Jadis JA100 Amplifier

[Ron Resnick]

Do any of our Jadis experts understand the various circuit designs of the Jadis monaural amplifiers?

It appears that the JA100 is a different circuit than the other monaural amplifiers. In addition to the output tubes and the usual 12AX7 and 12AU7, the JA100 also uses an EL86.

What is the electrical significance of the EL86?

What is the sonic significance of the EL86?

Thank you!

 

[DasguteOhr]

They added a stronger driver stage el86 because some models had problems, that's my explanation. In some models, the grid leakage resistance is too high.
You can't plug in all the power tubes that are recommended on the list.
Grid current flows, causes the coupling capacitors to charge up, that reduces the negative bias at the grid, more anode current flows and therefore more grid current flows and the whole thing builds up until you get smoke (but hopefully not flames).

The obvious fix for this is lower value grid 1 resistors BUT since those resistors are the effective load on the driver section we have another problem. The driver section is just too wimpy to drive the load if we reduce those resistors.
The EL 86 is the unloved step-sister of the EL 84 lower anodevoltage higher current. It was primarily developed for tube radios because it can drive small speakers even without a transformer. Great for tube radio manufacturers for cost reasons. When it comes to sound, as always, every manufacturer has its signature. I reject general statements.

 

[Argonaut]

Jadis also use EL86 in power supply regulation.

 

[DasguteOhr]

Jadis also use EL86 in power supply regulation.

Really? most jadis use at preamps ef 86 /el84 combo. Never seen el 86

 

[Argonaut]

Really? most jadis use at preamps ef 86 /el84 combo. Never seen el 86

Jadis Sarl JPL MkII Preamplifier - Bluebird Music

Jadis Sarl JPL MkII Preamplifier Distributed in USA and Canada by Bluebird Music

www.bluebirdmusic.com

 

[Argonaut]

If anyone has the schematic to JA100 all would be revealed.

 

[DasguteOhr]

Jadis Sarl JPL MkII Preamplifier - Bluebird Music

Jadis Sarl JPL MkII Preamplifier Distributed in USA and Canada by Bluebird Music

www.bluebirdmusic.com

Good EL84s have probably become too expensive. An el86 like this costs €5-10

 

[DasguteOhr]

please read the last two paragraphs of the page. That's where the problem I described occurs.

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