Alex
>> QUESTION: CAN I SAFELY RUN 1500 W OUTPUT PRESUMING I DO NOT EXCEED THE
>> 1.0 AMP Ip MAX CURRENT AT 2300 V AND THE 100MA GRID INMPUT CURRENT. i
>> GUESS I AM REALLY ASKING IF THIS AMP IS RATED ONLY FOR 1000W OR CAN/ARE
>> THESE AMPS NOW RUN AT 1500 W OUT CW/SSB.
The 8874 is rated at 350 mA each for CW, RTTY, et cetera. However, for
SSB voice service, 500ma each is intermittently allowed. However, this
does not mean 500mA on the meter when tuning up. One must tune up the
amplifier for SSB with pulses of current that produce 500ma peaks, as
could be seen on an oscilloscope. A safe way to tune up is with a CW
keyer, sending 50% duty-cycle dits at 50wpm, the plate/anode I meter
should indicate roughly 250mA per tube.
>> QUESTION: HOW RELAIBLE IS THIS AMP HISTORICALLY?
More stable than the average SB-220 and TL-922. Less stable than the
30S-1.
>>ANY BAD COMPONENTS YOU
>> WOULD AUTOMATICALLY CHANGE BEFORE TAKING IT SOUTH?
I would:
- Add more glitch resistance in series with the anode supply
- Add 200a-pk glitch diodes..
- Replace the carbon comp. electrolytic-C equalizer resistors with
Matsushita 100k ohm 3w MOF resistors.
- Inspect the electrolytics for white deposits around the safety vents.
- Test the tubes with a high-pot. tester at 5kV to see if there are any
loose gold melt-balls.
- Install lower VHF-Q suppressors.
- Install 3mS or faster switching.
- Bring heater leads to rear panel tip-jacks so that the heater v can be
measured.
>>hOW ABOUT SPARES?
>> ARE THERE ANY COMPONENTS YOU WOULD TAKE WITH YOU BESIDES FUSES ET ALL?
It has been my experience that it is not a good idea to arbitrarily
replace a blown component. Better to figure out Why the component blew,
fix the problem, then replace the component..
Rumour has it that the 8874 is going to be phased out. At some point,
you may want to modify the amplifier to take 2, 3cx800A7s -- which are
capable of 1.6a in SSB service and 1.2A keydown.
cheers
Rich...
R. L. Measures, 805-386-3734, AG6K
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