Voltage regulation for Joule amps

Sean, I know that I am not technically knowledgeable to go around making changes in this unit, if what you are saying is that a "regulated power supply" would be a replacement for the variac. esp. since the variac is connected to the main amplifier by two different power cords with different terminations (one male and one female, IIRC). That is the reason I was looking for something like the the Monster AVS 2000 of the Exactpower since I think what I need is something that would supply a constant voltage. The fluctuation at the amp (downstream of the variac) is about+1, -5 volts. I just double checked the manual and the indicated range is about 83-87 volts. It generally seems to sag more than go up, both in the magnitude of the change and the frequency of the change (i.e., it most frequently reads below the initial nominal setting). This causes the bias on the output tubes (6C33C-Bs) to drop from 27/28 to 23/24, and compromises the sound. The variac is near a warm air outlet and the amp itself is on an outside wall. Of course, it runs quite hot and I am sure alters the ambient temp around itself by several degrees. The variac is about 2-3' away and slightly lower down, but as I said, close to a warm air duct. Could these temperature fluctuations be having an effect on the voltage the variac delivers? As you can see, my knowledge of things electrical is quite limited. TIA. I will, of course, contact Judd at Joule tomorrow.

"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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I understand that the bias on the tubes will wander and I'm not too concerned about that. What I am concerned about is if the voltage wanders and the bias wanders and they both wander in the same direction, I will either end up with the tubes dramatically under-biased, resulting in a too-laid-back presentation, or dramatically over-biased, resulting in (I think) premature wear and/or failure (which I am told can be quite dramatic on this OTL amp!).

I own the Rites. Like yours, my voltage drops as it is warming up. After my amps warm up the voltage stabilizes in a range that doesn't affect sonics.

Reading your post, my guess is that you have the VZN-160s? Great amp! I have a suggestion that will get the most out of your amps:

When the amps warm up, turn the voltage up to the top of the recommended range. For a VZN-100 I think that's about 65 volts and for mine it's about 130 volts.

Next, bias the output tubes to read in the 29 range. Getting them stabilized in the 29 range will take a few passes through the buttons. I stabilize mine 29.5-ish...

Next, turn set the bias for your driver tubes right around 124. The bias will move a bit, but get it around 124.

Finally, sit down and strap in. You should get maximum harmonics and transparency at the same time.

The bias points will move around when the amp is warming up, so ignore all this when you turn things on subsequently. Keep your focus on the settings when the amp is good and warm and just drop me an email if you want to touch bases about anything.

Hope this helps

J

Jsl- Rites? Not sure what that (those) are. My amp is a VZN-80, which I imagine is basically a half of a pair of VZN-160s. I am told it can be modified to a monoblock, but based on my room and ancillary equipment, I cannot imagine going any further up the line in terms of power!! The recommended voltage is 83-87v.