The AM Forum

After I finish the TBW-4 Navy transmitter project I'm going to build this to pair with it. The transmitter will be high fidelity plate modulation, capable of both the 75 and 40 meter bands, and so it would be a shame not to give it a little power boost.

I have all the parts for the linear. The picture showing the iron has the B+ transformer in back and the 30H choke in front. There's enough DC resistance in the choke that I won't need to implement a soft start circuit. I'm using a 500pf Russian vacuum variable capacitor for the tuning control. Ebay sells 60mm auto brackets cheap, the red things shown around the ends.

I bought two NOS GS-35b tubes. The sockets are almost unobtainable, but fortunately there's a guy over here machining custom sockets that look better than the Russian originals. It is also shown in the picture. I also got the chimney.

Cooling is accomplished on the right with a toilet flange attached to the bottom of the RF deck under the tube socket. The white adapter shown couples it to a nearly silent bathroom fan that will blow more than enough air.

So there you have it! Still plenty of work to do finishing the transmitter, but once all this is done my voice should be carried worldwide on classic radio equipment.

Jon
KA1TDQ

Looks FB.

T

Sorry, whirlwide.

Jon

That tube lends itself to socket less operation, mounts in the dame size hole as a 3cx3000.  Matter of fact, a 3000 chimney works fine.

For 15 bu KS you can pick up a chimney at home depot.  Halo makes a bakelite type ceiling can light retrofit.  Have used up to 7.5kv with no issue.  Use the black one.

Socket and chimney, 15 bucks a tube.   Couple copper strip to make clamps for the filament.

Be aware that the cathode is tied to one side of the filament.  And depending on your anode voltage, you're gonna need a lot of diodes for bias.  I prefer one of the adjustable bias boards available on ebay for a nice board, schematic freely avail AB to perf board.  They let you dial idling current wherever you want.

It is imperative you cook those tubes overnight with just blower and filament voltage on.  Getter the gas out!

Good luck with the SDG&E bills and qro.  Makes me glad I moved to the island, electricity is cheaper here I think jow.

--Shane
WP2ASS / ex KD6VXI

I hear ya, bro. We switched to an electric range, bought a Tesla and we're getting the second one in a couple months. Preorder deal. I installed two 4-prong dryer outlets in the garage and those puppies suck some juice!

Thanks for the tips on the Ruskie tube. I'll be sure to gas it before I light it up. I decided to be fancy and go commercial with the socket and chimney. Go figure.

I'll post pictures of my progress. I'm sure you guys will get a BANG out of it. I'll make everyone's MOMS proud.

Jon
KA1TDQ

I can't tell if your chimmley is PVC or not but if it is, it would be wise to read this article from Tony King's W4ZT (SK) website regarding using PVC in an RF environment: https://www.gs35b.com/pvc/index.html

Jon
I like how your projects are always evolving! Keep it up!

Sam