Jadis PA 100 amp - Jadis becomes Jadis again

[jadis]

There is a red LED light and its accompanying fuse holder for EACH of the 12 power tubes. When the red light goes on, it means its fuse is busted. It could mean a bad tube or a power surge. Fuse change, or tube change is the answer.

 

[AudioLibertarian]

No pots or trimmers either from the top chassis.

View attachment 88545

SO how is it done then?! The Biasing? Does it say how in the manual if you still have it? Thanks

 

[AudioLibertarian]

If red light goes on and you just replace the fuse&tube, no need to bias it at all?! They would definetly mention such a feature after the nightmare DEFY owners had with electrocuting themselves.... I ve written both Jadis and the US distro and gotten no replies so far ..

 

[AudioLibertarian]

Jadis tech form Brooks Berdan store in California says to rebias the tubes one must open the chassis... I think there is thread on th DIY forums , you must hold voltmeter between the resistors, or something like that. A very involved procedure .

 

[jadis]

If red light goes on and you just replace the fuse&tube, no need to bias it at all?! They would definetly mention such a feature after the nightmare DEFY owners had with electrocuting themselves.... I ve written both Jadis and the US distro and gotten no replies so far ..

There is no need to bias. There is nowhere to do the biasing. There will always be a measuring pot and trimmer pot in amps with manual biasing. I have used CJ125, ARC D115 (1980s) VS110, VS115 and there were voltmeter pots and trimming pots in those amps. The PA100 has nothing. So I have just put in 2 brand new KT88s into the amp bec of failed tubes and I did not do anything other than put in the 2 new tubes to the socket It's been working for weeks now. I have written Jadis France many times and they give you a 1 sentence answer, if you're lucky, 2. I've even posted the bias question in Brook Berdan's youtube video on the PA100. No answer. I just chalk it up as a misprint of 'manual' biasing. All amps say 'automatic' except the JA 500 which says Manual, need to make adjustment for different kinds of power tubes, something like that.

 

[jadis]

Jadis tech form Brooks Berdan store in California says to rebias the tubes one must open the chassis... I think there is thread on th DIY forums , you must hold voltmeter between the resistors, or something like that. A very involved procedure .

I'd like to see that , as you can see from the 3 pictures I posted of the inside of the under chassis, there is not pot at all. you need TWO pot per tube to manually bias them, PA100 has 12 tubes, at least you will be seeing 24 pots, there is none.

 

[jadis]

Here is an example of a manual biasing amp ,the ARC VS115 and VS110. Notice the top plate has holes for you to TRIM the adjustment. And the back panel has 8 pairs of pots to stick the voltmeter into, while you trim the value to .65mA.







I have owned these 2, and did the biasing myself, they gave me a long yellow plastic thin screwdriver to trim the bias on the top plate. There are no such things on the Jadis PA100.

 

[jadis]

This is a high res file I got from the Jadis Italian site. You can save it and enlarge it to see if there are trimming or voltmeter pots. As it looks, you will run a risk of being electrocuted indeed if you try to tinker with this opened chassis while the POWER IS ON.

http://www.jadisitalia.it/FINALI/PA%20100/FOTO%20PA%20100/PA-100%20%20JADIS%20%20(6).png

 

[AudioLibertarian]

I'd like to see that , as you can see from the 3 pictures I posted of the inside of the under chassis, there is not pot at all. you need TWO pot per tube to manually bias them, PA100 has 12 tubes, at least you will be seeing 24 pots, there is none.

Here is it the link for that discussion relating to biasing of Orchestra integrated that includes replies from ex Jadis tech, some very itneresting info, however still not definitive, as I have been offered an ex demo PA 100, and need to make a decision now.

Biasing a Jadis Orchestra

Hello all. I’ve been lurking on here for a while now, but this is my first posting. I’m a fairly recent convert to valve/tube amps, and I’m trying to get to grips with the characteristics of different valve types and the mysteries of biasing etc. Although I covered basic electronics as part of...

www.diyaudio.com

The mere thought of having to open a 125 pound amp, and poke inside it every time one of the 12 tubes fails , ( or not to mention having to lug it to the technician), just terrifies me , despite having owned VTL amps in the early 90s. The amp is physically huge, and I carrying 125 pound box is not as easy as it used to be 25 years ago

 

[AudioLibertarian]

There is no need to bias. There is nowhere to do the biasing. There will always be a measuring pot and trimmer pot in amps with manual biasing. I have used CJ125, ARC D115 (1980s) VS110, VS115 and there were voltmeter pots and trimming pots in those amps. The PA100 has nothing. So I have just put in 2 brand new KT88s into the amp bec of failed tubes and I did not do anything other than put in the 2 new tubes to the socket It's been working for weeks now. I have written Jadis France many times and they give you a 1 sentence answer, if you're lucky, 2. I've even posted the bias question in Brook Berdan's youtube video on the PA100. No answer. I just chalk it up as a misprint of 'manual' biasing. All amps say 'automatic' except the JA 500 which says Manual, need to make adjustment for different kinds of power tubes, something like that.

