgin, ILLINOIS
    What baffles me is how you can put an electric current through a certain combination of tubes, capacitors, resistors, transformers, diodes and wire and stuff and stuff and magically it turns into music. I don't understand electricity because I can't see anything move...that's why I'm a mechanical engineer. So much easier....

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  4. fdwrench

    fdwrench Active Member

  5. bobabode

    bobabode AK Subscriber Subscriber

  6. kathiezman

    kathiezman New Member

    I am yet another newbie here. I wish I had found your original thread a while ago. Very simple and yet informative. I too encourage you to expand upon this "For Dummies" approach. When you speak of output tubes in parallel. This means literally that the outputs are ganged together before the OPT? This does not cause any feedback or resistance problems for each of the ganged output circuits? What is the practical limit to such an approach?


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  7. Whatever1

    Whatever1 Active Member

    All things said and done, when the audio signal gets to the end of the amp itusally goes into a transformer. Wouldn't the quality of the transformer has a big role whether the sound went through tubes or transistors. I have a MC252 that I am told has a very tube like sound. If I went to a similar McIntosh amp would the sound change much compared to the maintenance ?
    That brings about another question... OTL amplifiers ?
  8. cnpope

    cnpope New Member

    I think the reasons for excluding OTL are slightly overstated here. I have made a couple of OTL amplifiers that use just two output tubes per channel, and they achieve 25W per channel. The tubes are powerful, it is true (Russian 6C33C), but fairly easily available. There is nothing particularly complicated or exotic about the circuits.

  9. rossmason

    rossmason New Member

    I have a question about transformer speaker outputs on my Audio Research D-90 amplifier.

    I just finished repairing my D-90 and it is back to sounding great. I am baffled as to why the output transformers for the speaker terminals are configured with the 4 ohm speaker connection grounded!! Why not the low end of each transformer?
  10. jazbo8

    jazbo8 Well-Known Member

    This is done to enable balanced negative feedback to the first stage.
  11. WopOnTour

    WopOnTour Hoarder Extraordinaire

    Nowhere man
    I was looking for a good place to post a link to this video discussing phase inverter theory
    I think it's quite good

    But if it's in the wrong place or already posted, please let me know
    Rockyhill likes this.


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  12. shelly_d

    shelly_d Not An Audiophool

    Alameda CA
    His diagrams leave off some important details, though he does state in explanation some "suggestions" as to why they work. He leaves off the critical resistor from the cathodes of the long tails pair to ground that actually lets the cathode of one drive the cathode of the second. I can forgive that omission. What I do have an issue with is the diagram of the paraphase inverter. His diagram put both the output of the first tube and the input of the second tube at the same level. The one resistor to ground in that image would not "bleed off some of the signal". That design needs 2 resistors to do that. One from the bottom tube ground as he showed and a second from the output of the first tube to the input of the second tube. That could be seen on the Fender schematic he posted as at the point that fed the signal to the 2nd tube was fed by resistors of differing values. Pause the video at about 18:28 and take a look at the point that feeds the 2nd tube. That is connected to the outputs of both phase splitter tubes, the upper tube by a 1 meg resistor and the lower tube by a 25 K resistor. That difference is the resistance I am talking about.

    Other then that is is a good explanation.
  13. Ntc76

    Ntc76 AK Subscriber Subscriber

    I'm as green as you can get. I really like the youtuber Uncle Doug he explains the basics in a way anyone can understand. I also think your article is very good for the new learner. Thanks!
    smurfer77 likes this.
  14. gvl

    gvl Super Member

    After quickly glancing through this topic, is it true that OTL adds the least amount of "tube color" to sound? My SS setup sounds a bit sterile and I'm interested in trying a tube buffer or a pre to see if it helps to bring in some life. Do buffers or preamps even come in non-OTL flavors? There is Darkvoice 336SE OTL available on Massdrop now which gets positive reviews, it can be used as a pre, but if it is indeed very transparent as OTL while it is good overall it may not work very well for what I'm trying to achieve. Thoughts?
  15. mhardy6647

    mhardy6647 AK Subscriber Subscriber

    Line-level vacuum tube components rarely have any transformers in the signal path.
  16. gvl

    gvl Super Member

    Thanks, that's what I suspected.


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  17. drtechno

    drtechno Active Member

    the common places for interstage line transformers are balanced audio configurations. Common in pro audio vintage designs. Balanced audio was not common in consumer equipment sectors.
  18. Analogdino

    Analogdino Active Member

    Thornhill, Ontario, Canada
    Start by reading the first few pages of any edition of the RCA Tube Manual... a wealth of information. Then check out the basic audio amplifier schematics at the back. Then graduate to RDH4.
  19. Fab4Vinyl57

    Fab4Vinyl57 Active Member

    New Jersey
    Thanks for all that info! I have a question... What type of tube amp would power a turntable w/o a preamp? I am looking to try to switch from a solid state receiver to tube power. Would I need a preamp in addition to the vacuum tube amp? Also, are these new 'combo' SS) tube hybrids useful for anything other than Digital DVD players, ipods, etc? Thanks a lot!
    Last edited: Mar 8, 2017
  20. TENER

    TENER Active Member

    Here is a link to some youtube videos on basic tube amps and how they work. I found them to be great. I hope they will help someone else also.

    TubeGator, lokerola, Rococo and 3 others like this.

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