Lightbulb of a valve.

[19Seventy7]

I replaced a D77 valve in my GEC, with what was said to be an equivalent by The Valve Museum, an EB91. I switched the set back on and the entire back lit up.

Having a look the valve was more of a lightbulb! I’ve never seen a valve glow so bright before.

Obviously something isn’t quite right so I swapped it back for the original D77 which glows normally.

Are the EB91 and D77 not equivalents?

Not being familiar with valves I wondered if maybe they do glow bright or maybe it’s faulty?

Just thought it was interesting

Thanks
‘77

[paulsherwin]

They are equivalent, but that certainly doesn't look right. Maybe the EB91 is faulty or mislabelled.

Can you see the double diode structure within the valve? I wonder if it's actually a Dx9x with a 1.4V filament.

[ms660]

The EB91 is well known for it's illumination properties at switch on but should settle down very shortly after.

Lawrence.

[agardiner]

I wonder if there is a short between heater and screen. Do you have a valve tester? If not, maybe try another EB91.

[Lloyd 1985]

There are EB91’s in my TV22, and none of them glow that brightly!! Even when the decouplers shorted out! Show us a photo of the valve close up, so we can see what’s in it. Also if you have access to a power supply capable of 6.3V or there abouts, you could try powering the valve heater from that and see how bright it glows.

Regards
Lloyd

[Station X]

What type and model of GEC is it?

[19Seventy7]

Originally Posted by paulsherwin

They are equivalent, but that certainly doesn't look right. Maybe the EB91 is faulty or mislabelled.

Can you see the double diode structure within the valve? I wonder if it's actually a Dx9x with a 1.4V filament.

I did wonder too if it was mislabelled but as it looks the same as the one on The Valve Museum I thought no more of it

The EB91 is well known for it's illumination properties at switch on but should settle down very shortly after.

I thought it may have done that too, but it barely dimmed. I've a couple radios where the valves light up at switch on but fade down quickly, this stayed bright.

I wonder if there is a short between heater and screen. Do you have a valve tester? If not, maybe try another EB91.

Tested with my DMM and doesn't appear to be a short, but unfortunately no valve tester nor another EB91

There are EB91’s in my TV22, and none of them glow that brightly!! Even when the decouplers shorted out! Show us a photo of the valve close up, so we can see what’s in it. Also if you have access to a power supply capable of 6.3V or there abouts, you could try powering the valve heater from that and see how bright it glows.

That's fascinating really, I'm surprised it didn't go O/C or something really considering how bright it was, the photos don't really do justice.

I tried taking some photos but my phone just didn't like it. It was either blurry or grainy so the photos are useless, but it looks identical to the one here if that helps.

No power supply either at the moment, would like to get one though

What type and model of GEC is it?

It's a GEC BT318, thread's here if you're interested. I started from page 3 as thats where the interesting bits are.

Thanks all
'77

[agardiner]

Happy to test the valve for you if you would like to send it. (tester, not a set)

[19Seventy7]

Thank you, I'll take you up on that offer if you wouldn't mind, just out of curiosity. Not sure when I can post it but it wont be too long.

Thanks
'77

[agardiner]

Will PM you details.

[6SN7WGTB]

If not too late to the party, isn't the EB91susceptible to heater-to-cathode leakage?

Not quite sure that would make it glow like a bulb however.

[ms660]

Originally Posted by 6SN7WGTB

If not too late to the party, isn't the EB91susceptible to heater-to-cathode leakage?

Quite a few of the ones I came across in TV's sure did.

Lawrence.

[The Philpott]

Recommend if you post a valve and choose to put it in a stout cardboard tube, it works out cheaper if you then put the tube inside a square or oblong box! Having seen the sorting hubs the conclusion i came to is that poster tubes cause problems on the conveyor belts and have to travel a different path.
Dave

[JonSnell]

As the valve is 17mm diameter, I put this size in a couple of inches of 3/4" or 18mm plastic water pipe.
Keeps them safe.

[John_BS]

I have a large number of 6AL5's if you need any more.
John

[19Seventy7]

Originally Posted by The Philpott

Recommend if you post a valve and choose to put it in a stout cardboard tube, it works out cheaper if you then put the tube inside a square or oblong box! Having seen the sorting hubs the conclusion i came to is that poster tubes cause problems on the conveyor belts and have to travel a different path.
Dave

As the valve is 17mm diameter, I put this size in a couple of inches of 3/4" or 18mm plastic water pipe.
Keeps them safe.

Unfortunately as I got the valve out to post it I dropped it, luckily the glass envelope survived but theres now a few little bits rattling round inside. I ended up connecting 4 AAs together to make a temporary tester and with 6v was still glowing brightly

Good to know though for future reference, so thank you both, will keep that in mind

I have a large number of 6AL5's if you need any more.

Thank you for the offer, I think I'll take you up on that if you don't mind? I'll PM you now

Thanks all
'77