• RE: EL-34 PP schematic - caffeinator 09:00:09 02/14/08 (1)
  In Reply to: RE: EL-34 PP schematic posted by mqracing on February 09, 2008 at 22:07:59

  Just curious what the nominal power output is?
  
  

  ---

  • approx 30 wpc..... (nt) - mqracing 09:42:58 02/15/08 (0)
    In Reply to: RE: EL-34 PP schematic posted by caffeinator on February 14, 2008 at 09:00:09

    ...
    
    

    ---
• MQ 060 - NewbieBaby 10:07:36 02/13/08 (2)
  In Reply to: RE: EL-34 PP schematic posted by mqracing on February 09, 2008 at 22:07:59

  I interpreted this was phased out of production (bought 2 as the sunset). Is the reference to a different PT (I do note the "R")?
  
  

  ---

  • and one other quick note..... - mqracing 11:17:55 02/13/08 (0)
    In Reply to: RE: MQ 060 posted by NewbieBaby on February 13, 2008 at 10:07:36

    If we were to build the MQ 470 is would be a very much hot-rodded version of the original using many of the design concepts that we have incorporated in our transformers with the EL suffixes.
    
    What did GM say--- this isn't your grandad's oldsmobile :=)
    
    but, interestingly, the architecture of the original dyna coil is one of the few designs in the world that really are optimized for UL operation. See Norman Crowhurt's seminal article on "optimizing a trans and circuit for UL operation" for further details which was reprinted in an early Glass Audio magazine. Other nice thing about the ST 70 output is that it operates conservatively from an AC flux density point of view.
    
    With the changes I have in mind--- incorporating the EL techniques that we've used successfully in other signal handling tranneys--- I think this trans would rock in this circuit.
    
    MSL
    
    
    
    

    ---
  • RE: MQ 060 - mqracing 11:10:50 02/13/08 (0)
    In Reply to: RE: MQ 060 posted by NewbieBaby on February 13, 2008 at 10:07:36

    Hi. The MQ-060 is out of production. We simply used several of the voltages and etc of this trans in our mockup. But notice that we only are using one of the two 6.3 vct windings. Note the differing part number on the print (MQ R-060M). Our intent would be to build in monoblocks. And in actuality--- I would probably design a whole new power trans for this EL 34 circuit.
    
    But no dice on bringing back the MQ-060 :=).
    
    MSL
    
    

    ---
• Why not help out the phase splitting with the input transformer? - Scholl 16:59:19 02/12/08 (1)
  In Reply to: RE: EL-34 PP schematic posted by mqracing on February 09, 2008 at 22:07:59

  If you're going to use an input tranny you might want to consider integrating a preamp circuit with the total design too. From what experience I have with input transformers, I’ve found I couldn’t use just any preamp to drive it. If the design focus was shifted so that the input transformer was now a preamp output transformer it could handle the phase splitting too. Little tiny transformers split phase very well.
  
  Built it and lets us know how you like it.
  
  
  

  ---

  • RE: Why not help out the phase splitting with the input transformer? - mqracing 09:45:01 02/13/08 (0)
    In Reply to: RE: Why not help out the phase splitting with the input transformer? posted by Scholl on February 12, 2008 at 16:59:19

    Hi Scholl:

    you wrote:

    ::::If you're going to use an input tranny you might want to consider integrating a preamp circuit with the total design too.::::

    as drawn this circuit would be for someone who wants to go direct from their cd player to their amp--- but need provisions for volume discrimination. The 10K input impedance should be sufficiently light enough load for the vast majority of cd players with solid state outputs.
    As well as many tubed cd players with sufficiently low output impedance.

    :::From what experience I have with input transformers, I’ve found I couldn’t use just any preamp to drive it.:::

    this is a bit too vague--- big difference btwn driving say a 600 ohm (or lower) input trans and an input trans with a 10K or higher input impedance. And, of course, quality of the input trans comes into play--- as well as how lossy it is (i.e., what the insertion losses are).

    And the above of course is also dependent on the capabilities of the source--- what is it's output impedance and etc.

    
    ::::If the design focus was shifted so that the input transformer was now a preamp output transformer it could handle the phase splitting too.::::

    awe... but that component (preamp output trans) would be in a preamp not the front of a power amp---

    point well taken--- that you can split phase on the output of your preamp--- our B7 preamp outputs have 500\600 ohm nominal center tapped secondaries--- from which you could derive a differential signal by simply grounding the center tap.

    But in that case I would build that person a different amp--- deleting the volume control as well as the input trans--- and going directly into the LTP with the differential signal from the preamp.

    Once you move past the really straightforward implementations--- say just having a simple RCA single ended input--- then you need to do a moreso through systems analysis--- to see what a person needs or doesn't need.

    But your point on splitting at the preamp level (small signal) is well taken. But what I had in mind in initially drawing up the circuit as shown is the person wanting to go from cd player with single ended output directly to the power amp.