Jadis have replied with 2 sentence email: Bias is Manual, and I can use EL 34 in it (although they don't say whether its just plain substitution, or what adjustments need to be made), but NOT the Kt150 tubes, and have given me the address of the distro in USA,, (who is in Canada) and pretty much useless, and does not answer any inquires rregarding their product, and force you to get in touh with your local dealer, who also NVER replies. Just not customer oriented folks, (or as some folks in NY would call "a chain of dicks") and do not inspire any confidence to spend lot of money on their product so I ll think I will pass , as much as I would like to get one. Not worth the trouble!

 

[microstrip]

Here is it the link for that discussion relating to biasing of Orchestra integrated that includes replies from ex Jadis tech, some very itneresting info, however still not definitive, as I have been offered an ex demo PA 100, and need to make a decision now.

Biasing a Jadis Orchestra

Hello all. I’ve been lurking on here for a while now, but this is my first posting. I’m a fairly recent convert to valve/tube amps, and I’m trying to get to grips with the characteristics of different valve types and the mysteries of biasing etc. Although I covered basic electronics as part of...

www.diyaudio.com

The mere thought of having to open a 125 pound amp, and poke inside it every time one of the 12 tubes fails , ( or not to mention having to lug it to the technician), just terrifies me , despite having owned VTL amps in the early 90s. The amp is physically huge, and I carrying 125 pound box is not as easy as it used to be 25 years ago

IMHO you should also get a decent tube tester. If you carry preventive maintenance - just measuring the tubes and taking note of the values every 500 hours - probably you will discard the tubes that can create problems before having any issues with the amplifier.

Some Jadis amplifiers need carefully matched tubes - Jadis became known for being non reliable mainly because the factory matched tube sets are expensive and owners often use poorly matched, not pre-aged tubes. The same for some Audio Research amplifiers. Amplifiers having individual tube bias, such as VTL or conrad johnson are less critical in this aspect.

 

[AudioLibertarian]

IMHO you should also get a decent tube tester. If you carry preventive maintenance - just measuring the tubes and taking note of the values every 500 hours - probably you will discard the tubes that can create problems before having any issues with the amplifier.

Some Jadis amplifiers need carefully matched tubes - Jadis became known for being non reliable mainly because the factory matched tube sets are expensive and owners often use poorly matched, not pre-aged tubes. The same for some Audio Research amplifiers. Amplifiers having individual tube bias, such as VTL or conrad johnson are less critical in this aspect.

I ve owned Jadis Defy in mid 90s , I know Wanted to give another try as I missed their colorful musical signature, but alas, not to be I guess.... Considering getting CJ Classic 120 SE now

 

[jadis]

Here is it the link for that discussion relating to biasing of Orchestra integrated that includes replies from ex Jadis tech, some very itneresting info, however still not definitive, as I have been offered an ex demo PA 100, and need to make a decision now.

Biasing a Jadis Orchestra

Hello all. I’ve been lurking on here for a while now, but this is my first posting. I’m a fairly recent convert to valve/tube amps, and I’m trying to get to grips with the characteristics of different valve types and the mysteries of biasing etc. Although I covered basic electronics as part of...

www.diyaudio.com

The mere thought of having to open a 125 pound amp, and poke inside it every time one of the 12 tubes fails , ( or not to mention having to lug it to the technician), just terrifies me , despite having owned VTL amps in the early 90s. The amp is physically huge, and I carrying 125 pound box is not as easy as it used to be 25 years ago

You just showed a Jadis Orchestra amp. I'm talking about a PA 100. My PA100 does not have that trimming pot which is shown in the Orchestra picture.

 

[jadis]

Jadis have replied with 2 sentence email: Bias is Manual, and I can use EL 34 in it (although they don't say whether its just plain substitution, or what adjustments need to be made), but NOT the Kt150 tubes, and have given me the address of the distro in USA,, (who is in Canada) and pretty much useless, and does not answer any inquires rregarding their product, and force you to get in touh with your local dealer, who also NVER replies. Just not customer oriented folks, (or as some folks in NY would call "a chain of dicks") and do not inspire any confidence to spend lot of money on their product so I ll think I will pass , as much as I would like to get one. Not worth the trouble!

For sure I will never use an EL34 WITHOUT a tech man doing something inside the amp. Your experience is pretty much the same as mine regarding their email style and local dealers' problems. I have good friend here with another PA100 and he accidently broke 1 tube and had replaced them with a used matched pair. Plug and play, did not do any biasing because as I have said and shown, there is no trimming pot to adjust anything on top or under.

