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 Post subject: Add Pilot Light ????
PostPosted: Feb Tue 12, 2019 4:22 pm 
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Joined: Oct Fri 02, 2009 7:47 pm
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Location: Shamokin, PA 17872
If an AA5 does not have a pilot light, can I
add one without causing a problem ???
THANKS !!!
Joe
Shamokin


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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Tue 12, 2019 4:34 pm 
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While it's possible, original circuitry will determine just what modifications are necessary. Most of the later "lightless" AA5 use the rectifier lamp tap as a current limiter for B+ supply. Lamp tap isn't part of heater string, so will require wiring alterations, not so easy on a PCB type radio.

In some of their high end, series string, AM-FM radios, Zenith used a small power transformer solely for dial lamps.

Do you have a model in mind or is this a general question?

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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Tue 12, 2019 5:18 pm 
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Look at schematic for an AA5 that uses a dial light. Fada 855 is a clear example. Note the plate connection. 35Z5 or 35W4. Both tubes have the dial light tap. The light bulb socket must be insulated from the chassis. Problem is going to be mounting the bulb to shine on the dial scale. Also space the distance from bulb to plastic dial cover to avoid the heat from bulb warping the dial scale cover.


Last edited by thunderbird281 on Feb Tue 12, 2019 5:25 pm, edited 1 time in total.

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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Tue 12, 2019 5:25 pm 
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Well since you are altering it anyway, you could use an LED and a resistor in series right at the power switch across the AC line. White LED for dial or colored for pilot. I could figure the value of the resistor up. I think I just used my resistor decade box and reduced resistance till the led had several volts across it and seemed bright enough but not super max brightness. Probably a half watt resistor would be fine for the small LEDs. Then it should last as long as the radio so no sockets or bother. Plus no heat to speak of, for plastic dials.


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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Tue 12, 2019 5:29 pm 
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Quote:
right at the power switch across the AC line.

You would need a diode of the appropriate voltage rating (1n4006) in addition to a dropping resistor. Reverse voltage on LED are pretty low. I have done this with diode and a capacitor to eliminate the resistor without dropping resistor. For a 10 ma led the power dissipation of the resistor becomes

110 volts x 10 ma = 1.1 wats, but 1/2 cycle = aprox 1/2 watt. Of course in a tube radio a 1 watt resistor is not a problem..

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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Tue 12, 2019 5:47 pm 
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Here is an example of using capacitor to limit current to led. The reverse voltage diode protection across the LED, the 1 K is to limit current surge to charge the capacitor on each cycle of the line.
You would get double the brightness using two led's back to back.


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LED110V.png
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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Tue 12, 2019 6:06 pm 
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So the LED across AC looks like an open reversed biased and is only drawing some few mA. when conducting and illuminated. Never found there to be any issue with it with a correct sized resistor to drop the applied voltage. OK you could put another diode reversed across the LED to keep the current and voltage constant at the LED. IN any case, an LED will save you changing bulbs and worrying about heat on plastic dials. IF you must use a bulb you need to mount a socket and figure out where to tap into the radio with said bulb. Or you can use a resistor for line voltage with that too, but the bulb may need a larger wattage resistor than an LED.


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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Tue 12, 2019 6:50 pm 
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If I add an LED for a dial light, I use the cathode current of the output tube to light it. Most AA5s have a cathode bias of 7 volts and a cathode current of about 50 mA. I change the cathode bias resistor to 220 ohms and then divert about 20 mA to light the LED. That also makes one side of the LED socket go to B- which is often the chassis. The resistor in series with the LED to get the current to 20 mA will depend on the bulb but usually something around 50 ohms works OK.

Jay


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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Tue 12, 2019 7:36 pm 
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Location: Austin, Texas
pauls.ironhorse wrote:
Quote:
right at the power switch across the AC line.

You would need a diode of the appropriate voltage rating (1n4006) in addition to a dropping resistor. Reverse voltage on LED are pretty low. I have done this with diode and a capacitor to eliminate the resistor without dropping resistor. For a 10 ma led the power dissipation of the resistor becomes

110 volts x 10 ma = 1.1 wats, but 1/2 cycle = aprox 1/2 watt. Of course in a tube radio a 1 watt resistor is not a problem..

