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Re: LL1660 "Alt U+"?

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KevinC

(M)

In Reply to: Re: LL1660 "Alt U+"? posted by kasra on November 16, 2004 at 16:58:10:

For the Euridice, I would use an LL1660/25mA in connection alternative Q.

Kevin Carter
K&K Audio
www.kandkaudio.com

Follow Ups:

But.. - kasra 08:31:16 11/17/04 (10)
..given that I already have a pair of LL1660/18mA, what conection do you then recomend?
Thank you!
- Re: But.. - KevinC 09:00:27 11/17/04 (9)
  Connection alternative Q
  
  Kevin Carter
  K&K Audio
  www.kandkaudio.com
  - hm... - kasra 03:23:06 11/18/04 (8)
    Alt. Q with 18mA does only allow 18mA, are you mening it still will work?
    Thank you.
    - The story on output level and saturation in a SE transformer - KevinC 06:20:00 11/18/04 (7)
      This is a question that is often asked: I want to use an LL1660 transformer that is gapped for 18mA with a tube that I am running at 25mA, so can I do it? The answer is as you might expect: That depends! It depends on the output voltage that you ask to get from the transformer. In line stage use where, normally, you are only asking for 0.5-3vrms, then the answer is "Yes!" This is because the 18mA bias spec puts the flux in the transformer at about one-half of saturation flux and at that point this transformer is capable of up to about 50vrms output. You have offset the core to a ~40% higher flux point at 25mA, but you are only asking the transformer for about 5% of its capability at 18mA, so this offset doesn't force the transformer to the edge of saturation with your signal needs. If, however, you were insisting on the whole 50vrms, you would be out of luck at 25mA, because the added DC current in the transformer ate up a lot of that audio signal capability. It's a tradeoff between accommodating DC current flow and AC signal flow in the transformer.
      
      Kevin Carter
      K&K Audio
      www.kandkaudio.com
      - Re: The story on output level and saturation in a SE transformer - klaus 01:55:51 11/30/04 (2)
        
        In Reply to: The story on output level and saturation in a SE transformer posted by KevinC on November 18, 2004 at 06:20:00:
        
        Good explanation, Kevin. What about more subtle variances?
        Here's my case. Fixed-biased 6C45P (Vg=-3V, Vp=250V, Ip=25mA) loaded into LL1660-30mA-AltU driving 6C4C pushpull. 120V peak-to-peak across secondaries. 30mA transformer is too bass shy and needs replacement.
        (schematic here http://www.klausmobile.narod.ru/projects/pr_14_final.htm)
        Are there any chances the 10mA version (20mA in Alt-U) will work in this setup (25mA current) or the only solution is 18mA version? What will I gain (in terms of inductance or frequency)? Alternatively, what's there except 1660 that can do the job?
        
        Re: The story on output level and saturation in a SE transformer - KevinC 04:41:02 11/30/04 (1)
        
        In Reply to: Re: The story on output level and saturation in a SE transformer posted by klaus on November 3, 2004 at 01:55:51:
        
        Your schematic and your post are not in agreement with each other (1660/10mA in schematic). The appropriate transformer to use these days would be the LL1660S/10mA in connection alternative B. It gives somewhat better high frequency balance than the LL1660/10mA in alt U. But either will work. The operation of the 6C45 at 25mA exceeds the 1/2 Bmax point somewhat with the LL1660S, but it will only matter in loud passages if your speakers demand these power levels. The substantially higher primary inductance will help with the bass.
        I have never tried the 6C45 fixed bias, but never liked the sound cathode biased. Someone told me yesterday that it sounds much better at low plate voltage (100v) and moderate current, but of course, drive swing would then be pretty limited. Consider the triode-connected 7788 or E55L as potential alternatives.
        Kevin Carter
        K&K Audio
        www.kandkaudio.com
        
        Re: The story on output level and saturation in a SE transformer - klaus 07:06:49 12/05/04 (0)
        
        In Reply to: Re: The story on output level and saturation in a SE transformer posted by KevinC on November 3, 2004 at 04:41:02:
        
        Thanks for the tips!
        Yes, 10mA was wishful thinking - for a while I'm stuck with 30mA interstage. Oddly enough, rewiring it to primaries in series didn't improve much in the bass department - just cut the gain.
      - Kelvin, if we only need 3-5V from the output of a pre-amp, - akltam 06:24:42 11/20/04 (1)
        
        In Reply to: The story on output level and saturation in a SE transformer posted by KevinC on November 18, 2004 at 06:20:00:
        
        then it would be in fact more advantages to use smaller gap than the current on the tube ???
        For example, let say I am running 25ma on the tube, then with a 18ma gap LL1660, I have a larger inductance than a 25ma gapped 1660, right, thus at least the bass performance will be better.
        Alan
        
        Re: Kelvin, if we only need 3-5V from the output of a pre-amp, - KevinC 06:58:38 11/20/04 (0)
        
        In Reply to: Kelvin, if we only need 3-5V from the output of a pre-amp, posted by akltam on November 2, 2004 at 06:24:42:
        
        Given the output voltage restrictions you cite, that is true.
        
        Kevin Carter
        K&K Audio
        www.kandkaudio.com
      - This should be in your FAQ. - akltam 23:51:08 11/18/04 (0)
        
        In Reply to: The story on output level and saturation in a SE transformer posted by KevinC on November 18, 2004 at 06:20:00:
        
        Excellent explanation.
        Alan
      - Thank you! - kasra 06:22:47 11/18/04 (0)
        
        In Reply to: The story on output level and saturation in a SE transformer posted by KevinC on November 18, 2004 at 06:20:00:
        
        Thank you very much, I really appreciate the answer!

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