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Old 10th Apr 2014, 12:44 am   #1
audion_1908
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Default Building a Radio from Junk

I have a lot of boxes of valves most ex TV valves, some are unlabeled as it has rubbed off long ago, I can not resist the large boxes of mixed valves! lol
But some I can just make it out and I use a permanent marker to re-write the part number, and some viably look the same as others lose in the same box so are probably the same~ but what about the completely unknown ones? how should I electrically test them to work out what type they are, eg RF audio, mixer, and work out the pin out? triodes I would think would be easy, but what about the others!!!

Some time I want to build a junk radio, using parts I have made or are worthless, I am good at making capacitors and resisters and air core inductors are easy, the supply will be 24v DC from a off grid system, so probably fely clean power, but the supply could go from 24v to 28v, and the supply cables are a mix of 1.5mm and 2.5mm in a basic ring main in a field, and radials!
for the antenna there are some long steel cables on wooden posts I can use as an antenna, the DC power system must not be earthed for safety resions, but the first steel cable is about 1ft off the ground, maybe could be a virtual ground? the other about 6ft and the top one 7 or 8ft high and about the cables are about 180 meters long, and there is a second parallel set of steel cables about 6ft beside the first, I can connect to the steel wire in the middle but probable not be allowed to cut it, and they are about 1cm thick! it will be only used in summer so the wood should be fely dry.
24v is very low for ht but with a clever circuit it would be fine, and if the valves are 6.3v I can string the heaters in strings of 4, but often TV valves had odd heater voltages for series heaters, for 0.2 or 0.3amp strings

I plan to build a 1930 cathedral/Tombstone style wooden case for the radio, I will also build the valve sockets as well, as I did that when I was starting with valve radios years ago and did not have any valve sockets and only had 1 valve! and the radio worked well but the frequency was way to low, lol I also want to have a go and building the transformers!
I will probable have 2 or 3 amps max at 24v dc to run the radio so I could use a lot of valves, 20 to possibly up to 60!! (3 amp / 0.2A = 15 X 4 (for 6.3v heaters) = 60 valves!)
It can have base upto 3ft by 2ft and 3ft high, and has to be under 30kg, and lift able by one person, my version of the USA 32v farm radios!
I will use new solder, wood glue, epoxy glue, unless I can get them free

I have boxes of 7 and 9 pin glass base 1940 to 1960~ valves that should yield plenty of unlabeled or out of speck valves!
also dim or dead magic eye tubes could still have a usable triode! as I think that they run the triode hard to get the phosphor-coated plate to light up, so a magic eye tube may be a good audio preamp?
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Old 10th Apr 2014, 8:38 am   #2
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Default Re: How do I identify unlabeled valves? to build junk radio

The easiest pins are the heaters, you can use an ohm meter to find out which pins are for the heaters. If the envelope is clear you might be able to follow the pins for anode and cathode, but with the grids you might be stuffed. However, if you have determined the heaters, apply a dc voltage to 300 mA, note the applied voltage and then go through the data sheets, you might be able to find out the valve code this way. Time consuming though.

You have an ambitious project ahead, please keep us up to date, interesting to know how you progress.
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Old 10th Apr 2014, 9:30 am   #3
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Default Re: How do I identify unlabelled valves to build junk radio?

Worth perusing the excellent r-type.org which has photos of individual valves that may help.

Part of the fun of junk box projects is not being tied down to using a particular valve in its expected role. Even TV manufacturers have used tuner valves in timebases and other RF valves in frame output circuits !

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Old 10th Apr 2014, 9:32 am   #4
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Default Re: How do I identify unlabelled valves to build junk radio?

If you have a local very old TV engineer (like me) he (or she) will probably be able to identify most by looking at them.

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Old 10th Apr 2014, 10:28 am   #5
audion_1908
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Default Re: How do I identify unlabelled valves to build junk radio?

about 10 yeas ago I used an IF TV valve with a 9v heater as a single ended valve audio amp as an experiment, I did not even have a valve socket for it the time and used crocodile clip leads, and biased at 50% of its max current, it sounded great!

Quote:
Originally Posted by ValvoStef View Post
However, if you have determined the heaters, apply a dc voltage to 300 mA, note the applied voltage and then go through the data sheets, you might be able to find out the valve code this way.
some TV valves are 200ma, I have loads of Z77 and EF91 they are the same valve just different makers, and are full pentodes with each element to a separate pin.
I have been thinking, I could practice testing the Z77's and also a build a prototype using them, the heater resistance will change with heat, so if I know the Z77 heaters resistance cold and I know it takes 6.3v 0.3amps, the online Ohm's Law Calculator tells me the hot heater resistance is 21ohm and it uses 1.89 Watts, and I know all indirectly heated valves run at the same temperature, I should be able to use that data to work out any valves amp rating that will lead to its voltage, them found to the closest whole number.

and I dont think I need to know the part number, but it would make things much easier, all I need it the heater specs, pin out and what type of valve it it, and max emission, and a basic curve trace, as I change the grid voltage? as I will be running the HT way under max.

