[Rob Quay]

Hi Phorum users, 
I came back from Kutztown last week with a radio my wife REALLY liked- a RADIOLA 28. Studying the schematic and setup instructions it’s apparent that I’ve got quite a challenge in front of me. Unlike many radios I’ve restored there’s no U-tube help available. If anyone has experience with, and is interested in helping with, restoring this beast please pitch in. It’s been a display piece and is very nice looking. It even has the antenna! I hope you’re able to help. Thanks! - Rob

[Radioroslyn]

You might want to look around at the different models of RCA sets that have those catacomb construction. I think I've seen some vids on rebuilding them.

Have fun [Image: https://philcoradio.com/phorum/images/sm...wisted.gif] !

[Rob Quay]

Thanks for your replies. This restoration is starting to look like a deep dive for information. I’ve dug into potted circuits before but I had a decent schematic with capacitor and resistor values. Let the games begin! - Rob

[Chas]

You don't need Youtube video to repair a Radiola 28! It will only mess you up!

I have done several 28's, 25's and the 812, 24, 26 series. All before there was WWW/Internet.

This IS NOT a shotgun replacement project!!! There are NO paper caps inside and only one resistor.

There are NO vintage schematics with internal part values! Each catacomb was custom tuned and aligned on jigs when built then potted. Meaning, any values found and published by others are for that cat that was measured...

A change in a cap in the IF or oscillator will be off and the cat may oscillate or fail to work.

There are no replacement tubes that will substitute and not have oscillation, volume, distortion problems.

The RCA Service notes have the schematic but the schematic in Gernsback's is more user friendly...

Follow the RCA guide on how to make the resistance/continuity measurements  Do that first. Use a VOM not a digital as readings will be deceptive with a digital.

Do all the checks and keep a list of errors.

Then melt out the wax, it is a blend of spruce rosin and bees wax potting.
Can is suspended by the cat body with end hardware and tube top plate removed. Oven set for 265F, after 90 minutes can will begin to slide off to a foil tray. Increase temp to 285, what happens is the volatiles will evaporate causing the melt point to increase, may raise oven temp again but do not go over 295, the compound will then drip off of the components. The melt out is complete when drips once a minute. Pour off potting compound into a mold for later use if desired. Do NOT return the compound as the heat has set a new pour point that is too high for the coils AND the result will also shrink much more and that is what breaks the internal wires.

There are two audio transformer, they are 3:1 do not use the inexpensive transformers, these have been reported to cause audio oscillation. Verified by an ARF member...

There are several failure modes in the cat... Broken RF/IF coil wires, open transformers and "open" grid leak. Leak is 8.2 or so megs, use a 2 watt carbon so leads will not have to be spliced. The grid leak can have a lower value but below 2 megs is problematic possibly a failure of the shunting grid capacitor.

If a coil wire is broke at the coil start, game over, get another cat... Pressing apart the common lamination stack for the IF's will destroy the IF performance despite replacing the coil.

Pay careful attention to the broken wires and the coils they are associated with, there may be cloth tape tags with numbers but these were not recorded by RCA to any data sheets and may not be consistent with anyone's later recording of these numbers.

It is very rare, some 8-tube cats actually have IF adjustment mica compression caps. There is no recorded data why or how, can be seen as tiny holes in between the tube sockets.

There were two manufacturing types of all the Catacombs, the circuits are identical but audio transformer laminations are different, they work the same.

All caps are precision clinched open mica, built to be temperature compensated of brass and steel. THEY ARE FRAGILE and must not be pushed or prodded or de-soldered as the leaves can be broken and the capacitance decreased. They never fail unless messed with...

There is also a neutralizing cap, it is a wire within a sleeve and mimics the capacity of a '99, do not mess with it...

The resulting rosin left on components is fine, do not attempt to remove it only what is needed to repair broken wires. Use 91% alcohol to clean off excess rosin not denatured as the later will leave a whitish deposit.

