Hi Larry,
It looks like you are hear alone so I will join you. What is wrong with the K850?
I don't mean what need repair but why is it a less than desirable unit? I am not familiar with the Yamaha line but so far the K1000 doesn't look like too bad of a unit if we could get parts. I got the heads for the K1000 that you sent me but I am not sure any of them are going to do. I will have to do some research but a Teac Head at this point might be your only choice if you are willing to go along with that- it all depends on if it will fit correctly.
I put a Teac head into a Aiwa unit once.