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 Post subject: What type of pilot lamp bulb would work with a 36AM3 tube?
PostPosted: Jun Sat 15, 2019 4:50 pm 
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Location: Pennsville, NJ 08070
I have an excess of the 100ma 18/36 volt AA5 tubes that I would like to put to use in some of my sets which have a pilot lamp. As you may know, the 100ma tubes came late to the tube radio party in the early 1960s, being the 18FX6, 18FY6, 18FW6, 32ET5/34GD5 and of course the 36AM3 rectifier. As far as I have ever seen, no set originally using this lineup ever had a pilot lamp, and the tube manuals seem to give conflicting and vague advice on the use of a pilot lamp with the 36AM3 tube. Some such as RCA said the heater tap can only be used for current limiting and not to drive a pilot lamp. Sylvania from what I have seen said it could, but gave no advice on what type bulb would work.

Digging through Google, I saw a reference that said in passing the heater tap would in normal use only be 4 volts anyway. I assume that would mean if I want to swap this set of tubes into a set with a pilot lamp, I'd need to replace the existing bulb for one rated for 4 volts and I assume 100ma.

I know I can keep the existing standard 150 ma tubes and call it a day, but I'd like to make use of these and it would be an interesting learning experience to see if I could settle the heater tap question for the 100ma 36AM3 and see if it would work with the proper bulb without re-wiring the radio (simply by finding the right bulb to work with the 36AM3).

Thoughts? I had not found much searching Google for a 4V bayonet base bulb. So perhaps the reason the tube manuals are vague about using a pilot lamp with the 36AM3 is because such a bulb compatible with the voltage and current involved doesn't exist and nobody picked up the gauntlet to make such an animal.



Thanks,
Joe


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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Sat 15, 2019 4:56 pm 
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The GE datasheet for the 36AM3 says:
Quote:
The heater tap is provided to allow a portion of the heater to be used as a current-limiting resistor (See schematic). It is NOT intended for panel lamp operation.

Emphasis mine.

Datasheet here: https://frank.pocnet.net/sheets/093/3/36AM3.pdf

- Leigh

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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Sat 15, 2019 6:02 pm 
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You might try an LED replacement lamp.

If it is too dim across the 4V tap, add a series resistor and run it from the 32V tap.

Warm white might be the better color.

The pinball machine parts guys have these in various bases and colors.

Ted


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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Sat 15, 2019 7:36 pm 
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I've used the 100ma tubes as a direct sub for the 150ma, for dial lamp I used a #1850. Be advised, the 1850 has a extremely fragile filament, if you want it to live through turn on/hot restart surges install a pair of 6v zeners connected cathode to cathode across lamp.

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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Sat 15, 2019 7:52 pm 
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Leigh wrote:
The GE datasheet for the 36AM3 says:
Quote:
The heater tap is provided to allow a portion of the heater to be used as a current-limiting resistor (See schematic). It is NOT intended for panel lamp operation.

Emphasis mine.

Datasheet here: https://frank.pocnet.net/sheets/093/3/36AM3.pdf

- Leigh

BOTH -- Sylvania & Tung-Sol say tap can be used for dial lamp tap.

Sylvania was the designer & registrar of tube.

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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Sun 16, 2019 3:35 am 
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Location: Pennsville, NJ 08070
35Z5, thanks for the helpful information and confirming what I thought I remembered seeing about the 36AM3. I've got some lamps ordered today and will give it a try. I like using these 100 ma tubes in sets with plastic cabinets and/or printed circuit boards since they produce less waste heat driving the cathodes than the traditional tubes do. Since they're pin for pin compatible (as long as you swap the whole set out at once), they're one of the best tube substitutions going. I've found they perform just as well as their 150 ma counterparts, except I never knew what to do for sets that use pilot lamps. Now I have an idea.


Thanks again,
Joe


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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Sun 16, 2019 3:27 pm 
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Interesting to note that no manufacturer recommends connecting a pilot lamp to the 36AM3/36AM3A versions of this tube. Sylvania and Tung Sol say it can be done with the 36AM3B version, but it appears a shunt resistor is essential for such operation—and they don’t tell you the value, which means you are on your own if you do it. The B-version has controlled heater warm-up time, and this may be necessary to support a pilot light. Maybe RCA and GE never listed the 36AM3B.

Zener diodes and LED pilot lights were not around when these tubes were developed so it might be possible to come up with a modern way to add a pilot light to a set with a 36AM3/A. But it would take some experimenting and maybe the loss of a few tubes or diodes before the right “formula” was found.

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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Sun 16, 2019 10:32 pm 
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One watt zeners across lamp are fine. I've not seen a heating issue using ½w.

