This is the 3rd and update to my HeathKit SB-200 Amplifier Project.
The amp has been running fine since I’ve got it going. I had a resistor pop in the parasitic suppressors and I think that the amp is running too hot in temperature for little time I use it. At this point I am placing the blame on the two muffin fans that are currently “Cooling” the tubes. I am thinking that the fans are not providing enough air to cool the tubes fast enough. When I was replacing the parasitic suppressors, I performed some modifications (see update #1) and ordered a new fan from Harbach Electronics to see if it would make a difference.
I also held out on performing a couple more modifications because I had to fabricate some parts to encase the glitch resistor so if it were to pop, most of the resistor mess would be contained. The fan was placed on back order so It gave me time mark up and cut the lexon glass to sandwich the resistor with.
The fan kit does come with installation instructions which at first were a little difficult for me to understand. This was due to the fact that the new fan is a modified replacement of the original fan that came from Heathkit and I had purchased the amp with PC type fans. There is pre-assembly you have to do to the fan before installing. It involves removing a couple of screws on the fan that stick out and replacing them with shortened screws. Then you have attach aluminum spacer blocks to the fan which the block also has holes spaced out to fit in the orignal pattern of the fan from Heathkit.
The installation is pretty simple and straightforward. The kit comes with new rubber grommets to absorb any minor vibration that the fan causes.
You can either cut the wires near the old fan and tie into them or what I did was un-solder the old wires and wire the new ones in place.
I initially wrote this article in early may. I wanted to do some other upgrades at the same time but the New England QSO party was really close so I decided just to do the fan. The install went easy and would like to thank those at Harbach for rushing out the part. I made sure the fan was balanced as much as possible and I was able to use the amp during the entire contest. It’s a tad bit louder than the PC Muffin type fans that were in there but you can actually feel more air being pushed with the replacement fan. Over the past months the amp has performed very well. I should find more screws to secure the hood and the sheet metal covering the tubes/rf deck as it tends to rattle during operation.