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Post by Robert Wesley on Aug 15, 2019 15:42:01 GMT 12
Hello ,
I am new to this forum, I have had some Radio Valves that I have got given to me to restore and I am asking for some advise if possible.
I have electrical background but I don't have a strong radio or Valve knowledge. I was wondering if anybody has any experience knowledge with the Pacific 518J Raido I have only found the 518 Drawing and I have figured out that the J version has different valves Loktal type.
My question is I would like to install a Raspberry Pi Internet of things to this . I have set the raspberry pi with software that will play music via bluetooth / wifi , it has a output signal headphones that I would like to connect somehow to the circuit.
What I would like to do it have the function to switch so that the radio can connect to a external source (raspberry pi) a headphone jack has three wires left right and common I undestand the radio only has one speaker.
Is it possible to connect a external signal . I was hoping to change one of the switches at the front with a extra pole or any other suggestions would be helpful.
<iframe src="https://drive.google.com/file/d/15JjS2UdVtPeU1SAoOFRmxBcKXi3MJ47W/preview" width="640" height="480"></iframe>
Cheers,
Rob.
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Post by robwesley on Aug 15, 2019 15:45:14 GMT 12
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Post by dada on Aug 15, 2019 15:59:43 GMT 12
Hi Robert, you could use the "gramo" input on the back of the set - take 2 x 1k ohm resistors from the let and right headphones and connect together to the top gramo input terminal. Use the lower gramo terminal to connect to the headphone common. Select gramo on the radio set (assuming it works fine as a radio - ie all is OK with the actual radio itself) and provide a suitable signal to the headphones. No major modifications required - assuming the set works well beforehand.
Cheers, David
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Post by robwesley on Aug 15, 2019 16:08:17 GMT 12
I have began restoring this radio and have replaced all capacitors.. I have still have to replace the valves. The issue is that the drawing is for a 518 and I have a 518J the valves are different Loktal type (7S7 , 7B7 , 6SQ7GT, 7C5 , 7Y4) but no drawing explaining where teach one is equivilant to. I have already stripped back and re varnished and put new grill cloth on the front.
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Post by robwesley on Aug 15, 2019 16:09:49 GMT 12
thanks David for the quick response , I will try that . Cheers.
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Steve
Society Members
vintageradio.co.nz
Posts: 727
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Post by Steve on Aug 16, 2019 8:00:03 GMT 12
Hi Rob, I restored a Regent version of this set a few years back and came up against the same problem. I just replaced all capacitors like for like. Use 630v poly caps for all the wax and paper ones and 500v electrolytics for the power supply and as mentioned combine the stereo channels into the gramo input. I wouldn't go replacing valves unless you need to as you'll possibly find they are fine.
You might find the switch mode power supply for your Bluetooth unit plays havoc with the set so either build a linear power supply for it with a 7805 and a big electrolytic and feed that from a bridge rectifier off the heater feed (you may need a better low dropout regulator because of the low heater voltage you're starting with... 1117-5 perhaps)... Or find an old transformer based wall plug power supply... Or just switch it off when not in use. Others may have other tricks to solve this problem if you have it.
Keep us posted.
Cheers, Steve
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Steve
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vintageradio.co.nz
Posts: 727
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Post by Steve on Aug 16, 2019 8:09:54 GMT 12
Just on the valve equivalents, where I note the valve line up on vintageradio.co.nz I always do it in order, from RF through to power supply and then the magic eye if a set has one, so the octal lineup and loctal lineup can be directly associated
Octal version: 6SA7, 6SK7, 6SQ7, 6V6, 6X5
Loktal version: 7S7, 7B7, 6SQ7GT, 7C5, 7Y4
7S7 is the mixer valve
7B7 is the I.F. valve
6SQ7GT is the detector and first audio
7C5 is the audio amplifier
7Y4 is the rectifier.
I think the chassis positions are similar or the same as the octal equivalents. If you look at the Regent version on the site you'll find a valve layout diagram that was glued inside the cabinet of my one... That should help.
Cheers, Steve
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Post by robwesley on Aug 18, 2019 10:23:50 GMT 12
Thank you for the help
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Post by robwesley on Aug 20, 2019 12:47:47 GMT 12
  I start up the radio after some changes to capacitors and hearing some strange sounds decided was unsafe and disconnected , I noticed the insulation coming out from one of the transformers and I think I will replace both transformers. Does anyone know where I can get a replacement for both of these ? Any help would be greatly appreciated. Cheers, Rob. |
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Steve
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Post by Steve on Aug 20, 2019 15:24:33 GMT 12
First you're going to want to find out why that's happening. Have you accidentally shorted something on the secondary side? I have, in the past, accidentally shorted the 6.3V heater chain and this caused exactly what you are describing in that set. What are the specs of the capacitors you used in the power supply? Are they hooked up the correct way around?
I wouldn't go replacing anything until you know why (and if) you need to.
The big one is the power transformer, the smaller one is the choke. In my one the choke had been eaten by mice and I had to remove about two layers of windings and re terminate it...
Cheers, Steve
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Post by robwesley on Aug 20, 2019 18:49:12 GMT 12
Hi Steve,
I checked the secondary windings and measured 1 Ohm and primary around 200K. I was soldering the active primary windings with soldering iron and must of got it too hot as I had trouble re soldering wire. I can see all the yellow insulation melted down. I had replaced a capacitor which i thought was the wrong way around as the negative arrow should point closet to earth. with the two red wires coming from the secondary winding I assume is the heater 7Y4 valve which I just replaced.
I am hoping it's just broken down over time and if there is anyone I can buy new transformers would be appreciated.
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Steve
Society Members
vintageradio.co.nz
Posts: 727
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Post by Steve on Aug 21, 2019 18:38:37 GMT 12
Hi Rob, the negative doesn't always go where you might expect in vintage radios - sometimes there are more negative parts of the circuit than the chassis... always go with the schematic. In this one the curved plate is negative.
Typically finding a new transformer for these old sets means finding something with similar specs and making it fit - you'll need something with 2 x 6.3V windings and around 300-0-300V for HT. The transformer shouldn't be too hard to track down but a choke might be, so if thats ok I'd leave it alone. Absolute worst case you could pay to have it / them rewound but I'd look for replacements first - there are a couple of NZVRS members who rewind transformers. Most of my spares are for pre-war radios and typically have 5V / 6.3V so I probably don't have anything suitable - others may have something. There is a guy on Trade Me who often has vintage radio power transformers for sale every now and then, but I can't recall his user name...
Cheers, Steve
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