Hallicrafter S120

[KA3AUX]

Good Evening, I am new to this forum but have been reading some of the posts on and off for the last few weeks. It looks like a lot of great knowledge amoung the folks that frequent this forum.
I am new to restoring Boatanchors so I'm starting slow. The S-120 that I'm restoring has a gloBar resistor in series with the filaments of the tubes and the dial lamps. It is R20, 880-100 ohms(?). The end wire came off of it. I don't know if it burned off (no obvious burn marks) or the previous owner was playing in it and broke it.
I am trying to find a source to purchase one. Anyone have any idea who may sell them?
I'm not 100% sure  how they work but if the knowledge from my electronic classes 27 years ago still serves me, I vagly remember that upon powering up the resistance is 880 ohms and start to drop to 100 ohm after heating up. Hopefully I remembered that correctly.
Also, there is a multi capacitor in it that may need replaced. It is a 40ufd, 40ufd, 60ufd 150 volt electrolytic. If I can't find one I guess I will have to get single caps to replace it.
I have looked through Antique Electronic Supply and Radio Daze. I havn't had much luck in those catalogs.
Any suggestions would be greatly appreciated.

Thanks

Rick
P.S. Sorry for being so long winded...

[WB2WIK]

If a resistor changes resistance over time, it's a non-linear resistor like a thermistor, which changes resistance with temperature.

I think the S-120 fed all the heaters in series directly from the 120Vac line without a transformer (it was a cheap POS, $69.95 brand new in 1962 -- I bought one then -- big mistake) so this isn't a big surprise.

You could substitute a regular WW resistor without it mattering much.   The only objective is to have the "whole string" including all the tube heaters and the resistor drop 120V at the current drawn by the lowest current heater.  Whatever that is.  Not critical.

My opinion is that the S-120 will never be "collectable" because it simply isn't good enough; and if you depreciate $69.95 over a period of 45 years at $1 a year, it's now worth $24.95.  Maybe.  Probably less.

I'd shoot it and put it out of its misery and get a real receiver.

:-)

When I "traded up" from an S-120 (c. 1962) to a National NC-125 (c. 1950) that was a huge "step up" in performance that I'll never forget.

WB2WIK/6

[KA3AUX]

Thanks for the info. I will try a 100 ohm WW resistor to see if it works.
Like I said I'm starting small with this receiver to "get my feet wet". I also have a Hallicrafters S-38C and a SX-25. So I do have a couple of other radios to work up to.

Rick

[KE3WD]

http://www.globar.com/

[KA3AUX]

I tried the 100 ohm resistor  and it causes a current rush. The lamps look like they are going to blow for a brief second. I think I need a better way around it.
I wonder if putting a delay circuit in would help any? Sort of what is used in amplifiers.
Has anyone seen this problem and how did you get around it?
I havn't found anyone who sells globar resistors to the consumer level yet.

[KM5Z]

> I tried the 100 ohm resistor and it causes a current
> rush. The lamps look like they are going to blow for a
> brief second.

This radio has pretty much the same tube lineup as the S-38. It does away with one tube by using a selenium rectifier.

I have both radios, and the S-38B does the same thing, as it lacks the 'globar' resistor. If you can find them somewhere (mouser.com, etc), you need a
'Negative Temperature Coefficient Thermistor'...

See:
http://www.sxlist.com/images/www/hobby_elec/e_resistor.htm

...Under 'Thermistor'.

> I wonder if putting a delay circuit in would help
> any? Sort of what is used in amplifiers.

Too complicated - I think you can fix it if you can find a close approximation to the thermistor.

Try: http://octopart.com

This is a sort of global parts search. He searches digikey, mouser, newark, etc all at the same time for one part entry.

I entered 'globar' and found at least one NTC thermistor at Newark:

http://www.newark.com/jsp/search/productdetail.jsp?SKU=38C4165&CMP=AFC-OP

Newark, I think, sells to anyone; just open an account. Mouser.com and Digikey.com are all great parts houses and tolerate small orders.

BTW - I think the S-120 a swell receiver. It's a general-coverage, consumer-grade model. It ain't ham-grade. But mine's a 'daily driver' here at my desk at work!

73
Mike Yancey
KM5Z
Dallas, Texas

[KA3AUX]

Mike,
Thanks for the reply, I never thought of using thermistor. I will have to get one and try it.
Sorry for the late response. I get busy with "life" and the hobbies get pushed aside...

Thanks
Rick

[WB4LFC]

I owned An S-120 for several years.Bought it in 1964.
It was modeled after a type of design called the "American Five".That was design popular with with radio manucturers in the 50's and 60's.
Take my advice and chunk it!The S-120 didn't receive very well.They are not very sensitive and not very selective either.They were hard to get single sideband to work because you had to fiddle with the BFO control to make it work.CW worked pretty good.
I made several contacts on CW with mine using a home made transmitter.
There are lots of better radios out there.