Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Dec Thu 05, 2019 11:26 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 96 posts ]  Go to page Previous  1, 2, 3, 4, 5  Next
Author Message
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: May Wed 29, 2019 1:28 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 14378
Location: S. Dartmouth MA 02748-1225 USA
jrehkopf wrote:
Jim, are you saying that you have 121 volts on the grid with the speaker plugged in? How are you measuring that?
I CAN understand that measurement. From B+ to grid.

Jim wrote:
...voltage from the speaker lead to the grid....
A useless value for determining a problem :roll:

Issue with measuring voltages on battery radios is the ground is not always ground, not always B-... Blah, blah.

The RCA Service Notes "should" tell the common point for taking voltage measurements Use that point for the negative of the test instrument AND for the return of any signal injection. For safe signal injection the .01mf down to 1000pf series coupling cap to the probe will work to protect the instruments.

Going forward, suggest wrapping tape around the test probe metal shank and any screwdriver that may be in use. A slip of a naked tool could put a B+ surge into the filaments and send five '99's to the happy hunting ground....

ALSO, be sure the power source common is happy being connected to the test equipment common return...

YMMV

Chas

_________________
Smith's Ale Gives Strength, Smith Bros. Brewers, New Bedford MA


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: May Wed 29, 2019 5:18 pm 
Member

Joined: May Sat 30, 2015 11:49 pm
Posts: 900
Location: Keystone Heights, FL, USA 32656
Maybe a bit off topic, I thought I would try the naked tube test suggested in the NA article mentioned above. Here is a UX199, 3 volts filament, about 42 volts B, showing 6 mA on the meter, good tube. Also test good in my tube tester, also works good in a radio.
Need to be very careful when hooking this up. Big pins A voltage; small pins B voltage. DO NOT MIX THESE UP!
Jeff
Attachment:
DSC03612.JPG
DSC03612.JPG [ 354.33 KiB | Viewed 741 times ]

_________________
Jeff
“Nothin’s worth nothin ‘till somebody wants it.”—Irv Metter


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: May Wed 29, 2019 6:16 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 14378
Location: S. Dartmouth MA 02748-1225 USA
Not O.T. at all, radio needs working tubes!

Always connect filament first and test for lighting. Then test leads for "B" battery but do NOT connect to B+, wait. light filament then double check where B- is, then connect "B" for reading.

Yes it is a risky test because of shorts and accidental contact to B+ and destroying the tube.

Build onto bread board, could be made "less risky"...

Chas

_________________
Smith's Ale Gives Strength, Smith Bros. Brewers, New Bedford MA


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Sat 01, 2019 4:53 pm 
Member

Joined: Feb Tue 27, 2018 11:46 pm
Posts: 41
I tested all my tubes with Jeff's setup except using power supplies instead of batteries.

One power supply was for the filament and the other for the plate-grid voltage. I set the filament to 3.3V and the plate-grid was 43V (using the power supply I built for the Radiola).

None of them indicated any current flow.

Where can I find tubes that are guaranteed to work? I saw on the forum that 30 and 31 tubes could be used as replacements. The filament voltage is the only difference. Do you agree?

Jim


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Sat 01, 2019 7:20 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 14378
Location: S. Dartmouth MA 02748-1225 USA
Place a WTB in the ARF classifieds for the x-'99's.

Ask for tested for emission. If the seller guarantees them all the better. Avoid Songbird, my experience these are more fragile that Radiotron or Cunningham. Silvertone have a box plate and seem to be more consistent.

You will also need an X-'20 for the power output though not essential.
---------------------------------------------------------------------------------------------
Do recheck you emission test set up, a reversed "B" battery or the negative connected to the wrong polarity "A" may yield no emission. Be very careful, of the "B" connections...

IMHO I would not opt for other types of tubes, that will only complicate the radio troubleshooting. The "A" battery or setting will have to be lower for a 30 and higher for '01a. The range and control-ability of the rheostats will be different. There may be excessive gain with 30's and oscillation could occur for both 01a or 30 meaning the neutralization will have to be re-adjusted. Those problems may or not occur but they could be on top of the balance of the set may still be "broken".

BTW the 30 has an oxide filament, cannot be rejuvenated..

