[TN Allen]

I have 3 Radiola 18s, after replacing the volume control rheostat, one works well, so far, and I like the sound. I have 2 RCA 100 speakers that sound muffled. I looked at disassembling these to repair them, but the screws are frozen in the pot metal and have been damaged by someone earlier. I did look inside one speaker enclosure, the speaker mechanism looks interesting, but repairing these will need to wait. I have a nice 2K Ohm primary to 8 Ohm secondary transformer connected between the speaker output jacks on the Radiola 18 and a Jensen K950 PA speaker. In my opinion, the sound is remarkably good and clear for a 1928 radio. I suspect the Jensen speaker is fairly efficient and that this contributes to the sound quality. A few other speakers I tried were not nearly so good.

I've tried the 2 sets that don't work, the power supplies seem to be the problem. Rather than risk the one good set by using its PS to try the other 2 tuners, I've assembled a new power supply to try the two non-working tuners. It isn't wired yet, but is ready to be. This also seemed like a good way to learn about the way these sets work. I'm thinking that it might also be interesting to try building just the audio section of the tuner, the #26 & 71 tubes, and using a CD player, 78RPM turntable or other sources.

I have the Radiola Guy information and various other materials with schematics for the Radiola 18. I think I understand some of the circuit, and have been thinking it might be possible to assemble the section of the schematic including tube number 5(UX-226) & tube number 6(UX-171-A), and connecting the source(CD Player & Etc.) to the grid of the UX-226. I'm certain it's not quite that simple, and that additional circuitry is required. I also would need to know the specifications for the transformer between UX-226 and UX-171-A, and find a source for it. If anyone has suggestions for this project, I'd appreciate hearing these.

If there are other amplifier suggestions using different tubes that are compatible with the Radiola PS, I'm interested in that possibility as well.

[Arran]

The RCA 100 loudspeakers also have a paper cap in series with the coil, so that may cause distortion if it is failing. The power supplies are fairly simple, electrically, but it would probably be a good idea to replace the paper filter caps for reliability, you can find substitutes at Mouser, along with some of the antique radio restoration suppliers. Antique Electronic Supply can furnish replacement audio interstage transformers that will work with the Radiola 17 and 18 type sets, unless you want to try a solid state substitute, The front ends of these are fairly simple, basically just RF coils with some neutralizing capacitors, not sure how reliable the resistors are but that's easy to check.
Regards
Arran

[TN Allen]

Hello Arran,

Thank you for the response and information. I found this interstage transformer on Antique Electronic Supply's website. It is for the Radiola lll. Is this the transformer you suggested?

https://www.tubesandmore.com/products/tr...ment-audio

Thank you

[Radioroslyn]

So after reading three paragraphs I think what you are seeking is a transformer to connect the 26 plate to the 71A grid. I would go with this one https://www.tubesandmore.com/products/tr...tage-10-ma  The one you pick is for a particular set which is a collectible hence the $60+ price.
I'm cheep.

[MrFixr55]

Edited 12/21/22
The P-T156 transformers offered by AES *Antique Electronic Supply) do seem to work well for this app. I have a Radiola 16, 17 and 18, along with a 100A loudspeaker. I used the P-T156s on the 16 and 18 successfully. The cabinet for the 100A speaker is pot metal which swells. This is possibly the reason for your not being able to remove the screws. The speaker is a magnetic type very common for the era and not known for being high fidelity. There is a "PI" Filter that acts as a low pass filter. However, they were much less expensive than the GE "Kellog - Rice" Electrodynamic speaker, the archetype of all dynamic speakers that followed. For best fidelity, any good 8" speaker with a 2K Ohm to 8 Ohm output transformer will do. (A transformer from an AA5 AC DC Radio is just what you need.) Your Jensen is just the trick. PA Speakers with a 70V Matching transformer work well. Use the 0.5W 0.75 W or 1.0 W tap

The Radiola 17 and 18 used the new "AC" Tubes, the '26, '27 and '71A. The existing 01A tubes, used on the Radiola 16 and many battery operated radios dating back to 1921, would hum horribly if the filaments were powered by AC.

What are you using as a transformer for the power supply that you are building? The 26s operate on 1.5VAC, the 27 operates on 2.5V AC and the 71A runs on 5V AC or DC.

