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300b with Tangos need help

82.225.58.128

Hi,

Could any body be kind enough to indicate a good schematic for a 300b amplifier using the following "Iron":

All Tango (older versions)

Output : XE-20-S
Interstage : Trans NC-15
Choke : MC-10-2000

Many thanks
Tim

Follow Ups:

RE: 300b with Tangos need help - elektron 16:23:21 11/07/09 (0)
Tim, hi. Old Tango interstages. I like them. In a SET with 6900 driving NC-15 to Type 50 (or 300B) to Tango XE-60-5SNF. Also 1/2 6SN7 to drive NC-16 to Type 45 to MQ DS-050. Beyond beautiful. Transcendent. A musical jewel. Here are the NC-15 specs. Zp is 10K Ohms. Minus 2 dB down points are 35Hz to 35KHz (rp=10K Ib=7mA). Max DC 15 mA. 50H (Ib=5mA)
rp=7~12K. The XE-20-600S is not intended for 300B. Zp=600 Ohms. It is intended for 6C33C. DC max = 320 mA. -2db 4V rp=Zp 30Hz-100KHz. For 300B you would want 3.5K although I prefer 5K.
do some tests, here are my results - eyes 05:03:31 11/07/09 (2)
I don't know offhand what rp the NC15 likes, but here are my results of various tubes with a Hashimoto A105 (wants an rp of ~5K). I went with 6S4As biased at 14 mA, rp ~ 4K at that operating point. Cheap and good sounding, intended for vertical deflection amp duties so designed to drive an inductive load. Would have tried 12bh7s but NOS ones are ridiculously priced. 6GK5 seemed ideal from an rp standpoint but didn't "measure" well so I didn't try it. YMMV

/eyes

Edits: 11/07/09
- RE: do some tests, here are my results - danlaudionut 06:14:48 11/07/09 (1)
  Eyes
  
  The NC15 was designed for 6SN7 use.
  The 6GK5 has 2/3 the rp of the 6SN7
  so it would be fine.
  
  DanL
  - RE: do some tests, here are my results - eyes 17:30:47 11/07/09 (0)
    I disagree. I find that high mu triodes don't do well with ITs. YMMV,
    
    /eyes
RE: 300b with Tangos need help - danlaudionut 10:27:12 11/06/09 (20)
Tim

How about this.
Nice gain and works good with your interstage.

DanL
- RE: 300b with Tangos need help Excellent Circuit - -3db 11:45:34 11/12/09 (0)
  Thanks for this MR. DanLoudAudioNut.....excuse the spelling...hhehe
  
  I like the whole thing...battery bias...the 12k resistor from the 300B anode....all in 2 stages...I believe in 2 stages so my last bit was direct heated pentode to the output 2a3...battery biased..nice, but some hum....I have always wondered about the 6gk5...interesting tube...
  
  a 12BZ7 might also get you there....very interesting....
  
  Good Luck in your pursuits,
  -3db
- I like it! - twystd 14:46:37 11/06/09 (17)
  Very nice Dan, I like it, however, don't you think that cathode bypass cap on the 300B is a little low? The 3Db down point is about 7hz, which puts it about 1.5Db down at 28hz. For those of us that go full range with our amps, it might not be enough. For example, my speakers are flat to 30hz. I have a 300B amp with a 3.5K OPT, and a 1K ohm cathode resistor, there was a noticeable improvement in bass when I went from a 47uf bypass cap to a 120uf cap.
  Don't mean to rain on your parade, it's really a nice idea. I like the fact that you wouldn't need a preamp stage. Battery bias, and voltage regulation on the driver stage as well, very kewl.
  twystd
  
  Edits: 11/06/09
  - actually - PakProtector 17:31:36 11/06/09 (13)
    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.
    - 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)
        
        In Reply to: RE: actually posted by twystd on November 06, 2009 at 17:53:35
        
        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)
        
        In Reply to: RE: actually posted by danlaudionut on November 06, 2009 at 18:19:05
        
        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)
        
        In Reply to: RE: actually posted by twystd on November 06, 2009 at 21:23:38
        
        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.
  - RE: I like it! - danlaudionut 15:46:42 11/06/09 (0)
    Twystd
    
    According to my calcualations
    the F3 point is 4.7Hz.
    Even with a 7Hz -3dB point then
    the -1dB point would be 14Hz
    and it would be flat at 28Hz.
    First order basics here.
    
    DanL
  - OK, but... - Allen Wright 14:52:56 11/06/09 (1)
    ...what is the LF saturation frequency of the OPT?
    
    It's smart to have the prior electronics rolling off a little before this point - because saturated OPTs really hurt the bass tonality. I'd be very surprised if the OPT can go to 7Hz at near full power.
    
    Regards, Allen (Vacuum State)
    - RE: OK, but... - twystd 15:05:30 11/06/09 (0)
      I admit I don't know, as I didn't measure it, but my ears sure liked it.
      
      twystd
- RE: 300b with Tangos need help - Tre' 11:15:51 11/06/09 (0)
  6GK5 mu of 78.
  
  No need for a line stage. Good, low Rp of 5400 and pretty linear looking tube.
  
  I just might have to try that. Thanks.
  
  Tre'
  Have Fun and Enjoy the Music
  "Still Working the Problem"

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