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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Jan Sun 21, 2018 1:21 am 
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Location: S. Dartmouth MA 02748-1225 USA
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What will looking at the insides tell you?
What color leads from the new transformer are connected to what terminals. Unless this is a "new" ERLA unit.

A polarity reversal, may, stop the radio from working or set up uncontrollable audio oscillation.

Blue to plate, red to B+, green to grid and black to A. Even though the Carborundum is involved, the arrow is anode, the bar the cathode. A substitute germanium diode would connect the same.

Pass a flat bastard file over the bottom of the tube pins, the lead will oxidize on the surface and make poor contact. The tube sockets in the tester grab the sides of the tube pins.

Chas

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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Jan Sun 21, 2018 1:48 am 
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Went through and checked all connections, did find a loose one, and cleaned tube socket contact points. Now adjusting the tickler and tuning capacitors sounds like it may be working but not sure. I have not found instructions on tuning a radio like this with two 6 position selector switches located underneath the variocoupler. Left one has a direct connection to the ground post and right one has direct connection to the antenna post.
The closet radio I have to this set up is a AK big box model 20 and it has one 3 position selector switch and no variocoupler. It may be working and the problem may be I just do not know how to tune in stations on this one. I have it grounded to a copper cold water pipe and about 60 feet of wire strung from the ceiling, this antenna set up has worked well with my other radios.

I plan on running 18 gauge wire around the attic in the spring which should make a far better antenna.

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Last edited by atwaterkent1 on Jan Sun 21, 2018 4:27 am, edited 1 time in total.

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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Jan Sun 21, 2018 2:45 am 
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Latest Update - I was able to tune in one radio station but not clearly. I can barely make out what is being said. The right hand side variable capacitor doesn't seem to make any difference when I tried to get the station in clearer, that seemed strange. I also have the knobs in the center of the variable capacitors that move only one rotor on the end of them. Radio is working to some degree now but need to get better reception.

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Last edited by atwaterkent1 on Jan Sun 21, 2018 4:26 am, edited 1 time in total.

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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Jan Sun 21, 2018 3:39 am 
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Gary Schneider just emailed me, he has a good exact match for the .00025 cap and a .0015 cap. Is the .0015 cap close enough to the .002 to use if I have to?

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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Jan Sun 21, 2018 4:05 am 
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Dan,

There is no "tickler" in this radio, it does not regenerate, it will not radiate an RF signal.

The coil device is a tapped variocoupler. The primary is tapped to select the optimum match to the antenna and the rotor the appropriate coupling. The first tube it is connected to is an RF amp coupled to an RF transformer to the reflex tube that is a second RF amp to another RF transformer. Then to the carborundum detector coupled to the replaced audio transformer, audio signal routed to the reflex tube as audio. Then to the first stage jack/ and 2nd audio transformer, input to the third tube that functions as an audio output to the 2nd stage jack.

Essentially it is a three tube set functioning as four tubes. An amplified crystal set...

When a tuning element fails to select or "tune" there is a problem in that circuit. All resistance must be brought to zero.

The tuner condensers in that radio have a set of vernier plates, they are parallel connected to the primary plates. The construction of this brand of condenser is problematic after 90 years. The end plates are made of "condensite" a form of hard rubber, it is brittle and warps ever so slowly under tension. This means there is imperfect contact to the rotor at the contact blades.

The variocoupler rotor may also have imperfect contacts as well as the tap switches on the primary.

I will suggest taking apart the variable condensers if the Simpson shows anything above zero ohms across any of the plates both the stator and the rotor. You may have to burnish the parts at the points of mechanical assembly to improve continuity.

Handle the end plates with great care as any offset strain when assembling could crack them. It is the sulfur vulcanizing in the hard rubber that puts an oxide film on the metals. It is referred to as "out-gassing". You may be able to reverse the end plates such that any warping will bring the rotor wipers into full contact. In doing so use great care in re-tightening. Applying gentle heat with a heat gun will allow the hard rubber to re-conform with reduce danger of cracking. Sometimes various washers can be exchanged to get the desired low resistance contact.

BTW Did file the bottom tips of the tubes and is there good tension from the socket contacts to the tips of the tube pins? A brown haze on the contact blades must be burnished until it is shiny.

At the risk of repeat, there is no grid leak or grid condenser in this radio there is no detector tube.

Are you operating with the three substitute components, the detector and two mica caps or the originals?

If at anytime the radio comes up to performance don't attempt to do any of the tasks I suggest above unless the Simpson says there is a problem.

Oh, it won't hurt to have two different values for the cap that is across the1st audio transformer. The other cap is not all that critical it bypass RF from reaching the primary of the second audio to reduce distortion.

The reproduced schematic does not show a cap at .00025mf, why it is/was in this radio may have more to do with controlling an oscillating problem. You might do well to draw the schematic to be sure just where the questioned caps are.

Last post for the night...

Chas

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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Jan Sun 21, 2018 4:24 am 
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I have the replacement detector and original capacitors in the radio as of now. I will do as you advise and let you know how it goes. Thanks again Chas, goodnight.

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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Jan Sun 21, 2018 11:40 pm 
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Hi, Dan. Me again. I think you said the referenced schematic does not match your set, but your description of the 6 position switches matches exactly. If you zero your Simpson on ohms, X1 and hook one lead to ant and the other to ground the ohms should go up and down in steps as you turn each of the taps, one at a time; for example, 1.2, 1,8, 2.4, etc. Something to check.

