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Old 14th Apr 2014, 7:43 pm   #41
audion_1908
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Default Re: How do I identify unlabelled valves to build junk radio?

There is also the 1935 Grunow model 6HB, and grunow 620 and possibly more,
The dynamoter has shock mounts between it and the steel box, and and is mounted on a thick piece of black felt, but the felt is probably not original
The whole unis is just on a self in the radio above the hard working valves! this shows a dynamotor powered home radio could work ok, but it could be that they just used lower power and rpm quieter dynamotors in the home radios? and the one I will be picking up is military rotary converter Type 52 could be very noisy! I will have to see

http://www.antiqueradios.com/forums/...c.php?t=102849
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Old 14th Apr 2014, 7:52 pm   #42
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Default Re: How do I identify unlabelled valves to build junk radio?

Quote:
Originally Posted by G6Tanuki View Post
At risk of violating copyright, I might be able to photograph the relevant pages.
that would be great!
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Old 15th Apr 2014, 2:08 am   #43
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Default Re: Building a Radio from Junk

I have been going threw my new box of valves and found 4X very worn PL81 it is a line output pentode, heater 21.5v @ 0.3 amps and rated at 40ma, I need to keep going threw and the valves and data sheets, but a set of 4 of PL81 could be right the job!
I will have to see how much emission is left, the tube looks overcooked! so about 3.75 watts for 2 push pull output, or 7.5 watts for all 4 tubles
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Old 15th Apr 2014, 7:44 am   #44
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Default Re: Building a Radio from Junk

PL81 like EL84 always look overcooked, but test them and you should find some usable ones.

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Old 15th Apr 2014, 1:02 pm   #45
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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 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
Just power-up the heater on a reasonably chunky diode, and stick a high-resistance voltmeter between anode and cathode. You'll see several hundred millivolts.

If you want less than this, use a potential divider. You'llonly have a few microamps available, so you'll have to use megohm-sized resistors, but that should not be a problem.
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Old 15th Apr 2014, 6:24 pm   #46
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Default Re: How do I identify unlabelled valves to build junk radio?

I understand, very clever! so it works similar to grid lead resister for biasing a valve, and I have some D77's that I never thought I would use and loads of TV HT and EHT rectifiers to use!
I only have one high-resistance voltmeter, its a vintage valve volt meter currently in storage, I saved after it got dumped by my old college, it still has its original rubber wire and 5 amp round pin plug on it! I have not tested it, but all my other meters are cheap DVM's or analog meters, so I will finally have a use for the discarded valve volt meter!

Quote:
Originally Posted by Radio Wrangler View Post
PL81 like EL84 always look overcooked, but test them and you should find some usable ones.
David
yes I am going to test them, ages ago I was fixing a 1950~ valve am/fm radio, and the audio output tube looked completely overcooked! but tested good! but the double diode/triode had no emission on the diodes, but the triode tested new! it is valves like that one that will be useful to this build.

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Old 15th Apr 2014, 8:34 pm   #47
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Default Re: Building a Radio from Junk

Quote:
Originally Posted by GrimJosef View Post
If you plan to share the room with the dynamotor
Tis' mine (soon not to be) it's a rotary converter much quieter than a dynamotor (if my understanding of a dynamotor is a motor connected to a dynamo), I guess a small wooden box round it would make it almost inaudible, it's not that loud on it's own. It only spins to make AC so it can act as a transformer, not to generate power from a motor, where all the power required goes through mechanically.
 
Old 17th Apr 2014, 3:38 am   #48
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Default Re: Building a Radio from Junk

as far as I know rotary converter's, dynamoters and rotary transformer's are the same, thanks to merlinmaxwell I have a great working rotary transformer! on the plate it has A(crown)M, rotary transformer, type 52, REF. N10k/568, input 24v, out 6.5v 2.5a, 250v 50ma, serial no. L.H. 29932, dose any one know the max recommended HT smoothing capacitor? and a pic of a type 52 with its end caps? and a copy of a manual would be great!
with the dynamotor I can now have a good audio output!

I also now have a VT224 transmitting double triode! thanks to merlinmaxwell the VT224 has 6.3v heater, and can take a lot more power than the dynamotor can supply, so if I use it, it will have an easy life, it can take 80ma per triode! so 160 ma total!! the dynamotor can supply 60ma max, the only downside is it needs -50v on the grid, so I could use a cathode bias resister and lose 50v off the HT, or maybe a grid leak resistor? its a bit high for a grid bias battery! lol maybe this valve would be better used in a transmitter or mains powered audio amp? but 1 valve push pull is cool!

and thanks to Pamphonica and his box of mixed tv valves I have 4 PL81 for use in the audio amp, the PL81 pentodes look very worn but could still be good, the PL81 has a 21.5V 0.3A heater, the 21.5v can be easily padded to 24v, it looks like it has a max 45ma and grid -24v, but some of the data sheet is unclear to me? more reading needed, but a set of 4 in push pull would do well, and have an easy life, I need to look up all the other valves

I have found out about the pl500 pentode television line output valve or sweep tube, it has a heater 27v 0.3v so could be run off the 24v system directly and can be run up to 100ma!, I think I may have some PL500 in storage! so if I have 2 of them, even very worn they would work great!

so at the moment its between using 4X PL81 or 1X VT224?

