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smaller coils (and a 12MHz target)

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Marko

Fri Aug 25 2006, 12:20PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Steve why is your name flipped over?

Great work BP.. (just not to be fully offtopic)

ragnar

Fri Aug 25 2006, 01:39PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

yes evetS, each board (tentatively) is a 6.5MHz class-E amp. Until I build a class-H modulator or get my funky linear modulator working, audio is by frequency modulation, which works quite acceptably if you hang around on the inductive side of the Fres (f > fres)... then again, as soon as I increase the modulation depth for greater sound output, the nonlinearity turns it all to crap. =P

The difficulty is getting them to work without interfering with each other

And since you guys have gone quiet, I'll tempt your feedback with more pics...

maybe I need to pull a TDU and hint that I'm not disclosing information until I get signs of interest ^^

Mmm, burning the midnight CO2 at 2:20AM

Aw, you guys are boring. Really. =P No fun whatsoever.

[Edit: Triple post, totally against the rules and stuff]

Wilson

Sat Aug 26 2006, 01:09PM

Registered Member #78 Joined: Thu Feb 09 2006, 11:27AM
Location: Sydney, Australia
Posts: 133

How come your stuff always seems so elegant

My work looks like crap next to it XD

Avalanche

Sat Aug 26 2006, 01:37PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

Does that case all slot together then?

However it goes, that's going to be one incredible case.

...

Sat Aug 26 2006, 09:43PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

What kind of volume are you getting out of it? With all 4 going you should 'only' need like 80db out of a single coil for plenty for a decent listening volume...

That box... It is...

A few more dials on the front would be nice tho

I want to see what you resonators look like to match that

I still think that the THz spectrometer I am working on is better tho...

Just don't tell anyone that I gave you that pic

ragnar

Tue Aug 29 2006, 02:50AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Mmm, 1200W of RF at up to 6.5MHz... the FCC is gonna lynch me.

Anybody dare to comment? ^^

Bet nobody but SteveC can guess the magical secrets behind this GDT, either...

...

Tue Aug 29 2006, 04:14AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Looks good

Me wants plasma hehe

You have me stumped with that gdt; if I didn't know that you only had a single fet I would have guessed it was a 4:2:1 gdt for some pure evil purpose... The ~12 turn winding is definantly going to the ucc's (looking at the shot of the bottom of the boards) and somehow the 2 other windigs end up going into the screw terminals... The 4 diodes appear to be set up as a bridge rectifier... Ao I am going to have to guess that it is a power isolation transformer, it is fed by the ucc's and has a center tapped primary giving somewhere arround 10v out being regulated by the resistor/zener and filtered with the little cap. The asemectrical windings (ie 3 for the red and 6 for the blue) would imply that you are putting out something like +30v/-15v, but their are only 2 terminals and the output windings don't appeat grounded so I can't imagine why you would have done that

ragnar

Tue Aug 29 2006, 05:42AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Not a bad guess at all, Peter!

This little innovation puts a DC bias voltage on the gate so long as the gatedriver is running.

What you see there is a green 11-turn primary going to the UCCs. This cops +/-15V direct drive from the UCCs (with capacitor decoupling).

The 2-turn orange secondary therefore has +/-2.7V present on it, which you'd hardly think is enough to swing a FET, but together with a little added inductance (five turns of enamelled wire around my screwdriver, slipped off and soldered in series with the gate), the leakage inductance of the transformer resonates with the mosfet's gate capacitance, rising back up to about +/-14V. (Q is about five).

The six-turn winding in blue is fullwave rectified with a bridge of 1N4148s, giving about 8V. From the bridge, a 3K resistor limits the current, charging the little capacitor. The zener diode limits the capacitor's voltage to 6.2V.

Now the orange secondary is simply added to the blue bias circuit, resulting in a ~+20V/-8V drive on the FET. A 10K resistor is connected across the DC blocking/smoothing/bias capacitor, and it bleeds down very quickly when the gatedriver is turned off. It's almost foolproof. If the DC biasing circuit fails, the gate drops to +/-14V. The DC bias circuit is powered by the gatedriver, so you can't end up with a FET left on. Hooray!

...

Tue Aug 29 2006, 02:27PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

And I though that putting a 1k resistor across the gate was genius

I like your resonant gate drive, it sounds like something I would see in a commercial piece of equipment (that I would be staring at going wtf?!? ) The joys of classe'

As to the whole problem with this thing being a 1.2kw rt transmitter... Could you put the resonators in a Faraday cage? I bet if you spent enough time on it and then gold plated it it would look as good as the rest

Self Defenestrate

Wed Aug 30 2006, 01:23AM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

I am halfway to completely lost in this thing, but wow-E thats looking sharp!

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