Hybrid Amplifier

Being a builder of amplifiers for many years and owning many of the commercially built amps from Heathkit, Drake, Amp Supply, Dentron, Command and others, I decided it was time to build one that had all of the best features. Everything I've built normally had external power supplies made with the idea that big was best, huge transformers and filter caps and even 866 tubes in the earlier ones. The RF decks always had over rated parts in the tank circuits and big blowers.

I decided to make a list of what I thought was important to me as a DXer, Rag Chewer and Contester:
   1. Cover 160 through 10 meters including the WARC bands.
   2. Single desk top cabinet.
   3. Quiet.
   4. Quick band change.
   5. Instant on.
   6. Full legal limit output.
   7. Plate Current, Plate Voltage and Gird Current meters separate, no switching.

The RF deck of the Drake L-4/L-4Bs had the quietest blowers, but forces one to do pressurized chassis and use chimneys. The Heathkit SB-220 was next and did not use a pressurized chassis or chimneys. The 3-500Z requires no warm up and presents a great choice of being able to drive a pair of them with the pretty much standard 100 Watt output radios of today.

After checking out new cabinets and finding the costs just prohibitive, it was time to do some eBay searching. I happened to come across a Heathkit HL-2200 chassis and cabinet missing just the front plate which I didn't plan to use anyway. More searching for a few weeks and I came up with a high voltage transformer, filament transformer, plate and loading capacitors, tube sockets, filter capacitors and fan. Now I had pretty much all the basic pieces and only needed to start filling in.

Found or had these items: plate choke, 6 to 1 drives, band switch, tank coils, 12 relay, filament choke and meters.

Went to a local sheet metal shop and had them cut a front panel to match the size of the back panel, found meters at Futurlec on the Internet, just couldn't find three matching correct meters on eBay, and if I did the seller had his starting price way too high. Holes were cut in the front panel for the meters and two guide holes to mount the panel to the chassis. Keep in mind I'm the type of guy that uses eye ball guess and place.

Now it was time to start filling in the holes and putting things together. The band switch in the above picture was replaced with a complete tank circuit from a Amp Supply LK500-ZC seen in later pictures. Since most of today's transceivers have antenna tuners like my IC-756PROII, I decided to forgo dealing with input circuits since 3-500Zs grounded grid input would be normally under 100 ohms anyway.

Some of the transformer leads had to be lengthened and shrink tubing was used for better insulation. I fabricated my own diode stack for the location that was picked to install on the bottom of the chassis. Picked an antenna relay location and fabricated the input output connections.

I had found the original breakers from a SB-220 and set up the ac input so that the amp could be run on 110 but I find much better efficiency at 220.

Decided to use standard toggle switches and 12 volt indicators since I already installed a 12VDC supply to run the antenna relay, cost and maintenance were future concern.

I also made a list of every part and piece that went into this project to come up with a total cost including New Tubes, $623.52 we'll have to add the paint job later. Yes I agree you can probably find a used SB220 for this price but it won't have 160 or WARC bands. This one has a band switch that covers 160, 80, 40, 20, 17, 15, 12 and 10 meters. And one last thing, I can say I built my amp!

Wait till I build my next one