Additional Preamp Tubes

The ones in the Link are readily available.

The pair are 60 years vintage and comes with measurements.

The Valves are not M8137, and these Mil Spec Valves do have the edge, as quality selection was the overriding precedent for them during production. 

I have a purchase method you might want to propose if additional support is easily achieved.

I inform the vendor of my intention to have the Valves remeasured when received, and that if the new measurement taken does not match the readings shown with the Advert. A full refund is to be sought, and valves are to be returned.  

https://www.ebay.co.uk/itm/287430489477?itmmeta=01KWS2CWYZ5APGJREV1J3QQ5A6&hash=item42ec313585:g:OzQAAeSwUypqRLD7

 I owned the BHK pre when it first came out. At the time, the actual BHK - Bascom King - seemed to believe that the very best tubes for his creation were Tungsran PCC88's. I remember that Upscale Audio had a bunch they were selling to BHK owners. The tubes required that you changed a jumper inside the chassis. I bought a pair, and it wasn't my cup of tea. But that's what the guy who made the product thought at the time...

David

@signaforce ,

I’ve used about 20 different brand 12au7’s and variants through the years.

Amperex, Telefunken red tips, Mullard, Westinghouse, Cifte, RCA black plates, CBS Hytron to name a few. Hands down my favorite are Amperex 7316 pq’s.

If ChatGPT didn’t mention them, it used very incomplete references.

They are pricey! If you go with Mullard cv4003, get the m8136 version.

The Amperex 7316 gives you the clarity of a Telefunken with the warmth of the Mullard. Best of both worlds.

What about the Amperex 7316?

Or the RT/RTC/Mazda/Belvu 12AU7?  Not the chrome plates.

I find that they still provide a high level of detail, just in a smoother fashion, if that makes any sense.

For a very affordable option, try the East German RFT, which is often labeled as National.

@pindac @thecarpathian @bbroussard @dtorc Thank you for your recommendations.
Early on I read of the favs of King’s for the BHK. Not sure why, but never considered them. 

2 for the Amperex 7316, & strong praise. Added. 
The CV4003 Mullards I am considering are the M8136 version. What does that mean?
BTW, the nice thing about tubes is even expensive ones are cheap compared to components or even cables & can have a profound effect on your sound. Thanks!