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In Reply to: edge of redness posted by thermionic emitter on October 12, 2006 at 17:01:40:
I am re-titling my original note. Sorry to have been less than clear. As stated above, I either have two problems or none or one. Why would plates show dull red after powering down the amplifier? That is the main issue. Secondary is why one tube's filament is brigher than the other. This is an earlier Ming Da with under chassis bias pots but no information is available from distributor on how to set them. Thank you. --Tom
Follow Ups:
Tom,The increase of the dull red intensity is an optical illusion. Because the 805s filament gives much more light than the dull red anode, your eyes can't see the dull red. After switching off the amp your eyes take a few seconds to adjust to the lower light level, in fact they become more sensitive (pupil dilation). That’s why the dull red appears to increase in intensity but in fact it's decreasing. To view the dull red anode when the amp is operating you'll have to use a light to screen out the filament light.
The light screen can be made from a peace of black paper with a hole in it, which is about half the size of the anode. Hold the screen about half way between your eyes and the tube so you can't see the filament light anymore. Now you should be able to see the dull red anode.
So is it normal for these plates which are quite thick to exhibit this dull redness?
I don't know if it's normal for an 805. If the anode is dull red and dissipation is below 125W I suppose it's normal. Check the anode power dissipation.
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