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K&K Audio / Lundahl Transformers

KT88 monoblock

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1. If one were to build (for lack of large enough chassis ) the KT88 monoblock in three boxes, the logical parts would be
L and R power amplifiers and
a driver common to both channels.
Each would be connected with say 2 ft cables.
Which placement would be better for the interstatge transfomer:
the power amplifier box with th KT88s and the bias voltage arrangement or
the driver side with the 6BX7GT tubes ?
2. The photo of the KT88 monoblock shows two 6BX7GT driver tubes, are the twin triodes connected in parallel in each tube ?
Thanks,
jormajj

Follow Ups:

Re: KT88 monoblock - jormajj 11:53:54 09/08/04 (0)
My chassis are
17 x 10 x 2 for the output stages and
17 x 10 x 3 for the driver
Thank you for your recommendations
Best regards
Jorma
Re: KT88 monoblock - rwalton 06:10:41 09/08/04 (0)
Hello,
I am working on these amps right now. I created a CAD solids model in order to avoid going through several iterations of prototype chassis/layouts. With very conservative spacing between components, these amps will fit into a 14 x 17 x 4 inch deep chassis (for each channel). You could definitely compress the layout further, though it might make assembly a bit more of a challenge. I'm not sure what your chassis size limitation is, but I'd be glad to forward the layout I have, if it would be of any help.
Regards,
Rick
Re: KT88 monoblock - KevinC 14:45:39 09/07/04 (2)
It would be rather difficult to separate the output stage from the driver because the IT has current for the 6BX7GT passing through the primary and bias, as well as signal, passing through the secondary.
Two 6BX7GTs were used to avoid the need for tubes with internally matched sections. Only one triode in each 6BX7GT is used. In my experience about 1 out of 5 tubes has a close enough match (defined as 10%, determined by current flow) to make a good differential amplifier. I can supply 6BX7GTs with the necessary degree of matching so that you can save the space, but they aren't cheap.

Kevin Carter
K&K Audio
www.kandkaudio.com
- Re: KT88 monoblock - jormajj 00:39:02 09/08/04 (1)
  The multipin connectors and cables connecting the driver to the output stages would carry either the IT primary or secondary signals.
  I'm looking for pros and cons of either way of connecting the three boxes.
  Connecting the secondary side would mean the cable needs to carry more signals ( 4 grid signals and + 4 bias voltages )
  Connecting the primary side means less signals, but would the driver tubes be happier driving the IT transformer directly or through a short length of cable ?
  - Re: KT88 monoblock - KevinC 06:21:16 09/08/04 (0)
    I guess that if I were separating the amp circuit there, I would place the IT with the output tubes and run the 6BX7GT plate leads through the umbilical. It's a realtively low impedance point in the circuit.
    
    Kevin Carter
    K&K Audio
    www.kandkaudio.com

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