10th Apr 2014, 8:03 pm | #21 |
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Re: How do I identify unlabelled valves to build junk radio?
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 |
10th Apr 2014, 8:58 pm | #22 |
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Re: How do I identify unlabelled valves to build junk radio?
One off-topic post deleted
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11th Apr 2014, 2:35 pm | #23 |
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Re: How do I identify unlabelled valves to build junk radio?
Would this procedure work for identifying the electrodes of a valve?
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11th Apr 2014, 8:42 pm | #24 |
Hexode
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Re: How do I identify unlabelled valves to build junk radio?
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 Last edited by audion_1908; 11th Apr 2014 at 8:54 pm. |
11th Apr 2014, 11:10 pm | #25 |
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Re: How do I identify unlabelled valves to build junk radio?
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.
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12th Apr 2014, 6:06 am | #26 |
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Re: How do I identify unlabelled valves to build junk radio?
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.
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12th Apr 2014, 6:18 am | #27 | |
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Re: How do I identify unlabelled valves to build junk radio?
Quote:
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. |
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12th Apr 2014, 6:22 am | #28 |
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Re: How do I identify unlabelled valves to build junk radio?
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
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12th Apr 2014, 6:36 am | #29 | |
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Re: How do I identify unlabelled valves to build junk radio?
Quote:
I have a non working dynamotor in storage, it may be 24v? but is a dead dynamotor junk? Last edited by audion_1908; 12th Apr 2014 at 6:49 am. |
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12th Apr 2014, 7:05 am | #30 | |
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Re: How do I identify unlabelled valves to build junk radio?
Quote:
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? |
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12th Apr 2014, 7:17 am | #31 |
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Re: How do I identify unlabelled valves to build junk radio?
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
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12th Apr 2014, 7:47 am | #32 |
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Re: How do I identify unlabelled valves to build junk radio?
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
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12th Apr 2014, 2:39 pm | #33 | |
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Re: How do I identify unlabelled valves to build junk radio?
Quote:
If you lost the bias altogether, at 24-30V HT I very much doubt whether any valve would be harmed either.
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14th Apr 2014, 9:01 am | #34 |
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Re: How do I identify unlabelled valves to build junk radio?
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? Last edited by audion_1908; 14th Apr 2014 at 9:15 am. |
14th Apr 2014, 1:17 pm | #35 |
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Re: How do I identify unlabelled valves to build junk radio?
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? |
14th Apr 2014, 5:17 pm | #36 |
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Re: How do I identify unlabelled valves to build junk radio?
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. |
14th Apr 2014, 5:45 pm | #37 | |
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Re: How do I identify unlabelled valves to build junk radio?
Quote:
Cheers, GJ
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14th Apr 2014, 6:21 pm | #38 | |
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Re: How do I identify unlabelled valves to build junk radio?
Quote:
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! Last edited by audion_1908; 14th Apr 2014 at 6:39 pm. |
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14th Apr 2014, 7:04 pm | #39 | |
Hexode
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Re: How do I identify unlabelled valves to build junk radio?
Quote:
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 Last edited by audion_1908; 14th Apr 2014 at 7:25 pm. |
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14th Apr 2014, 7:06 pm | #40 | |
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Re: How do I identify unlabelled valves to build junk radio?
Quote:
At risk of violating copyright, I might be able to photograph the relevant pages. |
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