Repair tips .

Here are some repair tips for "All American 5" AM tube radios. Oddball and puzzling problems I have seen and fixed.
General recapping procedures:

Old AA5 radios usually don't need new tubes. What *is* required are new capacitors to replace the old wax capacitors and electrolytic capacitors. Ceramics and micas usually don't need to be replaced, though. These old wax and electrolytic caps have lifetimes of maybe 30 years at best. And are at least 45 years old, so.... Replace these caps one at a time, so you won't lose track of where they connect in the radio. I usually never desolder the old leads, as the terminals can be rather fragile. Especially bandswitches (you really don't want to break a bandswitch, as repair or finding a replacement would be almost impossible!). Several possibilities exist: clip at terminals, clip at body of the old cap, or at a point midway between. Clipping at the terminals is reasonable *if* you can easily get in there to solder the new cap in. Be sure to reuse any spaghetti tubing to avoid shorting to something. If the new cap leads don't reach, or you can't easily reach the terminal, the "J hook" procedure can be done, if done neatly. Form small hooks on the old stub, and the new part's lead. Interconnect, and solder. Ideally, the leads should not form a kink, but be in a straight line. Sometimes, if there is existing spaghetti tubing, I'll slip the new part's lead into the tubing alongside the old part's stub of a lead, and at a point where both leads show outside the spaghetti, solder them together. The new cap should roughly occupy the same location the old part was in, especially in high frequency RF areas of the radio.

Be sure to use the same connection points for the new replacement parts, even if one is the ground. Ground loops causing hum can result if another ground point is used. The manufacturer selected suitable points to ground things, and to use other points can cause hard to find problems.

To repeat, do not remove all the caps and then install new ones. You risk forgetting where what went. Better to remove one cap, and install its replacement, one at a time.

Phil has a good web page on recapping radios you could read for more info.

If you want to make the new caps look like old ones, you could take the below image files, edit the values, and print them out and glue 'em on the new caps.



Transistor radios sometimes need recapping too!


Older transistor radios can have capacitor trouble. Those little electrolytic capacitors in Japanese made transistor sets can go bad, usually open. In the York radio above, all the electrolytics dropped in value to the nanofarad range. Symptoms can be low audio volume, squeals on radio stations, and such. Audio coupling and or bypass capacitors going bad by going too low in value can cause low volume and tinny sound. AVC filter caps going too low in value can cause oscillations in the RF and IF sections of the radio, as well as bad bypass electrolytics. If the bad caps have in fact gone almost open, one can check them by touching across them a good electrolytic cap and see if improvement happens. It is likely that all the electrolytics, being the same age and manufacturer, have all gone bad. Might as well replace them all while you have the set apart. Replace one at a time, and pay attention to which side the positive terminal goes to. As these old caps had a wide tolerance in value when made, a replacement can be within 50% capacitance and work fine. Higher voltage rating is also fine as long as it will physically fit (which shouldn't be a problem, modern caps are smaller anyway). Be careful soldering on those Japanese circuit boards as the glue that holds the copper traces down isn't too good in those old sets. It doesn't take much to lift a trace.


Use a cap to reduce or eliminate RFI from old fashioned non electronic ballast florescent lights.


Solder to aluminum? It can be done!


Copper braid soldered to an aluminum heatsink. Scrape the oxide under a solder puddle.

Everyone knows you can't solder to aluminum, right? Well, given the right method, it can be done. The reason it usually can't be done is there is always a layer of aluminum oxide in the way. Scraping in the air does no good, as a new layer of oxide forms in about a nanosecond. The way around that is to keep air from the freshly scraped aluminum surface. Short of booking a flight on the space shuttle, this can be done by a puddle of hot solder over the spot you are scraping. Solder then can attach itself to the aluminum before the air can get at it. Use a cheap soldering iron tip for this; *don't* use one of those fancy plated Weller tips, as it will get ruined by this process. You should see solder wetting the scrape marks. After you get what looks like a solder joint, test by tugging on it to be sure you didn't just glue it with rosin, but created a real joint. You'll need a big enough solder iron to get the aluminum hot enough to melt solder. You may need to do tricks like drilling a few holes around the spot to be soldered to, to reduce heat loss. Or create a tab. You've seen tricks like this in circuit boards and steel chassis.