Do expect hum! The '26 and '71A are touted as an "AC" Tube by the "P T Barnums" at RCA at the time (Read their ads that described reception by RCA radios of this era as being indistinguishable from live performances). However, being that they were both direct heated tubes, there will be hum. The 26 hum was mitigated by the slow responding low voltage high current 1.5V 1A filament fed by a supply with a variable rheostat for hum balance. the 71A Filament differed from the 71 by also having a more heater-like thoriated filament whose emission varied less during the peaks and valleys of the AC than the original 71 tungsten filament did. The real AC Tube in the set is the '27, the first true AC Tube with separate heater and cathode. This is the archetype of every voltage amplifier triode with a heater and sleeve cathode ever since. There was a big push to make what RCA referred to as a "Socket Powered" radio. The first radio in this series was the battery powered Radiola 16 which used 201As ('01As) for the 3 RF amps, detector and 1st AF Amp. The detector used a spring mounted 4 pin socket to minimize "microphonics. The "Power" Amp was a 112A, emitting 0.35 Watts at 135V Plate voltage. The Radiola 17 used the same chassis and almost all parts, except the detector socket and tubes as the Radiola 16. The 27 was used as a detector instead of the 26 as, for some reason, the 26, which is functionally similar to an 01A except for filament, was deemed as unsuitable for use as a detector. Possibly, the AC on the filament would raise the hum level, which was already objectionable by today's standards. The Radiola 18 was similar to the Radiola 17 except for the IF transformers which were "neutrodyne-like" without violating the Hazeltine patent, a slightly different power supply design and the use of "choke and capacitor" coupling instead of the transformer coupling of the Radiola 17 and the direct coupling of the Radiola 16. Note that the Atwater Kent 36 and 40s used the same circuit as the Radiola, while a Zenith of the same era used 27s for all tubes except the output tube. The RCA Radiola 60 Superhet, introduced the same year as the Radiola 18 also used 27s for all tubes except the output tube. This contributed to better fidelity through lesser hum. In addition, the Radiola 60 used a biased "Power Detector" instead of the grid leak detector used by RCA
BTW, Westinghouse and GE built almost all RCA Radios from its founding in 1919 till the acquisition of Victor, (who had started producing radios in 1928) and the introduction of the Radiola 80. Then the tables were turned and RCA built almost all GE and Westinghouse radios from 1930 till between 1934 and 1936.

The 71A has an output power of approximately 0.7W.

I built an RC Coupler with a switch and volume control that subbed for the non-existent radio phono switch. I was not impressed with the level of distortion using this as an AF Amp. The hum likely contributed to that. There are several discussions on the internet on single ended amplifiers and preamps using constant current power supplies, 01A and 71A tubes. (Other than the filament voltage, the '26 and '01A have very similar characteristics and the same base diagram.

Another source of distortion is the "grid leak" detector, which had higher distortion than biased detectors or diode detectors.

[TN Allen]

Thank you for the responses.
I'll use the less expensive transformer, I like saving money too.

I have a Hammond PT143 transformer with the required voltages except the 1.5V, I thought perhaps the 1.25V from the 2.5V CT might suffice for the #26 tube, or a resistor to drop the 2.5V to 1.5V. Unfortunately I am somewhat new to electronics. 

I'm using Radiola Guy's schematic and booklet for component specifications. 

I have included a photo of the PS. I think I have all the necessary components, but have yet to solder it all together.

[TN Allen]

I have this PS transformer:

https://www.tubesandmore.com/products/tr...v-70-90-ma

[MrFixr55]

Hi TN,

a wonderful layout on that power supply, beautiful looking.

IMHO, yes, using 1.25 from the 2.5V winding would work, assuming y\that you are installing the "hum balance" rheostats used in the original PS. An alternative, if you have them is to replace the '26s with '01As, get an old computer power supply and use the 5V DC to power all the tubes except the '27. There will be much less hum.

BYW, what is wrong with the original power supplies? These are usually reliable, although sometimes the filter caps (oil / paper style) short. You can test the transformer by simply removing the '80 rectifier and checking voltages. If the transformer is good, you can simply replace the caps and chokes. Do note that that even though they look similar, the Radiola 18 PS is different from the Radiola 17 or Radiola 60 PS.

