[Amps] (no subject)

[Manfred Mornhinweg]

Frank,

The NCL-2000 indeed works quite hot. The reasons: It is designed for a 
very high idling current, which results in excellent IMD but lots of 
heat; and it doesn't have chimneys on the tubes, so that the hot air 
only slowly leaves the cabinet, and heats up almost the entire top cover.
It's normal, and it will live a long happy hot life.

Carl,

> You can also operate SSB in the CW position.

Yes, you can, of course, but in the CW position this amplifier (like 
most) is biased in class C, even if only slightly so, and transmitting 
SSB in the CW position results in some audible distortion and an 
enormous amount of splatter. At least mine does.

I had a particular problem with the high bias of this amp: I live in a 
country where the line frequency is 50Hz rather than 60, and so the 
blower runs slower. The manual tells to de-rate the amp in this 
situation. The fact is, the high bias almost eats up the FULL 
dissipation capability of the tubes, under the reduced air flow at 50Hz!

Rather than building a 60Hz supply for the blower, I reduced the idle 
current. At 50mA still nobody reports audible distortion, and the 
splatter is no worse than that of other amps. At least not high enough 
for anyone to report it. So that's what I use. At reduced idling 
current, I can transmit SSB at full power without cooking the tubes.

The data sheet for the 8122 tube recommends that very high idling 
current, for best linerity. National Radio engineers simply designed the 
amp according to that data sheet, I guess.

> Member of NCL-2000 Design Team

Oh, then you could give us more insider info about this! It would be 
interesting to know if really the amp was based on the data sheet 
recommendation , and nothing else, or what other facts influenced the 
decision to use this high idle current, which is quite unusual in ham amps!

I'm quite happy with this amp, except for the LOUD noise of the blower! 
I modified the blower case to reduce turbulence, installed sound 
absorbing mats, and got some improvement, but it's STILL loud! After an 
hour or two using it, I start perceiving the blower noise more or less 
like a jet aircraft!

Manfred.

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