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In Reply to: RE: I like it! posted by twystd on November 06, 2009 at 14:46:37

it is the parallel combo of the cathode and the cathode R that needs bypassed( and this will be a fairly small resistance; 1/gm ).
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

Follow Ups:

RE: actually - twystd 17:53:35 11/06/09 (12)
From what I understand the impedance that needs to be bypassed is the impedance of the tube plus the load/mu+1 in parallel with the cathode resistor, which in this case would be in the neighborhood of 500 ohms. Am I wrong?

twystd
- RE: actually - danlaudionut 18:19:05 11/06/09 (11)
  Twystd
  
  You are right I stand corrected.
  It should be about 63uFd for 5Hz F3.
  
  DanL
  - RE: actually - twystd 21:23:38 11/06/09 (10)
    I messed up, it would have only been 3/4Db down at 28hz with the 47uf cap. I need to think more before I post.
    
    twystd
    - RE: actually - danlaudionut 23:21:08 11/06/09 (9)
      Twystd
      
      Sorry, still not right.
      2 octaves above F3 with a first order filter
      will give you a flat response.
      A factor of 10 before the phase is flat.
      2 octaves above 7Hz means that
      at 28Hz the frequency is flat.
      Like I said basic filter theory here.
      
      DanL
      - RE: actually - twystd 01:14:47 11/07/09 (5)
        
        In Reply to: RE: actually posted by danlaudionut on November 06, 2009 at 23:21:08
        
        Well, I guess theory is just that. I have 300B amps (Welborne Laurels), they have 3.5K OPTs, and a 1K ohm cathode resistor. They came with 47uf Solen cathode bypass caps. I changed them for 120uf Solens (that's what I had on hand), and noticed a very pronounced increase in bass. I've since gone to four 30uf 160V MBGO PIOs in parallel.
        
        The math says (Rp+Rl/mu+1)//Rk is the impedance we need to bypass. So (600(Rp)+3500(Rl))/(2.77(mu)+1)= 1087. Rk = 1000//1087 = 520.8 ohm impedance. I think we can both agree on that. At 7hz C=1/(2*pi*7*520)= 43.656uf so according to the theory, a 47uf cap should be flat at 28hz. Why do my 30hz (they fall like a rock after that) capable speakers reproduce so much more bass with a 120uf cap? I guess it must be my imagination, theory says so.
        
        I usually use 3hz as the frequency of interest which would indicate about 100uf. From previous posts, I see Tre' likes to use 2hz, which would indicate about 150uf. He uses 2hz as he claims the phase is correct. I don't know about the phase thing, but it is interesting, and I will look into it.
        
        twystd
        
        RE: actually - awsjr 06:39:33 11/10/09 (2)
        
        In Reply to: RE: actually posted by twystd on November 07, 2009 at 01:14:47
        
        how on earth do you fit (4) of the MGBO's in your Laurel ?....do you have a picture of the inside ?....I am in Brushy Creek....maybe do a listening session at yours and / or mine ?....thanks -Al
        
        RE: actually - twystd 08:59:59 11/10/09 (1)
        
        In Reply to: RE: actually posted by awsjr on November 10, 2009 at 06:39:33
        
        Not only do I have the 4 MBGOs inside the chassis, but I also have a Lundahl choke for the choke loaded mu stage, a potted vintage filament choke, and batteries for the battery bias. On the top of the chassis, in between the power and output transformer, I'm installing a huge 100uf 1000V MBGO for the power supply, it's even bigger than the transformers.
        
        Almost the entire wooden sides of the chassis have something attached to them. Now I'm trying to see if I can fit one more 20uf 430V MBGO to replace that Solen cap, that is the last power supply filter cap for the driver/mu stage. I'd send you a photo, but they are apart right now, pending the permanent attachment of the big MBGO on the top.
        
        A listening session sounds great, always like to meet another audiophool in the area. I have a couple of other audio buds in the area. We get together from time to time to listen to different projects, perhaps you'd be interested as well. Send me an email through the asylum, so I have your email address, and we can do a listening session.
        
        twystd
        
        RE: actually - awsjr 05:44:24 11/11/09 (0)
        
        In Reply to: RE: actually posted by twystd on November 10, 2009 at 08:59:59
        
        yikes....that'll be something to see....email sent....thanks....
        
        RE: actually - danlaudionut 01:29:18 11/07/09 (1)
        
        In Reply to: RE: actually posted by twystd on November 07, 2009 at 01:14:47
        
        Twystd
        
        I think you may be hearing the phase change
        which accounts for the increased bass.
        When bass is out of phase you lose impact
        and so the bass is duller and muddy.
        Sounds like you should stay with 3Hz
        so that your 30Hz phase is flat.
        
        Same for high frequencies too.
        Design for 200KHz F3 for flat phase
        on your treble.
        
        DanL
        
        RE: actually - twystd 09:28:48 11/10/09 (0)
        
        In Reply to: RE: actually posted by danlaudionut on November 07, 2009 at 01:29:18
        
        Dan, do you know where I might learn more about correct phase?
        
        twystd
      - RE: actually - Michael Samra 00:20:14 11/07/09 (2)
        
        In Reply to: RE: actually posted by danlaudionut on November 06, 2009 at 23:21:08
        
        Dan
        Try the 120uf bypass..You figuring a flat response at 28hz assuming you are 500 ohms with the added parallel impedance of the tube.This is why I measure but I would try 120uf and I am almost sure you will like it..You can always take it out.
        If the power supply waveform isn't pretty,neither is the sound in most cases.
        
        RE: actually - danlaudionut 01:23:18 11/07/09 (1)
        
        In Reply to: RE: actually posted by Michael Samra on November 07, 2009 at 00:20:14
        
        Michael
        
        I would think it would be more likely that
        the impedance of the OPT is lower at
        the lower frequencies and not the tube.
        
        DanL
        
        RE: actually - Michael Samra 15:38:05 11/07/09 (0)
        
        In Reply to: RE: actually posted by danlaudionut on November 07, 2009 at 01:23:18
        
        Dan
        you are right but its still allowing the tube to see a lower imp with the combo of the cathode resistor and the OT...At any rate,try the 100 or 120uf bypass and tell us what you think.
        If the power supply waveform isn't pretty,neither is the sound in most cases.

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