That's ok, but the transmitter is also loading into a 25 ohm load, or
2:1 SWR. Not that that is particularly bad, but it might limit the
transmitter capability.
Have you ever used a scope to see what the signal looks like? I know
several people who have used this method, but none have ever really
evaluated the signal quality.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
John Hudson wrote:
This is why I use a 100 watt dummy load, is has the capability to dissipate the
heat of 75 watts.
----- Original Message -----
From: drakelist-boun...@zerobeat.net<drakelist-boun...@zerobeat.net>
To: drakelist@zerobeat.net<drakelist@zerobeat.net>
Sent: Tue Apr 26 10:59:55 2011
Subject: Re: [Drakelist] L-4B reduced power
Curt -
That is yet another way. I'm not sure why using reduced loading would
make the output non-linear.... It's a 'linear' amplifier which implies
that it's 'linear' from zero to full output. It may be that one of the
lower level stages are distorting, but I'm not sure why they would.
Using the Mic GAIN to reduce output is ok, but you begin to run into S/N
problems in the AF and BAL MOD stages. Your three dB pad would
certainly help in that regard. Of course you always have the
'possibility' that the MIC GAIN gets left too high from barefoot
operation or other accident which would probably blow the grids, (but
perhaps not.)
Obviously the 3 dB pad has to dissipate whatever power is not fed
through to the amplifier. Short duty cycle of SSB might help somewhat,
but TUNE and even CW could make for a very hot box!
Certainly ANY of these arrangements should never be attempted without a
scope!!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Curt Nixon wrote:
This is just my own experience running a T4x into a KW linear that
needed 30W of drive (pair of 4cx300 grid driven)
While the T4 loading control will reduce the output, it tends to make
the output non-linear from the T4X. It is better, signal quality
wise, to tune the load control properly and back off the power using
the RF Gain control.
In order to keep the gain control in a reasonable range, I used a 3dB
attenuator in a small box in between the T4X and the Amp. This was a
simple device made up of a TEE network of Ohmite non-inductive resistors.
Use the formula for resistive attenuators for values.
Very small, monolithic attenuators are now available from the likes of
Anaren, and can be mounted on a small heatsink and work beautifully
also. Sometimes available on auction for cheap.
Still a good idea to use a monitor scope to be certain that everything
is running in a linear manner. Loading and mismatch of T4x output and
the Amp input can lead to much distortion and be non-apparent by
viewing meters.
FWIW
Curt
KU8L
kc9...@aol.com wrote:
Garey,
Hi...
I was just reading a post you made on reduced drive to the L-4B from
the T-4any.
You mentioned having the load at 0.
Are you talking the T-4any or the L-4B as to the loading on 0...I
suspect it is the T-4any.
What if we load up the T-4any to a lower power out by putting the
loading somewhere in between 0 and the max smoke position??
Are RF attenuators available somewhere? If this is the preferred way
to do it?
Who know...I might want to use my Alphs 91B with the T-4any? In that
case I need 5-30 watts of drive.
Thanks,
Lee
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