Hi Jim, I used to own an Ayon CD-5s which employs a quad of 6H30 triodes in the output stage. I upgraded the factory EB's to a quad of matched 6H30P-DR's, so I might be able to offer some insight. The DR's are mil-spec tubes which were made in the Soviet era for sensitive military applications such as the Soviet space program. As such, they had to be more accurate, reliable and have longer tube life. Upgrading the output tubes to DR's will provide a good improvement in resolution /frequency extension, noise, dynamics & durability (10,000 vs 5000hrs).

The person to speak to is Chris at PCX who is the President. He buys most of his stock from 1986. I recall Chris commenting he preferred the sound of stock from that year, but Chris will tell you that all mil-spec 6h30DR's prior to 1991 all sound about the same, with very minimal variance. PCX also test over 3 of 5 specs (ie: the most critical specs) and supplies tightly matched quads with the individual measurements for each tube recorded on the tube box. That said, PCX are currently out of stock of the DR's, but you could email him and enquire if he is likely to be getting any stock in future.

If you prefer warmer sounding output tubes, you could also consider cryo-treated EH Gold pins which are another excellent option (and quite a bit cheaper). Here is a link fyi -
cryoset.com/catalog

It is generally accepted the 6h30p-DR is the best variant of the 6h30 tube, although ultimately it depends on your personal preferences. Hope that helps

Cheers,