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I've misplaced my manual and cannot remember ther proper procedure for biasing the Mark III's. I just put new tubes in and need to reset bias.

Any help will be appreciated.

TIA

The manuals for all diytube boards are in the first message
in their respective forums ...

http://www.diytube.com/phpBB2/viewtopic.php?t=923

I saw those. I thought there was a more detailed description of the bias process. The balancing between each pot and which pot went to which tube.

Showing my ignorance but these things were up around 900mv and would not come down much. I know I'm just not doing the steps in the correct order.

Pull all the tubes, especially the rectifier tube. Verify your bias voltages are within normal, expected bounds. This diagram might help...



Point H appears at the control grid of the output tubes, pin 5. You should be able to get between -42 volts DC and -67 volts DC depending on the position of the main bias pot (the one on the chassis). Adjust the trim pot on the Poseidon board so that both power tubes will see the same bias voltage. Then set the main bias pot so you get the maximum negative bias voltage (about -67 volts DC). Now put in all your tubes, and begin the biasing process.

Ty_Bower wrote:Pull all the tubes, especially the rectifier tube. Verify your bias voltages are within normal, expected bounds. This diagram might help...



Point H appears at the control grid of the output tubes, pin 5. You should be able to get between -42 volts DC and -67 volts DC depending on the position of the main bias pot (the one on the chassis). Adjust the trim pot on the Poseidon board so that both power tubes will see the same bias voltage. Then set the main bias pot so you get the maximum negative bias voltage (about -67 volts DC). Now put in all your tubes, and begin the biasing process.

I think I can figure this out. Again though, what is the biasing process.

Look at page ten of the TubeZone manual. I think Ned explains it pretty well.
http://www.diytube.com/unidriver/poseidon-tz.pdf

If your tubes are reasonably matched and you balanced the grid voltages before you started, you can probably just warm up the amp and use the chassis pot to get the idle current right up to 65mA or so (650mV reading across the 10 ohm cathode resistor). Check to see the left and right readings are still matched, and use the trimpot on the board to adjust if necessary. Finish off by again using the chassis pot and bring the idle up to 70mA. Again, check the balance and trim if needed.

Check the tubes again after fifteen minutes, then a third time after an hour. If they seem stable you're probably good to go.

Thanks Ty!