Consider picking up one of those Sterling or other brand tube rejuvenators from the 20's. For a noob this is a simple flash/age/test device for 99's and 01's. there are other brands of the rejuvenators.

Prices for '99's are all over the place.

YMMV

Chas

_________________
Smith's Ale Gives Strength, Smith Bros. Brewers, New Bedford MA


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Sat 01, 2019 7:29 pm 
Member

Joined: May Sat 30, 2015 11:49 pm
Posts: 900
Location: Keystone Heights, FL, USA 32656
Be sure to verify that the fuse in you meter is good. Easy to get fooled by that.

_________________
Jeff
“Nothin’s worth nothin ‘till somebody wants it.”—Irv Metter


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Sat 01, 2019 8:25 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 14378
Location: S. Dartmouth MA 02748-1225 USA
jrehkopf wrote:
Be sure to verify that the fuse in you meter is good. Easy to get fooled by that.

Jeff,

Head scratch for a moment...

The fuse in the current shunt in the meter Y/N?

I have to rationalize the O.P's work bench. I have dozens of single range meters in cases I use for manual setups like this...

Chas

_________________
Smith's Ale Gives Strength, Smith Bros. Brewers, New Bedford MA


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Sat 01, 2019 11:52 pm 
Member

Joined: May Sat 30, 2015 11:49 pm
Posts: 900
Location: Keystone Heights, FL, USA 32656
Yes, the fuse in the current input circuit. I am referring to my Fluke, don’t know what kind of meter Jim has. Very easy to blow the fuse and not know it. Then every time you try to measure amps the reading is zero.

Hope I am not confusing the issue.
Jeff

_________________
Jeff
“Nothin’s worth nothin ‘till somebody wants it.”—Irv Metter


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Sun 02, 2019 1:07 am 
Member

Joined: Feb Tue 27, 2018 11:46 pm
Posts: 41
OK - here is where we are.

Something is wrong with the meter I was using. Not the fuse so I don't know what it's problem is.

I used another meter and performed the tests again.

One of the 120's met the minimum spec - it was 20 mA. The other just missed it at 14.7 mA.

One of the 199's showed no flow. The other 7 had currents of 6.3 to 9.2 mA easily exceeding the minimum.

Now what? I have what are supposedly good tubes but I can't apply a signal at the grid of the 2nd amplifier and get an output. Doesn't make any sense to me. Am I dealing with a ground issue I don't understand? I am using the common connections for ground of the power supply as my signal ground. Is this not correct considering the manner in which the speaker is driven? I have never seen a speaker driven in this manner. Any speaker I have ever seen is connected to the signal ground.

Jim


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Sun 02, 2019 3:39 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 14378
Location: S. Dartmouth MA 02748-1225 USA
wa4ywm wrote:
Now what? I have what are supposedly good tubes but I can't apply a signal at the grid of the 2nd amplifier and get an output. Doesn't make any sense to me. Am I dealing with a ground issue I don't understand? I am using the common connections for ground of the power supply as my signal ground. Is this not correct considering the manner in which the speaker is driven? I have never seen a speaker driven in this manner. Any speaker I have ever seen is connected to the signal ground
Jeff, Kudos for calling out the bad ma meter!!!

This the NA diagram which is the Riders diagram, which is the RCA diagram. A bit of playing with a pdf extractor, then a screen snap, then Gimp...

Use it for a reference as to what will be explained in up coming posts...

Attachment:
Radiola 20-1.png
Radiola 20-1.png [ 147.79 KiB | Viewed 714 times ]


All the battery connections are in the lower portion of the schematic, from left to right labeled "A+" to "135V".

The "A-, B-, C+" connection is the reference connection for voltmeter negative and the return or shield from a signal injector if used.

Attachment:
Radiola 20-2.png
Radiola 20-2.png [ 259.68 KiB | Viewed 714 times ]


Do this or repeat: Wire only the "A" voltage and set the ARBE for 4-1/2 volts. Follow the + and - as shown. Plug in the tubes, place the voltmeter into the two meter connections FWIR on the right side of the lower vertical panel. Turn on the ARBE after it was preset with no load. Turn off all rheostats and insert the tubes. Turn the battery setting to 3.3 the voltmeter should read 3.3 adjust the battery setting until it does. Turn on the set with the filament rheostat and re-adjust the battery setting to 3.3 according to the voltmeter. As long as the ARBE is not changed and the battery setting remains to yield 3.3 all is well...

