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The glass was definitely made using Philips tooling, but not necessarily in a Philips group factory. The seams are the giveaway.
In the latter years of the valve era many Philips valves were made elsewhere, and some of these overseas factories were rather careless in how they applied the factory code.
Z&I Aero Services were a British rebrander. Most of their valves came from Russia or Eastern Europe, but they would buy what they could.
In the latter years of the valve era many Philips valves were made elsewhere, and some of these overseas factories were rather careless in how they applied the factory code.
Z&I Aero Services were a British rebrander. Most of their valves came from Russia or Eastern Europe, but they would buy what they could.
They were cheap rebrands, so statistically the answer is more likely to be "not as reliable".
lol
Check for either "I61" or "I63" on the lower side of the glass.
How many seams are on top of the glass, 2 or 4? I can't see clearly in the pictures.
If it has 2 seams and either I61 or I63 on the glass they are Mullards UK.
Also, if they have a 3 or 4 digit date code starting with "B" they are made at Blackburn Mullard factory in UK.
How many seams are on top of the glass, 2 or 4? I can't see clearly in the pictures.
If it has 2 seams and either I61 or I63 on the glass they are Mullards UK.
Also, if they have a 3 or 4 digit date code starting with "B" they are made at Blackburn Mullard factory in UK.
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Date beginning with B is Mullard Blackburn. I61/63 could be Blackburn or could be elsewhere.
According to tube-classics.de the I61 and I63 versions were also made at Heerlen in the Netherlands.
According to tube-classics.de the I61 and I63 versions were also made at Heerlen in the Netherlands.
Exactly ! Any Philips licensee could produce valves to these patterns . Some licensees such as B.E.L (the probable manufacturer of the valve in question) and Ei (with their Telefunken style 'smoothplate' but with Philips-type bottle) did use some rather odd etch codes and did not necessarily build to the original patterns
316a
Ι61 & 163 were also used by Philips and Siemens,BUT not with 2 top seams (they had 4) and with a different date code.
So, as I said before, 2 seams+ I61/I63 and date codes begining with B were made by Mullard in Blackburn/UK.CV4004/M8137 with date codes begining with R were made in Mitcham/UK.They also had only 2 top seams and of course box plates.
If I remember well, the UK 161 had copper posts but not those made by Philips or Siemens etc...
Also , think otherwise, Philips with Δ on glass always meant it was made in Heerlen only.
And it goes on and on .......
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