Narrow-Bandwidth Television Association

smeezekitty wrote:12AX7s are only expensive because the audiophools use them but there is nothing particularly special about their characteristics

I quite agree. Same goes for things like 300B output triodes...there are plenty of alternatives, just virtually unknown, waiting to be 'discovered'.

There's a whole plethora of Compactron tubes for example, they're 'different', but they work just the same. For example, a 6C10 is a triple triode exactly the same as a 12AX7/ECC83 except for that additional triode. Bases/sockets can still be obtained. Of course the price is nothing compared to the better known versions...like a small fraction...'cos no-one wants 'em...

Or go with a different heater voltage/current, a 12.6V heater rather than the more usual 6.3V version. e.g. 12AQ5 instead of 6AQ5. Apart from the heater voltage and current, they're identical. Mix and match as you please! If you're building from scratch (generally us lot), why not? But if you're repairing an amp or whatever you really don't have much choice...

Steve A.

https://en.wikipedia.org/wiki/Compactron

http://www.junkbox.com/electronics/Comp ... ndex.shtml

...continuing on from above...

It's probably better to have a basic idea of what you want to do with the tubes, select ones that are available that should do the job at a sane price, then design the circuitry around them. For NBTV/SSTV there's no stringent requirements so there's quite a selection to choose from.

Don't forget to order a few spares...

Steve A.

Here's some of my tubes laying around yes some of the big ones would cost a bit i suppose, i see one dead one in the middle second draw ,not the best way to store them but out of danger most of the time .
There's always some thing collected over 40 years laying around ; )

Yes, it looks like you've got a gassy tube there...it's actually amazing that a metal-to-glass seal can hold that vacuum as long as it does! And not just one, each and every pin plus top cap(s) where fitted. Once upon a time we used to make things that were quality...

You should sit down and make a list of what you have...and give a few of them a birthday treat, a clean, but be careful not to rub off the type number etc...something to do on a wet Melbourne afternoon...plenty of chances there...

Mind you we've had 43mm of rainfall in the last 3 hours...but that's nothing unusual at this time of year...and yep, I got soaked on my bicycle...at least the rain is usually warm here...

The only trouble pre-used tubes is you don't really know their condition until you try them...but what the heck, if you don't try them they're gonna sit in those drawers forever...

Steve A

Steve Anderson wrote:Yes, it looks like you've got a gassy tube there...it's actually amazing that a metal-to-glass seal can hold that vacuum as long as it does! And not just one, each and every pin plus top cap(s) where fitted. Once upon a time we used to make things that were quality...

You should sit down and make a list of what you have...and give a few of them a birthday treat, a clean, but be careful not to rub off the type number etc...something to do on a wet Melbourne afternoon...plenty of chances there...

Steve A

Yes Wet it is ~

Also yes keeping a vacuum for some now a 100 years or more ,mine not so old but well made for sure !

That is the trouble with the numbering type used on valves easy to rub off ,i will look into listing them ,i really don't know what i have got apart from their from a lot of TV''s and radios .

We of cause don't have much of a need for them these days but they are interesting ,last time i used one was making an oscillator in the MHZ range for tuning in to a Crystal's resonance and was surprised it worked first go to me they seem easier to make things with all the high voltage dangers .

When in my teens (half a century ago) I always had more success with tubes than semiconductors, but times and I have had to move on. But when I got my first paying job the fact I knew a bit about tubes landed me the position. Other candidates had no clue what a pentode was. Decca Radar was still using tubes to pulse modulate magnetrons...but not for much longer afterwards...I got my foot in the door just in time...

If you know a youngster who's interested in electronics, steer them in the direction of radar. It encompasses almost everything and all disciplines of electronics I can think of...even today. Magnetrons (a tube) are still used...

Steve A.

A typical modern X-band (around 10GHz) 25kW Magnetron shown below...they haven't changed much since my days...it's roughly a 10cm/4^ cube in size...the mounting plate is the anode which has the waveguide output, the two silicon rubber leads are the heater/cathode where you apply a large (many kV) negative pulse of usually under a microsecond...

The magnetron in your microwave oven is usually around 3GHz (C-band) and designed for CW operation rather than pulse...

Hmmm. Magnetrons in a -oven are oscillating on around 2.45 GHz. That is a small band that is free to radiate High Frequency waves. It is also used by WiFi networks, Bluetooth and other wireless applications. It is also a resonancy frequency of water molecules, so water is dissipating the power of the incoming 13 cm waves. This will say that water in your microwave oven is wery well heated, but also that these waves, when used for communication are damped quite heavily by clouds and other rain. So it is not usefull for larger distances radio communication, but for small distances it is possible.

This is the reason that this band is given free to do all things that will interfere with radio communication. This band: 2.45 MHz is one of those ISM bands, for Industrial (HF welding) Scientific and Medical (HF heating) purposes.

In your microwave oven the tube is driven by single rectified negative going pure AC of about 2.5 kV. So be carefull when you open such a thing. The voltage is even more lethal than the 300 volt DC that you run the vacuum tubes on. And yes, it is a miracle that they keep their vacuum so long. I never had to replace a tube in my WWII radio from 1943. And yes I have replacement valves for all of them, but never had to use one of them. If the "getter", that black or siver mirror on the inside has changed to powdery white, the valve is leaky and you may discard it. At least one of yours in drawer 2 has this.

Steve Anderson wrote:
The first field is all the odd line numbers (1,3,5,7 etc.) followed by all the even line numbers (2,4,6,8 etc.). This has two benefits, though the frame rate is 25Hz (all 625 lines) the flicker rate is 50Hz. It also cuts the bandwidth in half from a pure non-interlaced 625/50Hz display.

It was derived from film projectors in cinemas. Although 35mm movie film is usually 24 frames per second, each frame is shown twice raising the flicker rate to 48Hz, sometimes three times to 72Hz. This is done with a shutter in the light-path synchronised to the film advance mechanism.

It was not. 25 frame rate with interlacing just comes from 50Hz mains. As well as the old 25 and 12,5 without interlacing.

24 for the cinema is nothing but rational. The norm was 16, but nobody respected the norm. So when it was needed to have a new norm for sound films, they asked projectionists around Hollywood what was their usual frame rate. And the results were averaged.

Both are close.
There is something interesting now, the digital cinema projectors are able to project 25 aswell. So there is no point to film at 24 anymore.

Steve Anderson wrote:
Postscript: If you've seen Chris Long's 'Slow NTBV' at half frame rate (6.25Hz frame, 200Hz line) that may be a worthwhile addition to this...I was quite impressed with it. It also means the video bandwidth requirement is halved to around 5kHz, perhaps more so. I wish I could find the link...

Maybe consider seriously my proposal. If done in software it is possible to take low frame rate, such as 6,25, and interpolate new frames in between. Smoothing out the movement.
There is already AI wich does this. I'm not a programmer so i don't know how to do this. All i can do is convert files according to different methods. But it is not in real time. But it actually works.

The goal is a bit different than what you are doing, but it can be another option to it.

Lowtone wrote:It was not. 25 frame rate with interlacing just comes from 50Hz mains. As well as the old 25 and 12,5 without interlacing.

Quite correct. Perhaps I could have expressed it better..."The same concept to reduce flicker as done with movie films." Or something similar. Beyond that there's no real connection between the two outside of this context.

Steve A.

Exactly. 50Hz was chosen by AEG in Germany in 1899 for their generators.