Turn off the ARBE, connect all the "B" wires as directed on the schematic. Then connect the "C" circuit as directed. The "C" circuit must be used for the RF and AF amp. I do not recall if the ARBE can provide 22-1/2 C, if it cannot, lower the 135 volts to 90 volts and use -12 volts "C" only on the power output 120 tube...

The speaker must be a high impedance speaker and plate current flowing either through the speaker driver coils or through a matching device. The speaker is NOT connected to anything other than the plate of the last audio tube and 135 volts... If a horn is used that is not a balanced driver, the polarity of the speaker must be observed. The flowing plate current must pull the metal diaphragm inward to re-enforce the internal magnet.

The amplification dial puts lever action of a coil that places in phase RF back into the grid of the detector. This is important. Some "amplification" must be used or there will be little or no signal detected. Too much amplification the detector will fully oscillate and there will be whistles on the radio signal.

--------------------------------------------------------------------------------

To inject an audio signal, use a .01/630 cap in series with the audio "hot" probe, connect the shield or return to the "A-, B-, C+" connection. Do find out if the audio signal generator can have its shield return connected to ground. If it can't, use a .1/630 from the return wire to "A-, B-, C+".

A modulated RF signal can be injected before the first audio transformer, that is from the antenna up to the grid of the detector. Use the same type of capacitor isolating coupling for the RF. Modulated RF must be used because an empty carrier cannot be heard.

Do be careful of all probing that the probe does not slip and short the B+ to the "A" circuits...

The detector can be checked if it can go into regeneration by setting the tuning to the middle or approximately 1000khz. Using a transistor radio tuned to 1000khz, turned on and volume to 1/2, turn on the 20, move the amplification knob so the swinging coil lines up with the other coil. Move the 20 tuning knob back and forth. The transistor radio should give a loud squawking report as the oscillating detector sweeps RF through the tuning range of the transistor radio. Bring the amplification down or lower should stop the squawking from the transistor radio.

These are tests you can perform and note the results. If any test fails then use signal injection to discover where the failure is.

For this 20 failures could be from the installation of new components or the replacement audio transformer. The rest of the radio is subject to bad connections. ANY mechanical electric connection can fault. Best advise is to loosen and re-tighten all these connections. The RCA rheostats can have poor connection at the shaft and the wiper. Occasionally the resistance windings fail open.
Re-soldering of all connections is advised as granular corrosion effects the joint, they may OK good and even measure good, but won't pass RF...

Fair warning soldering to any connection of the variable condensers. The side plates are of a thermoforming material and my melt or distort. FWIR those connections are via lugs. Loosen the screw enough to prevent heat flow, re-solder the lug and then re-tighten...

YMMV

Chas

_________________
Smith's Ale Gives Strength, Smith Bros. Brewers, New Bedford MA


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Mon 10, 2019 10:02 pm 
Member

Joined: Feb Tue 27, 2018 11:46 pm
Posts: 41
Chas,

Here is what I have now.

1. I conducted your test to see if the detector is regenerating. I did hear the squeal at 1000 KHz on a separate radio.

2. I am now using a scope to do some tracing. I used my function generator to create an AM signal and was able to trace the signal to the detector. I also observed a signal on the grid of the detector that varies from 530 KHz - 1250 KHz as the Station Selector is moved from one end to the other.

During this process I discovered that the primary of the first audio xformer is open. When I checked for continuity at the beginning of this whole adventure, I didn't pay attention to the actual value read which was 38K (the resistance of the resistor in parallel with the primary).

This brings up my first question. My understanding is that the windings in both xformers are the same. Is this true? I am wondering because the secondary of the first AF xformer measures 8.3K and the secondary of the second xformer measures 1.5K (the new one).

3. I still have the same audio issue that I have been discussing all along. This time I injected a signal at the grid of the first audio stage and traced the signal with the scope to the grid of the second stage. The is no signal on the plate of the second stage. I tried the other 120 - same result. I also cleaned the socket in the manner you described. I also cleaned the pins of the tube with some emery cloth.

