sparks-wit: 65- Dial lamp

Dear Radiofriends,

I need to replace a dial lamp of this Sparton 65.

Looking at  its schematic I could notice that it is a  A-1519.

Unfortunately I don't now what it means.

Do you help me to find out   its voltage and current?

Thank you in advance

Mário Coelho

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Dear Mário,

I do not see a schematic on the model page. If you happen to have one, why don't you upload it?

Thanks,
Mark

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Dear Mark,

Thank you for your reply.

I use to upload in Rmorg all the schematics I own. Not copied from other entities.

I  sent several ones. You can see my score in Rmorg (in my collector's profile).. 

For this Sparton I got the  information about its dial lamp from a schematic which you can see in Nostalgia Air http://www.nostalgiaair.org/Resources/866/M0018866.htm. 

I'm  sure  you understand  that I may not copy it  to send to Rmorg.

About the dial lamp data, have you any information?

Best Regards

Mário Coelho

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Hello Mario,

that's understandable, even though Rider's may be considered public domain today.

A question out of curiosity: are you able to confirm the value of 25 ohms for the R14 that is in parallel to the dial lamp?

Com os melhores cumprimentos,
Mark

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Bom dia Mário,

I have had a look at the schematic and came to the (calculated) conclusion that you'll need a dial lamp of the value 6V 0,06A for that model. The A-1519 is only a part number.

The layout is calculated for a mains supply of 119V (see page 3 of schematic), that's what I didn't notice at first. So please disregard my question about R14, but please calculate for your self to make sure I made no error.

Hope that helps.

Regards
Mark

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Guten Tag Mark,

Thank you for your reply and for your calculations.

Meanwhile I measured the parallel resistor. Its value is 26,5 ohms.

----------------------o-------------------

I also tried to calculate the dial lamp data and  Yes I agree with you. 

My calculations are as follow:

The sum of all tube lamps are: ((4x6,5)+(2x25)) = 75,2 V

The cord resistance is 126 ohms , so  126 x 0,3 = 37,8  V       then  75,2+37,8 = 113 V    

The  dial lamp circuit voltage might be   119 - 113 = 6V 

The current in this circuit is 0,3A, divided by the resistor and by the lamp in parallel.      

to the resistor :  6/24 =0,25A,   to the lamp:  0,3- 0,25= 0,05A    

Dial lamp  might  be more or less  6V  0,05 A

But in this set the parallel resistance is 26,5 ohms

Then  6:/26,5=0,226     and        0,3-0,226= 0,07     

Well 0,06A  is in the middle. It is OK.

Do you agree?

Freundliche Grüße

Mário Coelho

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Boa noite Mário,

the resistor is specified @ 25 ohms, not 24, which makes 0,06A for the lamp. In any case, it's not to be taken too exact and even with 5% tolerance you get to 26 something ohms, so your 26,5 is OK anyway.

Both values seem to be fairly common, so this should not be too difficult to find. Do you still have the broken lamp? Mostly, so I'd guess, the problem is finding a lamp that comes in the original shape.

Anyway you're welcome - even though such calculations are very (too) easy for the most people around here, I am not very familiar with them, so it was fun to excercise :-)

Regards,
Mark

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Guten Nacht Mark,

Thank you for your  correction. 25 ohm it  is, so 60 mA is the recomended value.

The original dial lamp, in this very damaged and now restored set, was not found , so I can't imagine if that lamp was tubular or spheric.

Base is E10 .

Maybe somebody knows which kind of lamps were used in those radios in those old days.

Grüße,

Mário

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bon noct  mario, i have a military trans/receiver of ancient vintage here ,its called a radio compass unit , us army , sparks -with .there is a dial bulb fitted with a baynot type base i.e push in and turn , exactly like an old fashioned rear light car bulb , 6v , i dont know the amp measurement  , it might be worth ur while trying an old type single filiment 6v motorbike bulb in ur set , i did this with my old pre war philips and it works a treat , good luck with ur project , fondest regards maitiu.

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Good evening Dear Maitiu,

Thank you for your kind reply. Nice to ear that  Sparks-Wit had used bulbs of that kind in radio trans/receivers.

As I said in my last post, lamp's base is an  E10 . Only I'm not sure about the bulb glass shape and diameter. 

Thank you for  wish me luck with this project.

Fondest  regards also

 from Portugal

Mário

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I fear the inrush current might kill Your 50 or 60 mA lamp pretty soon.

Just by experience my best educated guess would recommend a #40 dial lamp, which is a 3¼" tubular 6 volt 0.15 amp screw base type.
This is the closest approach to the standard bulbs I could find.
It should be fairly common. Anyway it is still available e.g. at Antique Electronic Supply.

Good luck,
KoBi

 

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Hallo,

As always, I'm very pleased to have a reply from Herr Konrad Birkner. His experience over USA radios is well known by all members. Thank you for your help..

Yes. Our calculations are suitable if we have a progressive increasing current, not for a peak of current ,when all coomponents are "cold" and the resistance of heaters circuit is the lowest.

In this case , like others, the switch on peak of current is very high. and the 60mA lamp may becomes the  weakest component.

This same problem was post by me about one Philips 209U.

 http://www.radiomuseum.org/forum/philips_209u_overvoltage_has_an_explanation.html

There, at the end of the last article I Made an answer but I got no reply:  :-)

"Meanwhile I found in some papers that R30 was placed to protect the scale lamp. Can it be a Varistor (variable resistor)? It has a strange shape."

Maybe here, in this Sparton, should be suitable to use a varistor  to absorb that peak. Do you agree?

Best Regards

Mário

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Dear Mario,
Thanks for kudos!

Well, a varistor would cure the problem. But I do not believe in varistors in the early 1930's. And Sparton clearly specifies a wirewound 25 ohms resistor.

It is a matter of taste how to proceed: Either to spare the component by use of a varistor, or to remain original...

On the other hand I am convinced that a 60 ma bulb was never considered here....

It is now up to You

Cheers,
KoBi

 

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Thank you M r. Konrad and John for your  replies,

Yes, I believe that one must keep the original design of old radios. This Sparton had  a 25 ohm resistor not a varistor.

About  the dial lamp:

 Its value is not related in schematic. I've to choose a lamp which doesn't  colapses immediatly.

 So, I believe that, though the calculations aim  to 60mA, should be  safer  to choose a 0,15A  as Mr. Konrad's expertise  advises.

Best Regards

Mário

 

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