Below are 2 schematics from N/A, one for the Radiola 18, (similar to the schematic from Radiola Guy). The other is for the Victor 7-11, a radio / phono combo that uses the Radiola 18.

http://www.nostalgiaair.org/PagesByModel...040317.pdf (CAUTION! Do NOT use the voltage chart in this diagram, it is fr the DC Model!)
http://www.nostalgiaair.org/PagesByModel...040265.pdf

These are the same schematic, just presented differently. (RCA did not own Victor at the time). These may be useful. Unfortunately, no specification is given for the rheostats or resistors in either schematic. However, the schematic for the Radiola 33 is similar to the Radiola 18 and does contain resistor values (except for the rheostats), and also a voltage diagram (use the values for "Tubes in tester" and have the tubes installed in the radio. the schematic for the Radiola 33 is below:
http://www.nostalgiaair.org/PagesByModel...040328.pdf

You can measure the rheostat values, but you have to disconnect the wires from the transformer and tube sockets.

Hope this all helps! Best Regards and God's Blessings during this Holiday Christmas and Chanukah season!!

[TN Allen]

A belated thank you for the many useful suggestions.

I have returned to this project after a few medical distractions, and have started soldering the connections. I teach at a small engineering college, Maine Maritime Academy, and after describing this project we concluded students in the campus Radio Club may find it interesting. Consequently I'm back at it. I will greatly appreciate any additional assistance regarding the following.

I suspect using the single 5V filament supply on the new power transformer on both the UX-171-A and UX-80 may not work well as it is also part of the output circuit. This is an uneducated guess on my part as I don't understand tge circuit well, but suspect 2 5V power transformer outputs were used on the original transformer to separate the UX-171-A filament circuit from the UX-280 filament circuit. I have a 5V 10A DC power supply that I think might be a good substitute.

I am also not certain about the audio section interstage transformer connections. The P-T156 transformer has blue and red wires on one side which I assume are the input. These should connect to the UX-226 plate and the #7 connector on the terminal strip. The 2 green and single black wires from the other side have me puzzled. I know black is the center tap, but where are the 2 green wires to be connected?

I've attached photos of the top and bottom chasis plate.        

Thank you, tna

[Chas]

Separate filament windings are required for the 71a and the 80.

The PT-156 look carefully at the two green wires the one closest to the core is the start and will be the A- or bias connection the green closest to the outside of the core is the grid connection.

Or. measure the two windings green to black and black to green the winding that has the least resistance will be the A- side therefor that associated green would go to bias. The winding black to green that has more resistance because it has greater length, that associated green goes to the grid. Use a D'Arsonval meter to measure the transformer.

The P-T156 may not have sufficient plate impedance for the 26 tube so there may be distortion. Try adjusting the bias. If that does not work then another choice for the inter-stage transformer. This replacement transformer is bobbin wound, there are no layers of glassine between the windings...
 The 71a has a relatively high plate impedance look for a 5k impedance transformer.

See: http://www.radioremembered.org/outimp.htm

Much has been written and published in the Antique Radio Forum on the refurbishing of the 100a speaker. These too are very plentiful so finding a rebuild-able specimen is not hard.. The audio coupler fails or a coil winding. The speaker does much better with a magnet re-charge or the use of modern helper magnet.

The 1.4 volt filament supply must provide enough current, the 26 emission falls off rapidly below 1.25 volts.. You will need to provide for center-tapped hum pots on the '26's and the 71a.
Beware that early 27's are prone to heater cathode leakage, use a very late edition of the 27 for the detector.

Your building of a power supply is commendable but there are many 18's out there that have supplies that can be salvaged... Often the caps are still viable after nearly 95 years...

Chas

[MrFixr55]

Hi TN Allen,

Prayers for improvement in your health!

+1 on what Chas said.  the 5V power supplies for the 80 and 71A must be separate, because the 80 filament is about 180- 230V (for this radio) above ground.  The 71A filament is about 30V above ground. the 27 and 26 filaments are 9V above ground. So both voltage and bias, as well as isolation of the rectifier filament, is why the original power supply has separate filament windings for the 80, the 71A, the 27 and the 26s

Yes, the Radiola 18s can be found on "the Bay" often.  However, your building a power supply is a great exercise in electronics troubleshooting.  I can't find the article, but years ago, someone actually converted a Radiola 18 to a superheterodyne.  He built his own PS but I think that he substituted 24As for the 26s, which made the supply easier to build.

The hardest part of your supply is generating the 1.5VAC, as almost nobody builds a transformer for that value. 

You state that you have a 5VDC 10A Power supply. Do you have four UX201A (01A) tubes? If so, you can use that power supply for the 1st AF and the 3 RF tubes. However, you cannot use it for the 01As and the 71A together, and absolutely cannot use this power supply for the '80 filament. The 80 filament MUST be isolated from all other filament supplies.