    MSL
    
    

    ---

    Edits: 02/13/08
• More on fixed bias - gluca 16:14:25 02/12/08 (2)
  In Reply to: RE: EL-34 PP schematic posted by mqracing on February 09, 2008 at 22:07:59

  Ciao,
  
  thanks for sharing your ideas and experiences, I take Kevin's preference for cathode bias as a valuable suggestion for future buildings: I'd really love to try to this topology.
  
  -Batteries-
  Still looking at the schematic, I like to consider the ground as the best thing I can put under the cathodes of single ended and differential stages: it is rock stable over the time it and does not require any cap any heatsink and any devices at all so it cannot have any influence on the sound that's why I said "better". Batteries on the grid last many many months (but I understand this can really be an issue for commercial applications) and can be dead quite at -90dB and really comfortable, easy and cheap to work with. Those were the main reasons that make me pick up batteries every time I can, again ... those are just my rants and opinions with only a short experience on my shoulders. I'd really like to know from you, in case you give them a try, your findings.
  
  -Input trafo and splitting-
  Noted for future ideas. Great arguments. Thanks.
  
  
  Gianluca
  
  
  

  ---

  • RE: More on fixed bias - mqracing 09:49:52 02/13/08 (1)
    In Reply to: RE: More on fixed bias posted by gluca on February 12, 2008 at 16:14:25

    hi GL:
    
    I thought I had saved several of your schematics on my hard drive---- the only one I could find was your Water Babies line driver.
    
    Hey--- I've always liked your stuff and several times have been struck by a sense of your circuits being elegant and looking pretty darn nice on paper.
    
    You present good arguments for battery bias and fixed bias--- both are attractive to me on the DIY level. But for commericial products I think I prefer self-bias and juice from the wall :=)
    
    Do you have a website with some of your goodies on it?
    
    MSL
    
    

    ---

    • Website ... - gluca 09:38:59 02/14/08 (0)
      In Reply to: RE: More on fixed bias posted by mqracing on February 13, 2008 at 09:49:52

      ... not yet. Working on it, it will "collect all my few things before I forget them". Thanks for the kind wors. Here is the last amp in the process of making it. An 801A directly coupled to the grid of the 304TL, two separate PSUs using 866A's.
      
      Ciao
      Gianluca
      
      PS: Can you spot your FS100PF's shining in the dark? Lovely ...
      
      
      
      
      

      • I hope to turn it on tonight   (Open in New Window)

      
      

      ---
• RE: EL-34 PP schematic - SteveBrown 13:25:19 02/11/08 (3)
  In Reply to: RE: EL-34 PP schematic posted by mqracing on February 09, 2008 at 22:07:59

  Love it. Done something similar but sans grid chokes. On the negative supply for the phase splitter, will this need to carry all the current of the splitter, no? If so, looks like you're using a bias tap on the power tranformer. I've only known those to be rated for a couple ma, will it work okay for your design? Wait, what am I saying, you wind the things, right?! But a normal bias tap would not support, say 20 or 30ma, right? OTOH, I could be all wet, and frequently am. Again, love the plan.
  
  

  ---

  • RE: EL-34 PP schematic - mqracing 10:15:52 02/12/08 (2)
    In Reply to: RE: EL-34 PP schematic posted by SteveBrown on February 11, 2008 at 13:25:19

    Hi Steve:
    
    It's one of the advantages of building your own tranneys---
    
    since I've read your post--- I've been kicking around and mulling
    over---- the bias tap arrangement. We could also potentially just
    simply wind a separate bias winding independent of the high voltage
    winding.
    
    I'll share some thoughts with Kevin on this. thanks.
    
    Mike
    
    

    ---

    • RE: EL-34 PP schematic - SteveBrown 18:15:25 02/12/08 (1)
      In Reply to: RE: EL-34 PP schematic posted by mqracing on February 12, 2008 at 10:15:52

      One of the things I like about recycled Fisher PT's is that there is a seperate "Bias" tap what ran both the bias for 7591's and a couple filiments, consequently, no question about sinking the current for a CCS in the driver. I don't know of other vintage tfrs that do this, but I'll bet there are some. You know, a fab power tfr would have a 6.3v winding to take on 2x damper diodes, plus a 30v or so tap that is rated for 100ma for driver CCS. I think that's the cat's meow! Thanks for the response, Mike.
      
      

      ---

      • On the other hand... - 2wo 20:30:13 02/12/08 (0)
        In Reply to: RE: EL-34 PP schematic posted by SteveBrown on February 12, 2008 at 18:15:25

        You only need to sink 15-20ma per diff pair

        On the other, other hand. I wonder if taping a winding is more of a PITA, then adding one...John
        
        But it’s the sense of satisfaction I get, by getting it to do anything at all…
        
        

        ---

        Edits: 02/12/08
• More puzzling ramblings - gluca 04:08:50 02/11/08 (7)
  In Reply to: RE: EL-34 PP schematic posted by mqracing on February 09, 2008 at 22:07:59

  Mike, folks
  
  I am still looking at that EL34s output stage and the preceding chokes. Would it be easier (better?) to tie the cathodes to ground and use fixed bias at the grids? I usually have batteries under the grid stacking them up to the required voltage.
  