 

[jadis]

I ve owned Jadis Defy in mid 90s , I know Wanted to give another try as I missed their colorful musical signature, but alas, not to be I guess.... Considering getting CJ Classic 120 SE now

The Conrad 120 has holes where you stick a thin plastic screw driver to bias until the red light goes Off. Incidentally, the PA 100 came with Allen wrench for removing the grill cover and some small bars to strap changing impedance but of plastic screwdriver and no instructions on the owner's manual as how to bias. ARC amplifiers provide that information, with a diagram of the adjustment pots and measuring pots at the back.

 

[jadis]

Perhaps the best way is for you to check it out yourself the demo unit. Ask them to open the bottom plate and see for yourself if there are 12 trimming pots near the tube sockets and resistors. I did just that and couldn't find any and then bought a sealed unit.

 

[AudioLibertarian]

Perhaps the best way is for you to check it out yourself the demo unit. Ask them to open the bottom plate and see for yourself if there are 12 trimming pots near the tube sockets and resistors. I did just that and couldn't find any and then bought a sealed unit.

That is not feasible, as the amp is California and I am in New York, and seller's tech insists its a manual bias, so I highly doubt they will allow me to open the chassis even if I were to fly there in person. Ah well, life will go on

 

[jadis]

That is not feasible, as the amp is California and I am in New York, and sellers tech insists its a manual bias, so I highly doubt they will allow me to open the chassis even if I were to fly there in person. Ah well, life will go on

Understood. Good luck on your next amp. CONRAD is a nice choice. I considered that before I took the Jadis.

 

[mtemur]

A manual bias amplifier does not have to have trimpots. Sometimes manufacturer/designer calculates the impedance required for the circuit based on tube’s general characteristics and installs a resistor for each tube instead of an adjustable pot. I believe jadis PA 100 is designed like that. this kind of design is more like a manual bias cause it’s manually set in the factory and you need to change the resistor in order to change the bias. That’s a better approach in terms of purist circuit design but it has a major down side. You need to use perfectly matched pairs or quads that will behave same while they age which is almost impossible to accomplish. Most probably that’s why it has a fuse for each tube. If one of them ages differently and goes bad due to factory set constant bias, it triggers it’s fuse and saves the circuit. IMHO regarding it’s circuit design it can be called constant bias amplifier.
On the other hand a normal manual bias amplifier has pots to adjust bias according to changing conditions such as line voltage, tube age and characteristics.
Auto bias measures cathode current/plate voltage etc and regulates it automatically using a dedicated circuit which I couldn’t see in PA 100.

 

[jadis]

A manual bias amplifier does not have to have trimpots. Sometimes manufacturer/designer calculates the impedance required for the circuit based on tube’s general characteristics and installs a resistor for each tube instead of an adjustable pot. I believe jadis PA 100 is designed like that. this kind of design is more like a manual bias cause it’s manually set in the factory and you need to change the resistor in order to change the bias. That’s a better approach in terms of purist circuit design but it has a major down side. You need to use perfectly matched pairs or quads that will behave same while they age which is almost impossible to accomplish. Most probably that’s why it has a fuse for each tube. If one of them ages differently and goes bad due to factory set constant bias, it triggers it’s fuse and saves the circuit. IMHO regarding it’s circuit design it can be called constant bias amplifier.
On the other hand a normal manual bias amplifier has pots to adjust bias according to changing conditions such as line voltage, tube age and characteristics.
Auto bias measures cathode current/plate voltage etc and regulates it automatically using a dedicated circuit which I couldn’t see in PA 100.

Good explanation. I think the confusion starts with the word Manual. If this PA100 is Manual bias and the ARC VS110 Manual bias as well, then how does one get to adjust the PA100 without any trim pots and a manufacturer supplied plastic screwdriver like those provided by ARC and Conrad Johnson. Surely by Manual bias , Jadis France does not expect the owner to remove or replace Resistors when changing power tubes? Maybe it's called Fixed Manual Bias but upon checking the site of Jadis, it lists the Orchestra model as "Fixed - has to be adjusted when tubes are changed". It doesn't say this with the PA100. But having owned the Jadis 200 and checked the Jadis site, it lists the JA 200 as Automatic Bias when the top of the chassis is exactly the same with the PA 100, namely, with red lights and fuse for each power tube. There was also no plastic screwdriver provided in the JA200 , similar to the PA 100, none. It will be very irresponsible to tell the owner to find his own small plastic screwdriver or to let the owner de solder a resistor to find the proper biasing value. And the owner's manuals of both the PA 100 or the JA 200 do not give any instructions to bias or re bias the power tubes, at all. In contrast, ARC and Conrad Johnson's owners manual has a section for doing or adjusting the bias. I agree that lifting a 120 pound PA100 to lie on its side with an open bottom cover with LIVE voltage is a very scary proposition, into a circuit with no trim pots with open copper bars all over as shown in the pictures I posted. It will be a nightmare for the owner, to say the least. Thankfully, me and my friend, both owners of a PA 100, did not have to do that. We just changed a pair for power tubes. His was done 2 months ago and mine was 2 weeks ago, using matched pairs.