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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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27th Jan 2016, 9:32 pm | #1 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Eddystone 840A pilot-light bulb.
Can someone tell me what the rating should be for the pilot-light bulb on an Eddystone 840A?
The one in mine (12V 1.2 Watt) has always been exorbitantly-bright and has now failed; I suspect it's been swapped in the past for something inappropriate to "get it working again". The manual I have is strangely uninformative about the bulb's rating. Since it's wired in series with the heater-chain [two parallel strings of 100mA filaments] it clearly needs to pass 200mA - but at what voltage?? |
27th Jan 2016, 9:37 pm | #2 |
Dekatron
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,190
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Re: Eddystone 840A pilot-light bulb.
Shouldn't a 12V 1.2W bulb pass 100mA? If it's being expected to carry 200mA then no wonder it burns out.
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27th Jan 2016, 9:40 pm | #3 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: Eddystone 840A pilot-light bulb.
Thats exactly what the issue is - I know I need a 200mA bulb, but what voltage does it need to drop across it??
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27th Jan 2016, 9:54 pm | #4 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
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Re: Eddystone 840A pilot-light bulb.
Time for a little reverse-engineering, methinks.... I assume that the CZ is slightly muddying the chance of simple arithmetic. I think I'd temporarily fit a 100 ohm wirewound (playing safe!) in place of the bulb, measure the volts across an accessible heater(s) and, comparing it against what it should be (i.e. UAF42 @ 12.6V, UCH42 @ 14V etc.) fill in the proportionated gaps up to the nominal (here, 230V) mains, and, voila, something like the right bulb voltage should drop out.
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27th Jan 2016, 10:13 pm | #5 |
Nonode
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,152
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Re: Eddystone 840A pilot-light bulb.
Try a 6.5V 300mA bulb.
An RTVS service sheet (1950s) said that 6.3V 300mA miniature bayonet bulbs are standard in all Eddystone receivers. It will be under run and this will lengthen its life. |
27th Jan 2016, 10:25 pm | #6 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: Eddystone 840A pilot-light bulb.
Thanks! That's the sort of info I was after.
Truth is, the bulb's light only serves to illuminate a sad little green dot about 1/8-inch across behind a hole in the tuning-scale: I'd have been happy to replace it with a resistor but following your info my quest is now on for a 6.3v 300mA bayonet bulb or two. |
27th Jan 2016, 10:45 pm | #7 |
Retired Dormant Member
Join Date: Apr 2003
Location: Salt Spring Island, BC, Canada
Posts: 368
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Re: Eddystone 840A pilot-light bulb.
My 840C has a very similar valve circuit but had no dial light. I added 2 ea #44 bulbs (6.3 0.25A). They give ample light but do not run at full brilliance.
John. |
28th Jan 2016, 2:31 pm | #8 |
Tetrode
Join Date: Mar 2015
Location: Ashford, Kent, UK.
Posts: 93
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Re: Eddystone 840A pilot-light bulb.
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28th Jan 2016, 7:13 pm | #9 |
Tetrode
Join Date: Dec 2014
Location: Pembrokeshire, Wales, UK.
Posts: 68
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Re: Eddystone 840A pilot-light bulb.
The 3x pilot lights in my 888A are 6.5V 0.3A MBC BA9S Miniature bayonet cap 9mm single contact BC incandescent easily obtained from ebay. I assume yours would be the same specification. pete
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30th Jan 2016, 8:12 pm | #10 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: Eddystone 840A pilot-light bulb.
Thanks all; In my "bits I should have thrown out but never got round to doing so" I've found a couple of 6.5v 0.3A bulbs - "Cryselco" brand - with the right bayonet base.
Will be deploying one of them tomorrow. I wanted to get the right bulb in place before fitting the new-old-stock Philips RF/FC/IF-valves I have (acquired at last year's Newbury rally for £2 each...) and doing a realignment. I suspect the inappropriate bulb currently fitted has been dropping rather more volts than the original designer expected, causing less-than-full heating of the valves. |