Hi all,
My b-i-l suggested I join this group and seek comments.? My age is 75 & I've built electronic stuff for the past 60+ years.? My "ham Elmer" had a Globe Tx with a 4-250 modulated by 2 x 811's and powered by 2 x 866A's.? I've wanted to build something like this ever since.
The FCC changed the rules to 1500W PEP output so I will use my 3 new Penta Labs 4-400C tubes in a parallel, grid driven class AB1 configuration.? The basic circuit I'm using is a modified version of the one in the '66 ARRL Handbook.? ?Yes, I know a grounded grid circuit is a lot less complex & has fewer stability issues but I want a really "old school" project.? I will use a passive, resistor loaded, low impedance input rather than a tuned grid input to help with stability.? ?I also plan to use a band-switched PI-L output tank to reduce harmonics.? ?The amp bias and screen voltages will be switched in order to run class C so it can be plate modulated by 2 x 572B's.?
I plan to use a modified version of the power supply circuit, a resonant choke input, that Henry Radio used in its amps.? Hammond sold me a P. Dahl heavy duty filter choke designed as a Henry 2K replacement :)? I will use a bridge rectifier circuit with 4 x 866A/3B28 tubes.? Heyboer Transformer wound me a tapped primary 240 VAC plate transformer so my supply can be switched to provide either 1175, 1750,? 2350, or 3500 VDC at up to 1 A.
I have most of the parts I will need except for the plate output PI-L coils, but I have not yet started the build because I need to finalize certain elements of the design.
Comments are welcome!!
Larry - KF7EYF
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