The AM Forum

Hi !

I picked up an Elmac AF-67 at the Marlboro flea the other day.  Cute little transmitter.  Anyway, I'm going to design and build a new (internal) modulator, and I'm wondering about the RF tank components - noteably the tuning capacitor.  Is this capacitor sufficient to handle 175% positive modulation with, say, 500 or 600 volts (dc) on the final?

Any overall suggestions about the transmitter?

Thanks and Regards,

Steve

hey Steve,
Are you going to shwang the munkey that much? I guess you'll change out the 5881's to 3CX1200A7's??  hi
Just chattering
Fred

Hi Fred,

Well - what I was thinking was a high level series modulator.  Not sure whether this is going to be pulse width, class H or class A.  I'd be more than mildly interested in implementing a class H modulator at this voltage.   Small, simple, direct-coupled and ultra high fidelity :-)

Don't want to go too far if the tank won't do it.  Probably, I'd implement the modulator externally to test. If things work as planned, then move the modulator components to within the transmitter enclosure.

Good stuff !!

Regards,

Steve

Steve,
Sounds like a good application for an inverter stepping 120 up to 1200 volts peak.
Series modulator will be clean but make a lot of heat.  gfz

Enjoy the new addition Steve, went back to pick it up and it was gone..... Had my hands full already. You will do alright with it Steve, Thanks for all the knowledge you have provided over the years. I appreciate everything you have done to explain everything so well in a way that someone like myself can find my way around.

Wish I could have met you while I was there at the flea market. Maybe next time my friend.

73,

Fred

KC1XF

Hi Fred,

Thanks for the kind words.  Much appreciated.

On the parameters, I figure with class H, if the final is operating at around 100mA, I'll be dropping around 50 volts at carrier, so that will be about 5 watts of dissipation in the modulator.  Obviously more dissipation with positive peak modulation in particular, but that's to be expected with any analog system.  Good project !

Regards,

Steve

Hi Steve,
I would almost want to tackle a project like that, even though I'm getting great reports on my Elmac AF-67 with the outbaord power transformer/Heising (original mod trans was funky), and outboard audio driver through a backwards outpoot tranny to the grids of the 5881's. I'd love to say bye bye to the transformers and the biass battery. I drive an Ameritron 811 amp with it to give me 200 watts carrier. Your Class H approach would probably be super audio and no phase shifts. If you make such a modulator, please share the scheezo and parts list with us. ANYTHING for SUPER audio is for me and my little Elmac. Sorry Steve, I'm a follower not a leader. As long as I can see the darn parts...........hi
Fred

Steve,

Pretty sure I owned one of them once upon a time...

Little mobile type rig with chrome handles, scware meter with black fluting on it??
Is that the one?

I seem to recall, if that's the one, that it is all crazy spagetti wiring in there, packed tighter than sardines in a can in a garbage compactor??  ;D

Good luck squeezing anything into that box... if anyone can do it, Stever ur da master of spagetti wir-in!!  ;D :D ;D

        Can't wait to see this!


                    _-_-bear