In 1988 I acquired a D&A 12 tuber. It was black and looked more modern than the old gray or tan ones. It had 12 original D&A tubes with the black caps and double strapped plates. It's been a while but I'm almost certain it did have and external power transformer. I do remember when I offered it for sale, it sold fast and for good money.
I have heard several complaints about the performance of the 12 tuber not living up to the 10 tuber. Mine worked great and I suspect it had to do with the fact it had the best tubes available in it. No other 6LQ6 worked quite as well as the ones it came with.
I have heard several complaints about the performance of the 12 tuber not living up to the 10 tuber. Mine worked great and I suspect it had to do with the fact it had the best tubes available in it. No other 6LQ6 worked quite as well as the ones it came with.