French Valve: Filament Voltage?

[M0TAW Tony]

I have an old Radio Micro triode with intact filament. I want to use it in a one valve cct. At 2v it draws 40mA. I cannot identify the valve - it has a metal B4base, soldered pins and top pip. Question is : is this likely to be a 4v filament valve? I dont want to use the mechanical engineering trick of 'up to sheer and back half a turn' but current seems low at 2v?
Tony

[HamishBoxer]

This could be the french "Bi-Volt" type of which i have but uncertain as to what the voltage(s) are.

Anyone else know?

David

[jhalphen]

Hi Tony,

Please post a photo, i will then inquire on our French NG "Radiofil" & ask the experts for a visual ID of the valve type.

If you want to browse our forums as a reader, it's here:

http://retro-forum.com/

Main site: http://www.radiofil.fr/

If you can manage even pidgin' french, inscribe yourself & post! it's free of course.

PS: over the years, a huge amount of data has been scanned and made available for sale as club-member DVDs: radios, French, European, Philips, USA, test gear, military stuff, radio advertising, etc. - browse the section, you might find something you like!

Best Regards

jhalphen
Paris/France

[AVO_VCM163]

The Radio Micro usually has no other designation

It is most likely rated at 3 to 4v at 60mA.
See http://www.radiomuseum.org/tubes/tub...dio_micro.html
for more details of this and other types that could apply.

This type of valve should always be used with an adjustable series resistance to operate the filament at the minimum current acceptable for the required gain.

Roy

[paulsherwin]

I would hesitate before using a rare valve like this in a one valve radio project. There are plenty of later 1.4V filament valves to choose from which will work just as well (possibly even better.)

[M0TAW Tony]

Thanks to all who replied.
I am making a set in the style of 1920s so a B7G 1T4 would not be appropriate. A couple of images are attached the valve is 106 mm high and diameter of 35mm.
Tony

[AVO_VCM163]

This would have been a typical French radio using this type of valve from about 1925.

But get it operational with cheaper valves first of all!

Roy

[jhalphen]

Hi Tony,

Thanks! for the photos, i brightened them up a bit then posted a request for ID on RadioFil.

You can follow the topic here:

http://retro-forum.com/viewtopic.php?f=2&t=234896

I will translate interesting replies for you,

Best Regards

jhalphen
Paris/France

[jhalphen]

Hi Tony,

Are you following the thread about your valve on RadioFil?.

There have been several answers & photos, several seem to agree that your valve would be R-36:

http://retro-forum.com/viewtopic.php?f=2&t=234896

If understanding the comments is difficult, just holler!

Best Regards

jhalphen
Paris/France

[M0TAW Tony]

Hi Jerome
Yes, many thanks to you and all the French contributors. A picture tells a thousand words but I also made sense of the texts. In searching not only for the type/designation I am trying to find the filament rating. One of your contributors suggests 4V. This seems to be in line with a helpful reply I received from Andy Cowley who has a picture on his website of the valve (and also referred to by one of your respondents)
I quote from his reply as it may be of general interest:

"
This is probably a bright emitter, but possibly a 'dull'. Almost
certainly not an oxide cathode. French valves of this date are
_usually_ designed to run off 2 lead-acid cells so 4 volts. Even
a dull emitter lights up like a torch bulb, yellowish but still
quite bright. Brights are brighter (whiter) than an ordinary tungsten
light bulb.

Early valves (before 1923 or so) were almost all 4 or 6 volt. Single
cell (2v) valves only became popular after dulls took over.

Brights draw between 500 and 800 mA. Most early dulls draw 200 - 300 mA,
later ones got this to below 100 mA. 4 volt brights were basically all 'R'
types or pretty close. When used to transmit they were run on 6V at over
an amp, but with a much reduced life. This is very bad for dulls, as the
thorium on the surface of the filament will evaporate and they will have
to be reconditioned to regain emission. Reconditioning involves running
at hot bright temperature 2800k for 1 minute, then at a lower but higher
than design voltage so the filament is at around 2300K for 10-15 minutes.
Proper run temperature is around 1800K for dulls.

If you really want to get it working I'd try around 3.5 V and 200-300 mA,
assuming it is a dull. This won't harm a bright at all.

I suspect though that it will need over 500mA and around 4 volts to work
properly. "

Thank you again for being so helpful
merci beaucoup
Tony

[jhalphen]

Hi Tony,

Thanks! for the long explanation & i'm glad that RadioFil members could help out.

About "bright emitters", i don't know if this is the truth or an "urban legend": during WWI operating radio tubes were so bright that at night they would signal the position of the soldiers and hence attract ennemy fire, therefore the army requested that new tubes be supplied with the now famous deep blue coating to reduce light emission.

Good luck with your filament voltage tests,

Best Regards

jhalphen
Paris/France

[paulsherwin]

Originally Posted by M0TAW Tony

I am making a set in the style of 1920s so a B7G 1T4 would not be appropriate.

There are a number of octal valves which you could use - these are rarer than the B7G types and still out of period, but they would look fine to all but an expert. I'm thinking of the DF33/1N5 or DAC32.