Additional Preamp Tubes

Mullards as a Mil Spec in the models discussed, are the antithesis of a typical Amperex equivalent. That noticeable difference in the sonic trait does not make the Mullard a warm, rich Valve. 

The Amperex can in certain circuits be similar in the end sound produced to resemble cleaning a Blackboard with one's nails.

The Mullard is a much more desirable implement selected to clean the Blackboard.

Certain circuits with Copper used in Cap's and without metal films in use, might give up the Valves inclusion as being with added depth to the sonic.  

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.