This is the story about how I saved my Vector 500 HF Linear amplifier from the scrap bin by VE3TAZ.
Introduction
In the late fall of 1993 I picked up a new Kenwood TS-690S with a Vector 500 HF amplifier. It has been a great combination.
Ten years went by and I found myself with plenty of time to spend on the station. It was during this period that more time was dedicated to the hobby giving the station a good work out.
One afternoon the amplifier shut down. What happened?
Trouble Shooting
The fuses for the primary windings of the main power transformer had blown. The fuses were replaced and they blew again.
The transformer was isolated and all loads removed from the secondary windings of the transformer. Both fuses blew when power was applied. The power transformer had failed. It took many months to find the exact failure by unwinding the transformer a few turns at a time.
There was no information available on this particular amplifier. The bobbin was cut from the laminates and the transformer was unwound. A transformer manufacturer was needed to make the replacement.
Having spent several years as a test technician for a power supply manufacturer I was familiar with what was required.
Failure Analysis
During the transformer unwinding process the number of turns for the multiple primary windings and the configuration options for the 220VAC and 240VAC operation was documented. Noted were the number of turns for the tube heaters, AGC, cooling fan and the pilot lamp power. No shorted windings in any of these windings were found. A short at a kink in the 11th turn in the High Voltage winding was found. The magnet wire was kinked along the exit lead. The high voltage winding is the first winding on the bobbin. The high voltage lead exited the bobbin core along the edge of the bobbin passing through the entire high voltage winding. As this lead passed through the winding the high voltage between the lead and the windings increased to 1800 volts peak. The kink was on this lead. It was at this kink that the enamel insulation broke down and shorted the HV winding.
What Next?
With the specifications for the transformer in hand and with a few quality improvements to add the search for a manufacturer to make the replacement transformer began.
Teflon tubing was added to all the leads exiting the bobbin creating a much more robust power transformer.
Who Can Wind a Single Transformer?
The answer to this question was the most difficult to find. Manufacturers were simply not interested in winding a single transformer. There was one willing to listen and quoted a price for a single transformer.
After some e-mails back and forth I placed my order. A few weeks later my new and improved power transformer was ready. At this point in time it has been three years since the initial failure.
Installation
The replacement transformer was installed using the original mounting hardware. The leads on the new replacement transformer were long and colour coded. The primary leads were cut to fit onto the terminal strip with minimal slack. The secondary winding leads were soldered into the circuit boards. Standoffs were added to prevent the high voltage leads from coming into contact with the chassis. There were a few components damaged as a result of the failure. New 811A tubes installed. The relay contacts were cleaned. A capacitor and resister were replaced. The chassis cover was assembled and when the amplifier was powered up every thing came on. The amplifier has been in use for many years since this repair. Ten years as of this revision.
John Cognigni
These Web Pages are maintained by Don, VE3DDQ.
