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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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22nd Jan 2020, 6:03 pm | #1 |
Octode
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,611
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Using the PU jack
I am posting my experience connecting modern peripherals to 1930s radio sets via the PU jack, in case this helps anyone here. Most things were learnt through trial and error, asking questions here and googling. Below please find the things I wish I knew starting out.
1. On both my sets (GEC superhet 5 and Pilot u650) the PU jack requires an input via a 6.35mm mono plug. This automatically mutes the radio to allow sound via this 'line in' only. The problem is that not all 6.35mm plugs work. The overall length of the plug seems to vary by about 5mm. The shorter ones are a waste of money. I have found (after 3 attempts) that the kenable 6.35mm mono male to 3.5mm mono male audio cable (Amazon/eBay) works well. 2. There is a very well concealed mono mode on the later versions of android. This is accessible from Settings->smart assistance->accessibility->mono If you set this to mono and plug the 3.5mm mono plug in your phone's stereo headphone jack, you get great sound 3. If you can only get stereo sound from your device, you need a resistive circuit to convert stereo to mono. There is a thread here that explains how to make one. Alternatively, you can buy one from ebay, just search for 'smadt1 stereo to mono'. Its priced £7.99 but the seller accepted £6.50. Don't be tempted to use anything that shorts L+R - the sound will be terrible. 4. If you want to avoid cabling, there is a 3.6v 3 channel AM transmitter available on eBay or AliExpress (£10-£15) which i can verify works well provided it's very close to the radio. Hope this helps someone Gabriel |
22nd Jan 2020, 8:47 pm | #2 |
Hexode
Join Date: Jun 2009
Location: Cheshire, UK.
Posts: 363
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Re: Using the PU jack
Hi Gabriel
Thanks for posting about your experiences connecting modern devices to your old radios. I was particularly interested in the 'mono' option you discovered on Android - well-concealed, as you say! I was puzzled by your reference to a PU jack, as I'd not seen a radio with a jack socket fitted for Pick-up (or 'Gram') use. However, I looked up the thread on your Pilot U650 and lo, there it was. As David describes in that thread, insertion of a plug into the socket automatically mutes the RF/IF stages. It looks a nice set. Glad to see that you're enjoying using it. Last edited by Wellington; 22nd Jan 2020 at 8:48 pm. Reason: Name correction! |
22nd Jan 2020, 8:54 pm | #3 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
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Re: Using the PU jack
Also worthy of note: many now-obsolete-and-worthless mobile phones have a FM-radio function; these use the 'headphone' lead that plugs into the 3.5mm jack as the antenna.
If you fit a suitably-long lead from this to a plug that fits into your vintage-radio's "PU" input, you have quickly and cheaply converted your old radio to receive FM broadcasts. The phone usually doesn't need an "active" SIM, just a SIM of some sort so the thing will boot-up. |
22nd Jan 2020, 10:08 pm | #4 |
Octode
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,611
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Re: Using the PU jack
Wellington the GEC Superhet 5 BC3440K has one too. I don't think they're that uncommon.
The FM trick with an old mobile is great! |
23rd Jan 2020, 1:09 am | #5 |
Dekatron
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,316
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Re: Using the PU jack
My very basic Pixi4 smart phone (now surplus as my children bought me a better one for my birthday) works Ok without a SIM,and could probably be used to access internat radio if I cold be bothered.
As a schoolboy in the early 1960's i used to play my EL3585 tape recorder through the gram input of an old radio. I only ever saw UK-made radios with 1/4" wander plug connections for the Gram input, although did find 4mm connectors used on some Philips models. The radios always had a Gram setting on the waveband select switch. |
23rd Jan 2020, 8:06 am | #6 |
Octode
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,611
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Re: Using the PU jack
Talking about connections, has anyone of you used an AM transmitter for a true cable-less connection. I've got the one in the picture below (built a wooden enclosure for it) and you can hear the GEC receiving the MW signal (playing nirvana) from it in the video in the zip file. The USB cord is a modification I've done the recharge the battery. Range is only about 1m or so.
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23rd Jan 2020, 12:44 pm | #7 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,526
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Re: Using the PU jack
That'll be 1/8" for wander plugs. 1/4" for jack plugs, 4mm for banana plugs.
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23rd Jan 2020, 12:57 pm | #8 |
Dekatron
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,316
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Re: Using the PU jack
Indeed, sorry for the typo!
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23rd Jan 2020, 1:46 pm | #9 |
Heptode
Join Date: Feb 2013
Location: Rainham, Kent, UK.
Posts: 523
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Re: Using the PU jack
Just a thought, but I think my 30's Murphy has a 1/4" jack. If you use it I think you have to be careful to load it correctly as this can affect the bias on the next stage. Will check latter.
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23rd Jan 2020, 1:59 pm | #10 |
Octode
Join Date: Jun 2013
Location: Fleet, Hampshire, UK
Posts: 1,764
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Re: Using the PU jack
Ive seen those little "transmitters" on ebay, they work OK as you have seen, but not very well. They are just 3 crystal oscillators and a transformer, 3 for the different frequencies. Its about as simple as you can make yourself but they wont produce great audio like a better device would.
In terms of value, you would struggle to beat this device: https://www.nfor.nl/radioforumservic...PLL_AM_Osc.pdf Its IC based and uses a 4053 analog switch IC as the final. Very stable and running at 15v could well cover your whole house properly with the right antenna and other variables. It gets better range than my SSTran AMT3000 did A kit for building this circuit can be bought here for £15-£18 https://www.amateurradioshop.nl/ You need to use google translate though as its in dutch, I've found them very helpful by email as well. There are many different transmitters available, if you don't fancy building one the spitfire is ok, but I suspect the one I posted above is better. |
23rd Jan 2020, 2:00 pm | #11 |
Heptode
Join Date: Feb 2013
Location: Rainham, Kent, UK.
Posts: 523
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Re: Using the PU jack
Just had a look. Using the jack will open circuit the control grid and possibly cause damage on this particular set. "Murphy A4"
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23rd Jan 2020, 7:24 pm | #12 |
Octode
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,611
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Re: Using the PU jack
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23rd Jan 2020, 11:23 pm | #13 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,526
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Re: Using the PU jack
Well a floating grid isn't good news but on a low level audio triode with significant anode load resistance it's unlikely to damage anything. However the signal ground on the PU input isn't chassis ground, it's a bias voltage decoupled to chassis by capacitor. A PU of the day would simply have been a floating coil with no ground and low enough resistance to couple the bias to the valve OK. Any input with one side grounded would short out the bias if the chassis has an RF ground connected and reduce bias voltages on other valves including the output which might be unwelcome.
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....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
24th Jan 2020, 10:22 pm | #14 | |
Octode
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,611
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Re: Using the PU jack
Quote:
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25th Jan 2020, 12:05 am | #15 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,526
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Re: Using the PU jack
Not in terms of damage to the radio but grounding a point part way up the bias chain could be a recipe for hum. Best to use a floating (battery operated maybe) source or else feed the signal via a small audio isolating transformer. No particular high voltage isolation transformer is needed, it's not a safety issue.
__________________
....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
25th Jan 2020, 12:25 am | #16 |
Heptode
Join Date: Feb 2013
Location: Rainham, Kent, UK.
Posts: 523
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Re: Using the PU jack
Does the attached help of the Murphy A4.
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25th Jan 2020, 7:45 am | #17 |
Octode
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,611
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Re: Using the PU jack
Thank you both.
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