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georgehifi 12th November 2012 09:42 AM

Magnat MP-02 Plasma Tweeters
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Hi, I hope we have some Germans here as I have picked up a pair of mint Magnat MP-02 plasma tweeters, and to give them a good tune up I need to be able to get this only adjustment sheet I could find translated by a tech.
Hope some one can help with good translation

Cheers George

volkerw 27th November 2012 12:17 PM

Trying to do my best...

Alignment procedure for MP-02

1) Check supply voltage of the plasma driver circuit:
Unscrew the flame shielding ball. Connect dc voltmeter between ground and input of R19. Voltage should be 28V at idle condition.
2) Test if (HF) oszillator is operating: insert flame electrode and re-attach shielding ball. Connect a frequency counter to R19 / T1 by using a 1K resistor (for decoupling). Assure that no ambient light is shining on the 'phototransistor' (i think this means FZ1) . Switch on the unit. Counter should read approx. 27.11Mhz.
3)Check HF-voltage at base-emitter resistor (R21) of transistor PT9783 (T3). If HF signal is existant, check if L7 (the large output resonator coil) has good connection to C25 and if the ignition circuit (solenoid) is working correct. The (opened) circuit can be switched on only under subdued ambient light. If the little neon bulb (GL1 at L6) glows, the output tank circuit is de-adjusted or there is no flame electrode inserted. Carefully adjust trim capacitor C28 towards lower capacity. When plasma flame ignites, adjust C28 to maximum flame size and just turn back until flame starts to decrease.
4) If unit still fails to operate, change power transistor PT9783. Besure not to twist the transistor case while mounting. Use thermal compound for mounting. Observe that the transistor 2SC1306 has to be reinserted with isolation. After changing transistor, proceed alignment as layed out at 3.)

geraldfryjr 27th November 2012 12:34 PM

I remember that circuit as it is basically a CB transmiter at a very high power level.
I have had a few RF amplifiers back in the day that used the PT9783 and they are very rare to find.
And when found very expensive.

Semiconductor: PT9783 (PT 9783) - TRANSISTOR ASI - US$ Site

A single transistor outputs about 50 watts,

PT9783 datasheet and application note, data sheet, circuit, pdf, cross reference | Datasheet Archive

Since they were in 12 volt circuits I could use a MRF454 or MRF455 to replace them with.

But your circuit is at 28v and there is a MRF number for that voltage range only I don't know it off hand.

I can find it out for you if find that it is faulty.


jer :)

georgehifi 28th November 2012 09:48 PM

Thanks for the translation volkerw, mine are working fine, it's just that I'd like to have this as backup if needed.
Is this a translation as seen by a technician? As to be 100% safe this is needs to be translated by a tech fluent in German, your translation while good has me tilting my head at some of the proceedures.

Cheers George

volkerw 3rd December 2012 12:58 PM

Hello George,

"Is this a translation as seen by a technician?" - yes it is. While my english might not be the best, i tried to translate the text as verbatim as possible. It is really written this way and my head got tilted too at some points while reading the original instructions, so i added some explanational comments in paranthesises. I think the most valuable part of the manual is how to tune the the capacitor of the tank circuit and the procedure described is correct ( i tested it on my pair of MP02s years ago and it worked fine).

georgehifi 4th December 2012 12:24 AM

Great, thanks Volker

Cheers George

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