I've just bought a pair of Mullard GZ34s from the 1970s.

 

Both valves have the code B5A6.  According to my understanding of the information on the 'net, this means:

 

B = Blackburn

5 = 1975

A = January

 

...but 6? The lists show 5 as the highest number, being the fifth week of the month.

 

Does anyone know? 

It should be a 5. Is it an f32 or higher? Does it have a 7-notch anode plate structure? Can you share a close up photo? 

Edited February 20, 20251 yr by xlr8or

14 hours ago, xlr8or said:

It should be a 5. Is it an f32 or higher? Does it have a 7-notch anode plate structure? Can you share a close up photo? 

 

I am not too hung up about the minutiae of the valves' production - all I was  after was a pair of NOS rectifiers that I could afford that would be better than current production.

 

I'm afraid my photographic skills are not up to taking as detailed a photo as you have requested, but I can tell you that the valves have brown bases, with the Mullard 'shield' logo, 'GZ34' and 'British Made' on the glass (plus the code at the rear next to the base).  The valves themselves are quite weighty for their size and look well made.  The boxes are blue with red and white printing and 'Mullard The Master Valve ' on them.   

 

I bought the valves from a well-established eBay seller in China and they arrived well-packed within a week.  Of course, given the strange code I am now wondering whether they are Chinese knock-offs, but there again, why would anyone go to such trouble for the sake of a a couple of hundred dollars?

1 hour ago, Bronal said:

 

I am not too hung up about the minutiae of the valves' production - all I was  after was a pair of NOS rectifiers that I could afford that would be better than current production.

 

I'm afraid my photographic skills are not up to taking as detailed a photo as you have requested, but I can tell you that the valves have brown bases, with the Mullard 'shield' logo, 'GZ34' and 'British Made' on the glass (plus the code at the rear next to the base).  The valves themselves are quite weighty for their size and look well made.  The boxes are blue with red and white printing and 'Mullard The Master Valve ' on them.   

 

I bought the valves from a well-established eBay seller in China and they arrived well-packed within a week.  Of course, given the strange code I am now wondering whether they are Chinese knock-offs, but there again, why would anyone go to such trouble for the sake of a a couple of hundred dollars?

 

I was asking for those details to clarify authenticity. From the description provided, it appears you have fakes. Sorry ...

 

Edit: British made only appeared on the fat base f31 series in the late 1950's. The manufacturing date code would be B-number-letter only.

Edited February 21, 20251 yr by xlr8or