Much of the wiring terminates to 4-40 long brass screws, these are often loose in the condensite tube socket array, re-tight, some have solder in the nut, re-heat carefully and tighten. Leads that solder to the screw heads often break away, re-solder as needed.

Do Not cut away the whiskers from the terminal strip, extract solder from terminal and unwrap the stranded wire.

Whisker numbers and terminal numbers jump around OEM shows numbers in round circles and squares each respective of terminals and whiskers. Be aware not to mix oscillator coil wires. There is only one combination of the four wires that works, other 15 combinations will not work...

Rheostats often need a cleaning as well as jacks, the jack is removed with a hex key into the from of the jack, there is teeth that bite the wood in the jack frame.

Tighten (tease) all tube socket contacts, re-solder wires and replace audio transformers if need be. Put the cover on retest to the check list.

Follow the rest of the external neutralizing as in the RCA manual. The radio MUST have the correct loop antenna or the loop coupler. Do not directly connect an outside antenna or ground unless a loop coupler is used or several extra turns around the existing loop. Will need a loop link or coupler if radio is in a steel building or a cellar/basement.

When this radio is correctly working, it receives down to the local noise level. Even in DAYTIME I was copying NYC some 300 miles from my home, just the loop...
Beware, be sure you have a battery model and not an AC model. If it is an AC model it can be converted back to battery and operated from an ARBE, if not the RCA 104 speaker/SPU will operate.

The AC model will have a capacitor bank in the battery box these will ALWAYS leak and can be replaced with poly or electrolytic. On AC all filaments are in series and there is a resistor strip which re-arranges filament connections and creates bias. The meter jacks are disconnected and volume rheostat different. On the DC model the jumper strip puts all filaments in parallel. The two rheostats have different resistances, no external capacitor blocks.

I have several spare catacombs and three skeltonized radios that are used to re-align if cat I encounter has failed from a "restorer", fortunately, I have not needed to use them as I have only serviced cats that still have OEM potting.

May, have to mechanically re-align the tuning condensers, they can warp from the condensite side plates shrinking. Alignment consists of "egging" out the condenser mounting holes in the steel face plate, behind the wooden slant front.

If you need more info post here to get my attention.

If you want OEM cat audio transformers I may have a spare cat for salvage...

You can get new reproduction antenna wire (a close copy) if all the rayon has fallen off from an ebay vendor

https://www.ebay.com/itm/333181108573

GL

Chas

[Rob Quay]

Thanks Chas! Great stuff to know earlier rather than later. I sent for an Arbe-III yesterday and will need to float a loan for the tubes! The set was made as a battery unit but someone put a Radio Receptor Co. eliminator in the battery box which I don’t plan to use. The hookups don’t seem to match what the instruction manual shows. I’m not sure if an attempt to employ the old battery eliminator changed anything. This restoration won’t be a weekend job! I appreciate all the help and support. Stay tuned! - Rob

[Chas]

Radiola 28 Service Notes.pdf Size: 1.39 MB  Downloads: 112

Here are the RCA service notes.

There is no "official" service for the catacomb. The intent was that dealers were to remove and replace the entire cat as a unit and send back to RCA...

Thus the logo lead seals on the catacomb ends.

[Rob Quay]

Thanks Chas! It looks like I’ll be doing a lot of continuity/tracing with circuits. It would be great if there’s a record of the restoration process at the end of the road so that other folks can follow along. The “been there done that” gang is a valuable resource for newbies like myself. - Rob

[Rob Quay]

Some questions- 
1. Is the battery terminal strip (figure 2) the same thing as the catacomb frame assembly connecting strip (figure 3) in the service notes?
2. Note 16 says that there’s a neutralizing condenser between terminals 7 and 8 of the catacomb terminal board. I’m not seeing that on the chassis. 
3. There is a wire connecting two of the posts under the connecting strip/terminal board that doesn’t appear to be factory installed. Can that be a work around for a non functioning circuit or a change of wiring to accommodate the ancient battery eliminator that’s in the battery box?
4. The lead seals are missing from the catacomb but the rosin appears untouched inside. 
5. Does the row of wire resistors have to be removed if it’s necessary to get into the catacomb?
Sorry for all the questions. I don’t want to mess this up! Thanks. - Rob

