K&K Audio / Lundahl Transformers

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K&K Audio / Lundahl Transformers

LL1660 and/or LL1671 PP interstage duty

122.11.173.228

Bill Jaensch1

Hi Kevin,

I'm looking for an PP interstage for a design I'm working on. For context it would be a bit like the first two stages of a Karna with a 4P1L pair as the output transformers. Input/drier tube most likely to be a 5687, maybe a pair of triode connected 7788's or EC8010's or 6C545P's. I'm looking to run between 20mA (5687) up to potentially 30mA for the others, per tube.

Looking at the data sheets for the LL1660 and LL1671, they both say the Alt M models allow "some" dc imbalance. How much imbalance is "some" please"?

Similarly, it is not clear how much primary current is allowable in each of the primary windings in the At M configuration for either for these transformers. Guidance please?

Bear in mind that the design goal and execution will be to have each primary current matched as much as is practicable, but in a real world sense is it highly likely that the tubes will drift etc etc and I would rather have a bit of "overhead" in the current imbalance department as I feel taking this into account (up to say 5 to 10% of the current between the pair) rather than a transformer that only performs at its best with a limited level of imbalance.

Thank you in advance for your help.

Best regards,
Bill

Follow Ups:

RE: LL1660 and/or LL1671 PP interstage duty - KevinC 10:39:27 06/11/18 (1)
For the tubes you mention using in the first stage, I would be inclined to choose an LL1692A/PP. For the output driver stage the same will do well. I have used tubes similar to triode connected 7788s with excellent sonic results in such a stage.

Imbalance of the order of 10% is not a problem unless you are asking for output levels right at the edge of the earth, which depends on the turns ratio you decide to use.

Kevin Carter
K&K Audio
www.kandkaudio.com
- RE: LL1660 and/or LL1671 PP interstage duty - Bill Jaensch1 19:18:13 06/11/18 (0)
  Hi Kevin,
  
  thank you for your reply and feedback on the options, greatly appreciated.
  
  1692A and 1635 look to be in a similar ball park, so reading between the lines you are pointing towards the 1692A. :-)
  
  cheers,
  Bill
RE: LL1660 and/or LL1671 PP interstage duty - Bill Jaensch1 20:15:53 06/06/18 (1)
Just dug a little deeper: maybe LL1635/5mA could do the trick too?
- RE: LL1660 and/or LL1671 PP interstage duty - KevinC 10:42:03 06/11/18 (0)
  Yes, it's also a valid alternative.
  
  Kevin Carter
  K&K Audio
  www.kandkaudio.com

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