And thanks again for everyone’s help :-)
Today, I am working on my 1965 ARRL 6146B transmitter again. Right now, I only want to understand the correct operation of the CW function of the transmitter. I am performing these adjustments with the transmitter output connected to a power meter and 50 Ohm Heahtkit Cantenna dummy load.
Following is a reproduction of the complete ARRL article.http://www.bignick.net/6146B_Xmitter/6146B_Xmitter001.jpghttp://www.bignick.net/6146B_Xmitter/6146B_Xmitter002.jpghttp://www.bignick.net/6146B_Xmitter/6146B_Xmitter003.jpghttp://www.bignick.net/6146B_Xmitter/6146B_Xmitter004.jpghttp://www.bignick.net/6146B_Xmitter/6146B_Xmitter005.jpg
My question lies in setting up and “tuning” the transmitter. Most of this exercise revolves around reading the DRIVE and PLATE current values while adjusting PLATE and LOAD capacitors.
Quotes are from the ARRL Handbook (note, my comments are enclosed within square brackets)
“Note that the 0-5 milliammeter meter reads directly in GRID position, in the PLATE position full-scale deflection represents 250 ma. Cathode current.“
“With 80meter crystal installed (and 50 Ohm dummy load connected) set S2 on TUNE.”
“With C1 and DRIVE control, adjust grid current to 2½ ma. “
[OK, I can adjust to 2½ ma. DRIVE current with no problem.]
“With a key plugged into J2, set S2 on OP. Set C4 (LOAD capacitor) at three quarters meshed, and switch S4 (meter switch) to read PLATE current. Watching the meter, close the key and swing C3 (plate capacitor) for a plate-current dip.”
[OK, no problem, the meter dips down to: 2.7 ma. which is really 135 ma. of actual Plate current]
“If the plate current dips below 170 ma. (indicated 3.4 ma.), decrease the capacitance in C4 (LOAD capacitor) and again tune C3 (PLATE capacitance) for resonance.
The objective is to set the loading capacitor so that the plate current dips down to 170 ma.
Check the grid current after the plate circuit is tuned; if it isn’t 2 ½ ma. Correct it by returning C1 (PLATE capacitor).”
(END OF ARRL HANDBOOK QUOTES)
The best I can achieve when maintaining the DRIVE at 2½ ma. and adjusting PLATE and LOAD capacitance is a plate current dip of 2.8 ma. on the meter, or 140 ma of actual Plate current.
At this setting, the transmitter doesn’t always respond well to the keying. Sometimes I get some whoop and other times, the oscillator won’t start up which momentarily causes a large plate current draw!
BUT .. If I lower the DRIVE current to 1 ma., I can achieve 3.4 ma. of Plate current dip on the meter (170 mA of actual Plate current) right on the nose.
The transmitter behaves much better with the DRIVE current set to 1 ma.; the oscillator always starts right up, and the power out looks just as good as when the DRIVE is set to 2 ½ ma. (80 Watts)
Why do you suppose the transmitter is behaving in this fashion?
Is it OK to run the 6146B when the transmitter is setup in this manner? (I would think that less DRIVE current is better for 6146B tube life?)