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mk3 amps

204.17.79.89
Posted on May 29, 2003 at 11:57:17
dentaudio


 
Joe, I have your ccda board used without the regulator in my dynaco mk3 amps. The plate load resistors see 430VDC at the top and the 6922 plate sees 200VDC as per your specs. The 6550 tungsol output tubes have 525VDC unregulated on their plates. I have individual bias pots for each tube which is unregulated. I am using the 5AR4 rectifier. The output tubes are triode strapped (100 ohm 1W Resistors). The output transformers are by Magnequest (MQ431), direct replacement for the mk3 but with better bandwidth.
The power supply is: 22mfd/10H/225mfd/15H/94mfd (series-parallel)
using Blackgate and .22mfd + .022mfd Jensen copper pio bypass caps. The bias supply has 100mfd and .1mfd caps (Blackgate and Jensen pio)after the 1K resistor.

My question: Should I keep the 1.10V bias setting with this arrangement?

 

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Re: mk3 amps, posted on May 29, 2003 at 15:54:01
Joe Curcio
Manufacturer

Posts: 1261
Location: Northern CA
Joined: October 10, 2001
 I like to run about 45 to 50 mA for each output tube. Therefore if you have retained the original 11.2 ohm cathode resistor this would represent a bias voltage of 1.0 to 1.12 volts. (e.g. 45mA X 2 X 11.2 = 1.0 VDC) so you are within range. if you have changed the value of the cathode bias resistor you cna re-calculate the associated bias voltage from the above formula.

 

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