K_O_E_N_J
22 posts
Jun 21, 2012
1:16 AM
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hey,
I got a geloso g213 which is repaired by a amptech.
When I turn the volume to 7 there is allot of feedback, to much to play. Then when I turn the volume to 8/9/10 The feedback is totally gone! also the sound is much more "fatter" and there is more tube breakup. The amp is really pumping and I really like the sound and its really loud.
do you guys know why the amp is feed-backing at <7 and not at 8>?
Does it maybe help to lower the bias?
greats from holland
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5F6H
1243 posts
Jun 21, 2012
1:55 AM
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How is your "Phono" volume set? The 2 volumes affect each other.
Another possibility is perhaps a new volume pot was installed, some pots reach maximum value & then "roll off" again in the last part of the turn?
The setting of the controls will have a very, very small effect on the bias for the 2nd half of the first preamp tube. It will have no effect whatsoever on the idle current of the power tubes.
When we talk about "bias", we generally mean the no signal, dc idle current. However, this just sets the scene for actual performance under signal, so whenever you are playing, you are affecting the bias (it always goes "colder" relative to integrity of the AC waveform, but usually "hotter" with regards to heat & dc generated by your tubes)...though this is not in the manner that you suspect, or mean in your post.
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