[Chas]

1 - The battery harness terminal strip easily removable and has the battery harness connected (soldered) to it. It mates to specific terminals on the long terminals strip. It may still be present but it may be the terminal strip used with the 104 power unit.

Is there a large cap bank in the lower battery box? If so there should be one large block is a 4mf that is across the 24 volt filaments.

2 - It is in the upper right corner of the radios frame, if not, it is missing...

3 - There is no way to "shunt" anything inside the catacomb to effect a repair. However, it is possible to bring the plate circuit of the first audio out to feed an input transformer on a power amp like a 210. That mod is not internal to the cat as all 8 tube cats are identical, even in the Radiola 30 and any of the Brunswick/Electrola models. If you find a cat with 7 tubes, there is a block off plate covering socket eight, that cat is for a power amp but all internal circuits are present.

4 - No seals means the cat was repaired outside of RCA, returning the original rosin would create a failure soon as it shrinks considerably more. It is possible the shop had "fresh" potting rosin on hand.

5 - Yes, The strip should be removed to melt out the cat. I fear that the Receptrad power unit requires those resistors to set up bias and it means that all the filaments are wired in series. That is not good as an ARBE cannot provide 24 volts at 60ma...

Take a look and see if the voltmeter jacks have been disconneted or at least one of them...

You will have to find a jumper strip so filaments are in parallel. I will have search and see if I have one. Failing that a WTB in the classifieds for a 8 tube cat with the jumper strip.

Do the go/no-go test as described in the RCA notes. Note the defects and write down. If your lucky there will be no problems. The information is vital to locating bad circuits once the cat is melted out.

Manipulating an open cat is risky as the wires are very fragile.

The ARF classifieds may be a better source for old catacombs. Some 10 years ago I found several.

Be SURE you have the correct loop, a 28 loop is center tapped, check the continuity of the loop. If there is no center tap it is for a Radiola 25 and the wrong inductance, even if a tap is created.

Best to take before pix. As there are no early pix that are clear enough to deal with correcting altered wiring.

BTW there is at least on collector that saves cat rosin, used to re-stuff tubular capacitor ends...

Chas

[Rob Quay]

1. There’s no cap bank in the battery box. 
2. Is the neutralizing condenser connected to the end variable cap? If so it’s there. 
3. The voltmeter connections are intact. 
4. A picture of the cat is included (hopefully).                 

[Rob Quay]

Sorry- I got trigger happy with the photo!

[Chas]

You have a power harness... I cannot be sure it is correct for battery operation. Usually, the harness is backed by a long phenolic strip that holds all the spade lugs in the correct places.

Do not remove the harness, there is information there. Compare the harness with any of the schematics to find out what the terminals are.  Look up and under the edge of the cat there should be numbers molded into the composite socket array next to each wire (whisker). There are no markings on the long terminal strip but between the harness, and whiskers it should be possible to find your way around. Refer to the socket numbers and pins.

Then, do the continuity test using a VOM 1000/ohms/volt is best. A DVM will not show correct continuity reads especially when working around the transformers.

No need to record actual reading in ohms, it is irrelevant it either has continuity or not. Record any error to a list. Expect good audio transformer windings to be no more than 10k often lower.

You have the resistor strip. I will have to see if I have plain jumper strip that I can spare.

It may be possible to make one from perf board, wire and terminal pins. Or, with the correct data, strip off the windings and solder jumper wires. Hate to spoil a good resistor strip though.

Look at page 12 of the PDF this is the correct drawing for the DC battery version. Note the darker wires across the center, that is the jumper connections...