Looking at the schematic for the radio and the power supply, I would not worry too much about smoking your one good power supply.  The only thing that I would worry about are the 2 dual capacitors on the radio chassis, the 2 0.5uF caps that bypass the filaments and the 2 0.5uF caps that bypass the B+ supplies.  Best to replace them in all the chassis that you intend to use.  You could put fuses in the filament lines, about a 6A fast fuse in the 1.5V circuit for the 26's, a 2 A fuse for the '27 and a 1/4A fuse for the '71A

The following are the "Victor" schematics for the RCA Radiola 16.17. 18 in one document, for comparison purposes:

RCA Radiola 17 Fr RCA Red book.pdf Size: 214.91 KB  Downloads: 36

The following is a link to an article on Nostalgia Air on restoration of a Radiola 18:
http://www.nostalgiaair.org/References/A...la18-2.htm

My grandparents had a Radiola 17 which my Grandmother wanted to give to me for many years.  I used to play with it in her basement (the radio worked rather well) but Dad did not want to add it to my junk Oops- collection.  When I married and Grandma was selling the house, I could not find the radio.  Someone took it.  I ended up buying one from eBay back in about 2009, when working ones were going for in excess of $100.00.  I think I paid about $75 for the radio and shipping.  When I got all of the tubes, lo and behold, it worked.  Nowadays, you can't even give these things away, so you should be able to win a power supply rather cheap (except for the shipping).  Remember to ensure that it is an 18 power supply, not a 17 power supply.  However, the transformers are the same.

[Chas]

Good golly, inflation has even hit old Radiolas...

I have had three Radiola 60's paid $10 for the first two and $20 for the one I have kept. I have also had two 18's and one 17 they were all $10 each, Oh I DO have the lamp hoods .  Finally two Radiola 33 for $10 each and all have working power supplies...I have also had two Radiola 44's, traded one off as it had severe pot metal twisties. The good one I bought some 40 ya for $30 was fine but checking it some 20ya the dial no longer moves. I hope its not twisted to heck..

I also have a Radiola 22, the battery model. It's casting was stable last time I looked. I "should" get this working as it is the only battery TRF I have with screen grid tubes... This came to me for free in 1962 from an estate cleanout, I was 16 at the time..

All in all, never had to re-cap any of these old irons.

I did spend time with the 60 and critically tuned the front end and got the RF to track with the oscillator. I managed to get the radio down to the noise level. Receiving New York city daytime from Dartmouth MA.

Sorry, I do not have any parts for radios in this AC series...

Now if it was for Radiola's AR-812, 24, 25, 26, 28 & 30, those, I have bought a lot of junker parts. But I gave my Radiola 25 and 28 to the Connecticut museum.

Good Luck with the home made SPU... (socket power unit)...

Chas

[Arran]

By the way, if you have a power supply for a Radiola 17 do not run it without a load on the B+ supply, there was an oversight in the original design where the B+ would surge without a load and damage the input filter cap, something they corrected with the Radiola 18, as was mentioned the transformers are the same but the circuitry was changed. Both Radiola's 17 and 18 were engineered and built by General Electric for RCA, which may explain why there were Victor and Brunswick versions. In Canada Victor used whatever radio chassis they could get prior to the RCA buyout, so you see Victors with Northern Electric chassis, or American Bosch chassis, (the Bosch was really a Radiola circuit, built under license, with a different chassis layout), prior to the "Microsychronous" models of the 1929 model year.
Regards
Arran

[morzh]

Hmmm....looked at the 16/17 and 18 AC versions.
DOn't really see why they would do this unless the caps were specifically chosen for lower WV and did rely on the load to lower it.

http://www.nostalgiaair.org/PagesByModel...040317.pdf
http://www.nostalgiaair.org/PagesByModel...040316.pdf


The 18 also used 6th order low pass LC filter (3 LC), and the 16/17 uses 4th order (2 LC).
But that in itself should not be bringing the voltage up for the 16/17.

So what was the problem?

[MrFixr55]

Hi Chas,

The prices I quoted for Radiolas was back in the 2010s. They are very cheap now. I guess it is the usual eBay phenomenon, when first offered, they are a novelty and the sky is the limit, then the market floods and prices plummet.

I have heard cases where the filter caps (oil / paper) short but I have 2 17s, an 18 and a 60 and they work fine on the originals.

I haven't checked recently, but the lamp hoods were made form unobtanium. Charles Cutter, "The Radiola Guy" used to make and sell them but I don't think that he does anymore.