06-01-2024, 08:09 PM
There is but one 8 tube catacomb, they were built in FWIR two different facilities so the internals may not appear alike but hookup internally is the same.
The SAME catacomb can be for AC or DC.
The RCA notes are for the DC catacomb with a jumper strip attached...
This is an extracted test list for the 28-AC-Catacomb:
The test list above when done on the existing catacombs with the resistor strip, performed as described should be valid.
The EXTERNAL resistor strip for the Radiola 30 is different as the last audio tube is not used and output routed to a PA in the power supply. But the 8 tube cat is internally the same!
I CAN tell you the cat I provided has a bad second audio, I read the resistance to be open on one winding with a Simpson 260...
Look carefully at the RCA schematic that has the jumper strip. Then reference the terminals in the continuity chart, follow the circuit through the jumper strip schematic to the whisker numbers. I showed the whisker numbers in one of the images.
Since you do not have a jumper strip, the chart is not valid for a check list with a resistor strip...
As said in an earlier post, an ARBE will NOT support series filament operation (resistor strip) of the Radiola 28. The filament voltage is 34 volts at 60 ma. when in series.
The resistor strip purpose is to connect all the tube filaments in series AND provide bias, as the 104 supply does not provide the bias.
With the jumper strip the filaments are wired in parallel and connection brought out to provide bias via battery via the whiskers to the terminal strip...
With the resistor strip removed, referencing the terminals follow through to the whisker number, then complete the continuity test.
Pleas do not use a DVM for the continuity preferred is a low resistance VOM as low as 1000 ohms/volt. OR use the battery and headphones "click" test. Fair warning a click test of the audio transformers could result in a inductive jolt if handling bare conductors for testing.
If a certain CAPACITOR fails short. trace the wires to that cap internally, carefully de-solder the easiest end to get at. Do NOT push or swing the cap around as that WILL break the foils and ruin the cap and test in-place. If it is truly shorted it will show there, but it may be tinkering has been done to the whisker wires where they crossover in the top of the catacomb that is not potted and accessible.
Once your satisfied then decide which resistor strip to cut up and create a jumper strip. You may have to fabricate or cut at least one spade lug on the former resistor strip to be sure it makes the correct connections.
Note, the Gernsback Radiola 28 schematic has a internal wire error for the filaments inside the cat at tube #V6 & #V7. It shows the tubes permanently in series, that is not true, there is a missing connection "DOT" (connection) and not a "Semi-circle" (no connection)...
Useless information, there is a continuity error in the RCA test list for the 6 tube Radiola 25 catacomb.
So errors DO exist, but I have not seen any others for the Radiola 28...
If investigation proves the resistor strip is too "messy" to convert to a jumper strip. Post a WTB to ARF classifieds. The Philco Phorum may not have "Radiola" readers...
I note that some common jumpers on the resistor strip would have to be split to make it work as a plain jumper strip, It seems now tedious as well as messy...
Oh, the component numbers are not the same in the RCA vs the Gernsback schematic
Chas
The SAME catacomb can be for AC or DC.
The RCA notes are for the DC catacomb with a jumper strip attached...
This is an extracted test list for the 28-AC-Catacomb:
The test list above when done on the existing catacombs with the resistor strip, performed as described should be valid.
The EXTERNAL resistor strip for the Radiola 30 is different as the last audio tube is not used and output routed to a PA in the power supply. But the 8 tube cat is internally the same!
I CAN tell you the cat I provided has a bad second audio, I read the resistance to be open on one winding with a Simpson 260...
Look carefully at the RCA schematic that has the jumper strip. Then reference the terminals in the continuity chart, follow the circuit through the jumper strip schematic to the whisker numbers. I showed the whisker numbers in one of the images.
Since you do not have a jumper strip, the chart is not valid for a check list with a resistor strip...
As said in an earlier post, an ARBE will NOT support series filament operation (resistor strip) of the Radiola 28. The filament voltage is 34 volts at 60 ma. when in series.
The resistor strip purpose is to connect all the tube filaments in series AND provide bias, as the 104 supply does not provide the bias.
With the jumper strip the filaments are wired in parallel and connection brought out to provide bias via battery via the whiskers to the terminal strip...
With the resistor strip removed, referencing the terminals follow through to the whisker number, then complete the continuity test.
Pleas do not use a DVM for the continuity preferred is a low resistance VOM as low as 1000 ohms/volt. OR use the battery and headphones "click" test. Fair warning a click test of the audio transformers could result in a inductive jolt if handling bare conductors for testing.
If a certain CAPACITOR fails short. trace the wires to that cap internally, carefully de-solder the easiest end to get at. Do NOT push or swing the cap around as that WILL break the foils and ruin the cap and test in-place. If it is truly shorted it will show there, but it may be tinkering has been done to the whisker wires where they crossover in the top of the catacomb that is not potted and accessible.
Once your satisfied then decide which resistor strip to cut up and create a jumper strip. You may have to fabricate or cut at least one spade lug on the former resistor strip to be sure it makes the correct connections.
Note, the Gernsback Radiola 28 schematic has a internal wire error for the filaments inside the cat at tube #V6 & #V7. It shows the tubes permanently in series, that is not true, there is a missing connection "DOT" (connection) and not a "Semi-circle" (no connection)...
Useless information, there is a continuity error in the RCA test list for the 6 tube Radiola 25 catacomb.
So errors DO exist, but I have not seen any others for the Radiola 28...
If investigation proves the resistor strip is too "messy" to convert to a jumper strip. Post a WTB to ARF classifieds. The Philco Phorum may not have "Radiola" readers...
I note that some common jumpers on the resistor strip would have to be split to make it work as a plain jumper strip, It seems now tedious as well as messy...
Oh, the component numbers are not the same in the RCA vs the Gernsback schematic
Chas
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
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