K&K Audio / Lundahl Transformers

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K&K Audio / Lundahl Transformers

Expected Power Output

124.186.220.137

Kevin

Your new Kt120/150 amp project, what power output do you expect? Further, what B+ voltage and current are you going to run the output stage at?

Follow Ups:

RE: Expected Power Output - KevinC 17:22:07 09/13/15 (2)
The prototype amp has a 520VDC power supply. With KT-120s operating at 110mA per tube and a common cathode CCS to force the output stage to operate Class A1 differential, I get about 25w/ch in triode and about the same in UL with 4 or 8 ohm loads. More current gets you more power output, slightly better sound with each mA and shorter tube life. A classic trade-off!

Of course, there are other ways to connect the output stage to get more power. The output end of the input stage boards provides "uncommited" output pads that will accommodate fixed bias, separate cathode bias with bypass caps and common cathode bias with or without cap bias. It should be possible to get about 50w/ch with the output stage tubes connected for fixed bias.

Kevin Carter
K&K Audio
www.kandkaudio.com
- RE: Expected Power Output - Ejam 01:00:18 09/14/15 (1)
  Is the common cathode CCS one of yours?
  
  I was thinking of using the GU50 (I have a stack of them) with the 1620CFB output transformer at 600V, which I believe is the maximum for your PS board. Given your published input stage's output voltage at 225V RMS, I my sure this will be more than even to drive the output stage with 25% CFB. A separate screen supply for the GU50, maybe using your shunt regulator kit off the front end B+ of 400V regulated down to 250 to 300V.
  - RE: Expected Power Output - KevinC 04:45:56 09/16/15 (0)
    The CCS is one that is not yet on the web page, but is one of mine. It is capable of 400mA or more on the appropriate heat sink and has a very low temperature coefficient, so there is very little current change with warm-up.
    
    I have no experience with the GU50, but what you propose seems OK.
    
    Kevin Carter
    K&K Audio
    www.kandkaudio.com

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