WA6MHZ
06-20-2009, 10:56 PM
Today I hit a milestone. The High Voltage section of the Power Supply has been built and tested.
Previously, one hangup was the timing circuitry. I knocked that out last weekend, spending around 24 hours on getting it to work. Once working, I could proceed.
The timing circuit consisted of 4 sections and 3 timers.
Upon energizing the unit (Pressing START), a relay keys supplying power to the various transformers and circuitry required. But the High Voltage is not enabled until 2 minutes pass, which is the first timer. This is Filament warmup time.
Once that has passed, the High Voltage transformer is enabled, but it needs a slow start circuit. That is the 2nd timer. After 5 seconds, another relay shorts out 2 power resistors in series with the HV Xfmrs primary leads.
The next circuit controls the fan. It is turned on when the Main Power relay is keyed, but at Amp Shutdown, it runs for 2 minutes more. This is the 3rd timer.
That works great now.
But the High Voltage is not measurable, as it is somewhere around 2000-2500 volts.
I estimated it is closer to 2000, as I was able to measure the center of the diode voltage doubler with my Heathkit IM-11 VTVM. It read 1000 volts, so that means the HV must be about 2000. Can't chance measuring anything in the circuit with my Companies DVM. I break it, I BOUGHT IT!
The VTVM is not a company instrument. In fact, they complain when I have it out. They say it looks "OLD". Well , it is INDEED OLD! Probably made back in the mid 1960s.
I rigged up some meters on the front panel to give me an indication the voltage was there. I took a 1.5 mA panel meter, and put a couple 2 Megohm resistors in parallel to drop the HV to a measurable value. So 1mA means there is 2000 volts there.
Next step is to wire up the Screen supply. I am tapping off the Voltage Doubler to give me about 500VDC which will be regulated down to +350 with some Voltage Regulator tubes. Not sure how to figure out the Dropping resistor, but I will put a couple of 2K 10W resistors in series and see if that works. Somewhere there must be a formula to determine what the dropping resistor value should be. If it burns up, then the resistors were too small.
This Power supply chassis is HEAVY now!!!! And takes up most of the workbench.
Still have to start on the Actual RF portion of the linear. Hopefully that will be easier than the Power Supply.
73
Previously, one hangup was the timing circuitry. I knocked that out last weekend, spending around 24 hours on getting it to work. Once working, I could proceed.
The timing circuit consisted of 4 sections and 3 timers.
Upon energizing the unit (Pressing START), a relay keys supplying power to the various transformers and circuitry required. But the High Voltage is not enabled until 2 minutes pass, which is the first timer. This is Filament warmup time.
Once that has passed, the High Voltage transformer is enabled, but it needs a slow start circuit. That is the 2nd timer. After 5 seconds, another relay shorts out 2 power resistors in series with the HV Xfmrs primary leads.
The next circuit controls the fan. It is turned on when the Main Power relay is keyed, but at Amp Shutdown, it runs for 2 minutes more. This is the 3rd timer.
That works great now.
But the High Voltage is not measurable, as it is somewhere around 2000-2500 volts.
I estimated it is closer to 2000, as I was able to measure the center of the diode voltage doubler with my Heathkit IM-11 VTVM. It read 1000 volts, so that means the HV must be about 2000. Can't chance measuring anything in the circuit with my Companies DVM. I break it, I BOUGHT IT!
The VTVM is not a company instrument. In fact, they complain when I have it out. They say it looks "OLD". Well , it is INDEED OLD! Probably made back in the mid 1960s.
I rigged up some meters on the front panel to give me an indication the voltage was there. I took a 1.5 mA panel meter, and put a couple 2 Megohm resistors in parallel to drop the HV to a measurable value. So 1mA means there is 2000 volts there.
Next step is to wire up the Screen supply. I am tapping off the Voltage Doubler to give me about 500VDC which will be regulated down to +350 with some Voltage Regulator tubes. Not sure how to figure out the Dropping resistor, but I will put a couple of 2K 10W resistors in series and see if that works. Somewhere there must be a formula to determine what the dropping resistor value should be. If it burns up, then the resistors were too small.
This Power supply chassis is HEAVY now!!!! And takes up most of the workbench.
Still have to start on the Actual RF portion of the linear. Hopefully that will be easier than the Power Supply.
73