I once again checked the continuity from P5 to the speaker by injecting a signal (for the umpteenth time)- loud and clear.

What do you think? Two bad tubes?

Jim


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Tue 11, 2019 5:44 pm 
Member

Joined: May Sat 30, 2015 11:49 pm
Posts: 900
Location: Keystone Heights, FL, USA 32656
What did you do to fix the first audio transformer?
The audio transformers in both of my Radiola 20s show about 1.2k primary and 6k secondary ohms.

You can use a 199 tube in place of the 120, just bring the B+ down to 90 and C- up to -4.5.
Jeff

_________________
Jeff
“Nothin’s worth nothin ‘till somebody wants it.”—Irv Metter


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Tue 11, 2019 10:12 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 14378
Location: S. Dartmouth MA 02748-1225 USA
wa4ywm wrote:
During this process I discovered that the primary of the first audio transformer is open. When I checked for continuity at the beginning of this whole adventure, I didn't pay attention to the actual value read which was 38K (the resistance of the resistor in parallel with the primary).

This brings up my first question. My understanding is that the windings in both transformer are the same. Is this true? I am wondering because the secondary of the first AF transformer measures 8.3K and the secondary of the second transformer measures 1.5K (the new one).


Apparently the detector is "working" as B+ is supplied via a shunting resistor. The audio however, is not being transferred because the winding is open.

Yes both transformers are identical if they are OEM, from the images earlier in the thread at least one of the transformers is a Thordarson 6:1, this would explain the differences in readings. From issues with the amp it would be safe to assume that the second audio has problems too.

If that detector plate shunt resistor is not OEM I suspect it has been changed out to to a much lower value to reduce the amount of audio for the 6:1 transformer. FWIR that detector plate shunt resistor should be at least 100K or more.

The OEM audios are the same as the Radiola III in funky shells with a (red) terminal end plate.

Hammond makes replacement audios for the Radiola III-IIIA that are tapped, so they will fit all these radios, the tap would not be used for the Radiola 20 or the Radiola III. The OEM shells are reused but FWIK they are missing.

The Hammond's are the correct DC resistance as well thereby replicating the original.

I would suggest this route, post a WTB for used transformer(s) if they are good then O.K. but at least you will have the shells. The Hammond's use a high quality audio iron so there is some improvement in fidelity... One can find windings on the ARBE-III rite, but old transformers are still required and the iron gets re-used. Further, the old terminal plate is fragile, often gets broken.

I or Jeff can photograph the interior of a un-molested 20 so bus wiring can be replicated and where those transformers mount on the harp-like frame...

YMMV

Chas

_________________
Smith's Ale Gives Strength, Smith Bros. Brewers, New Bedford MA


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Tue 11, 2019 11:20 pm 
Member

Joined: May Sat 30, 2015 11:49 pm
Posts: 900
Location: Keystone Heights, FL, USA 32656
Chas, a correction. All of the photos so far are of my 20, not Jim’s. Don’t know what Jim’s looks like.
Jeff

_________________
Jeff
“Nothin’s worth nothin ‘till somebody wants it.”—Irv Metter


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Wed 12, 2019 3:27 am 
Member

Joined: Feb Tue 27, 2018 11:46 pm
Posts: 41
Gentlemen,

First, regarding the transformers.

The second stage transformer was found to have an open winding during my initial troubleshooting prior to my first post. I did some research on this forum and found that the P-T431 Coil Assembly from Antique Electronic Supply was the correct replacement for the transformer in the Radiola 20. I replaced the defective winding with this assembly. It has a 420 ohm primary and a 1500 ohm secondary with a 3:1 ratio.

The first stage transformer is the one that I just discovered the open winding in. It is the one whose secondary measures 8.3K. Thus, my confusion about replacements. Should I replace the first stage with the same assembly used in the second stage or will the radio not work properly? Do I need to find a different transformer for the first stage?

Second, regarding the tubes.

If I use a 199 in the final audio stage, what is the downside? In other words, why is a 120 used if a 199 would work?

Jim


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Wed 12, 2019 3:17 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 14378
Location: S. Dartmouth MA 02748-1225 USA
Jeff,

Sorry for the mistake...

wa4ywm wrote:
Should I replace the first stage with the same assembly used in the second stage
Yes..

