GCW-Grid CurrentLess Wonder

[flintstone mop]

Hello all
Happy New Year
I was reading through old ER's and found ER 118 FEB 1999.
Pg4 was a neat article about Tx's using sweep tubes and modulating with a simple 12AX7. Four Sweep Pubes and you can get 100 watts!!!
Is this something to pursue??? 100 watts 40M day time can provide for a lot of entertainment.
Fred

[Paul, K2ORC]

Yep, that's the February 1999 issue of ER in which Bob Dilworth W4LQE describes a unique grid modulation transmitter. 

Called the Grid Current-less Wonder (GCW) by Dilworth’s friend, the late Jesse Sherwood K4DLQ, the GCW takes a non-traditional approach to grid modulation of a Class C RF amplifier. In the GCW, the final is operated without grid current. This is done by application of negative grid bias, beyond cutoff, preventing the grids from going positive. 

Recognizing that traditional RF amplifier tubes like the 6146 when run in this fashion do not produce much power, the GCW employs sweep tubes like the 6DQ5 and 6LW6.   These tubes have a stout internal structure with a high amplification factor that requires only a small amount of drive.

According to Dilworth’s article, the GCW was able to produce "standard constant carrier AM output capable of 100 percent modulation with peak envelope power of 4 times the carrier level."   One of the transmitters described in his article used four 6DQ5s to produce a 100 watt carrier, modulated at 100% by a single 12AX7, with peaks of 400 watts.

Bob Dilworth wrote me that, "The success of GCW operation lies only in the selection of the proper tubes (high perveance 'sweep tubes'), biasing the control grids well beyond cut-off (-150V), and supplying adjustable RF and AF drive."   

I got together the components to have a go at a 100 watt GCW xmtr but then other matters intervened.  I assembled a notebook containing info and emails with Bob and others about the GCW.  Unfortunately, it appears that I won't be able to do anything radio related in my workshop for a while so my GCW project wil lie dormant for the time being.

[flintstone mop]

OK FB Paul,
Sorry to hear that there will be delays getting a replica of Dilworth's Tx up and running. I sent him a snail mail letter explaining my shortage of a junque box and retirement status. I hope he might respond with scheezo for the 100W Tx for 40M. I can purchase the components over a long period of time and assemble the Tx on an aluminum chassis as pictured in the ER. It certainly would be a worthwhile project to pursue, as it is a very unusual approach to a transmitter in the 100 watt class and not the weight of a DX100 and all of its drawbacks. And then again I could take the easy way out and "buy" one of those K7DYY class E Tx for $225.00 and be done with it. I still like to see some tubes glowing.....hi
My Titan linear is a nice amp and lots of reserve, but I can't see the pubes glowing. It's nice for the extra shove, 160M needs.
Fred