Peter -
See below...
Peter Hoon wrote:
Am having difficulty running our Drake T4XC into a QRO Technologies
DX 2500 Linear Amp.
Have tried injecting ALC from the T4XC into the DX 2500 (from the
jack on the AC4). With the T4XC gain set at the 11:00 AM position,
the T4XC sends about -8 volts max on SSB voice peaks. The DX 2500
can handle up to -20 volts of ALC. We still cannot get the ALC pot on
the front panel of the DX 2500 to sufficiently limit drive on voice
peaks. Perhaps with more practice and tweaking, we can find the
correct ALC pot setting. But so far no cigar.
You have this backwards. The ALC voltage FROM the Amp is used to reduce
the gain on the T-4X. You may or may not have enough ALC FROM the amp
to reduce the RF enough. One trick is to apply a variable negative
voltage to the ALC on the T-4X to reduce the output.
Tried completely closing the load control (full counter clockwise) on
the T4XC to reduce drive. But it only reduces drive to 60 watts CW
in tune mode, still far too much drive PEP in SSB. Even with plate
re-dipping with the changed load control, am concerned about possible
spurious products when the load capacitor in the T4XC is not at
resonance.
This is OK, but still too much power.
Tried reducing the T4XC gain control to the 9:00 AM position. But
fellows say our speech lacks the "presence" it has when running
barefoot with gain at 11:00 AM position.
You're running into the noise floor in the AF MIc Amp, GAIN needs to be
at least 10 to 11 O'clock for decent S/N. In TUNE mode you can see the
transmitter ALC cut in about 11:30.
Suspect the basic problem is that the T4XC gain control does limit CW
power output in Tune and CW, but controls speech amplifier gain (but
not PEP output power) in the SSB mode.
In TUNE, the Mic Amp is converted to an AF Oscillator and the tone is
fed to the Balanced Modulator via the GAIN control. In CW, the Bal Mod
is unbalanced by a DC current, and the frequency is shifted to within
the LSB filter. A separate section of the GAIN pot controls the current
applied, thus the amount of unbalance / carrier output.
The transverter output is too low, < 0.5W, and is only on 20M, just
capacitively coupled from the output of the Driver. The PA is turned
OFF by removing the Final Screen voltage.
73, Garey - K4OAH
St Charles, IL
Drake 2-B, 4B& C-Line,& TR-4/C Service Supplement CDs
<www.k4oah.com>
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