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Post by briano on Jul 26, 2022 8:26:57 GMT 12
Thank you Peter for your reply. Yes, I do not believe the lamp holder is made from plastic. Photo attached. I heed your warning about potential fire and protection. I'm sorry you had that awful experience and good you caught things in time. I appreciate you passing on your experience. You have got me thinking that, as well as fuses, if I need to place some sort of thermal sensor that could sit on/near the transformer and cut the mains, external to the radio. No need to make electrical connections inside the radio. Hmmm. Or maybe, fit a thin steel sheet under the chassis, to confine any dangerous failings? I really want to be able to use the radio on a daily basis. But, given your experience, would not leave it unattended. Thank you... Cheers, Brian Attachments:
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Post by Peter Walsham on Jul 26, 2022 10:43:56 GMT 12
Oh heck!
I certainly didn't mean to 'scare' you or make a mountain from a mole hill either. A radio fire would be an extremely rare thing to happen - it just happened to me! I will be very quick to point out that I hadn't 'got around' to fitting a fuse in to the radio I had burn. I am more than certain that if I had, the fire would not have occurred. Unfortunately, though, power transformer failure is quite common though - for various reasons. I would be quite happy to suggest you fit a fuse (and replace the filter capacitors in all cases), but I really see no need to go to extreme lengths otherwise. I often leave radios running all day unattended and not had a problem since - other than the odd blown fuse, certainly nothing that was likely to end up having another fire. I have a radio in my lounge that I run very regularly, and I am quite happy to leave it running when I'm not at home. That photo of the dial lamp does worry me a bit though. Although the insulation is phenolic and is OK, it shows a smaller 'MBC' lamp being fitted to a lamp holder designed for a bigger 'SBC' lamp. If the existing lamp can't slip forward, then all is well, but if it can (for whatever reason) then it's possible that the leaf contact that the wire is soldered on to could also move forward & short out to the frame of the lamp holder. This will cause a short circuit. Two suggestions: Replace the existing 'MBC' lamp with a 'SBC' one, or use a fibre washer to go over the existing lamp's centre contact (making sure the blob of solder is big enough to come through the centre hole in the washer - or make up a washer out of some stiff cardboard. High currents can flow in the 6.3 Volt heater circuit if a short does occur.
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Post by briano on Jul 26, 2022 13:00:10 GMT 12
Peter - Yes, I did fit the fuse in the phase line while I tested the radio, and will keep it when fitting the replacement transformer.
Most interesting about your comments on the lampholder. Yes, I can see the point you are making that if the bulb moves forward the 'live' terminal could move and short to the 'outer' connection. I will definitely do something on this. Thank you for pointing this out. Cheers, Brian.
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Post by briano on Aug 10, 2022 15:30:37 GMT 12
Hi Briano, Phone me on 027 4082163. I may have a transformer which would do. Cheers, For completeness, an update on the kind offer by "trombone". Amazingly, he had an exact same mains transformer that my grandmother’s radio had and generously sold it to me. After receiving the transformer through the mail, I carried out DC resistance measurements of the transformer primary, and the high-voltage secondary. They all looked normal. To carry out a ‘live’ test, I lifted the wiring off the old transformer tags. I then sat trombone's transformer along side the radio chassis. I connected alligator-clip jumper wires from his transformer to the respective wires under the chassis. The radio worked brilliantly, with the H.T. measuring 255-volts, and the CT of the high-voltage winding (at the ‘live’ end of the speaker choke) measuring -140v. If anything, the radio seemed more RF sensitive. (The old burn’t out transformer only gave me an H.T. voltage of 200v and CT voltage of -90v). Surface temperature checks on the windings looked acceptable. The surface temperature after 10-minutes rose from an ambient temperature of 21.5°C to 28.4°C. After half-an hour, the windings surface temperature rose to 37.4°C. I think quite acceptable. So, all very successful. Thank you to trombone. Remaining tasks for me include fitting the transformer properly, replacing the volume-control (noisy-intermittent at bottom-end), replacing the dial-lamp holder, properly insert fuse in mains phase-line, and transformer secondary C.T. line, fit permanent new mains cord with proper cable-clamp. Then, onto the cabinet, ha ha! Been waiting for some warmer dry weather. A bit cold in the garage at the moment-!!
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Steve
Society Members
vintageradio.co.nz
Posts: 724
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Post by Steve on Aug 10, 2022 15:53:58 GMT 12
I'm glad to hear its going well now! I believe from looking at it that the lamp holder in your set may be of the Radio Corp style that used automotive lamps, BA15s and the like. They made those in the factory.
Finding 6V versions of those here in NZ can be a hassle, but if you use any other more standard lamp fitting in its place, then the 6 or 6.3V lamps are far easier to come across. I've seen where someone smashed out the old bulb from a BA15s base and soldered in a smaller bulb, but you more commonly see what you have - a smaller lamp used and the side contacts of the holder just crushed in to hold it.
One thing Radio Corp did to extend the lives of their bulbs was use a coiled piece of nichrome wire in red spaghetti tubing as a low value inline resistor to drop a portion of the heater voltage going to them. They also had some transformers that had a special tap off the heater winding although these hardly ever show up in my experience - and since you already have a good transformer that won't probably be an option.
Good to see it coming together!
Cheers, Steve
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Post by Philconut on Sept 15, 2022 21:05:07 GMT 12
If you're still looking for a transformer I have a Beacon R04 380V-0-380V or an R03 300V-0-300V which you are welcome to have. Message me to discuss. Cheers John
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Post by briano on Sept 16, 2022 16:09:38 GMT 12
If you're still looking for a transformer I have a Beacon R04 380V-0-380V or an R03 300V-0-300V which you are welcome to have. Message me to discuss. Cheers John Hi John (Philconut). Thank you for your kind offer. "Trombone" had found a mains transformer he had, and kindly sold it to me. And, all tested inset and all works. I have yet to complete my restoration - I have got distracted in some genealogy research. And, building a dedicated table to hold my grandmother's radio. Photo of table-top and lower shelf uploaded here. I will have drawers under the table-top - one drawer to hide away my small low-power AM transmitter fed from an FM tuner/receiver. I have tested. The AM transmitter provides ample signal to deliver into the vintage radio through the existing ant. and earth wires coming out the back of the radio chassis. So, no modification to the radio. My set-up will also include a bluetooth receiver to give me streaming options from my iPod or phone. Back to the table I am building, I will stain it to match other furniture in the house. Once again, thank you for the offer of the transformer but I am all good. I appreciate the offer. Have a great evening... Cheers, Brian. Attachments:
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