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 Post subject: Power ON indicator for battery tube sets.
PostPosted: Jul Mon 05, 2021 3:57 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2290
Location: Monroe, NC 28112 USA
Right now I'm working on a two tube set using a 1T4 and 3V4. Available voltages are 1.2 and something over 35 Volts. How to add an easy to see lighted Power ON indicator? Apparently a typical Red LED (that I have in my junk box) will need about 2 mA to look bright enough. The whole radio only consumes about 8 mA. Is there another way??? There is if you have a dead 60 W equivalent LED light bulb around... This one has chips that are actually three LEDs in series... At very low current, the forward drop is about 7 to 7.5 Volts.... With only about 300 MICRO-Amperes passing through it, it gives off a really nice light. I recovered the chips by using a heat gun to quickly heat the aluminum circuit board and quickly whisking the LEDs off with a Popsicle wood stick.

Robert


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 Post subject: Re: Power ON indicator for battery tube sets.
PostPosted: Jul Mon 05, 2021 4:18 pm 
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Location: Santa Rosa, CA
How about putting a red LED in series with the 35 V to the radio? If the radio consumes only 8 mA, it should light the LED brightly. Of course, if you ever short the 35V line, you will probably kill the LED.

The LED will vary in brightness, depending on whether your radio is receiving a strong signal or not. More audio output means more battery current through the LED.

Rich


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 Post subject: Re: Power ON indicator for battery tube sets.
PostPosted: Jul Mon 05, 2021 5:52 pm 
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I like that! Good idea,!

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 Post subject: Re: Power ON indicator for battery tube sets.
PostPosted: Jul Mon 05, 2021 6:19 pm 
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Rich, W3HWJ wrote:
How about putting a red LED in series with the 35 V to the radio? If the radio consumes only 8 mA, it should light the LED brightly. Of course, if you ever short the 35V line, you will probably kill the LED.

The LED will vary in brightness, depending on whether your radio is receiving a strong signal or not. More audio output means more battery current through the LED.

Rich
B+ fuse "lamp" that actually lights...

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 Post subject: Re: Power ON indicator for battery tube sets.
PostPosted: Jul Mon 05, 2021 6:22 pm 
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Location: Monroe, NC 28112 USA
Rich.... Of course you are right.... I was just fixated on how to find a use for salvaged white LEDs

Robert


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 Post subject: Re: Power ON indicator for battery tube sets.
PostPosted: Jul Tue 06, 2021 12:59 am 
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Replace the on-off toggle switch with a rotary switch. Use a skirted knob with a cutout in the skirt. Paint the part of the front panel black where the notch is located when the set is off. Paint the area of the panel behind the notch when the switch is on fluorescent orange. No electrical power required at all and is similar to the indicators used on some vintage radios.

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 Post subject: Re: Power ON indicator for battery tube sets.
PostPosted: Jul Tue 06, 2021 9:18 am 
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Location: Ashland Oregon
You could put a couple of diodes in the B+ line and draw a couple of volts from across them to illuminate an old school T-5 LED. You won't miss a couple of volts on the B+ line at all.


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 Post subject: Re: Power ON indicator for battery tube sets.
PostPosted: Jul Tue 06, 2021 7:53 pm 
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Location: Lexington, KY USA
A single LED by itself is diodes enough for this application, since the total B+ current is so small.

Using a red color LED will result in a lower voltage drop than the part salvaged from a light bulb.

Three series diodes in parallel with a LED and a resistor would protect the LED from shorts. Just two series diodes would soak up all the current.

Older LEDs may not be very bright at the low B+ current. A newer, high efficiency one can be plenty bright.

Does anyone even make a T-5 LED? A common T-1 3/4 part should be big enough for a panel indicator.

Ted


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 Post subject: Re: Power ON indicator for battery tube sets.
PostPosted: Jul Wed 07, 2021 12:10 pm 
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Rich, W3HWJ wrote:
How about putting a red LED in series with the 35 V to the radio? If the radio consumes only 8 mA, it should light the LED brightly. Of course, if you ever short the 35V line, you will probably kill the LED.

The LED will vary in brightness, depending on whether your radio is receiving a strong signal or not. More audio output means more battery current through the LED.

Rich


One interesting thing about Class A audio output stages, the power consumption and B+ current is not greatly affected by the audio output level or volume. So the set's B+ current will be fairly stable. This makes this type of stage suited to battery use in one respect, but less suited in terms of efficiency. In some sets with effective AGC's the reduction in anode current of the radio frequency stages can reduce the B+ current somewhat on strong stations.
In push pull class B and AB though, the B+ current goes up pretty well directly with the volume level, and the B+ requires more filtering for this reason.

