Soviet East German Radio

[Terry]

The way the valve is graphically represented in the Philips valve data sheet sums it all up.

Yes and no.

To me, the clearest symbol is the one produced by Mullard and I have a copy of a data book around somewhere but not easily to hand at the moment.

The point is that there is no absolute standard here - thus the blobs for the cathodes in some European versions - or even the layout.

The clearest versions, in fact, show only two cathodes which simplifies the symbol and relates to the two separate cathode pins: see here and here.

Even clearer are symbols that disregard the pin layout but just show pin numbers for each electrode, thus eliminating all the connecting wire floating around inside the symbol.

To me, the important points about any symbol in a diagram are simplicity and clarity. Remember, we only need to know how the valve works in practice, not the finer points of its construction. 

If you disagree with that, why not include the mica supports, getter and anything else you can think of!

[pwdrive]

In the photo's I'm looking at of the valve there are 3 separate structures in it so must be three separate cathodes, the cathodes heaters are connected in series, the Philips data sheet and photo's of the valve seem to me to confirm that as per photo's and data here:

http://www.r-type.org/exhib/abc0014.htm

Lawrence.

[pwdrive]

Then there's some service data that imply 4 separate cathodes in the schematic but 2 separate cathodes on the valves pinout diagram:

https://www.doctsf.com/documents/schemat.../VHF71.PDF

Lawrence.

[Terry]

In the photo's I'm looking at of the valve there are 3 separate structures in it so must be three separate cathodes

Yes, but that kind of information is completely useless to someone who simply wants to use the valve in a design or to service equipment using it.

Anymore than the composition of the glass, the grade of mica or what metal the anode is made of is essential knowledge.

If you want to manufacture your own version of the valve, however, your requirements will be differ from those of the normal user.

[pwdrive]

I was just trying to help NM re his post #204 and post#207, The link I gave for the Philips valve data should help to clear up any confusion he had over the number of cathodes in the EABC80, the pinout diagram in that data sheet accurately reflects the valves electrode structure and any internal connections, not a lot else I can say.

Lawrence.

[Nowhere-Man]

I think the Foster Seeley diagram I have is what misled me a little. Last night I located a discriminator circuit closer to the design. After that, Lawrence's explanation made perfect sense. So, I figure so far as valve radio goes I can understand typical circuits. However, as to transistor circuits I understand very little.
I am officially on break from radio work due to urgent work to finish my boat although the weather has literally grounded me since the weekend.
At night I've been doing some stuff I think Lawrence would relate to in interest. I wanted to get a better understanding of modulation so was going over modulation percentage and PM plus FM. The very first introduction I had to this was via Chas Miller's beginner article but, when you start, it's hard to really grasp the concepts. Sometimes I go back to older stuff like push pull. And here's the very simple thing I learned: The power output of a valve will always be less efficient than the input because energy is lost in the plate heat and impedance. It's a simple but interesting point - especially when you consider the 40's engineers struggled over battery efficiency.

[ppppenguin]

The output power will always be less than the power input from the supply simply because of conservation of energy.

Beyond that there are limitations for each type of circuit. For example a Class A amplifier where the valve(s) or transistor(s) are always conducting can never be more than 50% effiicient. That's at full output. At zero output the efficiency is zero. Class B is much better and some switching amplifiers (class D etc) can approach 100% efficiency.

Finally no amplifier will achieve the theoretical maximum effiiciency for its type due to imperfect components. Such as ordinary ohmic losses in the output transformer.

This article is quite good: http://www.audioholics.com/audio-amplifi...er-classes

[Nowhere-Man]

Funny but I have to keep going back to stuff I thought I'd learned so amplification was on the agenda. Interesting point about push pull for me was the output waveform restores the original imput waveform. The imput being the AC on the anodes of the two power valves.
As to the other point Lawrence is very helpful and I find his advice always fits nicely with any other references I find. I am almost there now with the Saalburg schematic. Only practical thing I could do with is a decent diagram of a pushbutton waveband mechanism (including possibe pics). I couldn't find much info online at all. Pics of one disassembled would be useful.

[Nowhere-Man]

My boat project work has kept me busy most days. Carpentry is clearly a skill that takes some practise and I'm forced to try and knock frames together and so on.
At nights I've been looking at reactance FM modulation and limiter discrimination circuits. I must say my ARRL 1960 book is often pretty poor at explaining this. Many times I seek a tutorial online and you get some clear explanations. The circuit of the limiter discriminator in my book has an IF of 455 KHz. Actually I crammed as much as I can on FM and learned new stuff. Very often I will go right back to basic beginner material and may find better understanding of some of it. One very basic concept I revised is phase. The ARRL does have a terrific graph that shows how capacitor current varies from voltage peaks.

[Nowhere-Man]

Last night I had an unusual and unsettling dream about this radio. In the dream I'd had it switched on for a while and then I saw smoke billowing out. Then actual fire! In the dream I was then in a panic the fire would spread so i filled a bucket of water and threw it over the radio. Then there was just a clapped out shell left. When I woke up later I was glad to know it had all been a dream. A bit like the Dallas episode. Maybe the dream was triggered by an experience of seeing a Bush TV set go up in smoke many years ago.