Plasmatweeter

[Marco audio]

Only the choke with the resistor no capacitor, the impedance should be high for the frequency you like to avoid, that’s all.

Hello,

Unless i'm mistaken,it's almost linear :
0,15uh 100 Ohms
21mhz: 19,41 Ohms
27mhz: 24,66 Ohms
35mhz: 31,32 Ohms
40mhz: 35,27 Ohms
Value stays low...

 

[Lampie519]

It is to limit the power of higher harmonics. Second harmonic is ca. 40 MHz in your case.

 

[Norgaard]

It might be a while before I get the time to play with something similar - but thanks a lot for sharing the experiments and experience, truly inspiring!

Great work and that has to be one of, if not the coolest "mini-system" I have seen 🙂

 

[Marco audio]

Hello sirs,
Thanks for reply and coments.
Done with my phone:

YouTube

Voltage at Anode is too high for the g-807 tube: around 645v.I now replaced the 12ohms resistor by a 20ohm one at the entrance of the voltage doubler,voltage decreased to 630v.
The high voltage value is due to the high capacitance of the doubler's capacitors (almost 800uf mesured for each).600uf should be better.
I'm still waiting a 15k resistor to decrease the voltage at the screen.It's now 265v.It should rate around 250v.
I'm now thinking about Gu50 units who will work with a voltage tripler (almost 900v),and ionophones with g807 and 600v too.
Regards

 

[Lampie519]

I am not convinced that this high voltage is needed at all as the coil should work as a tesla coil. If you need high voltage for this speaker it does not resonate at its fundamental frequency. Best regards.

 

[Marco audio]

Hello, you speak about ionophone ,isn't it ?

 

[Marco audio]

PS:electrostatics headphones directly drived by push-pull amplifier are great and seem easy too build...

 

[Lampie519]

yes, i am talking about plasma tweeters with RF oscillator. A HV amp for head phones is not that complex. There are threads to be found here.

 

[Marco audio]

Hello,

I want to understand something, please...
On many schematics there is no cathod resistor.It means that the tube is 0v biased.
My point of view is ( perhaps i'm wrong ) that the intrance coil is a reactive load ( like a transformer ).
So load line pass though this operating point: Ua,Vg=0
In these case the authorized power is largely exceeded
But it works !
My 807 speaker with no cathod resistor works well.
Stc 807's report indicates 410 ohm for cathode resistor at 100 ma.(-41v for vg)
Dukane Ionovac 6dq6a 120 ohm (it works).
Any review ?

Regards

 

[Marco audio]

Basic Schematic,no cathode resistor

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[Lampie519]

This is an oscillator and not an amp. In this case there is always maximum drive on the grid (AC only). No need for a bias but you will need to use a choke to remove unwanted harmonics.

 

[Marco audio]

Thanks Lampie 519

 

[Lampie519]

Refurbished my old Tweeters (Frankenplasma's). The power supplies were broken and needed to be replaced. Only used the transformers. The tubes have been replaced in one set by 6HB5 tubes as i have a lot of these (used tubes from my old Acoustat amps).

 

[Marco audio]

Hello Lampie,��.
Nice Job,thanks for sharing.
You have rebuilded the power supply, isn't it ?
I see two tubes on the second picture: voltage regulators for modulation ? Constant current tap ?
Regards

 

[Lampie519]

The power supplies were really old and all electrolytics were dryed out. The tubes are shunt regulators for the screen grids (experimental). I am not sure if i leave them here or find an other solution.

 

[Lampie519]

I am happy for now so i leave it as is ( in a later stage i will place the capacitors on the opposite side of the board to keep them away of the heat from the power resistors), now i only need to create a second output on my premap or a XLR splitter as my power amps are dedicated direct drive amps. I will try my headphone amp for these tweeters as not much power is required for these.

 

[Marco audio]

Beautifull box! Bravo !
Should be tinted and oiled.

 

[Lampie519]

Thanks ! Maybe oiling would be nice indeed.