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 Post subject: Radiola 20 troubleshooting
PostPosted: Apr Fri 12, 2019 1:50 am 
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Joined: Feb Tue 27, 2018 11:46 pm
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I am currently attempting to get a Radiola 20 working.

Thanks to some great answers I got on another post I feel more confident about my capacitor knowledge of the Radiola.

I have replaced the 2 uF cap.

I had a bad winding in one of the audio transformers and have replaced the windings. I now have continuity through all transformers.

I tested the speaker by popping it with a 9V battery.

I also found a bad ground connection and fixed that.

I have the proper voltages on the tubes.

I get absolutely no sound out of it.

I have a function generator and a scope but I am uncertain of signal levels at various points.

Any help would be appreciated.

Thanks.


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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Fri 12, 2019 3:13 am 
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Hi

You have voltage on tubes but might help listing the levels?

Pin #2 is plate of tubes. Do you have positive voltage on pin #2 of each tube?

If using 99 & 120 tubes do you have 3 - 3.3 volts across filaments? If 30 & 31 tubes voltage on filament should be around 2 - 2.2 volts.

http://www.nostalgiaair.org/pagesbymode ... 040318.pdf

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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Fri 12, 2019 5:00 pm 
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Yes, what Norm said.
Also, download this, https://www.americanradiohistory.com/AR ... 3-1928.pdf.
Start on page 224 and do the testing RCA lists.
Jeff

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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Sun 14, 2019 1:42 am 
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Voltages are as follows:

Tube No. Plate Grid Filament
1 84 -4.5 3.25
2 84 -4.5 3.1
3 43 -4.5 3.1
4 84 -4.5 3.1
5 125 -4.5 3.1

I also have the service manual. Using it I checked continuity (that's how I found the open audio xfmr winding).

The tuning capacitors are aligned and all rotate together.

is it correct to say that I should be able to hear something?

Again, is there an effective way to use a function generator to inject signals?

Thanks again for the help.


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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Sun 14, 2019 5:47 am 
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Voltages are reasonable. You should hear something , maybe only noise. Tube number 3 is the detector. Touching the grid terminal, pin #3, should cause hum/noise if audio section is operating.

Move your antenna to the detector stage tuner. This should bring in signals and bypasses the RF section.

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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Sun 14, 2019 4:42 pm 
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What tubes are you using?
Normally you will hear a scratching sound when the rheostats are turned up.
Can't answer your question about a function generator, I use the "touch" method on the grid of the detector to check the audio section, like Norm said. Should produce a hum in the headphones.
-4.5 on the grid of tube 3 (detector) does not seem correct.

Operation of my Radiola 20 goes like this:
1. Hook up filament voltage, check for lit filaments, monitor voltage at the sockets on the front.
2. Hook up the rest of the voltages, double check and verify correct connections, including the -4.5 and -22.
3. Bring filaments up to about 3v and turn volume up, listen for scratching sounds in either socket with headphones, indicating amp section is working. When not moving these controls set is mostly silent.
4. My set will hear nothing without a good ground. Hook that up. Hook up antenna.
5. Set amplification at about 6 or 7.
6. Slowly tune from 0 and up, listening for a station. When something is heard use the tuning, amplification and both verniers to improve the signal for best sound.
This is best done with headphones to begin with. It is very easy to tune past a station and not hear it, it takes a hair second for the regen to work and it is easy to miss the signal if tuning too fast. My 20 is mostly silent between stations, as if it is not working.
I have two of these and they are two of the best sounding radios of this type that I have.

Jeff

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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Sun 14, 2019 5:47 pm 
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Guys,

Thanks for the tips - I will try some things.

Jeff,
You are correct about the grid of #3 - it reads 2.8. I was in a hurry when I typed -4.5.

What type of headphones can you use? That is a lot of voltage on headphones. All I have is the standard 8 ohm headphones.

Jim


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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Sun 14, 2019 7:42 pm 
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Jim

Needs to be high impedance phones, 2000 ohm. You could use 8 ohm phones along with a matching output transformer.

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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Sun 14, 2019 8:47 pm 
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wa4ywm wrote:
Guys, Thanks for the tips - I will try some things.
Jeff,
You are correct about the grid of #3 - it reads 2.8. I was in a hurry when I typed -4.5. What type of headphones can you use? That is a lot of voltage on headphones. All I have is the standard 8 ohm headphones. Jim
Voltage on the phones is no matter. A bit touchy if Brandes with exposed terminals, shock hazard.

Plate current must flow through the vintage phones to enhance the internal magnet, therefore, the phones are polarized. Current draws the iron diaphragm closer to the pole-piece. If the phones are un-molested there will be polarizing labels and/or a red thread in the cord braid. That red coded lead goes to the B+ to draw in the diaphragm...

Most of the bias on the grid of the detector is developed by electron flow in the detector. Measuring the detectors grid voltage will be misleading as the meter will load down the grid. Typically, the detector grid returns to the (+) filament circuit, via the grid leak and the tuned circuit.

If the radio will not go into and out of regeneration by turning the "Ampflication" control there is a detector problem. It can be poor connections to the tuned circuit, too low a grid leak value, grid condenser leaking, improper filament or plate voltage, open primary on the 1st audio transformer or a jack problem, weak or incorrect tube.

BTW there is not enough bias on the last audio tube, that can deplete the thorium in the last audio tube quickly thus killing that tube until it is rejuvenated.

