Below the following text, you will find the schematic and parts list for the 807 CW transmitter. I suggest you read the text carefully.
Notes:
- Plate current at maximum output power should be in the vicinity of 110 to 120 mA with a high B+ supply of about +750 VDC.
- You can use anything from +500 VDC to +800 VDC for the high B+ supply.
- You can use anything from +200 VDC to +300 VDC for the low B+ supply, but don't exceed +300 VDC because the maximum rating of the 6AG7 is +300 VDC.
- You can either build your own power supply or buy a commercially-made supply. Two great candidates are the Heathkit HP-23 and HP-23A. Use the 6.3 VAC output for the tube filaments, not the 12.6 VAC output! I recommend that you set the Low B+ selector to the 250 VDC position because the +300 VDC setting will probably run higher than +300 VDC at today's higher AC line voltages. You can also use the HP-23B, HP-23C, or PS-23, but you'll have to wire the tube filaments in series and use a 12 Volt pilot lamp bulb because those later models don't have 6.3 VAC filament outputs. The older Heathkit HP-20 will also work, as long as it's wired to put out 6.3 VAC for the filament voltage. The much older Heathkit UT-1 will work, although the High B+ is only +600 VDC, so your transmitter output power will be substantially reduced. Make sure the filament circuit is wired for 6.3 VAC. The Heathkit HP-23 and HP-23A supplies are quite common, easy to repair, and don't cost an arm and a leg, so they're really a good choice. Other vintage power supplies should work fine, too, as long as they put out the right voltages.
- If you want to build a power supply, refer to older editions of the ARRL Handbook from back in the "vacuum tube days". If you have a big enough chassis and cabinet, don't be afraid to build the power supply into the transmitter.
- You will find the tube pinout information in any older edition of the ARRL Handbook, GE or RCA Vacuum Tube Manual, etc. If you don't have an old Handbook, GET ONE. They're available on eBay and at hamfests. Until yours arrives, you can pay a visit to your public library. They should have one.
- Trimmer capacitor C1 should be adjusted for the least amount of crystal "chirp". Although a value of 8 - 50 pF is shown on the parts list, anything in that general range will work fine.
- Feel free to install several different types of crystal sockets, wired in parallel, so that you can use different holder types. The most common ones will be the ol' faithful FT-243 and the more modern HC-33/U, and you might want to include one of those big ol' sockets for BC-610 crystals. Alternatively, you can make up some adapters, which is what I did. Having more than one socket type means that you'll have more chances of finding crystals that you can use. Don't bother with those tiny little HC-18/U and HC-25/U crystals (the kind used in CB radios, scanners, and so on). They aren't designed for the kinds of voltages that this transmitter will present to them.
- SW1 is the "XTAL / VFO" switch. Setting the switch to the "VFO" position converts the 6AG7 oscillator into a buffer stage. The 0.01 uF capacitor that is switched into the circuit kills the tendency for the 6AG7 to oscillate.
- SW2 is the "Spot / Send" switch. It allows you to key just the oscillator so that you can "find yourself" with your station receiver.
- The oscillator stage is the classic "Grid-Plate" oscillator from the ARRL Handbook. For best performance, the ARRL recommends that you stick close to the component values shown in the parts list for the oscillator stage. I've found their recommendations to be correct.
- Be mindful of the DC and RF voltages present in the circuit when you pick your capacitors! I suggest you use capacitors with at least a 1 KV rating for those parts whose ratings aren't otherwise specified.
- I recommend that you make the 80m and 40m coils interchangeable so that the rig will work on both bands. There are several ways you can go with this. You can use vintage plug-in coil forms, which require a matching socket (you'll find 4-, 5-, and 6-pin styles out there). You can use octal tube sockets and tube bases (salvaged from some old "dud" tubes) for the coil plugs. You might get lucky and find some vintage James Millen jack-bars which will allow you to use B&W or Air-Dux coil stock. Just use whatever you can find, but be sure you can find enough to handle the number of coils you intend to use (two per band!).
- If you find coil forms that are some diameter other than 1-1/4", that's no problem. You'll just have to re-calculate the coil parameters. You'll find the formulas for calculating coil parameters in any ARRL Handbook (how's your high school algebra these days?). No, I will NOT help you do this. If you don't already know how, then you need to learn how. I'm not trying to be a "meanie". If you plan to build equipment like this, you'll have to know this stuff anyway.
- If plug-in coils aren't your thing, you can always come up with some kind of band switch arrangement.
- No, I don't know where you can buy these parts, so please don't ask. You'll have to scrounge for them, just like I did. Where should you look? Hamfests, surplus stores, electronic parts catalogs, other hams' junkboxes, eBay auctions, For Sale listings on QRZ.com, QTH.net, and the Usenet newsgroups, and so on. I've been known to buy other hams' old homebrew projects (from estate sales, etc) just to strip them for parts. Hunting for the components for a project like this is a big part of the fun!
