Tuesday, April 21, 2020

A little work on the Heathkit SB-200 Amplifier

The Heathkit SB-200 is a very popular HF amp, and very dependable. This one belongs to a friend, and had begun to vent the filter caps from time to time. It was time for a little work, so here we go....


Case removed, ready to remove inner covers...

The amp was in very good condition, just had a bit of dust to get rid of :-)

With the upper inner cover removed, it exposes the tubes, filter caps, etc.

I removed and cleaned the dusty tubes. This will help the tubes run a little cooler...

It has the original Cetron 572 tubes installed from the build sometime around 1980. Here they are, clean and ready to be reinstalled...

I also used compressed air to clean the RF compartment, and the rest of the amp.

Note the filter caps. The originals were much larger and only 125uF vs. the newer, smaller caps in blue that provide 330uF. This will yield a better filtered DC supply, and take up less space than the originals.

Here, you can see the power supply board refitted with new capacitors and reinstalled. All bleeder resistors were in tolerance and good condition.

While in the amp, I included a few updates. If you notice the two diodes attached to the back of the plate current meter, this provide protection in the event of a tube short or arc. I also installed HV glitch protection, and bias protection.


All finished, tested, and ready for re-assembly.

Here she is, headed back to her owner. This amp is extremely well cared for, and should last many years to come!