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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: safest way of biasing an amplifier internally posted by afg on January 25, 2006 at 00:47:45:
Well, if setting bias on an amp was as complex as has been written here, I wonder how I managed to do it when I was 17, back in 1965, and managed to live through it!
Some manufacturers install meter jacks on the chassis somewhere. This makes setting bias much easier.
Going inside the chassis to set bias is most safely done with meter probes that will clip onto a component lead or terminal lug. They are available at your nearest Radio Shack. If you keep your fingers away from anything and everything, and clip the leads on with the power off, you'll live through it.
Most of us have been bitten by B+ at one time or another. You usually live through it. Not always. You won't let it happen twice, though, for a long time. Try not to let it happen.
Most, or many anyway, manufacturers recommend NOT having anything across the ourput transformer, nor having anything on the input, although it would be ok to short the input. If the amp has input level controls, it's important to have them set to their lowest setting.
If the amp has a stereo/mono switch, it's important to have it in the stereo mode.
Bias is not so critical that you have to have a reference for your meter. If you're reasonably sure the meter is accurate to within .1 volts, you'll be fine. Even cheapo meters are usually close enough.
From there, use the manufacturers recommendations. If they recommend no load on the output, then don't go and put a load on the output. It should not be necessary, and in fact can affect the bias settings. This is because they are setting the bias at "idle" current. When the output tubes are loaded, you can see different readings on your meter.
After all the above, what is said below is most important:
By all means, go with what the manufacturer recommends and disregard anything you read on the internet that is contrary to what the manufacturer recommends.
Mark D.
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Follow Ups
- Re: safest way of biasing an amplifier internally - Mark D. 08:42:01 01/25/06 (0)
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