GL

Chas

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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Sun 14, 2019 9:36 pm 
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Norm,

I tried touching the grids on 3, 4 & 5. Heard nothing out of the speaker.

Guess I'm going to need to dig deeper to find the problem.

Jim


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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Sun 14, 2019 10:19 pm 
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Jim

What are you using for a speaker? Don't think we asked? Speaker needs to be high impedance or use it with a matching output transformer. A modern speaker with permanent magnet won't work without the output transformer.

You mentioned replacing an audio interstage transformer. Did lowest resistance winding go toward plate of a tube. Highest resistance should connect to grid of the next stage.

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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Sun 14, 2019 11:08 pm 
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Location: Keystone Heights, FL, USA 32656
What tubes are you using?
What is the resistance of the speaker?
If you are using a 120 tube for #5 Chas means to get the grid voltage down to -22.

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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Mon 15, 2019 12:42 am 
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Gentlemen,

The answers to your questions follow.

What tubes are you using?
199 & 120. I have spares which I tried.

What are you using for a speaker? What is the resistance of the speaker?
I have the Model 100 speaker.

If you are using a 120 tube for #5 Chas means to get the grid voltage down to -22.
The voltage is -22. I again made a mistake in my earlier posting. I had -4.5 on the brain.

You mentioned replacing an audio interstage transformer. Did lowest resistance winding go toward plate of a tube. Highest resistance should connect to grid of the next stage.
The highest resistance winding (secondary) connects to the grid of #5. The low resistance winding (primary) connects to the plate of #4.

Jim


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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Mon 15, 2019 1:34 am 
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Jim

Can you bring up filament voltage a little? 99 tubes are often low in emission. Increasing filament voltage brings up emission. You will notice tube manuals sometimes specify 3.3 volts.

RCA 100 speaker will work connected to this radio.

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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Mon 15, 2019 1:50 am 
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Jim,

Pasted text can be highlighted as a quote by selecting the text and clicking the [Quote} button. The quote tag can be made explicit by adding {Quote="name"] be sure selected text has the closing BB code, {/Quote] I have munged the BB code call so it will not be read for this example. The code would normally have: [ xxx ]

It is possible the tubes you have, have all been paralyzed, if you do not have a tube tester it is possible to set up a simple emission test with filament voltage, plate voltage and a plate current meter. Settings can be found online. The same setup could be used to rejuvenate the tubes.

Link: Nostalgia Air

As Norm said raising the filament voltage will work but avoid going over 4 volts, at 4-1/2 the Thorium will begin to get stripped at a faster rate, once all the Thorium has left the filament further voltage increases will be needed until the filament parts...

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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Mon 15, 2019 5:08 pm 
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Joined: May Sat 30, 2015 11:49 pm
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Location: Keystone Heights, FL, USA 32656
A couple of photos for reference.
Touching the detector grid pin. With amplification control (regen) set at about 7, mine makes a loud hum..
Attachment:
DSC03528.JPG
DSC03528.JPG [ 136.88 KiB | Viewed 1162 times ]

No-load voltages, black meter lead in upper meter socket on the front. ARBEIII battery eliminator for power.
Attachment:
DSC03529.jpg
DSC03529.jpg [ 137.85 KiB | Viewed 1162 times ]

Did you do the complete, page long RCA check list? If all tests pass the radio should play. If it fails even one of the tests, it won't play.
Resistance of speaker?

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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Tue 16, 2019 3:14 am 
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Joined: Feb Tue 27, 2018 11:46 pm
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Norm,
Raising the filament voltage did not help.

Chas,
I have an old Simpson 555 tube tester. Don't know if it works. The tubes fit in to one of the sockets but there are no settings for these tubes in the charts.

Do you know how I could test with this old beast?

Jeff,
I performed all the continuity tests if that is what you are referring to.

Jim


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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Tue 16, 2019 3:21 am 
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Test X99's as a 30 with increased filament to 3.3 volts. Most 99 read low. I'll put it this way, save any that move the meter on your tester…

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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Tue 16, 2019 6:28 am 
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With a replacement audio transformer I suspect there may have been some experimental alterations. I suggest that the entire circuit for the radio be traced and any errors noted, then corrected if they exist...

Refer to the Nostalgia Air article how to rejuvenate the tubes. The tube tester can be used but all connections to the plate and filament must be removed during the process. Yes, the flashing is a scary process, if the filament is already worn out the flashing will open it.

I suggest simply burning the 99's and the 20 at 4-1/2 volts for an hour with no connections at all to the plate or filament. This cannot be done in the radio as a bias is set up. It can be done with the tube tester by use of an interposer to break those connections, simply an old tube base with just the filaments to a tube socket.

The reason for no plate/grid connections is at elevated voltage the liberation of the thorium can cause it to migrate permanently off the filament to the grid and plate if there is any potential on those elements.

If any tube does restore some activity when tested then consider using the correct aging voltage if it further increases emission.

If some tubes still fail then follow the directions for flashing and aging. Nothing to loose if there is no emission, flashing may restore...

BTW my experience is Songbird brand tubes will not survive flashing :roll: Do not glue bases of loose tubes with super glue, it WILL pop the tube at the base line... Use Elmers white glue and wait a day for it to set...

Tube rejuvenation was a common procedure in the 20's. There were tube rejeuvenators made for such a task.

GL

Chas

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 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Apr Tue 16, 2019 6:51 pm 
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Yes, I was referring to all 26 tests, they all passed?
Hmmmm......

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