It would seem like the series LED is the way to go, as the current is plenty for modern efficient LED's.

There is another option, for some battery sets. If the B+ voltage is over 65V, a low striking voltage neon is a good option as super efficient and even "period correct" I once bought a large number of small neon lamps from eBay and graded them for striking voltage, some would start at as low as 60V others required more than 90V.

Another option if your filament battery has a good capacity would be a 1.2V Lens Ended bulb, you could drop its current a little with a series resistor to get a nice yellow-orange glow from it. This way you could possibly avoid the LED which is somewhat anachronistic in a tube radio.
https://www.ebay.com/itm/222685717160?h ... SwB4BZ6gHg


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 Post subject: Re: Power ON indicator for battery tube sets.
PostPosted: Jul Wed 07, 2021 5:10 pm 
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Joined: May Tue 30, 2006 4:46 pm
Posts: 10883
Location: Santa Rosa, CA
Quote:
There is another option, for some battery sets. If the B+ voltage is over 65V, a low striking voltage neon is a good option as super efficient and even "period correct" I once bought a large number of small neon lamps from eBay and graded them for striking voltage, some would start at as low as 60V others required more than 90V.


Could be a challenge to find a low strike voltage lamp. As the battery ages, the lamp may not strike. Also, only one electrode of the lamp will glow on DC.

Rich


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 Post subject: Re: Power ON indicator for battery tube sets.
PostPosted: Jul Wed 07, 2021 10:11 pm 
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I built a 3 tube regen awhile back, and used a Rat Shack green LED for the indicator;
https://www.radioshack.com/products/12v ... lder-green

It was too bright initially, so ended up using a 2 watt 1500 ohm resistor in series.


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 Post subject: Re: Power ON indicator for battery tube sets.
PostPosted: Jul Wed 07, 2021 10:14 pm 
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Joined: Jan Thu 16, 2020 12:29 am
Posts: 1521
Rich, W3HWJ wrote:
Quote:
There is another option, for some battery sets. If the B+ voltage is over 65V, a low striking voltage neon is a good option as super efficient and even "period correct" I once bought a large number of small neon lamps from eBay and graded them for striking voltage, some would start at as low as 60V others required more than 90V.


Could be a challenge to find a low strike voltage lamp. As the battery ages, the lamp may not strike. Also, only one electrode of the lamp will glow on DC.

Rich

It pretty easy to find neons with striking voltages in the 60 to 70V region, making them good if the B+ battery is 90V. If the battery is flat and they don't strike at turn on, you know the voltage has dropped below that level. But they are not much good to tell you anything as the battery goes flat.This radio uses a B+ of 90V and has a neon power lamp:


https://www.worldphaco.com/uploads/WORLDFETRON.pdf

Of course once the neon has struck, the voltage can fall quite low before they extinguish, especially if the current is maintained with a lower value series resistor. There is a way to use the neon lamp as a lower voltage indicator but it is seldom done. One method, its power source is mixed via two diodes and two resistors. One could be from say a 30V B+ in the radio. The other from the output of a small step up pulse transformer. At switch on a capacitor that was fully charged to the B+ voltage, is dumped into the primary of the transformer via a switch (A miniature CDI system) this strikes the neon. Then when that pulse has gone, the neon stays on from the B+ supply even though much lower than the neon's striking voltage.


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 Post subject: Re: Power ON indicator for battery tube sets.
PostPosted: Jul Fri 16, 2021 5:30 pm 
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Location: New York USA
Some old battery radios used a Relaxation Oscillator circuit, uses less current than a steady light and the blink attracts attention. Capacitor size affects the blink speed. https://www.researchgate.net/figure/The ... _337285609


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 Post subject: Re: Power ON indicator for battery tube sets.
PostPosted: Jul Fri 16, 2021 6:17 pm 
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Also came here to suggest the series LED. Put a small resistor across it to lower the brightness, if needed (8mA will be bright with a modern LED!). Put a 500 or 1k pot across the LED, then adjust to a good brightness, measure the pot and put in a fixed resistor.


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 Post subject: Re: Power ON indicator for battery tube sets.
PostPosted: Jul Wed 21, 2021 6:38 pm 
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A good cheap source of fairly bright LEDs are the LED Christmas light sets.

For the tuning meter in my Fisher 202 Futura Series receiver I used three green LEDs in series from a Christmas light set. Draws only 480uA and the meter is bright enough to be easily seen.


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