  Gianluca
  
  

  ---

  • RE: More puzzling ramblings - mqracing 10:10:55 02/12/08 (0)
    In Reply to: RE: More puzzling ramblings posted by gluca on February 11, 2008 at 04:08:50

    Hi Gianluca:
    
    
    you wrote;
    
    :::Would it be easier (better?) to tie the cathodes to ground and use fixed bias at the grids? I usually have batteries under the grid stacking them up to the required voltage.:::
    
    In some senses it would be easier (fewer parts?) to go with fixed bias.
    Would this lead to better sound? Don't know for sure--- but based on prior experience I have generally found that I like cathode bias.
    
    Kevin's idea of tie'ing the tail to the ground via the CCS--- is kind of neat in-so-far as it really simplifies things--- you don't need that large value bypass cap---- and this is not said from someone who suffers dogmatically from capacitor-itis--- but from a practical point of view--- the CCS's are less costly to implement than purchasing a large value film caps--- and it does tie things down pretty darn well---
    
    likewise--- someone else observed in a different response--- that the two CCS's in para cuts in half the load impedance of the devices--- my gut reaction is half of infinity (not infinity--- but utterly, utterly large) if still quite substantial--- more impedance than your likely to get from a choke in that position.
    
    But--- back to your query about fixed bias--- yeah, this circuit could be modified for fixed bias--- and perhaps it would also be worth an ear test.
    
    MSL
    
    
    
    
    
    

    ---
  • RE: More puzzling ramblings - KevinC 04:35:33 02/11/08 (5)
    In Reply to: RE: More puzzling ramblings posted by gluca on February 11, 2008 at 04:08:50

    To know if fixed bias is "better" you will have to build both and listen. (Batteries aren't too practical for commercial products for obvious reasons and I prefer to design for broader use.)
    
    I have found by listening that I prefer EL34 and 6550 output tubes used in push-pull applications "cathode biased" by standing them on a common CCS.
    
    
    Kevin Carter
    K&K Audio
    www.kandkaudio.com
    
    

    ---

    • Thanks. - gluca 05:09:52 02/11/08 (4)
      In Reply to: RE: More puzzling ramblings posted by KevinC on February 11, 2008 at 04:35:33

      I got to give this idea a try. I have some 807s lying around and 2540s too.
      
      Is there any reason on your choice for the splitter (which I like)? I mean, why one should not use the input tranny to split the signal?
      
      Ciao
      Gianluca
      
      

      ---

      • RE: Thanks. - mqracing 11:01:36 02/12/08 (0)
        In Reply to: RE: Thanks. posted by gluca on February 11, 2008 at 05:09:52

        Hi GL:

        you asked;

        :::Is there any reason on your choice for the splitter (which I like)? I mean, why one should not use the input tranny to split the signal?:::

        As Kevin stated in his response--- the input side of the voltage amplifier (6DJ8) reflects my design choices (i.e., that we do not use a phase splitting input trans).

        There are a whole host of reasons that I chose the architecture that is shown. I probably won't have time to address all of the issues--- so will just try to give some sense of what I was looking at and for architecturally.

        If our first active stage is going to be an LTP--- then why not let it do the phase splitting? It's there already (the LTP)--- and even if we did use a phase splitting trans at the input and derived a differential signal off of the secondary of the input--- then the rest of our circuit is going to be differential--- and our first active stage would still be the LTP.

        so--- since the LTP can split phase--- and do it very, very well--- it just seems to me moreso elegant to let the LTP do it's job and to then use the simpler and (in my opinion) higher performance 10K:10K single-ended to single-ended input trans--- which gives you a 1:1 turns ratio. The benefit of the 1:1 as we use it is itself severalfold.

        As we use the input trans--- you can hang a conventional series fed pot (like a P&G, PEC, Alps, etc) or a discrete series or ladder type attenuator off of the secondary--- which works quite well. If we wanted volume discrimination (i.e., control) off of the secondary of a phase splitting input trans--- we could not use the widely available solutions out there like the P&G RF-15 as just one example.

        Another consideration is that phase splitting transformers are not a walk in the park to do well. By this I mean--- ideally (in a platonic world) we would want the two halves of the secondary to be exactly equal in amplitude but opposite in phase--- so that we would want exactly equal (i.e., balanced) capacitances on each half to the center tap as well as exactly equal coupling from the single ended primary to the differential secondary winding also in terms of coupling (i.e., that the leakage reactances be exactly identical)--- and we would want it to have excellent bandwidth (pick your poison on what range this bandwidth should encompass) as well as low disortion and etc. But suffice it to say--- this is a challenge to do really, really well to the extent that I would like to aim at---

        Life could be simpler (if only the gods had been kind to us)---if our cd player (or other source) had a differential output then I would be spec'ing in a PP to PP input trans--- which by virtue of both sides being PP is actually easier to get the qualities I mention in the preceding paragraph (i.e., the equalities of capacitance and leakages) on both sides of the transformer than it is when the primary is single ended and the secondary is PP.

