Elmac AF-68 bias battery...

[kx9dk]

I recently aquired an Elmac AF-68 and looking for ideas how to provide the 22.5 volts originally provided by the internal battery. Any AF-68 users out there? Other mods/improvements for this radio?

Thanks,
Dave
KX9DK

[KB2WIG]

(2) 9V and (3) 1.5V's..  to get u runnin.....  if you want,another way, after you do a little more research, maybee try this.... 24 v xformer, diode, capacitor, a pot and a zener.... the transformer,diode and cap give you yer DC, series up a zener and the pot, tap off for the bias.. Your mighty Elmac should roar....   Elmac net on 80 M ( still on?? )     klc

[WA5VGO]

Why not eliminate the battery? Ground the center tap of the driver transformer. Lift the cathodes of the 6L6's and install a 22 volt 5 watt zener diode to ground. Bypass the diode with a 10 uf 35 volt capacitor. You never have to worry about the battery again.

73,
Darrell, WA5VGO

[K3ZS]

Do a search on AF-67 above in this forum.   There is a lot of info that will apply to your AF-68 also.   I have used the above zener in the cathode circuit in my AF-67, probably the simplest.   You can mount a heat sinked zener on the battery clamp to ground the zener anode.

[flintstone mop]

Hi Dave
I agree with the others. Do a search on the AMFONE forum. There are a few ER articles for improving the ELMAC transmitter. They can sound pretty nice if you eliminate the driver transformer for the modulators. I went through a lot of changes and even had to sub the mod tranny for a power transformer from an old tube stereo amplifer............My AF-67 cannot be used in a mobile but it sure sounds great!.
Did you get the power supply? There is even an ER article to build a power supply for the transmitter using 24 volt transformers.
Good luck.....it's a very nice Tx to modify and has a nice VFO

fred

[kx9dk]

Thanks for all the ideas.

I found that power supply article/schematic in the Feb 05 ER magazine. Jameco has all the parts plus the 22v zener for the modulator bias. Hope to have this unit on the air soon.

Thanks,
Dave
KX9DK