That is good to know. Given however, that the manufactures of the amps (e.g.
QRO, Ten Tec, etc) don't use the larger fans (split chassis or elevated
socket 130 mm tubeaxial), they derate their amps in key-down service.
I'm curious about how ACOM reportedly achieves its 'nearly silent'
centrifugal blower operation in the ACOM 1000 (4cx800). There are abundant
testimonials that the fan is 'hard to hear' from enough owners that they
must be doing something clever in that small chassis. They don't have a
substantial de-rating for key down operation either, (1000 watts continuous,
15 minutes max, unlimited with external fan). Given that it works and has
many happy owners, I wonder what the secret is?
I've got an EBM 30 cfm cent. blower on my 3cx1200, and though it isn't
noisy, it isn't silent.
----- Original Message -----
From: "R. Measures" <r@somis.org>
To: "Ed Briggs" <edbriggs@optonline.net>; <jsb@digistar.com>
Cc: "AMPS" <amps@contesting.com>
Sent: Thursday, December 11, 2003 10:47 AM
Subject: Re: [Amps] 3-500Z plate durability
>
>
> >...
> >With the 3-500zg, the real cooling issue is the keeping the glass-metal
> >seals cool enough.Typically, the use of a muffin (or tubeaxial) fan
blowing
> >across the tubes isn't sufficient to allow continuous operation at the
> >maximum ratings; this is why amp manufacturers (including Ten Tec, Qro
etc)
> >restrict the power to 650 or 800 watts respectively in 'key down' modes
like
> >RTTY, and also limit the maximum transmit time to about 10 minutes.
Through
> >the use of a better cooling system, (like an air system socket and
> chimneys)...
>
> ** I have observed that the glass-tube cooling system which produces the
> lowest glass temperature is not the air-sytem socket and chimney, it is
> the simple split-chassis tranverse fan system that Heath used in the
> SB-220. However, for Heath's method to work properly, the fan diameter
> needs to be slightly greater than the overall tube height. For example,
> a 3-500Z is about 140mm tall, and the Heath fan diameter is 150mm (6").
> Also, the Heath cooling system is c. 20db quiter than the high-pressure
> centrifugal blower needed with an air-system socket. However, the
> air-system socket/chimney has one big advantage: It impresses those who
> don't know what's what.
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