[mordy]

Please forgive me if this has already been answered. Is there any difference between 6ZH1P-EV and the non - EV variant?

These are Russian tube designations - because the Cyrillic alphabet is used the translation has some variants.
As far as I know the EV (EB) designation indicates longer life - 5000 hours. Otherwise the tubes should be the same. The DR designation indicates 10,000 hour life.
A regular tube should last approximately 3000 hours. The IR designation is only rated 500 hours, but it could mean in conditions in a tank and not an amp......

 

[mordy]

Thanks for the longer version.

In the early 50's National in Japan (Matsushiiita/Panasonic) bought tooling from Philips. As Oskari discovered, certain German tubes were made in Japan.

 

[Oskari]

In the early 50's National in Japan (Matsushiiita/Panasonic) bought tooling from Philips.

It seems that Matsush¡ta may have actually made 6AK5s.

No, I'm not saying that @grig's RTCs were made by Matsush¡ta.

 

[grig]

There's plenty of way to say that for sure.

like ???

 

[Oskari]

like ???

The seams on top. The way the tip was shaped.

 

[gibosi]

Here's a fairly good example of Philips tooling -- the four seams at the top and the shape of the tip:

An E91H / 6687 (Philips production code: 3L7 ⊿2L4)

 

[Scutey]

Please forgive me if this has already been answered. Is there any difference between 6ZH1P-EV and the non - EV variant?

Hi mattrudy80,

I think you will find that most if not all 6ZH1P have the suffix EV. I have several pairs of 6ZH1P and they all have EV on the end.

 

[rexhu100]

Learned a lot about tubes in the recent posts!

 

[Scutey]

Learned a lot about tubes in the recent posts!

When I got my LD I found this thread, and others absolutely invaluable. Some of the older posts are also full of useful info too.

 

[grig]

Here's a fairly good example of Philips tooling -- the four seams at the top and the shape of the tip:

An E91H / 6687 (Philips production code: 3L7 ⊿2L4)

mine is quite different, and i will put two picture and in case i can take many more....

 

[Oskari]

mine is quite different, and i will put two picture and in case i can take many more....

Different but same…

 

[grig]

Different but same…

the internal structure looks similar or almost the same, but is the sound as well .... ?

 

[gibosi]

From factory to factory, there are often small differences in the way Philips tooling was implemented. For example, in some factories, all four seams are not equally prominent and it appears that there are only two seams.

With regard to the internal structure of a tube, for example, an EF95 / 6AK5, again, there are often small differences from factory to factory, even though they are all constructed according to the instructions provided by Philips.

But no, tubes manufactured in different factories do not sound the same even though they appear to have the same construction. Since Philips purchased existing companies, for example Mullard, then one might say that the original company's "DNA" remains in that factory. And this residual "DNA" explains why tubes manufactured by Mullard sound different than those manufactured by Valvo, in Hamburg, Germany, or by Philips, in Heerlen, Holland.

 

[mattrudy80]

I picked up a lot of 6 International Servicemasters marked EF91/6AM6 GT BRITAIN. At first glance they appeared to be Mullard EF91 but I could not find any Mullards that had the tab bent up towards the top getter. Any help identifying would be much appreciated as they sound great.

 

[gibosi]

Do you see Mullard production codes on this tube?