[camateg]

Hello -

I just came home with a neat little RCA Model 100 cathedral which may have a lot of potential. Unfortunately, since it was raining and windy when I met the other party in the transaction, I didn't realize until coming home that the power transformer is completely gone (i.e. not present). :-(

I have a schematic in PDF form which is nearly totally illegible but suggests that the transformer has a total of 4 taps coming out, including the ends. The parts list suggests that I likely (should) have an RCA stock number 9045 transformer, but it seems that Google is not my friend today on this matter.

My questions:
- is is possible to find the specs or does anyone have the specs for such a transformer?
- is it "normal" enough to find a generic, modern replacement? Cost effective?

Thanks for any help!

Matt

[rghines1]

Not typical to see a series filament string in a radio with a power transformer.
You may have to consider rewiring the filament string in parallel including the dial lamp. All tubes are 6.3V heater filaments. Would need a power transformer with a separate 6.3V winding at 3 amps with a HV winding of 300V (no tap) at 60ma should be adequate. Won't be original but will get the radio playing again.

Richard

[Arran]

If it's a true cathedral set that places the tubes in the era before 6.5 volt tubes, usually 2.5 volt tubes like #24s and #27s or #56s and #58s. As far as I know they didn't normally make series string sets unless they were for a DC power line (not AC or DC). What is the tube lineup for this set, the only RCA model 100s I could find is an RCA Radiola 100.
Regards
Arran

[rghines1]

Same as RCA model 101
http://www.nostalgiaair.org/Resources/699/M0014699.htm

[Arran]

It looks like it's probably a form of cathedral tombstone, or maybe just a tombstone, other then Philco nobody else was making sets in true cathedral cabinets into the 6 volt era. That is a weird circuit, it appears that the tubes are in a series string, including the rectifier, and that the string is powered from a tap off of the high voltage secondary, probably 25.2 volts at 300 ma, there are no seperate filament windings. The closest Canadian equivalents to this set with four tubes still had filament windings, a 5 volt and a 6.3 volt winding, and a normal center tapped high voltage winding with a type 80 rectifier.
Unfortunately since transformer gone there isn't much hope of finding a new off the shelf replacement, if it were still there but burned it could be rewound. Unless you can find a replacement salvaged from a parts chassis, or by some miracle find a new old stock one, I think you will be in for a re-engineering project to get it running. It may be possible to find a transformer with a 25.2 volt 300 ma secondary, but as a stand alone unit, and find another for the high voltage side, or get a transformer for a set equiped with a type 84 or a 6X5 and rewire the filament circuit, it will require a 1.2 amp 6.3 volt filament winding. You could also go transformerless but then you would need something to drop the line voltage like a big capacitor or resistor if you don't plan to really alter the set. Unless you are really in a hurry to get it going I would put it aside for now if you have other projects pending.
Regards
Arran

[codefox1]

Agree, this is one of more bizzare power supply I have ever seen. Lots of options here, none too difficult.

I think you could possibly obtain a beefy control transformer (120/240 volt primary and 24 volt secondary at least 1 amp since we will derate as follows)

Seperate the 120 volt windings if they are tied together at the terminal to provide isolation. Use one of the primaries as the input, use the 24 volt secondary to feed the filaments, and the remaining 120 volt through a solid state voltage doubler. I've done this a few times with farm radios and it works out well.

You could also rewire the filaments in parallel and use a heat sinked! LM317 to provide the 6.3 filaments.