I have not used them, but I have a KPA-1 and a KBA-75 gold that are working. I was looking for info one day and spotted this adhttps://kahlaudio.com/products/kinergetics-kba-75-platinum-series-class-a-amplifier-legendary-2000-m...So I e-mailed him about who had serviced it before he listed it, and he wrote:
I usually go to Technotron in NYC for any service issues. They re-capped an earlier KBA-75 but the one I have for sale now was done by the customer's own contact (Capstone's electronics) in VA.