Restauration of RCA radio receiver
model Radiola 26






Great, I won ebay auction for a 20's american radio set !
This is an earlier superhet, a first generation battery powered radio.
I got some rare doc on the Web.

The supposed schematics -supposed, because in reference with texts, it seems that to hide precious superhet circuitry, RCA had potted components in container- is like this:

Fichier pdf  The schematics

Funny: our american friends give then name "Catacomb" to this container....
Does the fact that this box is located under the tubes sockets plate, and is airtight, such as the "Catacombs", or because my poor english does not allow me to understand this term ?
I think I'll be enjoyed to work on this set !

Six tubes are required for this set: UV199 type, 6 triodes with the same characteristics as WD11, except heating; so, I could make some replacement tubes... The UV199 embases are nearly the same as the 01A's of the AK20, so I could make replics.
The tubes are not here, but this is no so bad: no risk to be broken during shipping.

I got wiring diagram too, with continuity tests (proceeded from outside catacomb box)

Fichier pdf  The wiring diagram...


Now, I'm waiting for monster arrival....

1. The arrival

Great, the parcel has just arrived this afternoon!
It is intact and it has taken 6 days: gone from Ohio on 18, arrived in Normandy on 24!

It must be said that everything went well: no error, no falls, no lost....

Here are some pictures of the package, congratulations to Joe for the package!

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2. Inventory

Beautiful, this set. When closed, it's a simple wooden box : who might think that this is a radio set?

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When opened, it is not more explicit ... We must still admit that these battery-powered radios look a bit strange!

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As I got some photos on the Web of a Radiola 26 in very good condition, I can look at mine, and make a list of what to do.
A) the ebenistry has suffered an attack of moisture: the veneer falls off over a large area. Funny, in Europe, the battery radio-sets had plain wooden boxes, the veneer was used on mains-powered radio sets.

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Moreover, the door (loop antenna) fixation is weak and the whole ebenistry is not enough strongly assembled (corners in the brackets must be tired)

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B) handle is left (I noticed several photos it is rare to find the set with its handle), but the ties are there, and all the fittings too.

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C) the plate cover that hides the tubes is left too. (On other photos, I can see it)
D) the 6 triodes are not here (UV99)
E) when we shook the set, there are things that go around within
F) Horn speaker (HS) is here, it remains to verify whether it's coil is good...

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G) obviously, no batteries, but all the wires seem to be there.

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H) the manufacturer's plate is there, serial No.: 214452.

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For the moment, I can't say that this is a ruin: the body is tired, it's true, but who is not tired when 83 years old?
It remains to open the monster ...




3. Disassembly

I have not found any disassembly notice, then I shall note in the same time I shall do. I will take the opportunity to take some photos of disassembly.

A) removal of the grid that hides the HS. Simply pull the top to yourself and to provide the 2 peaks at the bottom. The fact remains that a single elsewhere.

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B) removal of the door. First, unscrew the antenna control knob at the top of the frame to disengage the top of loop antenna box, then pull it.

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Then unscrew the hinges. On the bottom and intermediate hinges are the wires of loop antenna. After unscrewed, it is necessary to cut off the 2 wires that are welded on back side of hinges, in a hole in the wood.

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C) disconnection of the power supply plug

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D) removal of HS (Horn Speaker). Simply unscrew the 2 screws that hold it on box, through the battery compartment.

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The HS is also hold on a third block; you need pull to the right to disengage block. Then unscrew the 2 nuts that hold the 2 wires, on LS body.

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I take this opportunity to measure the coil: about 1900 ohm, is a good sign!

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These wires cross two times through the body, it is necessary to drag the wires when radio chassis removal.

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Here is the HS outside the body:

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E) displacement of the 2 wires of loop antenna. One wire is soldered on a plug at the bottom of the box (which makes contact with the bottom hook), in the battery compartment. You must unsolder it, then you can then drag it from the hinge into the battery compartment.

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The other wire (intermediary hinge) has a wire that goes to the top hook. These 2 hooks could be used to fix the loop antenna at the rear of the radio set, instead in the front door. To get there, you must remove the cardboard plate fixed by 4 small nails.

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When unsoldered, the wire is free and as it does not pass through the body, then you can remove the radio chassis.

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F) removal of the radio chassis. You must remove 4 screws at each corner (not the two medians). Then, you pull up the radio chassis accompanying wires and powered cord through central hole.

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Here are some pictures of the removed chassis.
Seen from below:

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Retail local oscillator coils:

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One of variable capacitors:

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Elastic suspension:

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power decoupling cap.:

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Damper (red) and 2 capacitors:

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Box "catacomb"

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Seen from top:

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from front:

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disassembly check up:

Ultimately, it's easy to disassemble. Moreover, when removed from the body, the radio chassis is easily testable: everything is available (except, of course inside the catacomb!), and the whole may be tested as it is.
I found that the 2 red dampers of the catacomb have fully cured and that the 3 dampers holding HS also died.
The coil of HS seems good (at least its resistance ...)
By knocking on the walls of the catacomb I realized that they resonate as if the box was empty. Will I lucky that tar is potted only at the bottom?
When empty, the ebenistry seems easy to restore, after all, only the veneer, then with plasticine and wood veneer sheets, I should get out.
At first glance, this radio chassis is slightly different from the schematics that I have: I have not seen jack for external loudspeaker nor 5 / 6 tubes switch.
In addition, there are 2 plugs on the front panel of which I know nothing about the use (for the moment ...)
We can, by removing loop antenna form the door, to operate the radio set with an antenna that hooks to the rear.
The local oscillator coils do not seem to have suffered.
The decoupling capacitor on +90 B has inflated a bit. It looks funny, it is visible from the outside.




4. Check the real wiring, new schematics

A quick review of wiring to realise that indeed, there are some differences:

Fichier pdf  New schematics...

As there is no switch to select 5 / 6 tubes, the T11 transformer is in operation at all times, therefore connected to the anode of L5.
Similarly, there is no jack for external LS, the HS is therefore permanently connected to the anode of L6.

The 2 plugs are in parallel with the primary T11 (H1 and H2), we can connect the headphones. A capacitor filtering AF is connected between the anode of L5 and the ground (CU)

There is no antenna plug, nor coupling cap., however, the two rear hooks(A1 and A2) permit to install loop antenna.

For the rest, everything looks the same (except that I did not open the catacomb!)



Catacomb...