Mystery Valve

[Backtoreality]

Thanks to Tim (g4wim_tim) I have a selection of unknown valves the majority of which I have now identified (thanks to them all being Mullards with etchings!)
There are a couple that have got me puzzled however so I thought I'd show the experts!
Valve 1 there are 3 photos attached. The remains of a Mullard label are visible with the word Holland
There appears to be a code on the bottom reads Yk (I think) and L2D. I cant find the code Yk in the Phillips list of codes and I don't have another valve like it anywhere.

Valve 2 is just the one photo. The code on it identifies it as an EF86en. Is it really an EF86 with a top cap?

Any ideas about these?
Regards,
David

[VT FUSE]

There was a version,designed for specialist applications where a conventional double ended design conferred a small advantage (such as the 6BS7 Electrometer valve) ISTR they were made mostly by STC/BRIMAR and frequently had a CV number on them as they were used mainly by Military users-cannot bring to mind the number at present
I am no expert...

Mike

[Diabolical Artificer]

First one is an RF pentode, might be an EF80, 9 out of ten similar looking unlabelled valves turn out to be EF80's on the whole.

Thought #2 was a 6BS7 but maybe not.

Lawrence will be along soon to put us out of our misary.

Andy.

[G8HQP Dave]

The code might be Yk LtD. L means Mazda in Brussels. However, LtD might be the type code, not the factory code. Lt is EF80. In that case Y means Philips, Sittard.

[Backtoreality]

Thanks Dave, Andy and Mike,
I hadn't thought about that but looking at the codes again t makes more sense than 2.
Another EF80 with a different appearance!
Any ideas for the other valve? The only part of the code remaining is 9r1 but it's very clear.
David

[paulsherwin]

I agree it looks like a 6BS7, but I can't explain the etch code.

[g4wim_tim]

Glad you're having a bit of fun identifying them - they are only a small percentage of the unmarked types in the box.

Regards Tim

[VT FUSE]

Regarding the first valve,the most likely choice is EF80/85 but equally could be EF183/84 certainty of this would only really be proven by plotting curves and/or use of a characteristic meter.

[Cobaltblue]

Back in the day I used to spot the difference between EF80s and 183/184 before I looked at the numbers because the latter were shorter than the EF80 and with a shorter electrode structure


Don't know if this was always the case but I don't ever recall seeing a tall EF183/184

Cheers

Mike T

[VT FUSE]

All well and good but a later revision introduced EF80 valves with similar type of short perforated screens & electrode structure as seen in EFI83/4.

[Cobaltblue]

Originally Posted by VT FUSE

All well and good but a later revision introduced EF80 valves with similar type of short perforated screens & electrode structure as seen in EFI83/4.

Yes I have seen many EF80s with the short electrode structure they look pretty empty, but they still had the tall envelope.

I always assumed maybe incorrectly that the envelope had to stay the same height or it might not fit the screening cans or some other thing that depended upon the envelope height .

They may well have produced short EF80's I just don't recall any.

Love to see a study on the humble EF80 it must have the most diverse presentation of electrode structure of any common valve.

Cheers

Mike T

[G8HQP Dave]

As Brimar had the 6BR7 (similar applications to EF86) and 6BS7 (same, but with a top cap) maybe Mullard made a few EF86 with top caps?

[Maarten]

Originally Posted by Backtoreality

The code on it identifies it as an EF86en. Is it really an EF86 with a top cap?

Likely not. The base doesn't look like it's an enameled type either. What's the code please (both lines)? Also, if it's a special tube (industrial type): those have a parallel coding system.

[Maarten]

Something seems not quite right. Picture 1 and 2 show the same valve, but picture 3 (the base with the letters on it) shows another one? Picture 4 is the "not EF86" presumably.

The valve in picture 3 could indeed be an early EF80 using the pre-1956 date/factory coding but I would have expected type code YF instead of Lt so still a bit uncertain.

Upon re-reading I understand that pictures 1 and 2 indeed show another valve, with only the marking 9r1 readable? Even if you breathe on it and look under different lighting? 9r1 would point to an EF86 en, which given the looks of the base is again strange as the only en looking base is the one in picture 3...

[Heatercathodeshort]

The humble EF80.
The first picture shows the original version released in 1950 as part of the Mullard 'World Series' B9A television valves. Note the solid grey coloured screen on the top of the electrode assembly. These were manufactured in Holland and can be found in the PYE LV30 series.

2. The top solid screen has gone by 1952 replaced by an extended perforated screen.

3. By the mid 50's the screen has been reduced in height and remained like this until the end of production.

4. An odd ELPICO version of the EF80. It performs well.

Mazda badged their own 6F23 as EF80 in the 1960's. Easily recognized by its large holes in the outer screen.

There are probably more versions of it but life is too short to sort through several hundred EF80s! They multiply all by themselves. Regards, John.

[G8HQP Dave]

Originally Posted by Maarten

9r1 would point to an EF86 en, which given the looks of the base is again strange as the only en looking base is the one in picture 3...

What is meant by "en"? Is this a Dutch abbreviation?

Note that the first three pictures in post 1 are of one valve, which we believe is an EF80. The last picture is a different valve, which may or may not be a modified EF86.

[Cobaltblue]

Originally Posted by Heatercathodeshort

The humble EF80.

They multiply all by themselves. Regards, John.

True Dat

Thanks for the start of the study HCS

Yes I have seen a few different types over the years so different from the classic Mullard they are hard to recognise.

That ELPICO is a classic I wonder where that one originated?

Cheers

Mike T

[Maarten]

Originally Posted by G8HQP Dave

What is meant by "en"? Is this a Dutch abbreviation?

Note that the first three pictures in post 1 are of one valve, which we believe is an EF80. The last picture is a different valve, which may or may not be a modified EF86.

So the 9r1 code is on the valve in picture 4? Unfortunately I didn't dind 9r in the list for industrial valves, so no definitive answer there, but an EF86 with top cap seems a bit unlikely as it would have had another factory code (or none at all if sufficiently experimental).

en stands for enamel (I think as seals around the pins in the base, but that's not certain). This mostly seems to combine with fritted on flat plate bases as I think I see in picture 3. However pictures 1 and 2 show a normal style base so it might be just the camera angle in picture 3?

In any case, it matches the older way of printing the code for an EF80, so I think that part of the mystery is solved.

[G8HQP Dave]

Yes, I believe 9r1 is the code on picture 4. 9r is the type code for EF86 en. Or could 9r1 be a date code - so 9 means the Heerlen receiving valve group? Would that be a better fit with what may be an experimental valve?

[Maarten]

It has the wrong format for that. The only way I can think of that the code for an EF86 could end up on an experimental valve, if it was first manufactured as an EF86 and then manually modified, which seems highly unlikely. The "etch codes" weren't stamped on prior to evacuating as far as I know. Also it seems unlikely a modified EF86 was mass produced without its own code. So the most likely hypothesis remains that if that's the code, it would be an industrial tube.