Nice (inexpensive if purchased on Ebay) Mullard Blackburn 12au7's are the late 60's/early 70's which often have Amperex Orange Globe labels.
Can't access my tube cabinet right now, but the pair I'm currently running have GF2/B1K1 etched codes (early 70's).
They sound more like an Amperex Holland 12au7 than a typical/earlier Blackburn 12au7.
5-6 years ago you could buy NOS 5 counts on Ebay for $20, or so, as most thought them to be Richardson relabel's and/or fakes (the auctions did not mention the etched codes)
I thought they were of either RFT or Japanese manufacture, due to the sloped getter and dark flashing, only to find them to have Blackburn codes.
The Holland Orange Globe 12au7's of the same time period would be another good/inexpensive bet.
Look for TV-7 readings of over 100, per section, for an as new tube (my sealed units were typically between 105 & 110).
Can't access my tube cabinet right now, but the pair I'm currently running have GF2/B1K1 etched codes (early 70's).
They sound more like an Amperex Holland 12au7 than a typical/earlier Blackburn 12au7.
5-6 years ago you could buy NOS 5 counts on Ebay for $20, or so, as most thought them to be Richardson relabel's and/or fakes (the auctions did not mention the etched codes)
I thought they were of either RFT or Japanese manufacture, due to the sloped getter and dark flashing, only to find them to have Blackburn codes.
The Holland Orange Globe 12au7's of the same time period would be another good/inexpensive bet.
Look for TV-7 readings of over 100, per section, for an as new tube (my sealed units were typically between 105 & 110).