Bias- evaiuating audio equipment

I don’t understand the “badly informed about the biasing” statement you made. I talked to the owner of Jadis. You only have one bias pot for each bank of three output tubes. You are never going to get all three tubes in each bank to measure exactly the same even when the tubes are brand new, let alone when they start aging. When you have one bias pot for three tubes, you are setting an average bias voltage based on the voltage of each tube divided by three.

The tubes I bought it with were from Ram Labs. Who matches better than them? The second set came from Kevin Deal at Upscale Audio. Outside of Ram Labs, who matches better than them?

mep said:

I don’t understand the “badly informed about the biasing” statement you made. I talked to the owner of Jadis. You only have one bias pot for each bank of three output tubes. You are never going to get all three tubes in each bank to measure exactly the same even when the tubes are brand new, let alone when they start aging. When you have one bias pot for three tubes, you are setting an average bias voltage based on the voltage of each tube divided by three.

The tubes I bought it with were from Ram Labs. Who matches better than them? The second set came from Kevin Deal at Upscale Audio. Outside of Ram Labs, who matches better than them?

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Three points to consider. Unhappily generic sellers match their tubes using IP and GM for specific anode voltage and currents, that usually are very different from those that are used in amplifiers and they do not pre-age tubes. If you run your good quality tubes for 100 hours you will find that the drift of parameters will be very systematic during their lifetime after the burn-in. I always do it for my amplifiers. There is no magic in that. If you assemble matched tubes in parallel and they have very different currents they are not matched. Simple as that.

Second aspect, as I referred the Jadis has a mix of cathode self bias and grid bias and unless the tubes are too different or really bad it will keep the equilibrium for a long time.

A third point is that the Jadis (and many tube amplifiers) is very sensitive to mains variations. Our local dealer had a few problems that were immediately solved with the addition of an ExactPower unit, that stabilyses the mains to +/- 1% .

Please note I am not blaming anyone. But my perspective it that if many users have a lifetime of trouble free with a certain product, there should be an explanation for those who have problems. IMHO, in 99% of the cases when there is trouble with good quality tube amplifiers it was due to the quality of the tubes or mains variations. This does not mean that poor designs or badly assembled units, prone to frequent faults, do not exist. But I think the Jadis Defy / DA7 is NOT one of them.

Micro-I would argue that the Jadis Defy 7 is flawed both electrically and ergonomically. Electrically because I really feel that there should be one bias pot per tube so the bias for each tube can be set exactly and not averaged. In addition, if you blow a cathode resistor, you either have to nub off the leads on the blown resistor and solder to those leads, or spend two days disassembling the main circuit board so you can totally remove the blown resistor and do a through-hole solder job and reassemble the amp.

Ergonomically it’s flawed because I don’t care if the amp weighs 25 lbs let alone 100 lbs, you shouldn’t have to flip the amp on its side and remove the bottom cover just so you have access to the bias pots and the test points to measure the voltage. And I use the term “test points” loosely because you are really just sticking your meter probe on one side of the cathode fuse with the other probe attached to ground. That’s still not as bad as setting bias on an ARC VT-100 MKII amp that Kevin Deal refuses to sell tubes for because of the wacky bias scheme.

mep said:

Micro-I would argue that the Jadis Defy 7 is flawed both electrically and ergonomically. Electrically because I really feel that there should be one bias pot per tube so the bias for each tube can be set exactly and not averaged. In addition, if you blow a cathode resistor, you either have to nub off the leads on the blown resistor and solder to those leads, or spend two days disassembling the main circuit board so you can totally remove the blown resistor and do a through-hole solder job and reassemble the amp.

Ergonomically it’s flawed because I don’t care if the amp weighs 25 lbs let alone 100 lbs, you shouldn’t have to flip the amp on its side and remove the bottom cover just so you have access to the bias pots and the test points to measure the voltage. And I use the term “test points” loosely because you are really just sticking your meter probe on one side of the cathode fuse with the other probe attached to ground. That’s still not as bad as setting bias on an ARC VT-100 MKII amp that Kevin Deal refuses to sell tubes for because of the wacky bias scheme.

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Some designers feel that mixing tubes with very different parameters just fiddling different DC bias at the grids is poor design and compromises the performance of the output design. IMHO we should respect their view, unless we are experts in the subject and can debate it. Many brands use group biasing, including a few amplifiers that are considered some of the best sounding existing amplifiers. You consider they are all flawed. OK, but not my opinion. .

BTW, I was referring to electrical design, not ergonomics.

BTW2, I am biased - I spent too many fault free happy hours listening to Jadis electronics!