For the Bottlehead Crack you can use the following for preamp tubes: 12AU7, ECC82 (EU designation for 12AU7), 7316, CV491, CV4003, 5814, 6189, 5963, 6680, 7730, B749 tubes.
According to Doc B at the Bottlehead Forums, the following tubes can be used IF YOU HAVE INSTALLED THE SPEEDBALL UPGRADE: E80CC/6085, ECC802s, 13D5, 12BH7 tubes. You could also use a 12AT7 tube, but the gain will be way too high and you’ll have almost no volume attenuation.
So I thought I’d do a quick post on the 17 tubes I own and have had listening time with.
RCA 12AU7A
This is what came stock with my BHC. This is often referred to as the RCA 12AU7A “Clear Top”. It is a very neutral and dynamic sounding tube. With the wrong power tube combination, it can become too solid state sounding. A little more in the low end would greatly improve this tube. It comes across competently, yet left me desiring more bass.
GE 5963
5963 tubes have very slightly less gain than 12AU7 tubes. This is a good thing as you have more volume attenuation range. I feel this is a nice affordable upgrade to the RCA 12AU7A that I received stock. It is similar to the RCA but a shade warmer with better Bass quantity and quality. The mids and treble are very similar to the RCA, as is the soundstage…which I’d consider average. These can go for as low as $10 to $20, which is a steal.
IEC/Mullard ECC82
You have to be very careful when buying NOS Mullard tubes. There are a lot of fakes, as well as different companies that Mullard either manufactured the tubes for, or slapped their name on. Also tube labels were being used very willy nilly. To my knowledge, IEC, Heath, EICO all had involvements with Mullard, with Mullard eventually purchasing IEC. Regardless, this tube is pretty darn good. Much warmer and thick sounding in the bass and mids. Soundstage is above average. My tube is from the late 1960s…supposedly the Mullard tubes from the Blackburn manufacturing plant from the 1950s and early 1960s sound better and are more desired.
Philips ECG JAN 5814A
This tube is similar to the RCA 12AU7A and GE 5963, but it has way better defined mids, better treble extension, and wider soundstage. These can go for as low as $10 and IMO are quite a steal at that price.
Tung-Sol JTL-6189 (12AU7WA)
This is an excellent sounding tube. It is a military spec 12AU7. This tube is one of the more linear of the ones I heard. Deep and controlled sub-bass, no bloom into the mids, and good treble extension with some air up top. These are also very affordable.
Ken-Rad 12AU7 (pewter plates, slanted horseshoe getter)
I bought this tube for $24 and was surprised how good it sounded. It does lack air up top, but it has excellent tonality in the mids and bass. A nice and pleasant sounding tube at an affordable price.
Raytheon CK6680 (6680 Tube)
This is almost exactly like the Ken-Rad both build wise and sound wise. They are around the same price, so not much to make it stand out against the Ken-Rad.
Matsushita 12AU7
This is one of my favorites. I never knew this until after buying the tube, but Mullard lent technology to Matsushita and helped them set-up their plant in Japan. Philips also assisted in providing materials to Matsushita. There is some magic in this tube. They are among the most dynamic of any I’ve heard. They have a really good balance of a clean and airy top end, excellent warmth in the mids, and accurate but punchy bass. They have a very wide soundstage, but it never sounds too wide where it becomes artificial sounding.
Brimar CV4003 (ECC82)
The CV4003 is a British Military Spec version of the ECC82. This one is very similar to the Matsushita, but has more air up top and a less wide soundstage, but better detail and very dynamic. It might have slightly less bass as well, but it is really too close to call.
Telefunken ECC82
The first thing that you notice is the open and airy treble. The bass is tight and punchy, but impactful. The soundstage is very wide and it has a great 3-D image. The mids have a tendency to sound clean and neutral. This is also the least microphonic of all of the tubes I own. This is a dynamic, wide and almost W sounding tube.
Northern Electric 12AU7
Honestly, not much to write home about. For a new production tube though, this is pretty good. Too solid state sounding for my preferences, and the $49 price is not worth it IMO.
Siemens E80CC (6085 Tube)
Very detailed, solid state sounding. Intimate soundstage but very dynamic. The bass hits low into the sub-bass…but the quantity may leave some wanting more. The mids are ruler flat sounding to my ears. The treble is definitely forward, but never encroaches on sounding fatiguing. Bright sounding for sure, but not in a bad way.
RCA 12BH7A
More impact in the sub-bass than a lot of cheaper 12AU7 tubes. The mids sound a bit recessed, which sort of turned me off. The treble has some grain to it, but still an affordable tube option. Soundstage is above average.
Marconi 12BH7
This is similar to the RCA 12BH7A, but has a wider soundstage and no recessed mids. No grain in the treble either, but there isn’t much extension at the very top end. Neutral yet engaging sound quality.
GE 5692 with 12AU7 to 6SN7 adapter
I personally am not a fan of 6SN7 tubes on the crack. There are a slew of people that do like them though. This tube in particular sounded wide and had a great sense of 3d to it. But it suffered from the mids being too withdrawn, the bass sounding “one note”, and the treble was grainy and brittle.
Tung-Sol 6CG7/6FQ7 with 12AU7 to 6CG7 adapter
This is the better sounding 6CG7 tube and it sounds very similar to the JTL-6189 I went over earlier, but with better and more impactful bass, as well as a wider soundstage.
Raytheon 6CG7/6FQ7 with 12AU7 to 6CG7 adapter
Not much to say about this. It was similar to the Tung-Sol 6CG7, but way more intimate and narrow of a soundstage. Has really good upper mids and treble detail, but it can be overwhelming with the wrong power tube.
Adapters
Just a few pictures of the previously mentioned adapters.
In closing, the Telefunken, Ken-Rad, Brimar and Matsushita are my personal top 4 favorites. The Brimar and Matsushita are probably my top 2.
Any questions, please just let me know! I’m here to help. 