        Now... someone keen will observe that we do make some phase splitters and that I have previously posted a circuit here with the EXO-173 phase splitter--- and ask if this phase splitter is "good"----

        so, let us to look at it within it's specific applications context--- where I have shown the use of the 173 phase splitter was in a circuit with a single gain stage as the front end--- a lot of folks have as a preference that a single ended gain stage stage sounds better at the front end than a differential gain stage--- and I don't want to argue which is "better sounding"--- but just simply observe and state that this is a preference that some folks either hold or express---

        The main point being that if your going to use a single ended (i.e., not a differential) front end--- and your building a PP amp--- then your going to have to split phase somewhere--- and that is where we use the 173--- and note that the 173 is a single winding trans--- which has implications in both the use and performance of the design and it's resultant technical and sonic characteristics. In this position the 173 works pretty well--- it is not platonic perfect--- as no piece of iron in this world is--- but it does have very good capacitive balance btwn the two halves as well as tight coupling. In my view, it is the best way to split phase if your using a transformer to do this job.

        And--- we could design this same type of autoformer phase splitter for use as an input phase splitting transformer---but--- again--- the first stage of amplification would then have to be differential--- so why duplicate this ability to split phase with an input
        trans if we have an LTP on the job?

        Further along this line of reasoning--- I've been wanting to explore (down the road somewhere) the COMPACT amp---- which essentially recognizes the inherent possibility of using the PP output stage itself as the phase splitting mechanism. Again, it (the PP output stage) is there--- why not allow it to also function similtaneously as the phase splitter?

        These ramblings are just a few kernels of thought that I've been mulling over for a long time--- please understand that my comments, ruminations, and zany ideas are not proffered as the big TRUTH or as matters of fact or the only "right" way of doing things--- but instead I offer these thoughts (none of which have been completely flushed out in this post) as a way to give some insight into why I chose to use the architectures (circuit topologies) that have been shown both in this thread and an earlier thread (the PP design with the EXO-173 phase splitter).

        shew--- I better get to work---

        Mike

        
        

        
        
        
        

        ---

        Edits: 02/12/08   02/12/08   02/12/08   02/12/08   02/12/08   02/12/08   02/12/08   02/12/08   02/12/08
      • RE: Thanks. - KevinC 07:06:20 02/11/08 (2)
        In Reply to: RE: Thanks. posted by gluca on February 11, 2008 at 05:09:52

        Mike and I collaborated on this schematic and he chose active phase splitting. I would prefer phase splitting in the input transformer followed by an "H attenuator" type of volume control.
        
        Kevin Carter
        K&K Audio
        www.kandkaudio.com
        
        

        ---

        • "H attenuator" - Russ57 11:06:16 02/11/08 (1)
          In Reply to: RE: Thanks. posted by KevinC on February 11, 2008 at 07:06:20

          That is a stereo attenuator then? I was about to comment on the attenuator as shown.
          
          Russ
          
          

          ---

          • RE: "H attenuator" - KevinC 17:11:37 02/11/08 (0)
            In Reply to: RE: "H attenuator" posted by Russ57 on February 11, 2008 at 11:06:16

            Take a look at the link, bottom of the page.
            
            Kevin Carter
            K&K Audio
            www.kandkaudio.com
            

            • http://www.kandkaudio.com/linestage.html   (Open in New Window)

            
            

            ---
• RE: EL-34 PP schematic - 2wo 14:32:49 02/10/08 (1)
  In Reply to: RE: EL-34 PP schematic posted by mqracing on February 09, 2008 at 22:07:59

  I like the look of this a lot. I built Poinz’s 6V6 ‘Musical Machine’ and it’s one of my favorite amps. Mike you got to hear it, if not listen to it over in Norristown.
  I have another set of iron that I want to try with the CCS in the tail and a different input tube.
  
  How would a EXO-173 work in place of the BCP16’s? And if you would be so kind, could you expand on the decision to use a input transformer (1:1?) Other than being a transformer maker and all ;)…John
  
  But it’s the sense of satisfaction I get, by getting it to do anything at all…
  
  

  ---

  • RE: EL-34 PP schematic - mqracing 15:21:45 02/10/08 (0)
    In Reply to: RE: EL-34 PP schematic posted by 2wo on February 10, 2008 at 14:32:49

    Hi John:
    
    How's the new house coming along? Listening room ready to rock yet?
    We do need to get together more often--- just been burning some midnight oil with work and waiting out the cold to hop back on a motorized two wheeler again.
    
    You asked why the BCP-16's instead of the the EXO-173--- chiefly because of the vast inductance advantage of the 16's which allows spec'ing of a smaller size coupling cap--- and other advantage of the 16's is that two of them are still smaller than one 173 physically. With a change in coupling cap size you could spec in the 173.
    
    re: the 1:1 (single ended both sides) input trans. This trans has a nominal pri impedance of say 10 kilo-ohms. And we have across the secondary a 10K potentiometer (or series type attenuator) like the Penny & Giles. This trans is not doing or contributing to any phase splitting duties or functions--- the phase splitting is being done with the 6DJ8's.
    
