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replacement Lamp?

harry

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While working on the 16B , the "power on" red panel lamp bulb on the front has decided to call it a day, Can anyone point me to a supplier of these small bulbs,these are the same lamp bulbs as used in the 5, 12, 15, meg , trs 80 external HD units, used in the red, and green, square indicator lights, There are no markings on these bulbs,( just too small I quess) I have looked at digi- key, and tried to look at radio shack spare parts list for various hard ware, they do give there own part no. but no details? any help would be great. Thanks,

Harry
 

NF6X

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I don't know the answer yet, but here are some pictures for reference. The DIP is for scale, as I don't have any bananas handy.

IMG_3479.jpg IMG_3480.jpg IMG_3478.jpg
 

harry

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Hi NF6X

Hey thanks for putting pics up, pictures sometimes better than words! Hopefully these are still available somewhere?
 

MikeModifed

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I don't know either, but Roy T. Beck suggests,

"Connect a 470 ohm, 1/2 watt resistor across the red lamp socket on the front of each drive. The purpose of this is to allow the write protect to function regardless of the lamp. Without this, you may suddenly discover your hard drive has become write protected for no obvious reason; the real reason being either a burned-out lamp or one which makes poor connection in its socket."

https://archive.org/details/TRS-80_HD_Bubble_Repair_19xx_-

Mike
 

pski

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I don't know either, but Roy T. Beck suggests,

"Connect a 470 ohm, 1/2 watt resistor across the red lamp socket on the front of each drive. The purpose of this is to allow the write protect to function regardless of the lamp. Without this, you may suddenly discover your hard drive has become write protected for no obvious reason; the real reason being either a burned-out lamp or one which makes poor connection in its socket."

https://archive.org/details/TRS-80_HD_Bubble_Repair_19xx_-

Mike

Yes, the Tandy cheapos using the lamp filament as part of the write-protect circuit.

I would like to find a source for these lamps as well.
 

NF6X

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It's been a while since I was inside my Apple IIe, but I seem to recall that the burned out power indicator lamp in mine is of a similar style. It's also a two-pin lamp, but I don't recall whether it has the plastic base insulator like the one in the TRS-80 machines. I don't have time to open it up at this instant, but maybe this will give somebody a hint that leads in the right direction?

I had considered seeing if I could make a substitute (in the IIe) using an LED and a very small leaded resistor, but I haven't tried it yet.
 

NF6X

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I'm reminded that I have some military CUCV trucks, based on 1980s Chevy Blazers, whose charging systems don't work if the alternator warning lamps burn out.
 

Chuck(G)

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Looks a lot like a T-1 3/4 7381 bi-pin lamp. Shouldn't be hard to locate--6.3V

4436763.jpg
 

harry

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Looks a lot like a T-1 3/4 7381 bi-pin lamp. Shouldn't be hard to locate--6.3V

4436763.jpg

Hi Chuck, I have been looking at the T-1 lamps, and they are very close, the two wire pins on the originals are aprox 9.5mm long ( 3/8"), where as the T-1 range all seem about 6.3mm long( 1/4"), maybe snipping them off, and soldering longer pins will have to do, or maybe the 6.3mm pins might just reach, a case of checking the depth of the contacts in the holder I quess.

gslick... Thanks for link, some of those listed do look promising, and have long pins,

thanks

Harry
 

NF6X

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I took some measurements of the lamp in my 15 meg disk system:

  • 5V present in the lamp socket
  • Lamp draws 112mA at 5V
  • Pin spacing is 0.1"
  • Pin length is 0.39"
  • Overall length is 0.807"
  • Insulator diameter is 0.192"
  • Lead diameter is 0.020"
  • Glass bulb diameter is 0.12"
  • Body length is 0.411"
  • Recess diameter in the socket is about 0.24"

I don't see any good matches on that Mouser page. All of the 0.1" spacing bulbs are 14V or 28V. The 7381 may be too large. The 7715 would work electrically, but I don't know if it would work mechanically by bending the leads.
 
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KC9UDX

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Whatever you find, buy a box of them. These small incandescents are getting scarce!
 

harry

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It seems finding the 3/8" pin length will be the stumbling point! the Farnell lamps gslick has found looks favorite, and all the spec is done thanks to NF6X, I think I am going to have to get some and try, even if it means lengthening the pins. Great help, and response, many thanks.

Harry
 

NF6X

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Of course, you could simply install a LED in the lampholder.... :)

It'll need a series resistor, too.

BTW, I just opened up my Apple IIe. It uses a different bulb with 0.125" lead spacing. I don't know the normal operating current since I don't have a working one to measure.

ETA: I think a 7362 will be right for the Apple IIe. I'll try one out.
 
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KC9UDX

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I know they make LEDs that size with built-in resistors, with an overall rating of 5VDC. Unfortunately, internet searching doesn't turn up any for me at the moment.
 
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