Hi Everyone, it’s been a long time since my last blog entry. I’ve been so busy refurbishing amps and preamps! My wait times are getting a little long, but that’s a good problem to have. Customer emails were getting hard to track, so I’ve implemented Freshdesk, a cloud-based helpdesk ticketing system. (No affiliation.) Highly recommended! I can set due dates and track status, how long since I last contacted someone, etc… It’s reduced my own stress and improved my customer service. My queue may be long, but my customers are kept well informed.
I’m getting lots of interest in the GFA-565 replacement circuit boards, and doing lots of amp rebuilds with the new boards, with excellent results. A lot of these 565s that come to my shop have been previously repaired, but that leaked electrolyte continues to seep out of the fiberglass, and corrode solder joints and traces. Perhaps some of this is because the previous tech didn’t clean it enough, but I’ve come to believe the only certain repair is the new board.
My GFA-565 rebuilds now include Dale mil-spec RN55C 0.1% and TE 0.1% tolerance resistors in all symmetrical applications, and Dale 1% RN55C in others. Before this, I was hand-matching resistors from lots of 1% resistors. This was time-consuming, so I’ve just sprung for a bulk-order of the 0.1% resistors. Done. They have a better thermal spec than the 1% as an additional benefit.
This photo below shows two changes in my parts selection philosophy for amps. For one, after much searching, I’ve settled on capacitor types for the input coupling and inverting AC path to ground. The Kemet F461 is a very, very nice Polypropylene capacitor, with specs and measurements better in every aspect to the stock caps, which are pretty good already. Their dissipation factor is actually below my meter’s threshold at 100KHz, reading only 0.000. For this GFA-545, I use one in each location. The original caps were a very nice polycarbonate on the input, and a more ordinary polyester MKT-type to ground.
The other change is that I’m sticking with the stock ceramic emitter resistors as seen above, and no longer installing the big Dale LVR 1% emitter resistors as standard. These are becoming hard to get; hopefully they won’t be discontinued. And I’ve discovered the stock ones are actually quite good. Tolerances measure much better than their 5% spec, and they actually register a tiny bit less less inductance than the Dales. There are plenty of cost-no-object amps that use resistors like these, so I am no longer swapping them. I’ll keep offering them as an option.
Thanks for reading!