    We recommend this arrangement because it provides some ground loop isolation btwn components and it provides a nice stable load (with the 10K across the secondary) for your cd player to work into. The impedance that your cd player is looking into doesn't move around in this arrangement.
    
    Same stability of load impedance is achieved if you use (allow me to call it a AF choke) a choke which has also been designed to support well the 10K pot across (in parallel with) it's single winding. But now you obviously do not have the galvanic isolation btwn source and load.
    
    In a sense--- whether you use a single winding or a two winding device here (and you could also use a single (center) tapped choke as well--- if proportioned properly with the attenuator across a portion of the winding--- but least I digress too far) it also behaves in part as a grid choke. Kevin drew in the 1meg ohm resistance not really as the grid resistor but as a safety valve in case your contacts in the potentiometer ever pick up--- but again I digress.
    
    It's difficult to explain how the benefit derives--- what I have found is that many times using a choke (i.e., an inductor) shunted to ground of sufficiently high L (so that some other moreso purely resistive element will dominate in the circuit) just always seems to work well--- some argue that it's because the inductor stores energy (sort of how a plate choke instead of a plate resistor will allow the tube to approach moreso it's max theoretical gain) or I think of it as an inductive buffer--- since an L wants and tries to maintain a constancy of current flow through it--- it behaves sort of as a cardan cushion drive (for our moto guzzi fans) and takes the instantaneous snap out of and "cushions" the drive.... but, I'm taking some real leeway in poetic license here!!!
    
    Of course you can build this circuit without the magnetics at the front door--- and just simply come in through your RCA and hang an appropiately sized grid resistor to ground--- and this circuit should work well.
    
    And you can build this circuit without any magnetics where we are using the BCP-16 grid chokes. Just simply sub in appropiately sized grid resistors.
    
    MSL
    
    
    
    
    
    

    ---
• Sweeeeet! Just one question - - Mike Spence 13:40:35 02/10/08 (2)
  In Reply to: RE: EL-34 PP schematic posted by mqracing on February 09, 2008 at 22:07:59

  Hi Mike,
  Why the dual BCP-16 int the second schematic, rather than EXO-173?
  
  Thanks,
  Mike Spence
  
  

  ---

  • RE: Sweeeeet! Just one question - - mqracing 15:37:21 02/10/08 (1)
    In Reply to: RE: Sweeeeet! Just one question - posted by Mike Spence on February 10, 2008 at 13:40:35

    Hi Mike:

    Principally because of the much higher L that it offers--- allowing correspondingly smaller coupling caps for the same calculated 7.5 hertz resonance btwn L and C.

    And also because the physically smaller BCP-16 is a more efficient inductor--- given it's much shorter path length and the it's huge number of turns--- it produces L easily and without having to make it a boat anchor---
    the 173 though on a much larger core (core area wise) built with the very same grade of lam as the BCP-16 will only give you about 10 percent (very roughly) of the L of the smaller and less expensive BCP-16's.

    But remember the BCP-16 is a one pony show--- it produces L and that is about all you want it to do (on first blush)---

    the EXO-173 is designed to compete in a different pony show--- it is designed to work really well as a phase splitter--- it was never really designed to be used as a plate choke--- recall that the original Peerless of which this (the 173) is a modified version of a center tapped inductor (peerless part number 17173) that was used in the PP cathode circuit of a 6W6 which was driving the grids of an output stage in the 1570 altec amplifier.

    Our modified version--- optimized moreso for phase splitting--- is designed to be driven on just one half of the center tapped winding--- and to induce an equal but opposite voltage on the second half winding (the undriven winding). Though it can also be used (in a properly designed application) as a 1:2 step up or a 2:1 step down.

    But it doesn't have the huge L's to get out of the picture quite like the BCP-16 does--- remember that the trick here is to have a smaller pure resistance in parallel somewhere (when possible) that then becomes the dominating impedance--- so that the effective phase angle of the complex load impedance (the para combo of L and R) itself is not so reactive that it requires your driver (or source generator) to have to work hard.
    

    MSL
    
    
    

    ---

    Edits: 02/10/08
    • RE: Sweeeeet! Just one question - - Mike Spence 19:28:34 02/10/08 (0)
      In Reply to: RE: Sweeeeet! Just one question - posted by mqracing on February 10, 2008 at 15:37:21

      Thanks Mike - yep I like the R//L combo as well.
      
      Best regards,
      Mike Spence
      
      

      ---
• Ver-ry Kewl, Mikey. - Poindexter 09:49:48 02/10/08 (6)
  In Reply to: RE: EL-34 PP schematic posted by mqracing on February 09, 2008 at 22:07:59

  I had forgotten that topology completely!  That looks like something I drew for Piccard, with the NFB around the driver stage, there was a fauncy name for that.
  