If you have a 36AM3(std, A or B, I ain't picky) with burned out tap, could use the zeners and retain the #47 lamp. Using a #47, 7.5v to 8.2v zeners perform nicely. With zeners in series & opposite polarity, the pair give a voltage based on .707 of 60 cycle sine wave

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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Wed 19, 2019 6:39 am 
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YABUT..
Attachment:
GE OWENSBORO 36AM3 B 1964.jpg
GE OWENSBORO 36AM3 B 1964.jpg [ 237.17 KiB | Viewed 337 times ]
Attachment:
GE OWENSBORO 36AM3 B i.jpg
GE OWENSBORO 36AM3 B i.jpg [ 280.01 KiB | Viewed 337 times ]
Attachment:
GE OWENSBORO 36AM3 1964 ii.jpg
GE OWENSBORO 36AM3 1964 ii.jpg [ 158.99 KiB | Viewed 337 times ]

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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Wed 19, 2019 8:53 pm 
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That data sheet answers the question, the correct pilot lamp is a CM8-54, whatever that is. CM might stand for Chicago Miniature.

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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Wed 19, 2019 10:36 pm 
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Its not as much the filament string providing power to the pilot lamp, it is mostly the B+ power draw.

-Steve

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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Thu 20, 2019 2:48 am 
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Jim Mueller wrote:
That data sheet answers the question, the correct pilot lamp is a CM8-54, whatever that is. CM might stand for Chicago Miniature.

I don't have a CM catalog but in GE's 1974 miniature lamp catalog, there is no listing for a 54.

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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Thu 20, 2019 4:45 am 
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Location: Powell River BC Canada
I looked in GE miniature lamp catalogues here around the period. No CM-8
54 lamp.

I thought CM might mean clock module. So I went back to Canadian GE clock
radios in that era and found a few that wired the clock to the tap on the 35W4.

One used a Mazda 12 (miniature 2 pin) as a pilot across the low voltage part
of the 35W4 heater wiring.

The 100 mA tubes came about as oil/energy legislation. GE radios needing a pilot
could not use a number 12 because the 36AM3 heater is a new ball game.

So maybe an American GE, like the one shown, using 100 mA tubes will shine
some milli lumens on the question.
Attachment:
CGE clock radio with mazda 12 pilot.jpg
CGE clock radio with mazda 12 pilot.jpg [ 247.65 KiB | Viewed 271 times ]

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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Thu 20, 2019 1:48 pm 
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radiotechnician wrote:
The 100 mA tubes came about as oil/energy legislation. GE radios needing a pilot
could not use a number 12 because the 36AM3 heater is a new ball game.

Energy legislation in 1958?? That didn't happen.

In US, 100 ma tubes were 99% history by early '60s, energy legislation was still 10 years in the future. By late '60s tubes were history in table radios and late '73 energy when crunch hit, most TV were solid state, only a few hybrids remaining.

radiotechnician wrote:
So maybe an American GE, like the one shown, using 100 mA tubes will shine
some milli lumens on the question

I've never seen any US GE that used 100 ma tubes. For awhile were popular with Arvin(incl Silvertone) and RCA designed a few. RCA's advertisements spun their 34GD5(repl 32ET5) & 36AM3A making one believe they invented the whole string vs Sylvania. Almost as quickly as RCA introduced 36AM3A, Sylvania countered with the B version.

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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Thu 20, 2019 2:28 pm 
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Here is an RCA ad on the 100mA tubes from February 1961

-Steve

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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Thu 20, 2019 4:48 pm 
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The 36AM3B is rated at 580 mA peak ( the 3 and the 3A were 530). The B had 20 second warm up time. But RCA, in RC26, (1968) stated the heater tap was not to used as a pilot light voltage source.

This raises a question about controlled warm up time tubes. What is of interest,
the slope of heater resistance , or the emission from the cathode ? Everyone knows
the difference between a peppy 27 that shoots the tester into the good fast, and a slow
turtle that takes many seconds.

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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Thu 20, 2019 10:40 pm 
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radiotechnician wrote:
This raises a question about controlled warm up time tubes. What is of interest,
the slope of heater resistance , or the emission from the cathode ? .

I dunno, I've always been under impression "controlled warmup" in these late tubes was to allow series string to heat evenly. I've seen numerous slow warming 35W4 that did not start conducting for 30- 40 seconds, while heaters in other tubes are fully warmed and operating at (pick a figure) 20% over rated voltage. GE 35W4 were notorious for lazy warmup and I recently pulled a new appearing Philco out of a 1960 Motorola just because of that reason. In the tester with 35v applied, from cold it warms up in 12-15 seconds.

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 Post subject: Re: What type of pilot lamp bulb would work with a 36AM3 tub
PostPosted: Jun Fri 21, 2019 4:19 pm 
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Hmmmm, I wonder if you can use a ML-1819 light bulb which is rated at 28v@40ma in parallel with the 36AM3 filament with a resistor in series with the light bulb, but that might upset the filament voltage across the tubes...

Sal

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