Jadis PA 100 amp - Jadis becomes Jadis again

[jadis]

Phil,
How do the Chinese tubes sound? You always have the remaining originals if you need to go back to that approach!

Good luck!

Sel,

The Chinese tubes actually sounds fuller to me than the Russian EH Jadis selected tubes. Solid images and more body with clean bass and nice highs. Can't complain. Yes, I still have the originals but now they will sound 'leaner'.

 

[Ron Resnick]

JADIS Amps Are Overrated, Overpriced And Not Worth The Money

Please tell us in detail your support for each of these three comments.

Which Jadis amplifiers did you compare to other amplifiers in a system in which all other associated components were held constant?

Please list the associated components in addition to the amplifiers which were being compared.

 

[christensenleif@msn.com]

JADIS Amps Are Overrated, Overpriced And Not Worth The Money

very useful piece of information.......

 

[jadis]

I hope to learn something here if anyone can help analyze this.

My friend's PA-100 was just re-tubed yesterday to a set of 12 Psvanne KT88s, like mine.

His stock tubes are the original Jadis selected EH KT88s. Maybe an estimated 2,000 hours by now.

Before he had a tech install the new tubes, he took the bias readings of the old tubes.




K1- K4 indicates the group of 3 tubes that Jadis biases with a trim pot to 4.5 - 5.0volts. There was never an attempt to open the bottom cover to check the bias till now, at 2,000 hours. I am intrigued by how the bias in these 4 groups of trios behaved this way. K1 and K2 are the push pull partners, so are K3 and K4. The tube that is marked 'X' is a used EH KT88, untested, just plucked out as working in a Cary amp (Due to a red light /popping fuse of the original tube). My initial question would be, if the 12 tubes are left as such to play further for like 6 months to 1 year, will the tubes eventually go off due to the uneven push pull bias?

Second, how did a set of 12 brand new and Jadis tested tubes run into such uneven biasing given the knowledge that the 12 were closely matched to ensure an even aging process?

And 3, what does the 4.5v mean compared to the 3.5v group? Does it mean the 3.5v tubes are still 'stronger' than the 4.5v tubes? Any inputs are welcome. It's still a learning curve for me.

 

[MikeHorns]

I hope to learn something here if anyone can help analyze this.

My friend's PA-100 was just re-tubed yesterday to a set of 12 Psvanne KT88s, like mine.

His stock tubes are the original Jadis selected EH KT88s. Maybe an estimated 2,000 hours by now.

Before he had a tech install the new tubes, he took the bias readings of the old tubes.


View attachment 92127

K1- K4 indicates the group of 3 tubes that Jadis biases with a trim pot to 4.5 - 5.0volts. There was never an attempt to open the bottom cover to check the bias till now, at 2,000 hours. I am intrigued by how the bias in these 4 groups of trios behaved this way. K1 and K2 are the push pull partners, so are K3 and K4. The tube that is marked 'X' is a used EH KT88, untested, just plucked out as working in a Cary amp (Due to a red light /popping fuse of the original tube). My initial question would be, if the 12 tubes are left as such to play further for like 6 months to 1 year, will the tubes eventually go off due to the uneven push pull bias?

Second, how did a set of 12 brand new and Jadis tested tubes run into such uneven biasing given the knowledge that the 12 were closely matched to ensure an even aging process?

And 3, what does the 4.5v mean compared to the 3.5v group? Does it mean the 3.5v tubes are still 'stronger' than the 4.5v tubes? Any inputs are welcome. It's still a learning curve for me.

Phil, I don't have any experience with Jadis, but I'll take a stab at it.

I believe you place your voltmeter across a resistor to bias the current for each group of power tubes. Voltage/resistance = current in mA.

So if you have to crank up the voltage in K1 & K3 to 4.5v, it means they are probably weakened over time(one or more tubes). Tubes are made in batches but are not all created equal even in the same batch. It is quite common that some tubes drop out over a period of time. That's why you need to check the bias from time to time in case one(or more) drops out. The best way to find out is to use a tube tester and test each tube individually.

As a bit of advice, whenever I placed a new set of tubes, I generally bias the amplifier to the lowest level before I fire up the amp. After about an hour, I bias it to halfway. Another hour later, I bias to the full manufacturer's spec. And about a week later, I would check the bias again to make sure everything still holds up. This is a safe way to slowly break-in new tubes before they go into shock.

 

[jadis]

Phil, I don't have any experience with Jadis, but I'll take a stab at it.

I believe you place your voltmeter across a resistor to bias the current for each group of power tubes. Voltage/resistance = current in mA.

So if you have to crank up the voltage in K1 & K3 to 4.5v, it means they are probably weakened over time(one or more tubes). Tubes are made in batches but are not all created equal even in the same batch. It is quite common that some tubes drop out over a period of time. That's why you need to check the bias from time to time in case one(or more) drops out. The best way to find out is to use a tube tester and test each tube individually.