  Here's another data point; where I've been going with that since:
  
  
  
  I originally specced Kevin's transformer as the interstage, since he puts up those good datasheets on his site, but I didn't just say that, did I?  This setup is in answer to the problem of outputs that take a huge swing on the grid, but a pretty low plate voltage and thus B+, so that it's difficult to get enough plate voltage on the drivers.  My biggest puzzlement so far is how to de-hum the cathode circuit of a pair of DHT, but with a heater-cathode tube like the EL34 this becomes a nonissue.
  
  The diodes in the screen circuit are a very good idea, I use them in triode too.  They keep the screen signal off the plate, which is maybe the source of the slight looseness I hear in UL.  This might be a very good sounding amp.  I am myself puzzled by the duplication of the DN2540 in the cathodes; it's a mongo part, 40W if I remember right, and you're only burning about 4-5 watts in this circuit.
  
  Nice job, and thanks for the headsup.
  
  Aloha,
  
  Poinz
  
  

  ---

  • RE: Ver-ry Kewl, Mikey. - SteveBrown 13:52:31 02/11/08 (1)
    In Reply to: RE: Ver-ry Kewl, Mikey. posted by Poindexter on February 10, 2008 at 09:49:48

    Hum in the DHT? Yep, I recently completed a PP 300B and had to really wrestle with some hum. Now it is down to 5mv, and on my speakers, not audible from listening distance. Actually, I'v got a bunch more hum on the lams of my PT than I do from the amp (This IS NOT a MQ PT) - live and learn, huh? Anyway, I found the hum balance pot made no difference, so I just used the R's as you've shown (11 ohm, 5w dales) tide to the top of a cahtode R. I tried reversing the filiments on the tiodes and that did help a bit. One of the things that knocked the hum down well was matching 300Bs to find the pair that together had the least hum. In my amp the front end driver is a modified version of Allen Wright's PP1 using 6N6P's at 16ma each through a CCS in the cathode.
    
    

    ---

    • RE: Ver-ry Kewl, Mikey. - Jim Womble 13:13:23 02/14/08 (0)
      In Reply to: RE: Ver-ry Kewl, Mikey. posted by SteveBrown on February 11, 2008 at 13:52:31

      If you can use separate filament supplies for each output tube, you can then place a humpot on each tube. I use this on both 2a3 and 300b pp amps, and the hum levels on the 300b are less than .5mv, and about half that on the 2a3. I use 50 ohm pots with each side of the pot paralleled with a 22 ohm mills, so the pot actually works as a fine adjustment. Cathode r is then tied to the two wipers.
      
      

      ---
  • RE: Ver-ry Kewl, Mikey. - KevinC 04:39:24 02/11/08 (0)
    In Reply to: RE: Ver-ry Kewl, Mikey. posted by Poindexter on February 10, 2008 at 09:49:48

    The DN2540N5 is actually a 15w/100mA part and I don't like to use it with more than about 50-60mA running through it for thermal reasons, hence the double-up.
    
    Kevin Carter
    K&K Audio
    www.kandkaudio.com
    
    

    ---
  • RE: Ver-ry Kewl, Mikey. - mqracing 16:28:10 02/10/08 (2)
    In Reply to: RE: Ver-ry Kewl, Mikey. posted by Poindexter on February 10, 2008 at 09:49:48

    hi Poinz:
    
    Thanks for visiting and posting. Your always welcome here--- but some of your schematics have hierglyphics in them that I cannot decipher completely :=)
    
    We are currently working on expanding our range of small signal transformers as well as interstages. And (God willing) sometime in this lifetime I fervently hope we will update our website and make it more practical and informational.
    
    In the meantime--- remember that we have probably the largest audio archives of designs in the world--- with designs from Peerless, Acrosound, western electric, Freed, Western transformers (diff than WE), Triad, a few Langevin drawings, and etc. So our website doesn't and never will list all of the designs we have in our archives.
    
    The archives give us a base to work from--- it's not always possible to build everything in the archives--- sometimes we will run up against materials not being available for a particular design--- or will realize that the cost of bringing this design to market is absolutely out of whack with what it will generate is sales dollars coming in--- and a third restraint is that we are a small specialist workshop and have limited capacity--- and doing a single or a pair of a "new" design just won't work well for us in most cases.
    
    All that said--- we're just an email or phone call away. If we don't have or cannot rationally build you something--- I'll say so and perhaps be able to make an alternate recommendation.
    
    I'll ask Kevin about the gain issue--- as well as the 2540's---
    and hope that he can perhaps post when he has a chance to.
    
    again, thanks for coming over... stop in anytime.
    
    MSL
    
    
    
    

    ---

    • RE: Ver-ry Kewl, Mikey. - Poindexter 17:19:55 02/10/08 (1)
      In Reply to: RE: Ver-ry Kewl, Mikey. posted by mqracing on February 10, 2008 at 16:28:10

      Notatawll; the sponsor fora are info-rich places.  I don't like to bother you unless I have a defined question to ask, is all.
      
      I'll post you with a proposed operating envelope and stuff.  You can see from the schem mostly what's going on there.  I have new models for this year I'll show you too.
      
