Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang ---------------------------------------------------------------------- Ron -
These are good goals, but back in the 60's, (when 6JB6's were less than $3 each,) I ran three 4 Lines on autostart RTTY. They ran 24/7, and often made transmissions in excess of 30 minutes, AT FULL POWER. In this service, the finals lasted a little over two years, typically, with "end of life" defined as 100W output on 20M. Over about 8-9 years, only ONE unit failed. A 12BY7 driver tube filament opened. Not a single 6JB6 failed. Obviously each transmitter had a small fan attached to the back of the final cage, and maintained the cabinet top at or near room temperature, even after a long transmission. The real KEY to final tube life is to minimize "off resonance" operation. These transmitters were on fixed frequencies, and so were not going through "tune-up" after the initial setup.
If you peak the RF Tune and immediately dip the PLATE control, then "two-hand" the PLATE and LOAD controls for maximum output power, (using an external wattmeter, holding down that meter switch button makes it a LOT more difficult,) and then DIP the PLATE control as the last adjustment, (which shouldn't be required if the transmitter is properly neutralized, but should be done anyway,) finals will last for 5-10 years of "normal" amateur use. I have a T-4XB and T-4XC that have been running for over 10 years with the same finals. Both are used several times a week, primarily on CW.
By the way, a small fan on the receiver certainly won't hurt anything, (as long as it is quiet!,) but as noted above, three units ran 24/7 for 8-9 years with no fans, and NO failures. I turn my receivers on in the morning, and turn them off when I am through for the day. I have known guys who turn their receiver off when they leave the room for lunch!! NOT a recipe for long life of electronic equipment.
73, Garey - K4OAH Atlanta Drake C-Line Service Manual <http://www.k4oah.com> Ron Wagner wrote:
You can get really good tube life if: You never run any modulation that is over 50% duty cycle, and you never have the key down over a few seconds without leaving a break to let the tube cool. If you do tune with key down, let 30 seconds of cool for every 5 seconds of key down. Oh yes, run a low rpm fan to exhaust the final cage.
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