(Probably) trivial valve puzzle

[ricard]

Someone gave me a valve today asking what type it was. It's a GT form factor with octal base, with a top cap (connected to the anode by looks of things). It looks like an audio beam power tetrode. From what I can make out of the base connections, they are identical to the 6L6 except that the plate connection (pin 3) is on the top cap, and pin 3 is instead paralleled to pin 8 (cathode and beam plates).

I've read that early 6L6's had a top cap but I've been able to locate the resulting pinout.

Any spontaneious suggestions as to what it might be?

[Diabolical Artificer]

Could be a 6DQ6/A/B but the 6DQ6 has pin 3 NC. Could it be a 6146?

There are a few beam tetrodes like you mentioned originally designed for TV's but used in a few guitar amps like the Goldentone.

Andy.

[G6Tanuki]

Could it be a 2E26? http://www.r-type.org/exhib/aaa0830.htm

[turretslug]

The PL36/EL360 family are described as having pin 3 internal connection- possibly to cathode?

[ricard]

Thanks for the suggestions!

Apparantly the valve was found loose on its own when cleaning out a house, so my guess it would come from a radio, TV or possibly guitar amp. A PL36 sounds reasonable in that context.

I thought all the markings were wiped off, but there is small

437
X0D

near the base which sounds like some sort of lot/date code. I don't know if that gives any clue as to the manufacturer for someone.

[Herald1360]

43 is consistent with PL36 and X with Philips (Mullard)

[GrimJosef]

The code is almost certainly a Philips one and if that's the case the first two digits - 43 - identify the valve as a PL36.

Cheers,

GJ

[ricard]

Thanks! I had no idea that code could actually be that useful. I was just assuming it was a date and lot code of some sort. Is there more information on the net to be found on that type of marking?

From what I can tell the PL36 it seems was most likely to have been found in television receivers in the late 50's as a line output stage?

[dseymo1]

I've asked before, but have not been able to find out: since the 'house code' is etched indelibly on so many valves, why isn't the 'consumer' number marked in the same way?

[Radio Wrangler]

Also used in some Radar displays to drive radial deflection coils and for EHT generation.
Consumer numbers went on later when it was decided just what a valve was going to be sold as. The valve manufacturers often bought in each other's stuff, and then there were CV numbers. So the manufacturing code is the most dependable identification.

David

[ricard]

One would have thought though, that once it was decided what a valve 'was going to be sold as', given the scale of production, it would have been a small thing to add etched 'consumer' numbers, even if the initial run was just stamped. One technical reason I could imagine would be that etching a large consumer-readible ID would have weakened the glass, so it was only used for small 'in-house' number?

But it still begs the question: has anyone ever compiled a directory of manufacturer id's and where is that type of information to be found?

[GrimJosef]

Google is your friend . If I search for 'Philips valve codes' then Frank Philipse's scan of the original document http://frank.pocnet.net/other/Philip...CodeListAB.pdf is top of the first page. He has a clearer version on his website here http://frank.pocnet.net/other/Philip...ListAB-v10.pdf though.

The best list of Brimar codes that I know of is this one http://myweb.tiscali.co.uk/g8hqp/audio/brimarcodes.html. Again it's the first return if I Google 'Brimar valve codes'.

Cheers,

GJ

[G8HQP Dave]

Originally Posted by ricard

One would have thought though, that once it was decided what a valve 'was going to be sold as', given the scale of production, it would have been a small thing to add etched 'consumer' numbers, even if the initial run was just stamped.

Etching takes longer than printing, and is probably more fussy about exact conditions etc. Etching is part of the manufacturing process; vital for quality control. Printing the label is really part of the packaging process.

If you are making thousands of EF91, you might not know at that stage whether they will be sold as Mullard EF91, Philips EF91, Valvo EF91, Mazda 6F12, Brimar 6AM6, Marconi Z77 etc.

[ricard]

Point well taken ... as well as the bit about google, I think I instinctively put this type of information in the category 'stuff that people only have in the form of printed matter' (i.e. old catalogs or books) without remembering that given enough interest such printed matter invariably makes it way into digital form.

[RF Burn]

Contrary to popular opinion, the so called 'house code' applied to valves made by Mullard/Philips etc. and Brimar was applied after production testing and used to identify the valves while in buffer storage. This 'code' is not etched but applied in ink which tends to be more durable (over the years we find!) than the silk screened final markings applied to the valves once they were removed from buffer store and prepared for shipment to the required customer. As valves were produced in large batches, or production runs, then buffered in store, the final markings would depend on the customer which may be another valve maker/brand such as Mazda, Brimar, Philips, Adzam...... and they may need to be marked 'Foreign Made' if supplied to a foreign brand..... as well as traditional marking for the UK retail/spares market. Hope this clears things up a bit.

[G8HQP Dave]

Some later codes (e.g. from factories like Ei or BEL) sometimes appear to be printed but earlier ones do look like they are etched. Are you saying that everyone has got this wrong?

[Maarten]

I don't think either I've ever encountered a Philips two line code that was actually etched, but that's of course no hard proof yet. I will make sure to pay extra attention whenever valves pass through my hands.

However you'd be amazed at the amount of information on the internet that is simply copied from someone else without fact checking, so don't be too surprised if once in a while everybody's got something wrong.

[GrimJosef]

I've certainly seen examples of the two-line code that have been partially rubbed away, and I have even managed (to my embarrassment) to rub them away myself occasionally. I think that many, at least, of these codes are inked on, not chemically etched (which would be hard to achieve at the high speeds needed for mass production).

Cheers,

GJ

[G8HQP Dave]

OK. I have to bow to experimental data: if you can rub it off it isn't etched.

I once saw a claim on the internet that chocolate does not contain caffeine, and all the claims that it does are merely copies of an original false claim. Some claims may even be circular, so if you follow links supporting the claim you eventually end up back at the website you started from!

[m0cemdave]

I have also seen examples where the factory code has been partly worn away, so they definitely weren't etched.
I would describe it more as "indelible ink" in comparison to the more familiar brand and type marking which is nowhere near permanent. Or to be more accurate, "almost indelible ink" !