I soon found the seven pin valve base type plug that must be fitted if no external VFO is connected was missing. A look at the circuit diagram and the appropriate page of the handbook and I was able to make a new dummy plug. Once I had done this the rig started to show signs of life but there was very little audio output. What there was sounded good. After checking the voltages on all the valves (tubes) and finding them to close to those on the chart in the hand book it was time to resort to and old favourite bit of test equipment, a very modified Tandy Signal Tracer I bought from that store soon after they opened DownUnder, perhaps as long ago as fifty years.
It did not take long to find the source of the problem, it was the Audio Noise Limiter switch, it was open circuit in both positions. A squirt of switch cleaner and much pulling and pushing of the control and success, I was soon listening to friends on 40 Metres. It soon became obvious the rug drifted very badly, slowly falling in frequency by 20 KHz in the first half hour I had it turned on. Now I know BoatAnchor rigs drift but this was over the the top and there had to something very wrong. I tried out all the controls and I should have been suspicious of the Clarifier circuit earlier as this control did nothing. My first thought was the pot was open circuit.
My next adventure was to put it on air and see if anyone could hear me! There was a QSO going on somewhere in the 40 Metre band and so I asked if I could join in, one fellow was in Port lincoln accross the gulfs from me, and the other fellow was in Gipsland Victoria. That was an experiance for all three of us, wthey chased me up and down a segment of the band by as much as 3 KHZ and after about fifteen minutes I was satisfied the rig was going to work and it was time to see where the drift was happening. Time to write an email to Steve VK2YLD, why start out by inventing the wheel, see what someone who has worked on these has to say about the problem.
Here is the reply from Steve, with a little correction to what the varactor diode does in the circuit.
They will drift a bit through the first half hour or so, but yours sounds ridiculous!. As a first step, take a look at the VFO circuit, and there is a varactor diode that provides the Clarifier control on receive. Watch the voltage on this lead as she warms up and make sure it is stable at about half the 9 Volt rail that supplies the VFO. Problems with the mode switch and relays can cause 'leakage' on this line and pull the VFO around. Next, connect a counter to the output of the VFO and make sure it is the VFO that's drifting. Look at the frequency of the other oscillators to make sure the crystals are not in trouble. If it looks like the VFO (most likely), there are two adjustments on the VFO box top. One if the freq adjuster and the other is temp compensation. There is a temperature sensitive cap (PTC I think from memory), and this adjustment calibrates the compensation. Make sure the PTC is ok for a starter (and no dry joints), then the compensation needs tweaking.
After reading his email I was suspicious about the Clarifier control operation, it did not do anything and I was sure that area was what was causing the drift. As Steve had said, there is a varactor diode in the VFO circuit and I soon worked out it is used to shift the VFO about three KHz each way on receive only. A quick check of the voltage to the diode and I found it was zero not about 4.5 like a look at the circuit showed. After much poking round the circuity between the Tx/Rx relay and the switch on the back of the Clarifier control I found a dry joint on one of the leads from the pot to the Tx/Rx relay. This open circuit to the diode meant the voltage on the diode was only from leakages around the wiring this caused the VFO to wander up and down by up to 3KHz.
The Clarifier switch in a bit more complicated than the circuit shows, it is a change over switch and the brown shielded wire from the common terminal looked good but measured O/C. A quick hit with the soldering iron on the terminals on the pot and the rig was fixed. The switch switches between the centre of the pot and the two 47K resistors that provide half rail voltage when the Clarifier is off or the rig is in Tx mode.
Steve also has some modifications on his web site, fitting a computer fan to the RF PA cage, replacing the microphone gain pot with a 500K audio taper switch pot so the heaters of the PA tubes can be turned off when the rig is only being used as a receiver and replacing the RF Amplifier tube to get more performance on 20 Metres. I fitted the fan and used a bridge rectifier across the 12 Volt supply rail with a 470 uF electrolytic, an RF bypass and a 120 Ohm series resistor (resistor input filter). I then rummaged deep in the junk boxes and found a suitable 500 K switch pot and this turns off the 6SJ6 heaters and the fan circuit. I have not done the RF amplifier modification as my noise level here is quite often too high to make any difference to what I can hear.
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Written by and Copyright, Phil. Storr © Last updated 25th March 2014