W9AMR

The T-368/urt page


Here is a description of my T-368.

Made in America!

This T-368/urt transmitter was manufactured by B & W in 1952. They were the original contractor to build the T-368 for the military. Mine is serial number 22. One of the first ones produced. It was stock and had been put in storage after a military overhaul by the government in 1972. I was lucky enough to get the documentation from the overhaul with the transmitter. It was purchased from Fair Radio by W9BOE years ago and had never been put on the air until I got it! Rare stock find! I had a few bugs to work out mostly from the transmitter just not being used.

What is it?? It is a transmitter made for the American military. It weights in at about 700 pounds. It does full legal limit and transmits from 1.5 to 21 MHz. It has 3 removable decks. A Rf amp-exciter, modulator, and power supply. They all slide in to a large metal cabinet to make a complete transmitter. It has built in switching for antenna change over and receiver muting. It was designed to transmit 24-7 so as a amateur transmitter it is just loafing. The only modifications necessary for amateur radio is to improve the audio frequency response. It is very limited in stock form. There are several mods described below that I have performed to mine.

Modifications:

Mod deck: I replaced the stock 4-125a modulator tubes with 4-400a's. Added a second filament transformer to handle the extra tube filament currant and enclosed the bottom of the modulator tube sockets and added a fan to blow air up and threw the tube sockets to improve cooling. Two stages stages of audio filtering were removed that were used to restrict the audio frequency response and I added a adjustable negative feed back circuit to improve the frequency response even more. Moved to mic gain control feed point to the second audio stage. I also upped the values of the coupling caps between the audio stages and added a second mic input that is a Hi-z input. There are probably better ways to modify it but this way sounds great and has been very dependable for the last 2 years

RF deck: A few years ago I decided to modify the RF deck. I started by removing the high voltage from the tank coil by moving the B+ feed point from the center of the Pi-L network directly to the plate of the final tube and added a dc blocking cap between the tube plate and tank coil. The stock plate choke was replaced with a hand made one I made here in the shop. I also decreased the value of the bypass caps on the screen of the final and the high voltage B+ line. These mods made the biggest difference in the audio frequency response.

Power supply: Except for replacing the hi voltage rectifier tubes with solid state units it is basically stock.

Problems: It been pretty dependable for a 50 year old transmitter. I have had to replace the N connector on the RF out. The original one looks like it took a lightning hit at one time. I replaced it with a SO-239 connector. I had to replace all of the original ceramic Hi-voltage insulators on the deck interconnects. The originals were carboned up. I made new ones out of some feed threw insulators I got from a local neon sign shop. They are rated at 9000 volts and work great. If anyone needs any let me know and I will point you in the right direction. I replaced any cap I was worried about. I had the voltage safety interlock on the mod deck fail. I was able to rebuild it. That's about it!

Note: The mods to the RF and modulator decks greatly improved the audio quality by increasing the frequency response. Everything I have done is pretty simple and does not make any harder to work on. If anyone wants a better description of the mods just let me know. I would be glad to share the info. Not all the mods I have performed are my ideals. I have found a lot of useful information on the web and from other ham radio operators. Thanks to all that have helped!


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