Could you use a pentode or tetrode with all grids tied together with a 24V HT supply maybe for audio output?

there is the Tube Data Sheet Locator at
http://tdsl.duncanamps.com/
it is a great idea the have a loo in the valve at the grids!

I think the first thing to work on is the audio stage, and it can be tested with a old Walkman as the audio source, my Marconi 557 radio has 3 watts max audio output, I think it would take about 13 Z77 to get 3 watts! but it is an RF amp valve.

What is the needed audio output wattage for a medium sized room? the room is a large octagon canves strucher with a heavy wood frame with a diameter of about 26 feet or 7 metres, I will have to go with the more efficient push pull, with at least 4 valves in push pull
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Old 10th Apr 2014, 12:10 pm   #6
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Default Re: How do I identify unlabelled valves to build junk radio?

Wasn't the old Farm Supply 32 Vac? That would make any conventional radio feasible after the PSU transformer.

You should get a bit of anode current with only 24V on the anode and screen of an EF80 and four heaters in series will add up to about right. You'll also have plenty in any random assortment of TV valves!

Driving anything other than headphones will be a challenge...... for reasonable listening you'll need 200mW or so audio (think old transistor radio).
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Old 10th Apr 2014, 12:20 pm   #7
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Default Re: How do I identify unlabelled valves to build junk radio?

some basic calculations form say 2 watts should do it? but maybe 8 watts, logrithmic scales get me!!!
http://www.crownaudio.com/elect-pwr-req.htm
http://www.colomar.com/Shavano/spl.html
so maybe I should aim for 3 watts?
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Old 10th Apr 2014, 1:09 pm   #8
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Default Re: How do I identify unlabelled valves to build junk radio?

Quote:
Originally Posted by Herald1360 View Post
Wasn't the old Farm Supply 32 Vac? That would make any conventional radio feasible after the PSU transformer.
Farm supplies were generally 32VDC; some of the radios designed for this needed lots of valves [six low-impedance triodes in push-pull-parallel!] to get adequate audio-output.

One issue was grid-bias: with only 32V you don't want to waste any of those precious volts by using cathode-bias resistors. So some "farm radios" still had a grid-bias battery. The current taken from this was so low that it lasted for years.

See here: http://www.doctordelco.com/Dr._Delco...lco-Light.html for some history of 32V DC farm supplies.
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Old 10th Apr 2014, 1:16 pm   #9
audion_1908
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Default Re: How do I identify unlabelled valves to build junk radio?

Quote:
Originally Posted by Herald1360 View Post
Wasn't the old Farm Supply 32 Vac? That would make any conventional radio feasible after the PSU transformer.
The 32v DC system was used in the USA on farms upto the late 1930 ealy 40s, the 32v was made up of a string of large glass 2v lead acid cells, and was charged with a automatic delco light plant, and or with wind chargers, and there was a large array of appliances machines and gadgets for the farm and home available, but it was DC becose of the batterys, vibrator inverters where expensive and unreliable and lineted to low power high frequence 400hz~, and not reparable so radios where designed and sold to use 32v for heater and HT, there was rotary converters, think moter and generater merged, I think they where expensive and 60% efficient and only used by the military.

I think a standard single ended an RF valve on 24v HT could put a max of 0.12w or 120mw, but some of the valves are power valves for audio or coil deflection!

Quote:
Originally Posted by G6Tanuki View Post
One issue was grid-bias: with only 32V you don't want to waste any of those precious volts by using cathode-bias resistors.
yes the Z77 would waste 8.3% of the HT using a cathode-bias resistor!

I could use a grid-bias battery but when it gowns flat or leaks, the radio will work but destroy the valves, what about grid leak resisters like the 1920s?
in the 1920/30's small cheap dual range volt meters where popular to test HT LT and GB batterys, but they where not very accurate, they look like round pocket watches!

I will look into the 32v farm radio audio output, but the one I was looking at was 0.4w max!
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Old 10th Apr 2014, 1:38 pm   #10
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Default Re: How do I identify unlabelled valves to build junk radio?

Quote:
Originally Posted by audion_1908 View Post
what about grid leak resisters like the 1920s?
Some valves were designed to use very high value (5 or 10MOhms) grid-leaks and they provided their own bias by way of the "contact potential" generated when different metlas are at different temperatures.

Whether this would work with typical AC-heater indirectly-heated TV valves I'm not sure - I've only ever come across it being used with small-signal battery-type valves.
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Old 10th Apr 2014, 2:07 pm   #11
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Default Re: How do I identify unlabelled valves to build junk radio?

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?
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Old 10th Apr 2014, 2:09 pm   #12
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Default Re: How do I identify unlabelled valves to build junk radio?

There was a curious, neat little aeronautical beacon receiver (200kHz- 400kHz sort of range, IIRC, ie long wave region), the BC1206, that was designed to operate from 28V nominal aircraft supplies. It used this 28V directly for both series-connected heaters and HT supply (or A and B, as the US designers would doubtless have said). With no dynamotor, it was very compact, as suited a side console in something like a Mustang. The circuitry was very "mainstream", too- just goes to show what valves can do with rather less volts than we're accustomed to.
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Old 10th Apr 2014, 2:31 pm   #13
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Default Re: How do I identify unlabelled valves to build junk radio?

