EICO 720 tx, BUT NO MODULATOR...

[ve6pg]

..hi from tim...i have an eico 720, but not the 730 modulator...ok...what would it take, to use a solid state p.a. amplifier to modulate the '720?..

..tnx..

..sk..

[WU2D]

OK - here is my vote:

A 35-50 Watt output transformer from an old tube amp (hooked up backwards), an 8 uF oil filled cap and a 15 Hy 200 mA choke. This would give you a simple modified Heising arrangement.

Getting a little feedback around the iron back to the PA's driver and the three diode negative cycle loading circuit would be deluxe.

To prove principle:

Substitute a 5 Amp 6.3V Filament Transformer hooked up backwards as the transformer.

Mike WU2D

[w1vtp]

Here's an old thread.  The whole Heising scheme was modeled using PSpice, so there was no guessing.  Basically took a Hammond 60 watt transformer backwards with a Hammond 120 ma 20 hy choke.  I forget the cap but I think it was 2 mfd

http://amfone.net/Amforum/index.php?topic=16771.0

http://amfone.net/Amforum/index.php?topic=19876.0

Worked for me

Al

[WD5JKO]

Tim,

  You got some excellent advice on how to plate modulate that rig. I used to have a 720 with the plate modulator. I loaned it to a fellow AM'er local to me. Soon thereafter he had a stroke, a nervous breakdown, and a divorce. When the guy surfaced again, he had no recall of my little Eico...

  Anyway, I was wondering what your application might be? If it is to drive an amplifier, then you most likely have too much power. An alternative modulator would be screen modulation. That would cut your power to 15-20 watts carrier out, which is the sweet spot for many big G-G linear amps.

Jim
WD5JKO

[ve6pg]

..ya, it all sounds good...no, i'm not planning to drive an amp, just get the thing going, likely on 40....i got my dx60/hg10 going...lots of fun...werked dave, w9ad, and timmy this morning on 40 with the dx60...just trying to have fun with this stuff...also on the list is, repair my nc300, sx25 aligned, bc348..etc..etc...
..it's all good stuff...

tim..
..sk..