Hi Jim, and Jim,
Interestingly, my NCL-2000 blower is rather quiet and has never posed an
irritation. I'd be interested in hearing comments on that issue from
other owners.
I would specially like to hear from other users in 50Hz countries. The
problem with this blower is that when running at 50Hz it's very noisy.
Not a really loud noise, but a very irritating one, like a whistling
whine. Several years ago I tried running the blower from 60Hz obtained
from a signal generator into an audio amp and then a transformer, and I
found that apart from producing a lot more airflow, it was much quieter.
But routinely running it from such a system, or from a small pure sine
wave inverter, is a bit of an overkill, I think.
My suspicion is that at 50Hz some resonance in the impeller blades or in
the air around them gets excited, and that this does not happen at 60Hz.
The noise isn't the only problem at 50Hz. Lack of air flow is another.
To keep the tubes running at a safe temperature, I run this amp at much
less idling current than the design value. In theory this should degrade
the IMD, but in practice it remains good enough. With the low idling
current, I can run it at its full rated PEP in SSB without the tubes
overheating, despite the lower air flow and the fact that I'm at some
elevation, in thinner air.
One design issue I've never liked with the amp is the T/R relay, which
uses a 6VAC coil. This rules it out for use with modern transceivers,
unless one uses an isolation circuit. In my station, I use my StationPro
controllers for my amplifiers, which can accommodate any AC or DC
antenna, so that isn't a problem
I don't know if the Kenwood TS-450 would qualify as a modern
transceiver, but I use this radio with the NCL-2000. Its amp relay
output is a relay contact, I think a reed relay. I just added an RC
snubber in parallel, built into the connector, to avoid the big spark
that otherwise happens on switching, and which might destroy the radio's
relay contact after some time.
Im sure the oem blower could be replaced with one of the myriad of blowers
out there from ebm papst, or Dayton.
I tried to do that. I searched suitable blowers in eBay. The intention
was to use a brushless DC blower, and run it at full speed during TX,
switching down to a low "silent" speed 20 seconds after returning to RX.
But absolutely every modern blower I could find turns in the opposite
direction, relative to the original one! Given the shape of blower
cases, that's a problem.
I bought one anyway, a 12V-powered model that has an impeller almost
exactly the same size as the original, runs at 3700 rpm, and has the
motor in the center of the impeller, so it's far more compact than the
original. It has slightly better pressure and flow specs than the
original running at 60Hz. Running it at 11.5V produces the same
performance as the original, and without the whistling/whining noise.
But I found no way to install it! It would require seriously cutting up
the amplifier's chassis, re-locate a lot of parts, and so on. Space for
the 12V power supply was scarce too. Or else I could have cut a hole
into the case to fit the blower on the outside. Not nice, and not well
suited to the kind of slide-in cabinet of this amplifier. After months
with the amplifier resting on the shack floor partially disassembled,
and not coming up with any good idea, I put the original blower back in,
and that was it...
I probably won't do anything more with this amp. Instead I'm working on
my EER MOSFET system. The MRF1K50N has already arrived, some other parts
too, while some more parts are still underway. Preliminary experiments
have produced outstandingly good results, beyond my wildest
expectations: IMD3 levels of -50dB at 80% efficiency, along with the
worst spurs (located 200kHz away on each side) at -60dB. These results
came from a lower powered test amplifier using the EER approach I intend
to use in the big one. Now I hope that the big one produces results not
much worse than those!
Any tube amp looks lame compared to that, so I'm not really tempted to
invest any more work in the NCL-2000. It's a good amp, but
representative of the technology of its day, and it's half a century old.
Manfred
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Visit my hobby homepage!
http://ludens.cl
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