I also have been given an unlabeled nixie tube from merlinmaxwell, its an upside down numerical tube, I have decided as I now have an HT supply, I can use 1ma of it to light the nixie tube to show band its on! the nixie tube should be fairly easy and fun!to get working.

I also have a Mullard 7pin phototube from merlinmaxwell, its hard to read but something oCG?, could be a 90CG (mullard photocell 90CG is a gas filled photo cell, most sensitive to incandescent light sources and to infra-red radiation), I had decided that the junk box radio had to light up, but with the photocell I could do some cool things like it automatically switching a internal dim night light on at night, or dim the dial lights when used at night when its darker, and dose not need to be so bright!

mullard photocell 90CG
http://www.r-type.org/exhib/aai0277.htm

PL81
http://www.r-type.org/exhib/aaa0359.htm

VT224
http://www.r-type.org/exhib/aaa1369.htm

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Old 17th Apr 2014, 8:17 pm   #49
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Default Re: Building a Radio from Junk

The rotary transformer will produce DC so if perfect will not need a capacitor. In practice, put a 0.1µf disc ceramic capacitor a close as possible to the output for noise suppression. You could also use a big electrolytic to smooth current pulses.
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Old 17th Apr 2014, 9:00 pm   #50
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Default Re: Building a Radio from Junk

It is dc, but rectified by the commutator so will look like
http://brightsparkmagnetos.com/works...g/IMGP8108.JPG
http://brightsparkmagnetos.com/workshop/DBRig/index.htm

if only 0.1uf or so is needed, I can use one of my diy capacitors, but I dont know what size electrolytic to use? my 1938 marconi 557 uses 4 and 8uf capacitors, so maybe a 4uf will do, I would expect the frequency to be much higher then 50hz so 4uf could be fine, I will have to look up other dynamoter power circuits.

I have decided on what sort of plug to use, in keeping with the junk and 1930 theme I have decided on a light plug, the DC system it will be used on uses 16 amp 115v yellow water proof plugs and sockets, but there are ES and BC light fittings, I have chosen ES as I can guaranteed the polarity, I have a dead ES filament lamp, I wrapped the glass in plastic and broke it, I was planing on soldering the wires direct to the old filament wires, but they are way to thin, as they where designed for a 0.5 amp load and like thin fuse wire! and the radio when starting with the dynamoter spining up and filaments warming up will take a lot of current! so I carefully broke out the remaining glass, the glue stuff was a pain to get out! I hope it still works as I bent it a bit, I have ordered a high current ES lamp fitting to test and use it with, and now am on the look out for some 1.5mm or 2.5mm flex to solder in, I will use something like a bit of broom handle as a handle for my diy light plug, if it dose not work I have a spare dead ES lamp!
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Old 17th Apr 2014, 10:43 pm   #51
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Default Re: Building a Radio from Junk

My Dad was throwing out a car cd player that was missing its front, I saved it and took it apart for parts, I have one large smoothing toroid, 2 springs that may do to tension the tuning dial string, a 1n5404 power diode, rated at 3 amps 400v, that will be useful, and a device I had not seen before? its a spark gap for the antenna and it looks like a glass diode, if it dose not have too much capacitance I will use it, and a pile of tiny 16v 10 to 100uf electrolytic s some are 50v, and 2 16v 2200uf caps, and some unlabeled diodes.
and when I find dead CFL lamp I would have a 400v to 450v 4uf~ electrolytic for HT smothering, and some other useful parts.
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Old 18th Apr 2014, 6:48 am   #52
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Default Re: Building a Radio from Junk

I have got as far as having a dynamoter to supply HT for the audio output stage, (250v 50ma) and it looks like class AB push pull, or dual push pull, so upto 10w audio out ether way.

I will use the 24v as the HT supply for all the other valves
The shape of my radio will be based on a 1930 wooden cathedral radio, but with a illuminated round glass tuning dial, and a lot more knobs!

and for the specs AM from 500khz~ to 1.8mhz~ plus as much of the short wave band as possible, and agc bfo .

Tuned RF amp, mixer, oscillator, IF, IF, IF, bfo, detector, audio preamp, audio amp

so that is 9 tubes plus 1 to 4 more for the audio amp!
I have not seen any radio plans with three stages of IF but if I have AGC I can not see it being a problem and it may need the gain!