As you become familiar do not remove any connections unless they are confirmed with the schematic. It is VERY EASY to get lost in the 28.

Do confirm that the harness can be used. I suspect that there may be different connections for the "A" supply and possibly bias because of the resistor strip series filaments. Some temp relabeling of the wires with masking tape flags may help.

I'll check in a few days.

Remember, motorcycle mechanics fixed these radios 100 years ago, using the data we see now... Electronic Technicians had not been invented yet...

A good thought. The '99 tube as well as the 120, have thoriated filaments. When the emission gets low, they can be rejuvenated. That, makes it possible to get a better price on low emission tubes and chance that they can be restored to work...

Se here for rejuvenation:

http://www.nostalgiaair.org/References/A...lash08.htm

Have you confirmed the loop?

The top of the cat is cadmium plated and often has green cad. oxide. This can be removed chemically with sodium bi-sulfate, pool acid, then lightly buff. Seal with a wash of white shellac and it will retard turning green again. Solution is 2 oz dry measure to 1qt warm water. Acid works when there is no oil or greasy grime so dish wash soap first then acid dip, only 5 minutes, all in plastic tub, use plastic tools. Rinse with water. excess acid can go in pool or down drain... Store any acid solution in a plastic bottle...

If the acid is used to clean other parts, do not place parts made with mixed metals, the acid will electroplate metals but poorly and blacken them.

The large round RCA 100 cone will sound good, but this radio often had the UZ-1325 hard rubber horn.

Chas

[Rob Quay]

       
1. Yes, the correct 3 contact loop ant is present but it needs new wire. 
2. I have a nice 100 speaker to go with the radio. 
3. A quick check shows continuity through all tube sockets. 
4. I have a Jefferson Tube Charger that I’ve used with’01A tubes. 
5. The Radio Receptor 28 that came with the set seems an odd choice for the radio, no high voltage, no C battery hookup, mismatched battery harness. 
6. The more I study things the clearer the picture is. Thanks for your help!

[Chas]

1. Yes, the correct 3 contact loop ant is present but it needs new wire. 
2. I have a nice 100 speaker to go with the radio. 
3. A quick check shows continuity through all tube sockets. 
4. I have a Jefferson Tube Charger that I’ve used with’01A tubes. 
5. The Radio Receptor 28 that came with the set seems an odd choice for the radio, no high voltage, no C battery hookup, mismatched battery harness. 

1. You can get a very close replica of the Radiola loop antenna wire from Micheal Conrad here:

https://www.ebay.com/itm/333181108573

He & I collaborated many years ago I having braiders at the time, he also as well as having correct textiles.

Make the replacement wire as near exact to the existing length on the loop frame.

2. Be sure the internal coupler inside the 100 can pass the plate current for the 120 tube.

3. O.K. on filament connections but go through the complete list. Remember take the readings but the resistor strip is part of those readings, so a winding external can be open. The strip is going away be sure any no-go is internal to the cat.

4. Be sure the Jefferson tube rejuvenator can do UX-99's, FWIR it can do UV-99's but a V to UX adapter in the socket will allow U-99's. Do not plug a X-99 into the 201a socket, the higher voltages will blow the 99... That is possible to do with an adapter too.

5. The Radio Receptor would have been used with a "C" battery, there is no current taken from a "C" battery in "most" 20's radios, it will last for years. No high voltage meaning no 135 volts for the 120 tube. Well, use a 99 in the last audio and the 90 volts w/4-1/2 volts "C" works.

None the less any restoration of the RR supply will be a challenge too. The ARBE-III does it all.

Chas

[Rob Quay]

1. ARBE-III arrived today. 
2. Ordered antenna wire and tubes. 
3. Continuity circuit test finds 22 to G7 (condenser no. 2) shorted. P2 to G2 (condenser no. 5) shorted. Everything else checked out. That’s with the battery harness disconnected.