As a bit of advice, whenever I placed a new set of tubes, I generally bias the amplifier to the lowest level before I fire up the amp. After about an hour, I bias it to halfway. Another hour later, I bias to the full manufacturer's spec. And about a week later, I would check the bias again to make sure everything still holds up. This is a safe way to slowly break-in new tubes before they go into shock.

Thanks for your insights, Mike. Much appreciated.

 

[microstrip]

I hope to learn something here if anyone can help analyze this.

My friend's PA-100 was just re-tubed yesterday to a set of 12 Psvanne KT88s, like mine.

His stock tubes are the original Jadis selected EH KT88s. Maybe an estimated 2,000 hours by now.

Before he had a tech install the new tubes, he took the bias readings of the old tubes.


View attachment 92127

K1- K4 indicates the group of 3 tubes that Jadis biases with a trim pot to 4.5 - 5.0volts. There was never an attempt to open the bottom cover to check the bias till now, at 2,000 hours. I am intrigued by how the bias in these 4 groups of trios behaved this way. K1 and K2 are the push pull partners, so are K3 and K4. The tube that is marked 'X' is a used EH KT88, untested, just plucked out as working in a Cary amp (Due to a red light /popping fuse of the original tube). My initial question would be, if the 12 tubes are left as such to play further for like 6 months to 1 year, will the tubes eventually go off due to the uneven push pull bias?

Second, how did a set of 12 brand new and Jadis tested tubes run into such uneven biasing given the knowledge that the 12 were closely matched to ensure an even aging process?

And 3, what does the 4.5v mean compared to the 3.5v group? Does it mean the 3.5v tubes are still 'stronger' than the 4.5v tubes? Any inputs are welcome. It's still a learning curve for me.

IMHO this level of mismatch is strongly affecting the bass response of the amplifier and you should have the tubes measured. Unfortunately most meters just allow matching for transconductance (GM) not for plate current, the measurement you need more. At this point you should measure all the tubes and re-arranging the sets to have K groups with similar current.

Although I am not aware of the quality and accuracy of this particular kit and its meter, you can use this type of simple device to measure the relative current of individual tubes in an amplifier. https://www.ebay.com/itm/254343123731

 

[jadis]

IMHO this level of mismatch is strongly affecting the bass response of the amplifier and you should have the tubes measured. Unfortunately most meters just allow matching for transconductance (GM) not for plate current, the measurement you need more. At this point you should measure all the tubes and re-arranging the sets to have K groups with similar current.

Although I am not aware of the quality and accuracy of this particular kit and its meter, you can use this type of simple device to measure the relative current of individual tubes in an amplifier. https://www.ebay.com/itm/254343123731

Thanks Micro. Nice info.

 

[jadis]

As my Jadis PA100 is just on the side and not being used for many months, I toyed with the idea of putting EL34s in them , to have a change of flavor from KT88s. I emailed Jadis France about it and they replied that there is a need to change resistors , and a pin check for each power tube. It should be done by the local distributor. Just passing the info.

 

[Ron Resnick]

One gets to wonder why this brand has attracted so many followers with with erroneous detail, me included. LOL

Marketing literature and manuals also sometimes are inconsistent. Clearly we do not buy Jadis for precision in writing and accuracy in specifications.

Hopefully these discrepancies will be corrected over time.

 

[Ron Resnick]

Got a message from the local dealer that Jadis said the total power output with the EL34 tubes is the same at 150w. That is also what is mentioned in the Italian Jadis site as the latest production comes in EL34, KT88, and KT 120 with the same power rating of 150w.

How could this possibly be? (Unless the EL34s are biased so high that they are going to have short lives?)

 

[jadis]

Marketing literature and manuals also sometimes are inconsistent. Clearly we do not buy Jadis for precision in writing and accuracy in specifications.

Hopefully these discrepancies will be corrected over time.

Agree. But hoping they would be more informative in their manual as to the need and how to bias their manual biasing amps. Decades ago, Conrad Johnson and ARC mentioned those in their manuals, including present ARCs.

 

[jadis]

How could this possibly be? (Unless the EL34s are biased so high that they are going to have short lives?)

I agree with your question as well. The best place to know this accurately is by emailing Jadis France itself.

 

[Milimetr]

Any news here? Did you changed the tubes for EL34?

 

[Ron Resnick]

Any news here? Did you changed the tubes for EL34?

No, I never did.

1) I didn't want to sacrifice that many watts in output power; and

2) That switch requires different cathode resistors, and I did not want to do that surgery.

 

[Milimetr]

Last time I have compared two Jadis Orchestra one with EL34 and second one with KT120 and if I would have to pick up one it would be KT120.