Beginners questions... subs for missing/damaged parts

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Beginners questions... subs for missing/damaged parts

Post by lrom on Wed Jan 06, 2010 1:13 pm

I hope this question fits the new category. I am a beginner with a gutted AM "farm radio" Nipperette made by RCA. It uses the following four tubes: 1a7, 1n5, 1h5, 1t5. I have found a schematic for a Northern Electric Baby Champ B4000 which uses a similar tube set. This set was water damaged at some point, with some ash residue inside the cabinet so I assume it may have been exposed to fire.

There are a few components that will need to be replaced due to physical damage. Most of you would junk the set but it's the only one I've got so I will use this for a first experiment despite the flawed logic in attempting repair. Let me apologize in advance for how basic these questions must sound to you all, I can build and program a PC but I have no real idea what to do with an old radio (yet). Can anyone help with advice or resources on how to get replacements for the following:

1 - Tuning capacitor - it is dual gang, I assume 365pf for tuning and the other section for the oscillator. I was told 365pf/170pf on another forum was "standard" but I can't seem to find this value yet. I'd like to use the original tuning dial glass and markings, so I assume I need to be close but is there a little wiggle room when subbing these? Problem is serious corrosion, shaft no longer turns. I'll attempt to salvage it with cleaning if it cannot be subbed easily.

2 - 1st & 2nd IF cans - I have no idea how to substitute these, or even what the values are. Is there standard values to these components, or some way to determine based on the circuit? Coils appear to be open. IF frequency most likely 455 khz.

3 - Antenna and Ocillator coils - I have found "universal" replacements from Antique Electronic supply are available, again the originals are badly damaged. Will a universal sub work in most applications?

4 - Speaker - less than 1/2 watt with an impedance matching transformer suitable for the 1t5? I'm assuming I can use anything that will fit. Unfortuneately the original is completely missing.

Capacitors, resistors and tube sockets won't be a problem as they seem to be widely available. I'll build a 90v power supply for the radio, and I'm not going to worry about the cosmetic stuff until I hear some sound. I will also have what I think is the correct schematic shortly if it will help. Any clues & hints are appreciated.

best regards,

Lee / lrom study

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Re: Beginners questions... subs for missing/damaged parts

Post by Bill Cahill on Wed Jan 06, 2010 2:30 pm

The transformer on the speaker isn't a n impedence matching transformer. It's the output transformer. Are you sure it, and, spkr. are bad?
Are you sure coils, if's, and, tuner are bad?
Usually, if's, and, coils don't go bad.
Tha "ash" you talk about is likely battery acid that leaked.
If the tuner is coroded, it can usually be cleaned, and, made usable again.
May we see some pictures of this set?

You shouldn't need to replace the tube sockets either.
Bill Cahill
I guess this all depends on how bad the dammage is.
Pictures would definately help.

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Re: Beginners questions... subs for missing/damaged parts

Post by lrom on Thu Jan 07, 2010 6:18 pm

Hi Bill,

Thanks for the reply. I'll see if I can get a picture taken of the chassis on the weekend. It's not unusual but it sure is ugly. Very Happy

Speaker and xformer are entirely missing so a sub will be a necessity. The coils mentioned are all physically damaged (broken, torn wires, etc) with the possible exception of 1st IF, which was protected a little bit by the metal can.

Bye for now

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Re: Beginners questions... subs for missing/damaged parts

Post by sprman on Sat Jan 09, 2010 11:05 pm

Hi for the tuning cap try spraying it with Kroil to free it up.Once you have it free you need to clean it very very good with electronics parts cleaner.Cleaning up any acid will be a messy job baking soda and a bit of water mixed will clean that acid up.Then you need to clean up the mess.Sounds like you got your hands full there good luck with it.Sprman Cool Smile

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Pictures of the subject

Post by lrom on Sun Jan 10, 2010 5:45 pm

I disassembled and did some basic cleaning to get some pictures.

view of osc coil:


view of guts top:


view of guts bottom:


view of cabinet rear, chassis straightened out and reinstalled:


view of ant coil and tuner:


view of 1st if coil removed - dirty, may be ok:


I am a bit pressed for time this weekend but I'll break out my meter and check for continuity on some of the coils. The ant and osc coils have gouges in them so I am sure they are nfg. The second i.f. xformer has a leg broken off and was slightly crushed.