Here's one that drove me nuts for a while: Bad capacitors in an IF transformer. Symptoms were intermittent changings in radio signal strength. This was confirmed by measuring the AVC voltage. B+ was steady. Volume control set to minimum would remove the static sounds. So, it had to be upstream of the volume control, and the detector diode. Bad tubes? No. Bad contact on tube sockets? No. Plate voltages on the 12BA6 and 12BE6 were steady. Now, if the capacitor of the IF transformer LC circuit cuts in and out, that could do it. Spayed some ozone layer killing freeze spray into one of the IF transformer's bottom. No change. Did same to the other IF transformer, got some intermittence. Ah ha! removed the IF transformer, and took it apart. Turns out that the caps of the transformer's LC circuits are just silver plating on a sheet of mica. And the circuit connection is made by a press fitting of the metal terminal contacts sandwiched between some plastic. If the contact corrodes.... Intermittent operation. Removed the rivet that held the cap wafer in there, and measured the size of the caps. About 100pF. (Another IF transformer I just fixed used 150pF caps. So make every attempt to measure them before throwing them out. I tried to solder leads to the silver, no go. If you can't get a measurement, try using smaller caps and add more if necessary when the transformer is back in the radio). I soldered in some real silver mica 100pF caps to the under chassis terminals (easier to change if you can't get the transformer to peak). Your choice whether to put the caps inside the IF transformer can, or down below the chassis. Reinstalled the transformer, and it needed only some tweaking to be on frequency of the IF, namely 455KHz. If you can't get it to tweak, try a few pF more capacitance. I underestimated a little on the cap value, as it's easier to add than remove pF's. Operation over a few hours was steady, no more intermittence. Also, using undersized caps will make you adjust the cup cores closer together thus increasing the coupling factor "k". And yield a few more dB of gain. Be careful not to overdo it, or else you will get a pair of peaks with a valley between. You'll know if this happens, each station will start showing twice on the dial. Next to each other. Before it gets that bad, you'll notice distorted audio highs on stations. Because the carrier strength is lowered too much by the valley. So, back off by paralleling a few more pF's across the caps. BTW, if you compare the two IF transformers in an AA5 set, the more closely coupled IF transformer is a "diode transformer" and is designed to match the load of the detector. The looser transformer is an "interstage" transformer.

Leakage of current from primary to secondary LC circuits in IF transformers

As the IF transformer caps are adjacent to each other on the mica wafer, and if there is any overspray of silver between the two, this can create a leakage path from B+ or plate circuit to the grid or AVC circuit, or at the detector, introduce undesired excess positive bias on the diode detector plate. Symptoms of leakage can be "thunderstorms" of static from erratic B+ current from plate LC circuit to the grid LC circuit, and upset of AVC bias voltage (if it's the first IF transformer) or distortion of weak stations from some B+ leaking into the diode detector (2nd IF), pushing it into a region of more conduction per cycle of carrier. Very weak stations could be completely lost, as their entire carrier waveform is held positive compared to the detector cathode. Then the diode cannot do its job of rectifying the carrier, thus no audio signal. Partial non symmetrical (ie, not at zero crossing) rectifying of the carrier would yield audio distortion.

An alternative to replacing the mica wafer caps is to use a sharp knife to scrape away the leakage path, or even cut the wafer in two between the two caps. This can sometimes be possible in later circuit board mount IF transformers of manufacture other than K-tran. If the leakage path is the problem, this method avoids much disassembly and also you probably will not need to touch the alignment once you reinstall the IF transformer back into the radio.



Unused band going dead from long term lack of use: A tube with heater hot but without any current draw can eventually ruin the cathode. If an AM/FM radio was only used on FM, the AM converter tube (12BE6) may be weak or dead due to this. A few microamps current is all that is needed to keep the cathode alive. You can provide this for either the AM or FM (whichever is not being used) with a resistor of around a half megohm connected from the AM B+ to the FM B+. You could connect it right at the B+ switch contacts of the band switch. When FM is selected, a few microamps flow thru the resistor to the unused AM tube, and if AM is selected, current flows thru the same resistor to the FM front end and other FM only tubes. This won't fix a ruined tube, but should prevent new tubes from getting ruined by this.
Pilot light keeps blowing out: In an AA5, the pilot light is run off of a tap on the heater of the rectifier tube. This is to compensate for the differing "thermal mass" of tube heaters and light bulbs. That is, that tube heaters take longer to light up than light bulbs do. And the variation of resistances over time differs. Tube heaters and light bulbs when cold have less resistance. This is why the pilot light isn't just in series with the heater string. The bulb would get overvoltaged and burn out. The section of rectifier tube heater placed in parallel with the bulb is to absorb most of the warm up current (which is much higher than normal operating current) and allow the bulb to see only the voltage it is rated for. But if the rectifier tube's tap isn't done correctly, the bulb may still get too much voltage and burn out. Try swapping from a radio that does not have a pilot light the rectifier tube. The pilotless radio will work just fine with the pilot light blowing tube. Also a resistor of about 47 ohms in parallel with the pilot light should help.
Audio distortion in the output stage caused by a bad circuit wafer: Usually these are little ceramic resistor/capacitor circuit wafers. And rarely go bad. But I just had a bad one. Check the cathode and grid voltages of the output tube (50C5). Grid should be at zero, and cathode around 6 to 7 volts positive. If the grid seems to be a few volts above zero, there is a leakage path, probably the coupling cap from the 12AV6 plate.


