Recently I got curious about a sound of tubes produced based on the same technology and in some cases the same equipment, but in different places. One of the reviews was dedicated to EI 12ax7 produced on Telefunken’s equipment and the results were not equal at all.
This time I looked at Mullard’s 12ax7 production from UK, India & Canada. Now the process was supposed to be controlled by Mullard and technology should nave been used the same, so the results should be very similar – they are not.
- UK production is consistently creamy, deep and dark.
- Canada is brighter than UK, but at the same time maintains creaminess.
- Indian production is all the way up in the sky when it comes to brightness, much thinner sounding tube and not as detailed as UK or Canada.
So how do you not get yourself to a wrong country when traveling The Land of Tubes? Lookf for this sings of the real thing:
- Manufacturing & date code – Small letters on the bottom of the tube (could be up site down as well). Real thing starts with letter B and is followed by 2 or 3 letters and digits. Canada is marked by small r. Mitcham plant in UK is marked with capital R – if you find that – take it right away, it’s likely CV4004, which is a military 12ax7.
- Seams on the top – real Mullard has only 2. In canadian case, the seams 3 & 4 are not very visible. In Indian case, you can clearly see the 4 seams.
- Mica – Blackburn’s mica is missing a tooth between the plates on the top mica. Both Indian & Canadian tubes have the tooth.
- Hole in plate – UK made Mullard has only whole in the front parts of the plate. Canadian Mullards that I have also have holes only upfront. Indian tubes have holes in the back parts of the plates
Other things like grid posts – I’ve seen Mullard with Copper & Metal posts. It looks like later production switched to other material away from Copper, but I’ve never seen Indian or Canadian tubes with Copper posts.
Japanese produced Mullards could be destinguished by the same signs as well. Don’t rely only on one sign, use multiple.
Hope that helps to find the real thing.