Octal valve partially wrapped in brown paper...

[dougietamson]

I was given a box of approx 100 valves today, xmas came early

The attached photo will tell more than I can describe but it's a largish grey glass bottle with an octal base partially covered in brown paper which is covering any markings
Could it be a NOS GEC KT66?

Also in the photo are 2 possibly Russian/Former Eastern Block KT66 valves marked foreign that came in the job lot.

Next question do I peel back the paper until it reveals its secret?

Doug.

[Richardgr]

Every so often there used to be a bad batch of Caesium, one of the ingredients of the cathode, so the tube was radioactive, and the application of the brown paper was a temporary cure against the gamma radiation.

Unfortunately they have to be disposed of at an official disposal site, and you will find the address of one such site under my user profile. ;-)

[paulsherwin]

It does look like a GEC KT66, but all the ones I've ever seen are marked accordingly. I can't comment on the brown paper suggestion, though I suppose it's possible if the valves have come from an unusual source, such as a government lab or the military.

[dougietamson]

Originally Posted by Richardgr

Every so often there used to be a bad batch of Caesium, one of the ingredients of the cathode, so the tube was radioactive, and the application of the brown paper was a temporary cure against the gamma radiation.

Unfortunately they have to be disposed of at an official disposal site, and you will find the address of one such site under my user profile. ;-)

Np problem, send me a postal order for 200 guineas to cover the lead lined envelope and it's yours

[GrimJosef]

It could be an M-OV KT66 - Marconi-Osram Valve were the manufacturers of the original KT66. They might have been branded GEC or (yes, you've guessed it) Marconi or Osram. The brown paper won't have been original, so there will be nothing to lose in peeling it back, assuming it's not stuck to the glass. If it is stuck to the glass there might be some risk of pulling off a label or damaging any printing.

Since all we've got to go on is the shape and the internal coating on the glass we can't eliminate the possibility that it's a KT55 http://www.r-type.org/exhib/aaj0167.htm. A measurement of the heater current vs voltage would sort that out though.

To be honest it doesn't look to be NOS - the surface looks a bit marked and if that's the corner of a label peeping out from under the paper then it looks like it's been heated up. If you can see the glass pinch, maybe with a bright light behind it, then the presence or absence of black 'hairs' radiating from the feedthrough wires in it can indicate how much use it's had

It's worth noting that these valves are prone to going gassy if left unused for long periods.

The two smaller KT66s are really just 6L6s and in my experience they can be very unreliable. They might be OK in very low power applications, but I wouldn't trust them in any amp I cared about.

Cheers,

GJ

[dougietamson]

Originally Posted by GrimJosef

It could be an M-OV KT66 - Marconi-Osram Valve were the manufacturers of the original KT66. They might have been branded GEC or (yes, you've guessed it) Marconi or Osram. The brown paper won't have been original, so there will be nothing to lose in peeling it back, assuming it's not stuck to the glass. If it is stuck to the glass there might be some risk of pulling off a label or damaging any printing.

Since all we've got to go on is the shape and the internal coating on the glass we can't eliminate the possibility that it's a KT55 http://www.r-type.org/exhib/aaj0167.htm. A measurement of the heater current vs voltage would sort that out though.

To be honest it doesn't look to be NOS - the surface looks a bit marked and if that's the corner of a label peeping out from under the paper then it looks like it's been heated up. If you can see the glass pinch, maybe with a bright light behind it, then the presence or absence of black 'hairs' radiating from the feedthrough wires in it can indicate how much use it's had

It's worth noting that these valves are prone to going gassy if left unused for long periods.

The two smaller KT66s are really just 6L6s and in my experience they can be very unreliable. They might be OK in very low power applications, but I wouldn't trust them in any amp I cared about.

Cheers,

GJ

Thanks for the info.

Looks like I'll have to gently remove the paper.

Just out of interest, any idea when the GEC branded ones were made?

Doug

[dougietamson]

Originally Posted by paulsherwin

It does look like a GEC KT66, but all the ones I've ever seen are marked accordingly. I can't comment on the brown paper suggestion, though I suppose it's possible if the valves have come from an unusual source, such as a government lab or the military.

The job lot came with some interesting items, like the PD510 BNIB see photos below:

[dougietamson]

The reveal...

A used KT66 with a BBC label (with signs of burning).

The brown paper was there to steady the wobbly base.

[paulsherwin]

Still worth a few bob if it tests OK. You will need to find someone with a decent valve tester if you don't own one yourself and want to get a good price.

[Techman]

This will give some of you a bit of a chuckle

I had a bit of a concern with something that had caused contamination in the bottom of one of the boxes of old valves that I'd recently bought. I was careful not to handle particularly one badly contaminated KT66 box, when I happened to find one of those old plunger type grease guns wrapped up in old newspaper and oozing dried up grease, the same as on the valve boxes, and in another box of random bits. I realised that this grease gun had been stored in with the valves decades ago and had leaked grease, so long ago that it had virtually all dried up. the reason that the grease gun wasn't in with the valves when I got them was because various folk had been routing through everything and had probably jumbled things up.

So the moral of the story is that if you're thinking of storing away your old grease gun for a few decades (just like remembering to remove old batteries from items so they don't rot and leak everywhere, which I've also found amongst this stuff), is not to store it with your spare valves!

