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Curtain burner replace question

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Post by GaryRabbitt on Wed Aug 11, 2010 10:08 pm

Hi all,
I am trying to help someone with replacing a resistancecord. Radio is an Emerson 255
http://www.nostalgiaair.org/PagesByModel/923/M0004923.pdf

The set is so small, no room for a resistor or caps in the cabinet area.

I had suggested using a resistor to drop the 73v.

A member of the radio community who will remain nameless for the time being, set my friend a diagram on how to rework the set.
That would involve changing the 32L7 (.3A) to a 70L7GT (.15A filament) and the 12B8GT (.3A) to a 25B8GT (.15A) Tube pins for the filament also rewired.

Curtain burner replace question Emerso10_800x600


What in everyone's opinion would be the best way for this fellow to get the set working? I'd say leave the tubes original, add an outboard resistor box and leave it alone.


Thanks in advance.
Gary.

He would now have to drop about 22v.
The diagram below is what he suggested.

Upon making the change, he told me the cap across the line cord blew out.

To me, it looks like a little more work than necessary. I would assume the larger tube voltages would also add more heat to the little cabinet.

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Post by Bill Cahill on Wed Aug 11, 2010 11:10 pm

Where's the diagram? I'd say, though, use an outside resistance box with a 3 wire cord.
Bill Cahill

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Post by GaryRabbitt on Thu Aug 12, 2010 11:51 am

Hi Bill,
The diagram (sketch) should show in the post.
Or I have it here:
https://www.tuberadioforum.com/users/2514/34/20/40/album/pr/emerso10_800x600.jpg

If I get a chance, I am going to post on the ARF too. Hopefully someone else has had this conversion to do. The radio he has is nice, but doing too much modification woud not be the way I'd go. I thought originally about mounting the resistor on the chassis, etc would be ok. Seeing this is a very small set, that would be impossible.

Thanks Bill.

Gary.
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Post by Resistance is Futile on Thu Aug 12, 2010 8:34 pm

You will have an inconsistency, in that one tube has more current draw, but will be limited by the smaller current draw. So It will present a perfomance question.
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Post by GaryRabbitt on Fri Aug 13, 2010 12:14 am

Resistance is Futile wrote:You will have an inconsistency, in that one tube has more current draw, but will be limited by the smaller current draw. So It will present a perfomance question.

I'll pass that along to the fellow. Like I say, a large resistor and original tubes is the way to go.
He emailed me and has sent it off to another guy who thinks that diagram will work.
We will see. I didn't want to get too involved with converting this set, other than giving him ideas.

This is what I suggested to him originally. The new resistor would have to drop about 73v. With .3a tubes. X 3.3 would be about 240.9 Ohms.

Curtain burner replace question Emerso10

Anyhow, thanks for the help, I'll let you know how it comes out. I may contact the second fellow and see what he thinks Smile

Take care,
Gary.
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Post by butch on Tue Sep 14, 2010 3:28 am

hi gary;a silicon diode as a 1/2 wave rec. will drop v. to about 87 v. letting you use a smaller res..i have had good luck putting a unpolarized cap in the filament line. on this set around 6 uf ought to do it.the cap method has the atvantage of not putting heat in the cabinet athough it does take a few seconds longer to warm up and will no longer work on dc which i don't think is used anywhere these days anyhow.butch

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