      What hieroglyphics?  I try to make my schems as clear as possible.
      
      Aloha Nui Loa,
      
      Poinz
      
      

      ---

      • RE: Ver-ry Kewl, Mikey. - mqracing 17:30:42 02/10/08 (0)
        In Reply to: RE: Ver-ry Kewl, Mikey. posted by Poindexter on February 10, 2008 at 17:19:55

        Poinz wrote:
        
        "What hieroglyphics? I try to make my schems as clear as possible."
        
        Oh, they are. I was kiddin' about the iron that my friend Kevin imports
        from Europe. Tryin' to say I just couldn't recognize those (name and model) foreign characters (i.e., hierglyphics).
        
        that'll teach me to try to be cute.
        
        msl
        
        
        
        

        ---
• Needs more iron - mwiebe 09:49:27 02/10/08 (2)
  In Reply to: RE: EL-34 PP schematic posted by mqracing on February 09, 2008 at 22:07:59

  Mike,
  All those CCSs when you make such nice iron seems bad for business. I would like to hear more about the input phase splitter, which is complicated with the volume control and one end grounded rather then the center tap. It seems like the way you are using the input trans, you could just as well use the input autoformer you showed on an earlier design. The gain is a bit low, what are you using to drive this? Can you direct couple? I don’t know the low-plate voltage performance of the 6N23P.
  Matt
  
  
  

  ---

  • RE: Needs more iron - mqracing 16:10:06 02/10/08 (1)
    In Reply to: RE: Needs more iron posted by mwiebe on February 10, 2008 at 09:49:27

    Hi Matt:
    
    I've been meaning to get up some of the PP schematics you sent me---
    shew--- soon hopefully. Then you can field the Q's :=)
    
    What I have found attractive about this particular design is the possibility of building it with a smaller subset of ironware initially--- with the possibility of later "upgrading" the circuit as your pocketbook allows.
    
    So that the input trans is optional as well as the grid chokes. The phase splitting is done by the russian equiv 6DJ8's not the input trans. The input trans is single ended on both sides (as shown) and it is included in the schematic for a builder who wants a volume control at the amplifier site (i.e., that he will perhaps drive the input of the amp direct (sans preamp) from his source (say cd player).
    
    It is possible to spec in chokes in place of the DN2540's in the cathode circuits--- but these chokes are going to tend to be large--- much more expensive to implement compared to the cost of the 2540's--- and on paper specs alone not do the job nearly as well----
    
    that said--- I understand that paper specs and ear specs (ear preferences) might well diverge. But again--- I wanted to be somewhat practical and not price this ironwise well outside of the ballpark.
    
    My sense has always been--- first and foremost in an amplifier design--- put your hard earned dollars and optimize the output transformer first. The grid chokes, the input chokes, and etc can come later---
    
    what doesn't make sense to me is if you have a budget of X available for ironware--- and it is a finite budget--- first get the best output your budget can buy--- if the budget has some mullah leftover then start spec'ing in other pieces of iron.
    
    I see so many designs and so many diy'ers just going for the glory of "if iron is good" then ten pieces of iron must be better than one piece of iron--- so that they take their iron budget and divide into too many small slices and don't ever get the overall quality that a smarter division of funds might have obtained.
    
    It's the mindset that says I need an interstage, an input, and output, several plate chokes, etc--- so that my $800 dollars must now be divided
    up maybe six or eight or ten ways--- so the person winds up with six or eight hammond quality pieces of iron--- but they heard interstages are cool or good--- so they are happy.
    
    so--- again--- part of what I like about this circuit is you could start out with a moreso limited budget---- get the best outputs you can for the application and then later upgrade when funds permit.
    
    
    And Mat--- your right--- someone could use the single AF choke "input trans" that I showed in an earlier schematic with the volume control in parallel with it--- and I would even encourage folks to try this. If you do have a two winding (must be a 1:1) device--- with the volume control across the secondary--- just simply put the two windings in parallel (observing necessary phase conventions) and listen to it this way---- and tell me what your impressions are.
    
    re:gain. I let Kevin address this issue when he has the opportunity---
    
    thanks Mat--- I hope I answered your Q's--- if not let me know.
    
    
    MSL
    
    
    
    

    ---

    • RE: Needs more iron - mwiebe 19:11:57 02/10/08 (0)
      In Reply to: RE: Needs more iron posted by mqracing on February 10, 2008 at 16:10:06

      Mike,
      No wonder that input trans threw me for a loop, but I see your idea now, a P-P platform—something like the Seth iron package for pentodes, with similar upgrade path. I wonder if fixed bias on the outputs would not make it easier to scale for any output tubes someone wanted to use with the basic iron package. As I mentioned to you, I'm back 82dB speakers for a while as well which has forced me to P-P.
      Matt
      
      
      

      ---
• RE: EL-34 PP schematic - nullspace 09:08:16 02/10/08 (3)
  In Reply to: RE: EL-34 PP schematic posted by mqracing on February 09, 2008 at 22:07:59

  Very nice Mike. I always check out the forum early on Sundays for any kind of 'special' you might be running, and I suppose this qualifies...
  