The 120 FWIR has a slightly lower gain but has more robust plate dissipation (not much). The lesser gain is the grid spacing is larger. However, that means it takes a more negative bias to keep the plate current at "safe" level. Thus greater output wattage. It can drive a less sensitive speaker at a greater volume. The reverse is true for the '99. Therefore use the most sensitive magnetic speaker you have for the 20 if a '99 is used. Do lower the plate voltage and the adjust the grid voltage.

Chas

_________________
Smith's Ale Gives Strength, Smith Bros. Brewers, New Bedford MA


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Wed 12, 2019 4:29 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 380
Location: Bristol TN 37620
way4wym,

Following your discussion here. At this point, replace your open audio with the pt431
coil. While the resistance readings aren't the same, it will work fine in your application.

Regarding the 120 tube, you can use a ux199 and run it at much lower voltages.
The 120 came out to boost power and tone in dry cell sets, but came at a cost-
higher plate voltage (135 vs 90) and higher grid voltage (-4 1/2 vs -22) IMHO,
the higher voltages don't justify the gain - Run it on all 99"s. Seems your problems
are all in the open audio.

JMHO, just follow the schematic thru the set. You really don't need the signal generator
thru all the stages. If your set matches the schematic, and tubes are good, and speaker is
good, and eliminator is good, and antenna and ground are good, set should work. You say
all your externals are good - tubes, speaker, eliminator, ground and aerial. Replace the
open audio, and recheck the schematic.


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Thu 20, 2019 1:23 am 
Member

Joined: Feb Tue 27, 2018 11:46 pm
Posts: 41
Gentlemen,

The latest.

I received the winding and replaced the defective one in the 1st audio transformer. Both transformers are now working.

However, I still hear nothing.

I swapped the 2nd audio tube with the 1st audio tube which I know is working (I can see that it is passing a signal applied to the grid).

Is the 90V a high enough voltage for the speaker to operate?

I feel like I'm at the end of the rope and don't know what else to look for. I keep thinking that maybe I am making some sort of fundamental mistake.

Jim


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Thu 20, 2019 11:10 pm 
Member

Joined: May Sat 30, 2015 11:49 pm
Posts: 900
Location: Keystone Heights, FL, USA 32656
Yes, 90 is enough for the speaker.
Refer to the drawing above; there is one wire going to terminal 1. At your power supply this wire should have A-, B-, C+, and ground hooked to it, Y/N? If yes, clip you black meter lead there and check the following...
All power sources connected, turned on, tubes removed, speaker plugged in to the right-most socket.
Left to right, plate socket should be 90, 90, 135, 90, 22.
Then grid socket of audio tubes, should be -22 and -4.5.
Report...

_________________
Jeff
“Nothin’s worth nothin ‘till somebody wants it.”—Irv Metter


Top
 Profile  
 
 Post subject: Re: Radiola 20 troubleshooting
PostPosted: Jun Fri 21, 2019 2:00 am 
Member

Joined: Feb Tue 27, 2018 11:46 pm
Posts: 41
Jeff,

I'm not sure what you mean by left to right but here are the plate voltages by position:

1 90V
2 90V
3 45V
4 90V
5 90V Note that this tube is now a 199 instead of a 120 per our discussion

These agree with the schematic. You show 22V for your last position. Was this a mistake?

The grid voltages are as follows:

1 -4.5V
2 -4.5V
3 +2.8V
4 -4.5V
5 -4.5V

Tube #3 (detector) is the mystery. The schematic indicates that for an open circuit the voltage should be +4.5. How can it measure 2.8V? I measured the voltage at the coil side of the resistor and it is +4.5V as expected. The grid side of the resistor is the 2.8V. I also observed that the voltage is 2.8V when operating. I'm really confused by this.

Jim


Top
 Profile  
 
Post New Topic Post Reply  [ 96 posts ]  Moderators: Marcc, Norm Leal Go to page Previous  1, 2, 3, 4, 5  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: addyboy, cwysong, Freeman, lorenz200w, SteveD and 16 guests



Search for:
Jump to:  




























Privacy Policy :: Powered by phpBB