The old Crosleys have a switch like that and tend to loose contact at the center where the shaft turns.

A question, in you last photos you have 3 wires hooked up from the arbe. Is the unused post connected to the B- post? And is A- jumped to B- on the arbe?

Jeff


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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Jan Mon 22, 2018 1:26 am 
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Hello Jeff,
The A- and B- posts are jumpered underneath the radio. I found the problem with the far right variable condenser, a wire leading to it from an RFT was broken inside the insulation. Not something you'd catch until you go through the radio jiggling wires. After soldering the wires I was able to tune in a couple of stations but they still come in pretty weak. I was able to tune in my AM broadcaster loud and clear so my problem at this point would seem to be signal strength. I need a longer antenna or the radio still has a problem pulling in stations clearly. I will try out your testing idea and let you know what i find. Thanks for your input.

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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Jan Mon 22, 2018 1:48 am 
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The tap with the lead from the antenna does as you say. The other tap with the lead from the ground doesn't seem to do much.

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Dan

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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Jan Mon 22, 2018 4:34 pm 
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Dan,

If your still having poor response from the ERLA, refer back to Jeff's post. Look carefully at the tap switch mechanism who's wiper connection is the GND post. Be sure the wiper has low resistance to the blade of the switch. Some sets had a double nut with a lug between and a length of flexible wire because a connection at the panel bushing was problematic.

If that is O.K. confirm if either switch jumps the same number of turns, IE one tap switch is 10 turns, the other 1 turn. Note if they are the same or different.

If above O.K. and noted, try the radio, if no improvement move ahead...

Try reversing the antenna and ground connections.

See if the problem of low response from the GND tap switch changes. If good done...

If not, check the ANT input circuit and the GND circuit, the switches and any other connection points..

There should NOT be any other connection, flying lead, ground plane or shield common connection to the tap switch busings, to any other part of the radio!! If there is, open that connection, then try the set. reverse ANT/GND again.

If the radio improves dramatically, done...

If not, leave the ANT/GND circuit fully isolated this is the best arrangement...

Locate a 400-500 pf variable condenser, this can be a new one or a vintage does not matter...

External to the radio put this variable condenser, the rotor to the GND connection and the stator to the ANT connection, connect the antenna and ground as well. The purpose is to tune the primary of the variocoupler in conjunction with the tap switches. IMHO the antenna is not favorable to the input of this radio it needs a longer antenna, the tuned input may well make the difference. The external tuning condenser is connected in parallel.

If this works, a more suitable vintage tuning condenser will be needed. A-K, Chelsea, EICo (Electro Importing Company) and Murdock made enclosed breadboard mount tuning condensers, some in the 400pf range, with thumb screws...

This condenser would have solved a similar problem as was encountered in the 20's...

BTW is the replacement AF transformer 5 or 6 to 1?

GL

Chas

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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Jan Tue 23, 2018 12:54 am 
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Dan, if it is picking up your broadcaster OK then the radio must be working. Sounds like it needs more antenna.

I think you can look at the 6 position switches as a coarse antenna range (ANT switch) and the GND switch selects 6 fine steps between each of the 6 coarse ANT settings.

Making progress...

Jeff


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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Jan Tue 23, 2018 1:46 am 
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Hmm,

I think I forgot to add, that either tap switch must not be looped to the ends of the coil such that the turns are shorted. Shorted turns will greatly reduce the efficiency of the variocoupler...

Chas

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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Jan Tue 23, 2018 3:51 am 
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Hi Jeff and Chas,
Didn't have much time tonight to work on the radio, will be back at it tomorrow.

( confirm if either switch jumps the same number of turns, IE one tap switch is 10 turns, the other 1 turn. Note if they are the same or different.)

Not sure what you mean by turns or jumping the same number of turns Chas.

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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Jan Tue 23, 2018 5:07 am 
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Quote:
Not sure what you mean by turns or jumping the same number of turns Chas
Ummm, same difference.

Actually a fault, of mine, I will substitute a synonym to make more interesting reading, more often than not, confusing.

What should happen is the blade of each switch should be connected respective to the ANT and GND posts only. If some how the beginning and end of of the input coil of the variometer are connected to the blade, as the switch goes from tap to tap the windings will be shorted. The beginning and end of the antenna coil should be on the last point of the of each respective switch.

I'll repeat, at no time should there be turns shorted by the switches.

Chas

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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Jan Wed 24, 2018 2:53 am 
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Checked out everything suggested and did not find any problem. The replacement AFT is an exact 6 to 1 match ERLA. Will start planning for wiring the attic on Monday. Should have a couple hundred feet of 18 gauge wire up within the next two weeks, hopefully that will solve the problem. In the mean time I will hunt down a condenser as you suggested Chas.

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 Post subject: Re: ERLA Radio Repair/Replacement of Audio Transformer?
PostPosted: Feb Fri 09, 2018 3:36 am 
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Attic antenna installed today and hooked it up to my ERLA. Radio is now working and I was able to pick up several stations. I still have a problem with the left variable capacitor I haven't figured out yet. All the connections seem fine but sometimes when I go to adjust it everything cuts out and then comes back in. Nothing obviously wrong visually but I'll keep working on it. At least it's working now and I certainly could not have done it without all the help everyone gave me, so thank you all (especially Chas who I think put as much time into getting this radio running as I did! :lol: ).

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