Building a Radio from Junk

[Ed_Dinning]

Hi Audion, you need to build a Sussex valve tester, or possibly a simple version of it. That will sort the valves nicely.
You will probably find that the "receiver" valves from your collection easy to identify as they are the smaller ones. It should then be easy to identify triodes or pentodes as well as double valves by inspection. If you are only after a low power set then you should find plenty of valves that will work, even at 30v HT.

Ed

[AC/HL]

One off-topic post deleted

[julie_m]

Would this procedure work for identifying the electrodes of a valve?

1. Apply power to heater. (Start with a low voltage, obviously, and work upwards gradually until the glowing filament looks about right; pay special attention to 6.3 V, 100 mA and 300 mA.)
2. Apply HT of about 50 V through a 47 kΩ resistor (so as to limit current to not much more than 1 mA) and micro / milliammeter between each pair of (non-heater) pins in turn.
3. If you have the negative lead on the cathode and the positive lead on the anode or any grid, current will flow.
4. Don't leave the valve in this state for long, as playing at being anodes probably won't do the grids any favours.
5. Having identified the cathode, now keep the negative lead of the HT supply here.
6. Arrange a negative supply (positive to cathode) of about 15 V, via a resistor of about 1 MΩ.
7. While current is flowing from "somewhere" to the cathode, apply negative supply to each (non-heater) pin in turn.
8. If you have the negative supply connected to a lower (i.e., nearer the cathode) grid than the positive supply, the HT current will be cut off, by normal valve action.
9. A pin where current cannot be cut off by applying negative volts to any other pin, must be the first (control) grid.
10. A pin that cannot cut off current to any other pin by having negative volts applied to it, must be an anode.

It will only break down where two grids share a pin, because the lower grid will cut off the current flow. For instance if you have something that tests as a hexode with G2 and G4 common, you will only be able to identify K, G1, G2, G3 and A. But then, it should be possible to work out the final details from a valve data book.

[audion_1908]

thanks for the info ajs_derby, I was thinking of not using anything with more grids then a pentode!!! but I will see.

I have been looking at 1920 valve data sheets, and they used -15v to -30v grid bias, with grid bias batterys or grid leak resisters, and like more modern valves the higher the HT supply the higher the needed GB supply, the problem I have is that the TV valve I have been looking at use around 3v with an HT supply of 250v, so for an HT supply of only 25v the GB voltage would be under 1v, so to low to use a grid bias battery and maybe to temperamental for a grid leak resister? I will have to test it, but may have to use a cathode bias resister, but 0.3V to 1V is not much to lose off the HT supply

[Herald1360]

A low GB voltage doesn't preclude using a battery to supply it- simply reduce the battery voltage to what is required with a potential divider- it need only take a few microamps from the battery.

[G8UWM-MildMartin]

Are you absolutely determined to use the 24V for HT, or would you be open to suggestions of using a dynamotor or, more in keeping with the period, a vibrator (or solid-state replacement, possibly in an original-looking can) and transformer to make the project much easier? I believe it'd be a good trade-off against the heater currents required to get even mediocre performance, particularly with the necessary multiple valves in the output stage, otherwise.

[audion_1908]

Originally Posted by Herald1360

A low GB voltage doesn't preclude using a battery to supply it- simply reduce the battery voltage to what is required with a potential divider- it need only take a few microamps from the battery.

the problem is to get a stable output voltage the potential divider has to sink 10X the current the load will use, so the grid bias battery will run down 11 times faster, and will need a switch, ganged the the main on/off switch or a relays? but is a relay failed the valve would get damaged.

I have been looking at audio output transformers, it looks like for 3 watts push pull a power transformer with working dual 120v primary's, and dual 7v or 8v ish secondary's rated at 50va would work ok, and a 20VA may work, and 12VA with some possible distortion, it looks like the main difference between power transformer and audio output transformer is slightly thinner lamentations, and totally different coil winding patten! so it looks like I need to find a working power transformer with the correct specs, or a 0.4 to 1kg dead power transformer or better an audio transformer that is 0.4kg to 1kg, and rewind it, and I think as I will need 6 to 8 valves to drive the transformer, the equivalent valve plate resistance will be that much lower! so make the power transformer work better at audio, and easier to wind a custom transformer.
I would also need a dead small power 6VA or lower power transformer or better a dead small audio transformer to rewind to be used as a phase splitting transformer.

[Radio Wrangler]

A dynamotor or vibrator supply would add inefficiency, but then building an audio output stage with multiple output valves is not going to be efficient either, and the heater power consumption will be high.

