Have you ever looked at an old piece of equipment in need of restoration but weren’t sure about how to start the project? Or just needed some inspiration to get started?
KN3B begins with a collection of photos and a description of the condition of his amplifier before starting the project.
He then presents his objectives for the project and lists the replacement boards which would be used.
The next phase of the of the project included rebuilding arc-damaged plate tuning capacitor, constructing new parasitic suppressors, removing a power cable extension, and removing replacing old or failing capacitors.
Then a series of upgrades were installed and modifications were performed to modernize the amplifier so that it would become the new primary amplifier in [KN3B’s] station, capable of running 1KW+ for extended periods of time on most bands, with all the modern upgrades that would extend its life for another 20+ years and allow it to be keyed by modern rigs. 1
At the conclusion of his blog post KN3B reports these lessons learned:
This project took almost exactly 3 months to the day from picking up the amplifier to getting it on the air. After the cost of the amplifier, the Harbach kits, and several orders from Mouser, I believe I am in to the project for just under $1,000. I would do it all over again, if I were to find another SB-220 in the same or comparable condition.
Tube gear is resilient and can clearly take a lot of abuse. Even with the clear evidence of mistreatment and damage to some passive components, the rest of the amplifier was no worse for the wear.
Point-to-point wiring is so simple that you can work on it if you know how to flow solder. Don’t be intimidated by tube amplifiers, they are pretty simple and the schematics are easily digested if you know the basics.
Carefully inspect each and every circuit in your amplifier before you order parts from Mouser, otherwise you’ll spend about $35 in extra shipping charges because you had to order two capacitors five separate times over the course of the restoration.
And finally, if you find an old beat up tube amplifier for a good price, take it home and restore it before somebody else does. 1
KN3B’s blog post is an excellent example of how to approach a restoration project and is well worth reading.
“Heathkit SB-220 Restoration and Modification”, KN3B, accessed December 26 2022, http://kn3b.com/heathkit-sb-220-restoration-and-modification/. ↩︎ ↩︎