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Re: Beginners questions... subs for missing/damaged parts

Post by Bill Cahill on Sun Jan 10, 2010 6:46 pm

I F trans. may be o.k.
Ant. coil may be toast.
Tuner doesn't look that bad.
I have a worse set, and, I'm going to save it.
It was peed all over by a resident mouse.
That's my little 4 tube Air Queen.
Bill Cahill

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Re: Beginners questions... subs for missing/damaged parts

Post by lrom on Sat Jan 23, 2010 1:11 pm

I could not find Kroil, but I sprayed some WD40 into the corrosion that had frozen the bearings. With some force it broke free and I was later able to flush some out some of the crud with some degreasing aerosol. With a little grease in the bearings it will actually rotate the full 180, although not that smoothly yet. I don't dare even try the trimmer cap screws, they look welded solid. Is it necessary to loosen or replace these? I assume it will "almost" be in tune if left alone unless related parts are subbed with items that are not at all close.

I am looking at some of the coils, I can get continuity readings in a couple of them so I may be able to reuse these. The windings are falling apart, is it safe to reattach them with a coating of something like GC Q-Dope? Should I be concerned about the caps in the IF xformers and how can they be checked? I have a digital multimeter with the basic features. Thanks again for all the responses.

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Re: Beginners questions... subs for missing/damaged parts

Post by sprman on Sat Jan 23, 2010 4:12 pm

The Q-dope should be ok.You have to do a complete alignment when done with everything.Dont forget to burn in all the parts.I play a radio a good bit every day for at least 2 weeks befor i do final alignment.yeah dont mess with the trimmer caps untill you do a alignment.Clean that bearing very good till its nice and smooth.You need a cap tester,that way you can be sure all caps are good.Sprmam : )

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Re: Beginners questions... subs for missing/damaged parts

Post by Resistance is Futile on Sun Mar 21, 2010 3:32 pm

That radio isn't in that bad a shape. A q-tip and some isopropyl alcohol will go a long way in cleaning that set.

stick the whole thing in a dishwasher, add a little detergent,don't use the sanitizing feature, as the extra heat will melt parts.

Air dry, safest is setting in the sun for a couple of days.
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Re: Beginners questions... subs for missing/damaged parts

Post by denver on Sun Mar 21, 2010 7:46 pm

Been there done that . Not trying to be smart but if it was me i would try finding another set . TIME AND MONEY going
to put in this set finding parts shipping caps resisters ect.
All kinds nice restoreable radios on the web I bought a nice working philco model 48 - 1256 for 24.95 just needs recap &odds & ends . But i know the felling of dang if ido dang if i dont . good luck . Denver Very Happy
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Re: Beginners questions... subs for missing/damaged parts

Post by Alfred Corbin on Mon Aug 16, 2010 10:05 am

I go with Denver. That's an awful challenge, and costly, for a beginner. For $10 or less you can find a set in reasonably good condition, maybe not working. A project like the one you describe could sour you on the whole future prospect of radio rebuilding.

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Re: Beginners questions... subs for missing/damaged parts

Post by sprman on Mon Aug 16, 2010 8:47 pm

Thats true all comes down to how much you like the set and how much you want the set to play! Look around for another set that does not play.Maybe you can get one good set out of the two..Sprman : )

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Re: Beginners questions... subs for missing/damaged parts

Post by Brig on Wed Feb 29, 2012 7:16 pm

"Most of you would junk the set. . ." Yes, you got that right.

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Re: Beginners questions... subs for missing/damaged parts

Post by Electronhammer on Thu Mar 01, 2012 7:43 pm

Welcome to TRF. Personally, I like a challenge. I say go ahead and resurrect this radio. You can do it! Very Happy
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Re: Beginners questions... subs for missing/damaged parts

Post by Bill Cahill on Thu Mar 01, 2012 7:53 pm

And, I agree.. I've resurected worse.
Bill Cahill

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Re: Beginners questions... subs for missing/damaged parts

Post by Resistance is Futile on Fri Mar 02, 2012 4:24 am

Just make sure you finish it just before easter, then you can really claim it was resurected. LOL sorry I jess had ta doo that. Embarassed clown
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