The original post said that this was going to run from an off-grid supply whose voltage can wander somewhat. If the off-grid supply has other uses like charging batteries for lighting, then making a more efficient radio will leave more energy for those uses and self-sufficiency can be achieved on days with less wind or less sun.

This sounds like a good application for doing things with transistors. Nice vintage ones of course.

David

[audion_1908]

Originally Posted by G8UWM-MildMartin

Are you absolutely determined to use the 24V for HT, or would you be open to suggestions of using a dynamotor or, more in keeping with the period, a vibrator (or solid-state replacement, possibly in an original-looking can) and transformer to make the project much easier? I believe it'd be a good trade-off against the heater currents required to get even mediocre performance, particularly with the necessary multiple valves in the output stage, otherwise.

the off grid supply is only 12v at the moment! but I will be upgrading it to 24v later this year, I am trying to avoid using semiconductors as that would make it to easy, and I dont think I could find a working vibrator in a junk pile and from what I have read they where RF and acoustically noisy, and had to be shielded and filtered, a diy or ex military dynamotor could be interesting! and its only the audio output that really needs the normal HT voltage.

I have a non working dynamotor in storage, it may be 24v? but is a dead dynamotor junk?

[audion_1908]

Originally Posted by G8UWM-MildMartin

Are you absolutely determined to use the 24V for HT, or would you be open to suggestions of using a dynamotor or, more in keeping with the period, a vibrator (or solid-state replacement, possibly in an original-looking can) and transformer to make the project much easier? I believe it'd be a good trade-off against the heater currents required to get even mediocre performance, particularly with the necessary multiple valves in the output stage, otherwise.

it would need to run off the 24v as everything is ecofriendly when possible, there is a grid 230v supply but that is manly for the fridges, but I will not use that, and the 24v is generated in site using the wing and sun, all the struchers are tempery, and set up each year, the radio would be run of the dc lighting circuit and have maybe 2 or 3 amps, but as I am in charge of the dc power system I could put in a circuit just for the radio, so I would have 5 amps maybe more, in a few years there will be a small hydro generator and it will have a 320v dc output, but the voltage will fluctuate up to 30v as loads switch on and off?

maybe I could use a dynamotor for now if I have a 24v one, and see what its like in the 320v supply later, maybe I could buffer the 320v~ dc supply with a diode and a large capacitor, how would the upto 30v fluctuations effect the audio?

[audion_1908]

Originally Posted by Radio Wrangler

This sounds like a good application for doing things with transistors. Nice vintage ones of course.

The off-grid supply charges 2 large lead acid batterys and runs all the sites lighting, charges all phones, and when sunny charges most of the laptops and runs 2 cool boxes, valves are not the best thing for the job but I think they are more interesting to look at and work with than vintage transistors

[Radio Wrangler]

OK, then there's a half-way stage with a transistor inverter making HT for normal valves. That way you get reasonable efficiency to HT, and you don't need multiple heaters in multiple valves to get reasonable audio output from 24V. You get the valves to look at, and more charge in your batteries.

David

[Herald1360]

Originally Posted by audion_1908

the problem is to get a stable output voltage the potential divider has to sink 10X the current the load will use, so the grid bias battery will run down 11 times faster, and will need a switch, ganged the the main on/off switch or a relays? but is a relay failed the valve would get damaged.

Isn't this rather straining at a gnat? If a valve requires 1V neg bias and is running in class A, it won't require any current from the bias supply. Even with a 10uA load, a C size alkaline 5AH cell will theoretically run continuously for around 500,000 hours or 57 years. This is clearly nonsense- effectively the cell will simply last for rather longer than its shelf life and may well never need to be replaced. You could probably get all the bias you needed from a stack of "copper" and "silver" coins with vinegary paper separators......

If you lost the bias altogether, at 24-30V HT I very much doubt whether any valve would be harmed either.

[audion_1908]

I have remembered I have 2 large transformers I got when I was at school! they where in two overhead projectors that where dumped, I still have them somewhere? the output was 24v at 10 amps and as high output filament lamps are sensitive the voltage the transformers could be good quality, and I think I know where they are, and would be useful to test the junk radio!

also I found an old post by chance, any one know what year RSGB Handbook it was in or have a copy!

"from G6Tanuki
I've got somewhere a WWII-era appendix to the RSGB Handbook, titled something like "A radio vade-mecum" which was clearly aimed at 'upgrading' amateurs to Army field-signallers, it's full of 'tips and tricks' like the accumulators-in-series-with-DC-mains-appliances, and a crude way (involving using a rapidly waggled pencil as a stroboscope) to tell if the mains you've come across on accessing a "forward position" is AC or DC.

