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Octal Mullard 5-20 stereo with KT88

primosounds said:
I am not sure that cathode bias is more reliable but it is less "problematic" especially for a tube newbie. The only thing i don't like about cathode bias for a kt88 is that you will be using 4 x 7 watt cathode bias resistors which will dissipate a lot of heat. Not only is that wasted power but also you need to account for locating the resistors in a location to properly vent that heat. Another thing is that the electrolytic caps for bypassing the resistors will have a significant effect on the sound quality.
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I've used impulse rated elyticaps with polypropylene bypasses.
 
Pio1980 said:
I've used impulse rated elyticaps with polypropylene bypasses.
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I agree that the bypass capacitors greatly improves cathode bias or, indeed, any other application where a capacitor is used as a charge reservoir at frequencies higher than mains.

Electrolytics are very slow capacitors and were designed for filtering in power supplies. Adding a bypass capacitor speeds up the response and eliminates much of the undesirable features of the electrolytic. It's why high-frequency designs use many decoupling capacitors. That's another name for bypass capacitor.
 
I also follow that concept. Whenever i use a cathode bias resistor on the power tube the attendant electrolytic cap is bypassed with a film cap of between 1 to 5% of its value, depending on what i have available. The only issue is it is somewhat hard to find film caps that are rated at 50vdc. 100vdc is readily available but much larger in size.
 
Marsman said:
Dandy, I have chosen a custom design for this amplifier. Do you have more information of the HF60 OPT's?
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Sorry, no I don't. There is a dedicated Eico section here you could ask, and an Eico Yahoo group. Also, you could reach out to HF60 owners in this forum in a separate thread.
 
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