Drake 2-NT Transmitter Re-Cap
I really love the older “Vintage” ham radio gear. I especially like the Drake radios. Drake produced some really fine radios, but went out of the Ham Radio business in the 1980’s. The radios are still great radios and perform nearly as good as some of the very latest ham radios made today. In particular I find the 2-B to be an absolute wonderful CW (Morse Code) receiver. There is something about the receiver’s AGC (Automatic Gain Control, also known as the Automatic Volume Control) that is just hard to beat on CW. I have had three 2-B receivers over the years. Not sure why I sold them but I did, and then I wind up wanting another one. I will try to hang on to the one I have now.
Recently I acquired a “new” addition to the collection, a Drake 2-NT CW Transmitter. I was always thought that these small “Novice” transmitters were very neat. One of the really nice features of the 2-NT is that it works well with several of the Drake receivers such as the 2-B, the 2-C, and the R-4 series of receivers. It also has built in antenna switching, receiver muting, and CW Sidetone as well as being able to do semi-break-in keying. All you have to do to send is hit the key and it switches to transmit and mutes the receiver for you.
Drake 2-NT CW Transmitter
I wanted to put together a vintage CW station, something that would be what a Novice station of years ago might be and it seemed that the Drake 2-B receiver and the 2-NT transmitter would be a great pair. I was using a Johnson Ranger with the 2-B for CW, but the Ranger is a very big and heavy transmitter for a 75 Watt (power input to the final amplifier stage) novice transmitter. Plus, it was clunky to operate, it was not setup for semi break in keying. Now, I like vintage, but let’s get real, I want to be able to actually use the rig the way I am used to working CW.
After checking out the 2-NT I found that there was a little hum on the transmitted signal. This transmitter is close to 40 years old, and in these older radios one of the things that needs attention, besides the tubes, is the Electrolytic Capacitors. The electrolytic capacitors are used as power supply filter caps, so when you see hum on the signal you can bet that the caps are going bad. The electrolyte in the capacitors drys out over the years and the filter caps don’t do a good job of filtering the rectified AC power into pure DC voltage. So I decided to “recap” the 2-NT with new, fresh, electrolytic capacitors.
Most of these older rigs used what were called “Can” capacitors. The can contained several large value capacitors in a single chassis mounted aluminum can. (I.E. the name Can Capacitors) With the advent of solid state electronics these high voltage can capacitors have gone away. They can be had from specialty suppliers like Hayseedhamfest.com, but they can be pricey. Since there was plenty room under the chassis for axial leaded capacitors, I elected to go with them for this re-cap. They work just as good and without pulling the bottom cover off the radio you would never know the difference.
Here is what we started with:
Before – Click on image to see a larger version
There are three capacitors in the can, a 60 uF for the “bottom” half of the voltage doubler for the High Voltage supply to the final, an additional 40 uF for the low voltage filter, a 20 uF for the screen voltage supply for the final. There are a couple of axial leaded caps, one 60 uF 450V for the “top” half of the voltage doubler and a smaller 20 uF cap for the negative bias supply. In shopping for caps, I found that you can’t always get the exact replacement. I had availability of 80 uF for the HV and LV supply, (originally 60 uF) and 22 uF to replace the original 20 uF caps. I ordered the caps from Mouser.com and had them in two days.
The can capacitor has lugs on the bottom that are very convenient for wiring, the leaded caps needed something to be wired too. So, I added two terminal strips. The first one I soldered to the chassis where the cap ground leg was soldered. That strip had one ground, and three open terminals. I moved the original wires from the can to the open terminals then wired the axial caps to them. I added one more ground terminal under one of the screws for the power transformed and wired the ground end of the 40 uF and 80 uF caps to it. The the final cap was the 22uF for the bias supply, the positive side goes to the ground on the 4 terminal strip and the negative lead to the circuit board where the original cap was wired.
So, after it is wired up this is what we have:
After – Click image to see a larger version
One final thing, on the cap for the “top” of the voltage doubler the capacitors case is at +300 Volts from ground. The new caps have a very thin plastic coating on them and I felt that the coating my break down under that voltage where the metal clip holds the capacitor. So, I trimmed a small part of the original cap’s cardboard cover and slipped it over the new cap where it contacts the metal clip. Just to be safe…..rather than sorry.
I double checked my wiring, did a few checks with an ohmmeter tests just to make sure I had everything wired correctly and then turned it on. It worked great. The power supply hum was gone and it has a nice clean signal now. The ole 2-NT is ready for many more years of service on CW.
Here is the “new” novice CW station:
Novice Station – Click on image to see a larger version
On the left is the Drake 2-NT Transmitter, in the center is a Hallicrafters HA-5 VFO (late 50’s vintage), on the right is the Drake 2-B Receiver and the Drake 2-BQ Speaker and Q-Multiplier. This novice CW station is much nicer than my original novice station back in 1965, which consisted of a Knight Kit R-100A receiver (that I built as a kit) and a homebrew (home built) 75 watt transmitter. The transmitter had three tubes, was built into a black wrinkle finished Bud Box purchased from Allied Radio. Looked right out of the late forties!
If you are into CW, check into the Sunrise Net on 7.123 kHz. The Sunrise Net is a daily CW net that starts at 1300 UTC seven days a week. QNI and say GM to the net!