ac.2. Improved CW Operation:
In the CW mode the rig’s relays are energized by the CW sidetone amplifier's sidetone
output driving the VOX relay amplifier. The audio (sidetone) drive to the VOX amp is a
bit on the low side for fast relay action, and at speeds approaching 20 wpm the first dot
sent is heard in the sidetone but isn’t transmitted due to the slow relay response time.
Correcting this is a very simple modification – simply replace the 470KΩ resistor R328
on the audio board with a 1KΩ resistor (Figure 2). This increases the drive to the VOX
amp enough to cause the relays to pull in quicker. Now the rig will key reliably at 20
wpm. The first dot tends to become shortened at 25 wpm but the rig is useable at this
speed.
Another annoying problem with these rigs is the fact the sidetone can be heard when
the rig is in the CW mode without the key actually being pressed. Although the sidetone
amplifier is in deep cutoff, there is enough coupling through the inter-electrode
capacitance of the tube to allow the output of the sidetone oscillator to be heard at a
constant low level even when the key isn’t being pressed. Fortunately this is also fairly
easy to correct:
1. Connect a .001 μfd disk capacitor (DO NOT use a higher value) from relay RL1 pin 1, to
ground (see Figure 12. Modification for Low Z Headphones).
2. Connect a piece of wire about 8” long from pin 1 of RL1 and run this wire through the same
opening in the shield as the wiring harness.
3. On the audio circuit board, replace 1MΩ resistor R326 with a 2.2MΩ resistor (Figure 2).
4. At the circuit board junction of R326 and C311, connect one side of a .005 μfd 500v disk
capacitor, and connect the other side of this capacitor to the wire from RL1 pin 1.
Modifications Page 86
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