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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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It is currently 18 Feb 2020, 05:19

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PostPosted: 01 Feb 2020, 08:52 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, Since the heaters are in series....just insulate it and not use it. Remember if you rectify the 12VAC ....with typical filtering it will produce about 2-3 volts higher DC voltage. It can be brought down to the 12VDC needed with a resistor . The actual value varies a bit, but is in the 1-3 ohm range . Use a 5 watt or 10 watt size as it dissipates a bit of heat. Also remember not to ground any part of the heaters as it will defeat the reference DC voltage applied to it that protects the driver tube from heater to cathode failure.

Good listening
Bruce

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PostPosted: 02 Feb 2020, 11:03 
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Joined: 11 Sep 2019, 10:56
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Thanks Bruce. I thought that would be the case but just wanted to check. Don't the three diodes in series prior to the smoothing cap. drop the voltage by just over 2V? Is a resistor still needed if these are present?

Rog


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PostPosted: 02 Feb 2020, 17:56 
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Hi, Yes that is a viable way to drop the voltage as well. Be aware that they will get hot. I used some a long while ago in a power supply for two KT88 Oddblocks. Everything was fine until the music faded out. When I checked the PS I found that one of the rectifiers (10 amp size used) had unsoldered itself. I was using fairly low temp solder then. Now if I use that method I fasten them to screw type terminal strips. Power resistors can also unsolder themselves BTW.

Good listening
Bruce

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