The box is actually not too bad to handle and it was the worst one to be contaminated - the surface of the cardboard just feels a bit waxy. I don't think that soaking the box in any sort of solvent is likely to do much good, so it's a case of either throwing the box away, or leaving as it is and just wrapping a plastic bag round it for storage - it's just slightly tacky now and only slightly sticks to the table top if left for a week or two without moving it

[dougietamson]

Originally Posted by paulsherwin

Still worth a few bob if it tests OK. You will need to find someone with a decent valve tester if you don't own one yourself and want to get a good price.

Is there a preferred glue to hold the base to the glass envelope?

[GrimJosef]

In the past people have suggested quite a few possible glues for re-attaching the glass to the base. Part of the problem is that the surface of the glass will have oxidised over the decades and this will change its properties. Substances which stuck very well when the glass was new may not do so now. Whatever you try make sure a) that it isn't at all electrically conductive, b) that it won't degrade when it gets very hot and c) if it dries very rigid that its thermal expansion/contraction won't crack the glass.

My favourite choice is a mix of one part clear nail varnish to two parts acetone. With the glass held firmly to the base using insulating tape over the top of the glass and under the spigot on the base, the brush that comes with the nail varnish can be used to bleed this mixture into the gap. I tend to use several dribbles of glue at each location, working my way steadily round the joint. It then has to be left for 24 hours to dry (12 hours really isn't long enough). The joint sometimes cracks apart again. If so then repeat the process one more time - the glue built up from the first try will have made the gap much smaller for the second one. Two attempts almost always works.

As far as the date goes, the code printed in the box on the glass - MC 10 - contains the date info. I can't remember the details off the top of my head, but I think Google will find them for you.

Cheers,

GJ

[dougietamson]

Originally Posted by GrimJosef

In the past people have suggested quite a few possible glues for re-attaching the glass to the base. Part of the problem is that the surface of the glass will have oxidised over the decades and this will change its properties. Substances which stuck very well when the glass was new may not do so now. Whatever you try make sure a) that it isn't at all electrically conductive, b) that it won't degrade when it gets very hot and c) if it dries very rigid that its thermal expansion/contraction won't crack the glass.

My favourite choice is a mix of one part clear nail varnish to two parts acetone. With the glass held firmly to the base using insulating tape over the top of the glass and under the spigot on the base, the brush that comes with the nail varnish can be used to bleed this mixture into the gap. I tend to use several dribbles of glue at each location, working my way steadily round the joint. It then has to be left for 24 hours to dry (12 hours really isn't long enough). The joint sometimes cracks apart again. If so then repeat the process one more time - the glue built up from the first try will have made the gap much smaller for the second one. Two attempts almost always works.

As far as the date goes, the code printed in the box on the glass - MC 10 - contains the date info. I can't remember the details off the top of my head, but I think Google will find them for you.

Cheers,

GJ

I'll give that a try today and leave it over night. I have some clear nail varnish.

I'll check the dcr on the filament and light it up and note the current draw/voltage drop.
Meanwhile I'll put together a simple point-to-point push pull LTP/output amp, I don't have a suitable SE OT. Can test the other foreign KT66 valves too.
I'll add 1Ω resistors at the cathodes and could also check the voltage drop across the anodes to CT of the output transformer windings, measure the voltages at each pin and variable -ve bias supply.

Any other tests/readings I could do while in service?

Tim Robbins has a doc on his site with the date codes:
https://dalmura.com.au/static/MOV%20...e%20coding.pdf

Looks like it's from March 1956.

Doug.

[Sideband]

Originally Posted by dougietamson

The job lot came with some interesting items, like the PD510 BNIB see photos below:

First pic is a D1 (EA50) signal diode with an original 3 pin base. Haven't seen one of those for about 50 years.....

[dougietamson]

Originally Posted by Sideband

First pic is a D1 (EA50) signal diode with an original 3 pin base. Haven't seen one of those for about 50 years.....

Thanks for the info, it's available for free if anyone is interested.

There are 2 large rectifiers, one is marked Brimar 5U4G, the other looks the same internally.

[M0FYA Andy]

Originally Posted by Sideband

First pic is a D1 (EA50) signal diode with an original 3 pin base. Haven't seen one of those for about 50 years.....

EA50s and the three-pin base are easy to find, but this one also has the little clip for the pin at the other end. These are not easy to find in my experience, as they are readily lost.

Andy

[David Simpson]

Doug, if you're ever likely to be up this way, or ken someone who might be, Covid Reg's permitting, I'll easily DC test a handful of valves for you. Seeing as you're related to Jock Tamson.
As GJ says, some Eastern European valves don't reach the GEC spec. for the likes of KT's & similar O/P valves.

Regards, David

[dougietamson]

Originally Posted by David Simpson

Doug, if you're ever likely to be up this way, or ken someone who might be, Covid Reg's permitting, I'll easily DC test a handful of valves for you. Seeing as you're related to Jock Tamson.
As GJ says, some Eastern European valves don't reach the GEC spec. for the likes of KT's & similar O/P valves.

Regards, David

Thanks for your kind offer David, actually it's about time I took the SAAB for a good run, hardly done any miles the last 2 years.

The box came with a Mullard 1956 ECC83 (mC1 revision long plates - holy grail for audio-eejits) and a Brimar 12AX7 with long black plates.

I'll test them in a simple circuit and then can select a few for a test on your calibrated equipment.

Doug.

[Peter F4VSA]

The thought that brown paper helps stop gamma rays, most amusing

[Radio Wrangler]

Originally Posted by dougietamson

I was given a box of approx 100 valves today, xmas came early

Ah, a few of those appeared on the Edinburgh scene a few weeks ago.

David