If you use one of the replacement 6.3V LEDs that looks like a #47 bulb, they normally include a full wave bridge rectifier in the bulb base. You don't need an extra diode with those. Without the rectifier, the resistor would need to be at least a 2 watt rating. A 12K, 2W, resistor would be at 1 watt power dissipation and provide about 9 mA to the LED.

The bulb replacement LEDs will also work with the capacitor dropper and you don't need the protection diode. The 1K resistor is still needed to prevent high surge currents.

Jay


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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Tue 12, 2019 7:59 pm 
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I have been thinking mostly in terms of AC in the range of filament voltages like 12 or 6VAC and a LED and resistor. I guess what might be the issue at 117VAC is that the voltage on the LED could exceed the PIV of said LED in the reverse biased condition, thus the reverse diode preventing that. In the instance of high DC voltages that would not be needed as the LED would always be forward biased. However I have a turntable strobe/inspection light that I made with an old AC cord and just the resistor and LED and it never showed any distress or failure in use so far. I have started using the LED 47 replacements in transformer powered radios that had 6V bulbs in them and great results with that.


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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Tue 12, 2019 9:46 pm 
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Joined: Oct Fri 02, 2009 7:47 pm
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Location: Shamokin, PA 17872
THANK YOU all VERY MUCH !!! It's just what
I thought. More trouble than it's worth !!!
THANKS AGAIN !!!
Joe


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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Wed 13, 2019 12:29 am 
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If you want to power the LEDs straight from the line voltage then this circuit works perfectly. The only thing, the capacitor should be an X type rated at 250V AC and not just any 200V capacitor. If you don't have all the parts to built this circuit then this exact circuit is built in most of the cheap Night Lights which are available in any Dollar Store.


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LED110V.png [ 7.85 KiB | Viewed 397 times ]
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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Wed 13, 2019 6:50 pm 
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Why not a neon bulb and resistor across the 120 VAC line uphill from the power switch?

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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Thu 14, 2019 7:07 am 
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I bought these when they were on sale.

Got a bag of them.

Attachment:
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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Fri 15, 2019 2:21 am 
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Joined: Jan Fri 23, 2009 1:10 am
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One simple solution is to use a LED night light. The LED's are in the base and it is easy to break away the glass bulb.


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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Fri 15, 2019 3:20 am 
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Location: Austin, Texas
jimsp wrote:
One simple solution is to use a LED night light. The LED's are in the base and it is easy to break away the glass bulb.

Some radios used the 120V, 7W, bulbs for dial lights. Any plastic in the area of the bulb was usually melted. I used to add a 1N4007 in series with the bulb to reduce the power before we had the LED replacements.

Jay


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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Fri 15, 2019 4:40 am 
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bcascisa wrote:
Why not a neon bulb and resistor across the 120 VAC line uphill from the power switch?
That is a great idea!

I had gotten a Hitachi clock radio years ago with the flop plate clock. It had two NE-2's w/resistors to light the dial... when the neons began to flicker I simple clipped them out and replaced with more NE-2's. The radio was used in the bedroom and was often played until I fell asleep so too bright a light was important.

Chas

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 Post subject: Re: Add Pilot Light ????
PostPosted: Feb Mon 18, 2019 5:10 am 
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wazz wrote:
So the LED across AC looks like an open reversed biased and is only drawing some few mA. when conducting and illuminated. Never found there to be any issue with it with a correct sized resistor to drop the applied voltage.
A resistor will not stop an inverse voltage (IV) appearing across the LED on the other 1/2 cycle. Always use an extra diode to keep any IV off the LED. They have low PIV tolerance... 5 volts comes to mind (but I've not looked it up!) I replace fuse lamps on AM/FM receivers with LED's... some use a 8 VAC supply for the fuse lamps, but I always use a backwards diode to protect the LED from even the 11.2 volts IV.
Cheers,
Roger

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