Source for cheap mod iron?

[K1ZJH]

Looking for some ideas for mod iron for a HB tx..

I have a Geloso 4/104 vfo assembly that I want
to use in a small AM/CW rig.  The plan is to have
a 829/5894 P-P  driving a 829/5894 (parallel) final.

Any suggestions on where to scrounge up a
modulation transformer, and are any particular
brands more problem prone than others?

Pete

[WD5JKO]

Pete,

   It seems strange to use an 829 in push pull to drive an 829 with sections parallel. That is the beauty of ham radio though. You can do this however you prefer.

   If I was starting from scratch I'd likely either use some of the new Antek toroidal power transformers as a modulation transformer, or using series modulation. The availability of the old iron is getting tougher these days, and then finding a replacement that is identical will be a challenge.

transformer:
http://stores.ebay.com/Antek-inc

These transformers offer off the shelf availability, but the available turn ratio's might not come out correct. Some one else was on this forum was using two of these cascaded for legal limit AM. You will also need a big choke and a HV coupling capacitor since the toroids will not handle much steady state secondary current. This approach with a solid state modulator is possible.

Series Modulation example:
http://www.amwindow.org/tech/htm/wb9eckseriesmod.htm

Here we get completely away from needing any big iron. The penalty is you need at least twice the B+,  and the modulator runs HOT since it is class A. An alternative is to run the modulator in PWM mode like Steve WA1QIX did on some of his early rigs.

You can also run low level AM, but from your post you prefer high level plate modulated AM.

I recall that Chuck WA0ZHH designed a cathode modulator for the Heath SB-220. I'm not sure if that is on line somewhere, but maybe someone will point to where that info is. This would be another good alternative, and make a big AM rig without a modulation transformer at all.

Good Luck!
Jim
WD5JKO

[KM1H]

There seem to be a fair number of 30-50W and sometimes larger single and multitap ones on Ebay over any particular month. It just takes work since many sellers dont even know what they have. Try several search words such as transformer, choke, coil, etc.

I scored a 125W rated modulator for $27 that was listed as a power supply early last year. Thordason multitaps and TZ-40's. Drove down to RI for it and picked up several other items, all at bargain prices. Guy buys storage garage auction lots.

Carl
KM1H