Typical circuit wafer.


Audio output transformer bad? In a pinch, one can use a power transformer with a secondary of 6.3V center-tap. The turns ratio of the 120V primary to 6.3V secondary is 20 to one. With an 8 ohm speaker as load, that works out to be 8*(202)=3200 ohms on the primary side, close enough to the 2500 ohms a 50C5 wants to drive. Output power will be a dB or so lower, but that will be not noticeable. If driving a 3.2 ohm speaker, use half of the secondary, ie, 3.15V. That's from one end to the center tap. That will look like 3.2*(402)=5120 ohms. Kinda high, but the output power will be half the original value. But you'll be back "on the air". Changing the speaker to an 8 ohm one would probably be worth the effort here. The frequency response of a power transformer will be adequate for an AA5 radio, but won't be hi-fi.
Bad sound when volume is LOW, seems okay when louder. AA5 radios use a class A audio amp. So it should work fine at low volumes if it works at louder volumes. If we had a class AB or class B amp, we could have crossover distortion. In the case of an AA5, suspect a bad speaker. A small amount of rubbing in the voice coil could do it. Do this test: disconnect the secondary of the audio output transformer from the speaker. One lead is enough. Measure the DC ohmage of the speaker. Using a similar DC ohmage speaker, connect it to the transformer secondary. Turn radio on, and listen to see if the distortion is still there. If not, original speaker is bad.
Just finished (or so it seems!) an AA5 repair. Symptoms were: low audio, occasional cracking sound, distortion on strong local stations. This after doing a re-cap of wax caps. The radio is an RCA 8X541 using octal tubes, and no graham cracker module in the audio section, but discrete resistors and capacitors. Could tell that the crackling was happening before the volume control, as the sound level of the crackling could be varied, and zeroed, by the volume control. Tried swapping tubes, not it. Also used a DVM to measure the AVC voltage, seems kinda low compared to other AA5's I've played with. I have a 100MHz o-scope and an isolation transformer, so I got out the "heavy artillery". With the scope I could see the modulated RF (actually the IF) carrier in the IF section. Could see clipping on the strong signals. I could also see rectified RF (if) at the top of the volume control. That shouldn't be, it should look like a filtered audio waveform. Could also see spikes correlated with the noise here, but didn't see the noise spikes in the IF stage. At this point, the final IF transformer is suspected. I see it has 5 terminals, one of which is grounded. Must be the infamous mica capacitor problem (leakage to B+, and poor contact). Tried cutting the ground connection, and problem went away. And the low AVc problem also went away when I added a 50pF cap from the top of the volume control to ground (to replace the function of the old cap in the IF transformer). That took care of the distorted strong local station, and the rectified IF waveform now looked like filtered audio. Radio has been playing nicely for the past 1 1/2 hours while I've been surfing the web and newsgroups on the 'net.
Rattling sounds: Sometimes a mechanical resonance will be present in a radio set. A rattle sound on loud passages of music or voice. This can happen when the audio from the speaker causes a mechanical resonance in some part of the radio chassis or cabinet (or between the two). This can be hard to locate and solve. You should get a sine wave audio oscillator that can be varied to sweep thru the audio range. This can be an old Eico or Heathkit. Also you'll need an AM transmitter (or FM if it's an FM only set). Click for a
tube, or solid state micropower transmitter you can build for this and other uses. Find an empty frequency on the dial, tune the transmitter to that spot. Feed the output of the audio oscillator to the transmitter to modulate it. Sweep the audio oscillator to check for resonant rattling in the radio under test. Try setting the volume of the set to max, but not into distortion. This method is actually used in TV production testing to catch bad TV sets with a rattling defect. If the radio passes this test, it should do fine on normal program material. Be aware that this test can be annoying to other people within earshot! Correcting the rattles can take a lot of trial and error. Set the audio oscillator to the frequency where a rattle occurs. Try tightening mounting screws on the speaker or chassis. Check sheets of wood or plastic that might be lightly touching. When you do find and suppress the rattle, sweep the audio oscillator again to be sure you didn't create a new problem resonance. This can be a royal pain in the you know what. Just be careful you don't overtighten screws or glue down something you may want to take apart later on. Be sure to check the speaker itself to see if it has any defects like a tear in the cone, or rubbing voice coil. Repair or replace accordingly.
Replacing selenium rectifiers with silicon diode or maybe a bridge rectifier.

