UPDATE on HEARING AIDS IN PHITSANULOK. I was looking into a hearing aid for the first time. Ended up at the Government hospital, audiology clinic. Long story short, they tested me and let me try their BEST hearing aid. The cost was 17,000 baht. Very inexpensive but very poor sound, much too noisy. Passed on that and tried this shop. https://www.facebook.com/ศูนย์การได้ยิน-และ-เครื่องช่วยฟัง-พิษณุโลก-785724724925424/. I don't know the English name, it's near the government hospital. It's the only hearing aid shop in town. They seem to specialize in low cost range but good quality aids. They really only offered me a choice of two. I got the Unitron T-max up 600 (BTE). The clarity of the sound actually surprised me, and the background noise was like normal sound, not annoying. Very good value at under 30,000 baht. The test was free, and cleaning and minor adjustments are free for a year. It seems to be very important to have access to "after service". They seem to offer a very limited range of aids, and their English is virtualy nil. Take a Thai friend. They are friendly and want to help.
One contributor suggested Phitsonuvej hospital, but I avoid them whenever possible as their "mark ups" are outrageous.