"I will, of course, contact Judd at Joule tomorrow."
Boy, i can already hear that conversation.... : )
The bias on most tube circuits will change due to both dynamic and thermal variations. As such, it is best to set them to where they should normally be and then re-adjust after the unit has thermally stabilized during NORMAL use. Better designs with tubes that are in better condition will remain within their nominal operating range once that is done. If the bias is all over the place during a normal listening session, the tubes aren't in very good shape, the circuit feeding them is unstable ( thermally or electrically ) and / or the voltage into the unit itself is far from regulated. Even if one has "good" tubes, a stable circuit and a regulated power supply, you'll still find that tube bias "wanders" just a bit. Tubes simply are NOT precision operating devices.
Other than that, i was not suggesting that you attempt to build a regulated power supply for this unit. To do so would be quite costly and require extensive electrical knowledge to do it right. This is probably most of the reason why we don't see precision regulation circuitry in most power supplies.
As far as temperature goes, i would be more concerned with the tubes & circuitry than the variac itself. So long as the variac isn't getting too warm, either through self-dissipation of energy OR your heating system blowing directly on it, don't worry about that.
I was looking for voltage fluctuations on the AC line itself, not after the variac. Due to the "step down" action of the variac, those variations will be reduced in significance, so we really need to see what is going on with the incoming power. Try measuring the AC voltage from the outlet feeding the variac with the system under load ( get some volume on it ) and then in another outlet or two around the house on other circuits. This will tell us if the wiring feeding your Joule is adequate and / or if the AC voltage is fluctuating from the provider. Sean
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Boy, i can already hear that conversation.... : )
The bias on most tube circuits will change due to both dynamic and thermal variations. As such, it is best to set them to where they should normally be and then re-adjust after the unit has thermally stabilized during NORMAL use. Better designs with tubes that are in better condition will remain within their nominal operating range once that is done. If the bias is all over the place during a normal listening session, the tubes aren't in very good shape, the circuit feeding them is unstable ( thermally or electrically ) and / or the voltage into the unit itself is far from regulated. Even if one has "good" tubes, a stable circuit and a regulated power supply, you'll still find that tube bias "wanders" just a bit. Tubes simply are NOT precision operating devices.
Other than that, i was not suggesting that you attempt to build a regulated power supply for this unit. To do so would be quite costly and require extensive electrical knowledge to do it right. This is probably most of the reason why we don't see precision regulation circuitry in most power supplies.
As far as temperature goes, i would be more concerned with the tubes & circuitry than the variac itself. So long as the variac isn't getting too warm, either through self-dissipation of energy OR your heating system blowing directly on it, don't worry about that.
I was looking for voltage fluctuations on the AC line itself, not after the variac. Due to the "step down" action of the variac, those variations will be reduced in significance, so we really need to see what is going on with the incoming power. Try measuring the AC voltage from the outlet feeding the variac with the system under load ( get some volume on it ) and then in another outlet or two around the house on other circuits. This will tell us if the wiring feeding your Joule is adequate and / or if the AC voltage is fluctuating from the provider. Sean
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