Some AM-FM hot chassis sets use many tubes, too many to string in a 35W4 tube rectifier. So a selenium rectifier was used. Like wax capacitors, these will fail in time. Best replace the function with a silicon diode like a 1N4007. Add around 50 ohms 1 watt resistor in series, and check the operating B+ voltage to be sure it doesn't go higher than the electrolytic cap's voltage rating. Electrolytics can take a temporary overstress for a short while, like heater warm up time. You can use one side of the old selenium rectifier as a tie point, but the other end of the selenium rectifier must have nothing connected to it!. It doesn't matter which end of the selenium rectifier serves as the tie point. Check to be sure there are no leakage paths to the chassis.


I replaced the selenium rectifier in one AM/FM set with a bridge rectifier. Full wave rectification, less power supply hum (120Hz vs 60Hz). The heater string runs directly off the powerline (via power switch). The mid point of the heater string will look to have minimal AC waveform in reference to the B- line of the bridge rectifier. But will have a DC bias of about half the B+ voltage. This is fine, cathodes like their heaters to have a positive bias. One end of the audio output tube (for example a 50C5) (#8 in the diagram) heater is probably already connected to one of the AC lines. Disconnect the heater line of the other audio output heater pin. This line, now disconnected (feeding to tube #7), now will be connected to the other AC line. See diagram. And at the old ground end of the heater string, usually the AM or FM detector/ audio driver tube (#1) (19T8 for example) disconnect from ground and connect to the now loose end of the audio output tube heater. This should minimize hum pickup from the heater line. A small cap of around 0.1uF 400V or more tied close to the heater string midpoint should help reduce the AC waveform some more by holding a bias charge between the heater string and the B- ground of the radio during the time the bridge rectifier isn't conducting. The bridge diodes only conduct at the peaks of the AC powerline waveform.

Pay special attention to the AC line lead dress around the volume control power switch for hum pickup. Hot chassis radios usually switched the local ground feed line to avoid hum pickup from 120VAC to local ground wires. This could ruin the advantage of full wave rectification (less hum, 120Hz vs 60Hz) if not taken care of. Look for trouble by listening to silent passages in radio programming with the volume control at half setting (hum pickup can be more severe at this position). Shielding may be needed.


Why some pre-war AM-SW sets are missing the SW coils


rec.antiques.radio+phono #147488 (9 more)
From: wa2ise@netcom.com (Robert Casey)
Subject: Re: Removing Shortwave bands from Japanese/American's Radios
Date: Sat Apr 08 19:40:53 PDT 2000
Organization: NETCOM / MindSpring Enterprises, Inc.
Lines: 50

In article <38EFD8C6.B534FD64@Flash.net>,
Doug. Houston  wrote:

>I saw lots of those sets in the shop where I worked / hung out during WWII.
>This is true for Japanese, German and Italian families. I believe that it
>was limited to non-citizens though. You still see posts on this NG about the
>missing SW bands. I've told this story many times.
 
My father had a Japanese American friend who was born in the USA.  And his
SW set was "circumcised" too.  They had my father do it.  At first he just
shorted the SW LC coils, but he was told he had to *remove*  all of the SW
coils.

This was in the New York city area, and the guy didn't get shipped to
a camp.  The authorities said they could accept my father vouching for the
guy's and family's loyalty to the USA.  But my father had to pay them
frequent visits to be sure they weren't spying or something....
As it turned out, the authorities didn't round up the Japanese in New York.

My father got 4F'ed because of food allergies and hey fever problems.
He met my mom in a defense plant.....

The day after the war was won and restrictions lifted, my father dropped
by his friend's place and he planned on restoring the radio by reinstalling
the missing SW coils.  But the Japanese American guy was so spooked by the
whole thing he declined.

When I was growing up in the 60's, I used to play with the
Japanese American's kids.  They'd either come to us, or we'd pay them
a visit.  Never had green tea before that.