It's really rather an intriguing read, including things like "You have been given a valve from a captured enemy radio. How can you determine the pinouts and likely working conditions to determine if it is a suitable substitute for the damaged one in your radio?"
G6Tanuki."

https://www.vintage-radio.net/forum/...9155&styleid=2

any one know which year of RadCom it was or if it was somewhere else?

Originally Posted by M0ALK Richard

Back in the 1980's (I think) in RadCom there was a short article where someone explained how to identify all of the pins in a valve including the grids by using suitable power supplies. Can anyone remember which issue it appeared in?

[audion_1908]

I have found a dynamotor! "rotary converter Type 52. 24V in 250@50mA and 6.3@2.5A out (DC of course)" I am picking it up in wendsday! as only the audio output valves need the full HT, I have 12.5 watts supply for the audio!! from what I have read dynamoters are 40% efficient at best! but I now only need 2 audio output valves not 6 or 8 or more!
https://www.vintage-radio.net/forum/...d.php?p=571966

now all I have to do is find a maintenance manual for the rotary converter Type 52, and spare brushed and grease!
the dynamotor looks great! but what did the end caps look like?

[kalee20]

Can you not use your off-line supply to charge a few more small 24V batteries? Then when you want to use your radio, connect them in series with the off-line supply.

If you want a bit of negative bias, consider an EB91 / 6AL5 / D77 double diode. Energise the heaters, connect the diodes in series, and you'll find you get over a volt of floating negative bias. How stable this will be over time,Idon't know - but it will be fun finding out! You could even use a diode-strapped ECC82.

[GrimJosef]

Originally Posted by audion_1908

... as only the audio output valves need the full HT, I have 12.5 watts supply for the audio!!

If you plan to share the room with the dynamotor you might find you need plenty of audio so you can hear it above the dynamotor. In a WWII military aircraft or a tank everyone would have been on headphones and the engine noise plus intermittent gunfire/bombing would have been loud enough that a bit extra from a dyno woulndn't have been obtrusive. But that's not always the case in a domestic setting.

Cheers,

GJ

[audion_1908]

Originally Posted by kalee20

Can you not use your off-line supply to charge a few more small 24V batteries? Then when you want to use your radio, connect them in series with the off-line supply.

If you want a bit of negative bias, consider an EB91 / 6AL5 / D77 double diode. Energise the heaters, connect the diodes in series, and you'll find you get over a volt of floating negative bias. How stable this will be over time,Idon't know - but it will be fun finding out! You could even use a diode-strapped ECC82.

I do not understand about how you use the valve diodes to make the negative bias supply? and anyway it looks like the TV valves would need under 1 volt bias supply not the 15 to 30 of the old 1920 valves! for instance the Z77 pentode from 1947 at full HT of 250v it needs 2v bias, so at 24v I think it would need 0.2v bias supply, so if I use the simple cathode resister then 0.83% of the HT will be lost in the cathode resister, I can live with that, especially at its not on the audio output valves that now have 280v supply!

I have read about valve TV using the heater chain to derive there bias supply!

the problem with extra batterys, is they are heavy expensive and a lead acid battery would get destroyed by not being charged 10~ months of the year when in storage, and if I did add 2 small sealed lead acid batterys I would still only have 48v HT, 4 battery = 72V, and each batter would need its own dc to dc converter and 3 stage smart charger!

I have received a box of junk valves today, and and some other parts!

[audion_1908]

Originally Posted by GrimJosef

If you plan to share the room with the dynamotor you might find you need plenty of audio so you can hear it above the dynamotor

from what I have seen the WWII military dynamotors where not acoustically shielded, they where in a steel box at best or just bolted to the back of the radio, and GrimJosef you are right it did not matter to them that it was noisy, but I watched some youtube clips of running dynamotors, and some are very loud, but I have found 3 home radios sold in the 1930's that used dynamotors!

The first 2 are 32v farm radios the Delco RA-3 (table model) and RB-3 (floor model) in 1932/31, the motor/generator set was known as the Electrifier, The Electrifier ran off 32 VDC and produced 140 & 70 VDC.
I could put the dynamotor in an external sound deadened box like the Electrifier!
http://kd4hsh.homestead.com/Delco_RA-3_1.html

[G6Tanuki]

Originally Posted by audion_1908

also I found an old post by chance, any one know what year RSGB Handbook it was in or have a copy!

It was the "Radio Handbook Supplement - companion to the Amateur Radio Handbook" - my copy doesn't have a publication date but it's definitely WWII-era as it has my late father's Army serial-number and mentions the Royal Army Ordnance Corps [in which he was enrolled before being moved into REME at its formation].

At risk of violating copyright, I might be able to photograph the relevant pages.