  I don't know much about PP circuits (yet), but could you tell me what the UF1007 diodes on the UL taps are for?
  
  With the CCS in differential circuits, I always wonder about tube matching. Wouldn't very close matches be required, and wouldn't they need to stay matched over their lifetime? Or am I making a mountain out of a molehill?
  
  Regards,
  John
  
  

  ---

  • RE: EL-34 PP schematic - KevinC 04:47:17 02/11/08 (1)
    In Reply to: RE: EL-34 PP schematic posted by nullspace on February 10, 2008 at 09:08:16

    Get me started on tube matching for push-pull amps....
    
    You need reasonably matched tubes in any PP amp, regardless of the means of biasing. There is the persistent illusion that if you have independent bias controls for each tube that you can do your own "matching", but it's not true. A "real" matched pair will have tube curves that can be overlain and nicely coincide. Adjusting the bias to get matching idle currents only addresses one point on those curves and ignores the rest.
    
    Having written all of this, I find that, practically speaking, buying "matched tubes" where the vendor finds tubes that give the same bias current at a fixed bias voltage is perfectly adequate in an amplifier such as Mike posted. Clipping is symmetrical and well-behaved with such tubes, indicating that they are each pulling about half of the weight.
    
    Kevin Carter
    K&K Audio
    www.kandkaudio.com
    
    

    ---

    • RE: EL-34 PP schematic - nullspace 08:05:00 02/11/08 (0)
      In Reply to: RE: EL-34 PP schematic posted by KevinC on February 11, 2008 at 04:47:17

      Thanks Kevin. I had always assumed that it wasn't a big deal, what with your PP linestage and Allen Wright's amps being well-regarded, but I figured I'd ask the question since I didn't know the logic behind it....
      
      Regards,
      John
      
      

      ---
  • RE: EL-34 PP schematic - mqracing 16:14:14 02/10/08 (0)
    In Reply to: RE: EL-34 PP schematic posted by nullspace on February 10, 2008 at 09:08:16

    Hi John:
    
    re: matching of tubes I'll let Kevin address this issue when he has a chance.
    
    there was, as I recall, a discussion of this issue over on Kevin's K&K board here on the asylum not too long ago on this very same issue.
    
    re: the uf1007 diodes on the UL taps--- see Poinz post--- he offers at least one view of the benefit of using these diodes.
    
    And thanks for the kind words.
    
    MSL
    
    

    ---
• Puzzled ... - gluca 05:16:00 02/10/08 (4)
  In Reply to: RE: EL-34 PP schematic posted by mqracing on February 09, 2008 at 22:07:59

  Why two (parallel) CCS under the cathodes of EL34s?
  
  Ciao
  Gianluca
  
  

  ---

  • RE: Puzzled ... - Steve Eddy 11:01:10 02/10/08 (3)
    In Reply to: RE: Puzzled ... posted by gluca on February 10, 2008 at 05:16:00

    Why two (parallel) CCS under the cathodes of EL34s?
    
    I can't speak for Kevin here, but a couple of possibilities come to mind.
    
    One is that he's wanting to avoid having to heatsink the devices. On an appropriate heatsink, they'll dissipate about 15 watts, but in free air, only about 2 watts.
    
    Another is that the devices he's using are depletion mode MOSFETs, which like JFETs have a maximum drain current they can supply (Idss in the datasheets). If you need more, you need to parallel devices to get it.
    
    Just a couple of hunches.
    
    se
    
    
    

    
    
    
    
    

    ---

    • You're right. - Poindexter 11:20:47 02/10/08 (2)
      In Reply to: RE: Puzzled ... posted by Steve Eddy on February 10, 2008 at 11:01:10

      I was scratching my head about this as well; I thought the device had more the ratings of the IXYS 10M45S, of which a single could be used, but it's actually not as butch.  150mA max, and that only up to about 8V drop or so, then it goes down.  They're actually running two in parallel fairly hard.
      
      Aloha, Steve,
      
      Poinz
      
      

      ---

      • RE: You're right. - GTCharlie 04:27:54 02/12/08 (1)
        In Reply to: RE: You're right. posted by Poindexter on February 10, 2008 at 11:20:47

        Just a thought : why not use one per tube, instead of parallel for both tubes, effectively halving the load. And then you can individually balance ...
        
        

        ---

        • RE: Output Stage Balance - KevinC 05:41:59 02/12/08 (0)
          In Reply to: RE: You're right. posted by GTCharlie on February 12, 2008 at 04:27:54

          See the thread at the link for my take on this from the balance standpoint.
          
          Separating the cathodes won't actually result in a working amplifier without bypassing the CCSs with capacitors or linking the cathodes with a capacitor. In addition, if you don't have the cathodes joined together, you sacrifice an important aspect of this topology, that is, the differential action.
          
          Kevin Carter
          K&K Audio
          www.kandkaudio.com
          

          • http://www.audioasylum.com/forums/KandK/messages/6449.html   (Open in New Window)

          
          

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