I will have to look into it but the tv valves for the deflection coil may be great, low inpedence and hi output but, by basic calcuation shows I will still need 6 to 8 min for the audio output! Maybe I will have to dig into my labled but not worth much tv valves.
The old 1920 valves needed a large grid bias voltage, I think upto 15v and the newer valves need 2v to 3v grid bios voltage, so the resister value is much more critecal, it will probably work, but just be more tricy to set up!
It looks like I am up to about 14 valves! For my radio, that beats my 2 valve regen and 4 valve allwave radios

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Old 10th Apr 2014, 3:09 pm   #14
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Default Re: How do I identify unlabelled valves to build junk radio?

I do not think that zero bias will generate enough current to damage the valve at low voltages.
You could use an EF91 or EF80 for most of the stages. I think the EF80 has an internal screen which may help.
For power, perhaps a PL509 would work on a lowish heater voltage. To pull a decent current, you may need a positive grid voltage which would need considerable drive power.
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Old 10th Apr 2014, 3:15 pm   #15
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Default Re: How do I identify unlabelled valves to build junk radio?

It would not take long to rige up a simple 2 valve regen radio, to test how well tv valves work with a grid leak on 24v HT, I don't think the low HT will efect thes gridleak bias from working? Years ago, I powed up a valve with a grid leak bias resister to show my dad, and it managed to pull the grid down below ground! But I think it would work beter with a valve that wants a large grid bias voltage, and easyer to setup, some data sheets have the max grid leak bias resister, so maybe exses voltage can damage the valve, or make it oprate strangly? valves used computer did not last long as most spent nealy all there time off and the cathode got poisened?

I will have to look up thes web site when I am on a larger computer and not my phone, but there was a trick, where you conected the control grid to ht to exelerate the eletron stream, and used the last screen grid as the control grid, I don't remember what hapend to the middel grid? But this trick was used when there was only 12v or 6v for the ht, I think one migit radio used 3v ht, and ran a earpeace!
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Old 10th Apr 2014, 3:37 pm   #16
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Default Re: How do I identify unlabelled valves to build junk radio?

Quote:
Originally Posted by audion_1908 View Post
I will have to look up thes web site when I am on a larger computer and not my phone, but there was a trick, where you conected the control grid to ht to exelerate the eletron stream, and used the last screen grid as the control grid, I don't remember what hapend to the middel grid? But this trick was used when there was only 12v or 6v for the ht, I think one migit radio used 3v ht, and ran a earpeace!
You could experiment with the "Space Charge" approach - see here:

http://www.junkbox.com/electronics/l...agetubes.shtml
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Old 10th Apr 2014, 4:08 pm   #17
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Default Re: How do I identify unlabeled valves? to build junk radio

Quote:
Originally Posted by audion_1908 View Post
some TV valves are 200ma ...
Some double triodes (ECC81, ECC82, ECC83 for example) are only 150mA between pins 4 and 5. It would be a shame to blow them up with 300mA given what they're now worth. Likewise EF86s, which are just 200mA.

Cheers,

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Old 10th Apr 2014, 5:55 pm   #18
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Default Re: How do I identify unlabelled valves to build junk radio?

I am not planing on blowing up any valves! and valves with heaters with different voltage and amp requirements can be used together on a 24v supply if you are careful and clever about it
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Old 10th Apr 2014, 7:41 pm   #19
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Default Re: How do I identify unlabelled valves to build junk radio?

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Originally Posted by G6Tanuki View Post
You could experiment with the "Space Charge" approach - see here:
http://www.junkbox.com/electronics/l...agetubes.shtml
thanks, that is the site! sadly some of the links do not work any more, as it has not been updated in a wile, it looks like you can use any grid as the control and the others as electron accelerators, but I would expect less gain the further you get from the cathode, and I would have to be careful not to overload the grids, but a lot of the circuits using space charge valves used cathode bias resisters?, I will have to try a Z77 wired up in veres strange ways and see how it works? one design only has a 50mw audio output and it fulls a medium sized room with no problem? maybe I dont need 2 or 3 watts?
To build a circuit like this the valve data sheet only gets you so far!
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Old 10th Apr 2014, 7:49 pm   #20
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Default Re: How do I identify unlabelled valves to build junk radio?

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Originally Posted by TrevorG3VLF View Post
I do not think that zero bias will generate enough current to damage the valve at low voltages.
You could use an EF91 or EF80 for most of the stages. I think the EF80 has an internal screen which may help.
For power, perhaps a PL509 would work on a lowish heater voltage. To pull a decent current, you may need a positive grid voltage which would need considerable drive power.
The PL509 wants 40V!! for the heater, running it at 24v would give me very little emission and under voting the heater so far would damage the heater coating, it would get cathode poisoning
I have loads of EF91 and EF80 I will have to see if any are unlabeled, they have distinct internals!
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