So far the controls will be,
1, off, heaters and dynamoter on, HT on (so a 3 stage switch to preheat the tubes)
2, volume (probably using a variable capacitor)
3, Tuning with reduction drive
4, Tone and BFO on/off
5, Band switch
6, audio amp input, radio, aux, aux, aux
I will also have a nixie tube to show you what band you are on

I will try to keep the only new stuff I use to epoxy resin (cheap grade), waterproof wood glue £1, lead/tin solder, fuses, small light bulbs, pvc and rubber tape, beeswax, turpentine, olive oil, Carnauba wax, paper clips (unless I can get a lot free) spare brushes for dynamoter.
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Old 18th Apr 2014, 9:28 am   #53
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Default Re: Building a Radio from Junk

I will also use new green tea.

I was going to build the speaker, but it looks like I need the efficiently of a manufactured speaker, so am looking for 1 large and one small to repair, I am good at making capacitors and have made loads in the past, some of my projects are still using early ones I build, and resisters are easy (carbon film on paper) but I do not know how stable they are! probably not much and they would have a very low wattage rating, I can build low ohm power resisters out of pensel lead I am also going to build the tube sockets and have a go at building IF transformers, and the tuning variable capacitor out of tin can lids! the variable capacitor used for the volume control will be made out of parcel tape and silver foil! I still have not found a good way to build variable resisters?
I will have a go at making some electrolytic capacitors, but I dont think they will be reliable, they will probably drift in value and need reforming if not used every few months or less and the liquid will need topping up.

some 1920's light/edition plugs
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Old 18th Apr 2014, 10:42 am   #54
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Default Re: Building a Radio from Junk

You may be able to adapt this method for making filament rheostats - esentially a coil of resistance wire, possibly from a toaster or heater, bent around a circular resistive cylinder, with a bent tin sliding contact. Possibly wood boiled in parafin wax as a core. Not sure about attaining higher values - possibly use as a vernier and have switched fixed resistors! Appropriate care for higher voltages.
I would be interested to see pics of your variable condenser.
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Old 18th Apr 2014, 12:07 pm   #55
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Default Re: Building a Radio from Junk

If you're making capacitors, then go the whole hog and make an electrostatic speaker.

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Old 18th Apr 2014, 5:30 pm   #56
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Quote:
Originally Posted by greenstar View Post
You may be able to adapt this method for making filament rheostats - esentially a coil of resistance wire, possibly from a toaster or heater, bent around a circular resistive cylinder, with a bent tin sliding contact. Possibly wood boiled in parafin wax as a core. Not sure about attaining higher values - possibly use as a vernier and have switched fixed resistors! Appropriate care for higher voltages.
I would be interested to see pics of your variable condenser.
I would have thought plaster of paris would be too soft! it looks a great way to build filament rheostats, but for a volume I would need 500k ohm to 1m ohm and logarithmic, same for the tone control bus probably linear, but the same system could be adapted to make a bank of switched fixed resistors! or tapping one custom resister, and a wax boiled wood core would be good, I have made wax boiled wooden blocks for a project years a go and they worked very well, and easy to work.
thanks for the info!

this is a very clever way of making a variable capacitor using just wide parcel tape and silver foil! the capacitance value is not consistent enough for tuning, but would be great for a volume or tone control, the self-made variable capacitor has a capacitance range of about 20 pF to 500 pF

The self-made variable capacitor
file:///G:/junk%20radio%20project/The%20self-made%20variable%20capacitor/Homemade%20rotary%20capacitor.htm
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Old 18th Apr 2014, 5:46 pm   #57
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Quote:
Originally Posted by Radio Wrangler View Post
If you're making capacitors, then go the whole hog and make an electrostatic speaker.
the electrostatic speaker looks interesting, but it would be hard to get the few KV for the EHT supply and getting the components for free, also it looks like it would not do well outside in what is in effect a very large tent, and a trace of morning due could course havoc!
but it would be fun to have a go at making one some time!

http://en.wikipedia.org/wiki/Electrostatic_loudspeaker
"Because of their tendency to attract dust, insects, conductive particles, and moisture, electrostatic speaker diaphragms will gradually deteriorate and need periodic replacement. They also need protection measures to physically isolate their high voltage parts from accidental contact with humans and pets"

The self-made variable capacitor, real link
http://translate.google.com/translat...de/bastel0.htm
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Old 18th Apr 2014, 8:37 pm   #58
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Default Re: Building a Radio from Junk

This project strongly reminds me of the WW2 Colditz/Stalag Luft prison camp radio designs, but with a modern-day/steampunk update.

What about a Mamod static engine for generating the HT via a dynamo, to give you a meths-powered MF rx? As long as the spark QRM was minimal.
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Old 18th Apr 2014, 8:56 pm   #59
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Default Re: Building a Radio from Junk

That's an ingenious condenser. I saw a similar one in a 1918 magazine. There are also the sliding cylinder and book types:
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Old 18th Apr 2014, 11:43 pm   #60
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Default Re: Building a Radio from Junk

You can use fixed capacitors with variable inductors. See 'permeability tuning' and 'variometer'

For home-made variable caps, try butterfly types to avoid sliding contacts.

I agree electrostatics outside would be a problem... but they sound stunning. Home made headphones article in WW. Not for the faint-hearted.

Fun!

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