[captainclock1988]

Greetings everyone, today I just bought a 1927 Eveready (National Carbon) Model 1 TRF radio for $75 from Facebook Marketplace and it is in really nice shape yet except for some dry-rotted rubber wiring and a torn speaker cone on the original speaker to the radio.

It came with a complete set of tubes and its original power cord was cut.

the cabinet is solid oak and some other stuff.

I was wondering if anyone here has any experience with these early AC powered TRF Sets and working on them as I don't have much experience with them as this is my first TRF set that I've ever worked on, and the earliest radio I've worked on so far.

See pictures below.

[captainclock1988]

More Pictures.

[captainclock1988]

As you can see in the photos the speaker cone is torn in several spots which I thought that maybe i could use the old brown coffee filter paper and diluted Elmer's glue trick on this speaker cone to repair it but the cone paper is of a different composition than the usual speaker cone material (its a  coated paper cone material as opposed to a traditional paper cone material which I'm not sure how coffee filter paper and diluted Elmer's glue would work on this speaker cone material.

Also I need new speaker wire for the speaker because the original speaker wire is damaged (its missing one of its pin plugs and the wiring is exposed in several spots.)
Does anyone know where I could source some new speaker hookup wire for this radio's speaker and have any ideas about how I could go about repairing this speaker cone? 

Thanks,

Levi.

[RodB]

Speaker cones are stiff because they push air. If you use a coffee filter to make the patch it will not be as efficient when it's time to push air. I use a stiff paper to patch holes and coffee filter paper to repair the tears. I also use acid free glue on the repair.

GL

Rod

[captainclock1988]

Thanks for the tip on the speaker repair. The rubber wire in this radio is roached. It looks as if the old rubber insulation on the wiring had melted from the radio being stored in a hot attic for many years and then the rubber had hardened after a while which had actually caused the rubber wires to "weld" themselves together where the insulation from some of the wires had touched each other when the insulation had melted years earlier.

Do you guys have a suggestion of where I might source some good replacement wire to replace the old roached out wires? I know unfortunately some of the wires won't be able to be replaced, like some of the wires coming out of the transformers (specifically the power transformer) but at least some of the wires that are going from the power supply chassis to the tuner chassis that feed the tube grid, filiment, and plate voltages to the tubes sockets on the tuner chassis. I looked at AES and they were all sold out of hookup wire, and I checked over at Radio Daze and they wanted almost $10 a foot for their hookup wire! 

[KCMike]

I think that price is for a 25 ft. roll. I usually order 3 or 4 colors at once.
https://www.radiodaze.com/20awg-solid/
Regards, Mike

[GarySP]

I beat the system a little with the wire. I buy less expensive bulk rolls of white (usually cloth braided cover) and keep several different colors of Sharpie felt tip pens around. I then draw a trace color on the white replacement in the color needed. Good luck! Take care and BE HEALTHY! Gary

[captainclock1988]

OK, So I figured out that this radio is actually a rebadged United American Bosch Model 28 radio and I'm going to need a 50,000 Ohm fuse style resistor to replace the old Plate Resistor that measures open on this unit, the 3 Meg Grid Leak Resistor is measuring fine but the Plate Resistor is measuring open.

As for the filter caps, they are self contained inside the "filter can" assembly which is a permanently sealed metal box that has to be replaced as one whole assembly, which contains a Filter Choke and 2 filter capacitos, which I'm assuming the filter choke is fine but the filter caps will need to be replaced, which I think what I could do about that is to just cut the wire leads from the filter capacitors out of the circuit (while still leaving the filter choke in the circuit and leaving the filter can assembly in the radio for appearances sake and for the filter choke function) and just wire in some replacement electrolytics to where the old filter caps were connected at on the radio chassis (which thankfully is fairly close to each other) and then go from there.

[RodB]

That's what I would do.

[captainclock1988]

Thanks Rod, as for the voltage of those filter caps, I'm assuming that a 450 Volt Electrolytics should be fine in place of the old filter caps? I'm asking because the service information doesn't specify a working voltage for the filter caps in the filter can. 

Also do you have a source for the glass fuse style resistors? I need a new one for my radio to replace the old 50K ohm Plate Resistor thats measuring open in this radio.

[captainclock1988]

Also I found a replacement speaker for my radio on fleabay for $40 and $20 shipping, I haven't bought it yet though because I need to wait until I get paid again which is this coming Friday, they actually had 2 of them for sale on there but the one they wanted over $120 for it which is way too much for the speaker in my opinion, especially since I don't make that much to begin with.

I also found a 50k Ohm wirewound resistor of the fuse style variety on ebay, would that work in place of the old glass fuse variety resistor?

[RodB]

450V should do fine on the electrolytic caps.

[captainclock1988]

OK, so I dug through my capacitor stash and I found a 4.7 MFD 250 WVDC Electrolytic capacitor and a 2.2 MFD 100 WVDC electrolytic capacitor, would those work in this radio to replace the old filter caps? Trying to repair this radio by trying to order as few items online as possible (the speaker and the plate resistor are the exception to that rule as those parts are about impossible to repair without ordering online).

Thanks.

[RodB]

I looked at the schematic and it doesn't have B+ voltages listed but some of the tube plate voltages are. The highest is 150 so I think 200 volts is your minimum for filter caps. You can get a better idea of the B+ by measuring the transformer secondary to the rectifier tube. The schematic lists the filter capacitance at 2 and 4 mfd. Therefore, the 4.7 @ 250 should work for replacing the 4. The 2.2 @ 100 volts is not high enough to handle the B+ of 200 V.

[Radioroslyn]

http://www.nostalgiaair.org/pagesbymodel...040767.pdf
http://www.nostalgiaair.org/pagesbymodel...040132.pdf

Personally I would go w/4mf film @630v. If you use an electrolytic
for #103 the ripple current is fairly high. This could cause it's premature
demise, film caps don't care about ripple current.
GL