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Bias Board

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I installed their AB-Q's in my PP monoblocks. Benefits I've observed include; large increase in tube life, bias drift eliminated, useful led indicators. Additional benefit is eliminated need to use matching tube pairs. Going on 5 years now, have paid for themselves many times over.
 
I've used a couple. They work as advertised. The startup time delay and ramp up of the bias current after warmup is nice.
 
These do work as advertised. I have used this board or another one very similar from the same vendor with no issues in 2-3 amps

However, I'm now over it as I'd rather adjust my own individual output tube bias. Personal preference.
 
Legrace said:
I installed their AB-Q's in my PP monoblocks. Benefits I've observed include; large increase in tube life, bias drift eliminated, useful led indicators. Additional benefit is eliminated need to use matching tube pairs. Going on 5 years now, have paid for themselves many times over.
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How do these boards increase tube life? I don't see any reason why that would be true.

Jack
 
A couple questions:

1) would a 100K volume pot work in my schematic?
2) How would you calculate (adjust) for a 2volt input signal?
Here are a couple I was looking at. I have a knob I wanted to use for volume control that was actually a VFO knob off some radio gear. It's about 1.75" diameter and made of machined aluminum; so it has a little weight.

EIZZ Stereo 100K 24 Steps Volume Potentiometer Audio Attenuator for 2 Channels HiFi Amplifier Speaker Turntable Recorder Gold Plated Copper Pins: Amazon.com: Industrial & Scientific

EIZZ Stereo 100K 24 Steps Volume Potentiometer Audio Attenuator for 2 Channels HiFi Amplifier Speaker Turntable Recorder Gold Plated Copper Pins: Amazon.com: Industrial & Scientific
www.amazon.com

www.partsconnexion.com

Audio Note 100K Stereo Volume Potentiometer Log (audio) Taper Solder Lug

Audio Note 100K Ohm Stereo Volume Potentiometer, Log (Audio) Taper, Solder Lug Never underestimate the importance of the volume potentiometer. It has a dramatic and clearly audible influence on sound quality. Get it right, and it is an open window to the musical performance...get it wrong, and...
www.partsconnexion.com
 
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TriodeLuvr said:
How do these boards increase tube life? I don't see any reason why that would be true.

Jack
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The mfgr website indicates users may gain as much as 2x tube life. My initial experience exceeds even this, @10,000 hours on current set versus typically 2-3000 hours prior to the change. Not a single tube lost over past 4 years, so have yet to find the ceiling. And as noted previously when I would lose a tube it would leave a stranded twin as my amps used to require matched pairs. With AB not requiring matched pairs these can come back into play, for even more savings.

Perhaps with more durable classic NOS type tubes the benefit would be less profound, but with modern tubes they do seem to save a lot of wear and tear on tubes making them last longer.
 
Legrace said:
The mfgr website indicates users may gain as much as 2x tube life. My initial experience exceeds even this, @10,000 hours on current set versus typically 2-3000 hours prior to the change. Not a single tube lost over past 4 years, so have yet to find the ceiling. And as noted previously when I would lose a tube it would leave a stranded twin as my amps used to require matched pairs. With AB not requiring matched pairs these can come back into play, for even more savings.

Perhaps with more durable classic NOS type tubes the benefit would be less profound, but with modern tubes they do seem to save a lot of wear and tear on tubes making them last longer.
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Matched pairs promote better distortion numbers, and that can't be fixed simply by providing equal bias. And again, there's no reason these boards should promote longer tube life in an AB1 fixed bias amplifier compared to bias pots (regardless of tube type or manufacturer). Sorry, but this appears to be a solution looking for a problem. IMO the money could be better put towards the output transformers or power supply components.

Jack
 
The AB installation process required that I remove the original manual bias pots. So nice not having to deal with those fiddly things anymore, now that was a problem lol!
 
That is a real problem. I have to adjust my amp every three or four years. What a nuisance! LOL.
 
Hey back to the auto bias boards, my amp is going to be separate rectified power supplies for each channel. And each channel will have 2 KT-88's in PPUL. Do you think that the bias board for 4 tubes would still apply, or 2 separate 2tube bias boards?
 
Stavee said:
Hey back to the auto bias boards, my amp is going to be separate rectified power supplies for each channel. And each channel will have 2 KT-88's in PPUL. Do you think that the bias board for 4 tubes would still apply, or 2 separate 2tube bias boards?
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Certainly if you're planning on tube rectfication that's a good way to go. IMO the 4 tube board is preferable to maintain identical bias across all 4 tubes.
 
You essentially have two monoblocks. Except they are on a common chassis. 2 boards is required. If you use one board, which power supply will you power it off of? The boards can be adjusted to exactly the same and they will not change.
 
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