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croccodillo 17th January 2007 02:51 PM

Parafeed output
Hi all,

I'm playing with my parafeed SE amplifier, now on my bench as a prototype: now it is using a SS CCS on the top of a single KT88, used as output tube (triode strapped).
Actually the CCS is an active current source, like the one developed by Nelson Pass for his amplifiers.

I have an 50 microfarad PP output capacitor, and a toroidal output transformer.

It works, but now I would lower the output impedance (from 2500 to 1500 Ohm), in manner to raise the output power without affecting too much the idle power consumption (now it is running at 600V, 100mA).

Moreover, I would eliminate the SS CCS, cause it dissipates a lot of heat, so I have to use a big heatsink.

My idea was to realise a tube CCS (already ready) with a KT88, and drive with it two KT88 (triode strapped), placed in parallel as output tube.

Would it work? I mean: the upper tube, used as CCS, would drive a 1500 Ohm load, and I'm not sure it can do that.
Another option would be to use two KT88 in parallel also for the CCS, but I don't have them available (I would need 8 of them, two as CCS and to as output tube for each channel).

Or I can use my four KT88 for the CCS (two for each channel), and found a different tube for the output (maybe some real triode).

What do you think?

Thanks in advance,

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