![]() Even though a tube can take it easily, maybe the vac cap is more vulnerable to seal failure. However, there is also the issue of constant thermal expansion and contraction that is probably not good. Using two tubes that are balancing the load, it should be less. From experience, I've found that when running a 4X1 ultra-conservatively in class C, the exit air 2" away usually will not get above 95 to 110F degrees. I monitor all of my tube exit temperatures with a dedicated digital temp readout for each rig. wiring up the RF deck with copper flashing right now.Ĭarl: You make a good point about exit tube exhaust onto the C1 vacuum variable. How do you propose to keep that ancient glass vacuum variable from melting down? Even a ceramic one would be affected. Post by: ka4koe on April 05, 2013, 07:36:27 PMĪctually that RF layout is potentially scary. We dump some of the food scraps there, thus the Easter egg shells. Steve, that is one of the dormant vegetable gardens in the background. Also, a shelving platform to support a second level. There are some unique ways I am supporting the vac variables as well as use of the front panel for supporting RF components. You may like the parts mounting and layout I am using. Then put the panel next to the coal stove for a day to bake it. I use standard enamel spray paint from Ace. I used to use Greenlee punches, but I like these better. Once we buy the drill bit assembly, the various saw sizes are cheap. I use a standard 2.5" hole saw for the meter holes that can be bought at any Ace hardware. I plan to make my own IBM-blue cabinets too. The sheet for the panels was found at the recycling metal scrap yard. What paint did you use on the panels and what do you use to cut the meter holes? Title: Re: New 4-1000A modulated by 4-1000A's AM Project - Fabio II Reborn No more plexiglass except for the viewing windows. So, it's mainly the RF and modulator decks that are being built from scratch and will be much improved. The solid state driver (designed by Frank/ GFZ) is from the original Fabio I - and the screen and grid supplies are recycled, as well as the sequencer. The HV power supply is already built - it's the common supply in the shack giving 2, 3 or 4KV. ![]() I expect first light testing in about 2 weeks. I should have the parts mounted in a day or so and will post some more pics. The satin-white panels will have black lettering to match other rigs in the shack. There is a 4-step relay sequencer used to key each stage in a controlled manner - to reduce arcing tendencies. The modulators will be run as grid-driven AB1 stages, (with 1000V screen voltage) for maximum cleanliness. A broadcast RCA 1 KW modulation transformer with 75H of Heising reactor inductance will be employed. The modulators will be driven by a solid state MOSFET audio driver with heavy negative feedback from the moulation transformer secondary back to the 1 volt low level stage. There will be just one audio transformer - the modulation xfmr, to minimize phase shift. (HV, plate current, screen current, grid current and fils) The class C RF final will be neutralized, use a very large bandswitch, vacuum variables with counters, quiet squirrel cage blowers with Variacs and full metering. The two chassis layouts are almost finished too. I'm not particularly fond of drilling and blasting, so glad to have this stage finished. The modulator panel is on the left and the RF final panel is on the right. ![]() Notice the tube viewing holes at the bottom. They will front a 4-1000A plate modulated by a pair. Not much to see yet, but here are the finished and painted aluminum front panels. I also wanted to make some big changes and improvements on Fabio I anyway, so here is the all-new FABIO II under construction! The class A linear is FB on SSB, but makes just too much heat and blower noise for AM use. The old Fabio 4X1 rig was torn down to make room for the new class A linear amp system last year. I've had great luck with 4X1's in the past and miss them dearly. Well, since my 24 pill class-E rig blew up last week, (Rico Suave) I decided to go back to tubes.had been freezing in the shack this winter.
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