Technical information

under the switch. The parts list does not note matched, but they sure need to be reasonably matched if
you want to transmit and receive on the same frequency. Maybe the junction deteriorated over time. I
suggest using 1N914/1N4148 diodes matched with a Fluke. My balanced modulator HP diodes work
but are really too frail for this duty.
PA Neutralization
Connect a dummy load and place rig on its side or face down. Set to 15 meters, load up. Now adjust
the neutralization capacitor, only accessible on the PA bottom area with an insulated screwdriver for
max RF output at the PA current dip point. Be careful not to key down very long each time. If you don’t
use an insulated screwdriver, you deserve to be thrown across the room.
Lamp Replacement
I didn’t have to replace any bulbs. This is a good thing because my fingers could never reach into the
dial drums to twist the bulb. This looks like more disassembly is required and a rear challenge. I know
one thing for sure; make sure you replace with #1826, 16 or 18V Volt 0.15 Amp bulbs only. Using 12
volt high current bulbs generate too much heat and will damage the unobtanium drum. The little wheat
bulbs in the meter are easy since they are pushed in through rubber grommets from the back. Once
again, use only the right bulb - 12 volt 50 ma.
DD-103 Digital Display
I hooked up a DD-103 digital display to the LO XMT output (J103). This way it displays actual frequency
by using a minus 6.187 MHz offset programming in the DD-103 unit. The DD-103 powered, one
transistor interface is required. I soldered to the backside (possible without board removal if you are
careful) on the LO board to J103 pin 1. This sample point makes it easy in the DD-103. All that’s
required is to subtract the IF frequency. I used one of the phone patch RCA jacks to get the signal out
of the box. I never run phone patches so no loss.
X-LOCK VFO Stabilizer
Since I decided the rig was definitely a keeper, I installed X-LOCK in my external VFO. If you follow the
directions below, a nice side effect is the first character distortion on CW gets fixed since the VFO
voltage no longer blinks off/on during T/R transitions.
The finest stabilizer available today is the X-LOCK kit. The X-Lock locks a VFO to a crystal source to
provide drift free operation. This design takes a fresh approach to the "Huff-Puff" Frequency Locked
Loop technique by using a processor to measure frequency and compute correction signals. The X-
Lock employs a 100mSec count period to produce 10Hz "lock points" against which the host VFO will
be held. Dual regulators are used to supply the digital and analogue sections of the circuit which in turn
are optically coupled to produce an exceptionally clean control voltage.
The X-Lock will accept input signals from a few kHz up to 50MHz to provide up over 6 volts of control
range. Features include auto lock/unlock during tuning, RIT detection and fast re-lock, power on reset
auto centering, and a dual colored LED to indicate lock and input states.
Your VFO must have a reasonably good sine wave and not drift more than 40 Hz / second before X-
LOCK can do its magic. The Tempo 2020 meets these requirements quite well.
Website and manual download: http://www.cumbriadesigns.co.uk/x-lock.htm
See installation detail pictures in the gallery below.