>
>Conrad Field wrote:
>
>>  I just had a visit from our 85 year old great uncle that had lived here
>> in Central California during World War II.
>> He informed us that the government had paid local radio shops to remove
>> the short-wave bands from all Japanese's
>> American radios... They were ordered to bring in the radio's and he
>> would remove the short-wave (and leave the
>> broadcast band) so that they could not receive "secret messages form
>> abroad".. This was early 1942, a year
>> before they started to round up the Japanese Americans and put them into
>> camps...  I took a look at my mother's
>> year book (1942) and was surprise to see 4 or 5 Japanese in every high
>> school class.
>>   As my mother was watching her Japanese girlfriend board the train, she
>> was wondering if us "German"
>> Americans were next.... After all both family's came over to America at
>> the same time in the late 1800's...
>> Sort of sends a chill down your back, doesn't it....
>>  Any of you out there ever heard or know of this???

Asbestos in radios, what to do about it

1. At present, asbestos is known to be hazardous only if inhaled. Although there is some ongoing study on ingestion, the results are so far not alarming. Certainly less alarming than the results on arsenic, lead or cadmium.

2. Asbestos will become airborne only if friable (easily broken into small pieces). It becomes friable primarily if disturbed. There are three significant forms of asbestos as it was commonly used in consumer articles: Chrysotile, Amosite, and Crocidolite. Of these, chrysotile (white asbestos) is the most likely fiber to be found in that mat in your radio.

3. Asbestos that remains in place or can be made to remain in place is NOT hazardous.

Safing (encapsulating): Most (not all) of the asbestos used in domestic radios is included in a soft mat, either woven (rare) or non-woven (common). Usually it is held together with either a cementicious or gypsum-based binder together with several other fibers. The trick is to replace the binder with a more permanent and less mechanically vulnerable material. The EPA and OSHA recognize many sorts of encapsulants, including the binders used in both Duco Cement and Amberoid Cement. (Personal comment: I recommend Amberoid for its distinct color and the fact that I find it somewhat easier to use and less expensive that Duco. But the processes are identical. Amberoid will also maintain the insulating properties of asbestos, I am not sure if Duco will do the same.)

Mix the material of choice (Duco or Amberoid) with equal parts by volume of Acetone and soak this diluted material into the asbestos mat. It will re-glue the mat in place and bind all the fibers together. Allow to dry and soak again. Do this work away from flame or any source of flame. Do this work outdoors if possible. Do not attempt to brush, clean or vacuum the mat prior to treatment. Glue ALL of it down.

The times when the insulating mat are most likely to be disturbed are when the chassis is removed or reinstalled in a radio. Given that the original binders were not all that effective in the first place, and that they were made with deliquescent materials (gypsum or portland cements) it is very likely that some of the fibers will have become loose over the years, and may be disturbed when the chassis is moved or removed. If mice have inhabited the radio, this is a certainty. So, some initial cautions MUST be taken. And given that some here will neither admit to the hazard nor take any precautions, and that others here may not have the financial resouces to "have it done", what I suggest here is not offered as a way to eliminate a significant risk, but a way to reduce it at least in part.

First: Work out of doors. If you choose not to believe in any risk, it is still unfair to introduce asbestos into a house (or household) where it may remain a hidden hazard forever. Work over a large leaf-and-lawn bag if possible.

Tools:
1. Good particle mask. Must be effective from .1 to 10 microns (a human hair is about 50 microns in diameter). Because asbestos fibers are small and light, they can be suspended in the air for long periods. This is NOT a paper painter's mask. But once obtained, may be retained for multiple uses.

2. Small spray bottle filled with a 15:1 water-to-dish-soap solution. You will need a couple of ounces for the process, and about a pint at the end to soak the debris.

3. Strong paper towels... those that will not dissolve in soapy water.

4. Small, soft-bristled disposable brush. About 1/2" wide or smaller with at least 1" bristles.

5. Single-edge razor blade (not always necessary).

Spray the soap solution around the base of the chassis before removal. Make sure that the entire perimeter where it touches the asbestos is saturated and damp. This will hold the fibers from becoming airborne as the chassis is removed.

Remove the chassis carefully. Use the razor blade if necessary to cut loose the mat from the chassis. The idea is to leave the mat in place and not on the chassis.

Look on the chassis. If there are any visible particles of the mat on or in it, they must be collected and removed. For this, you will use the towels, the brush and PLENTY of the soapy water. A wet asbestos fiber will not become airborne. Soap is the wetting agent. Take your time and be thorough. Clean ANYTHING, even spider-webs or other material from the chassis. Be sure that it is clean.

Gently spray the inside of the radio cabinet with the soapy water. This would be those areas around but not covered by the mat. Wipe this down with the paper towels and repeat. The idea here is to capture any bits of asbestos that may have come loose from the mat.

Allow the cabinet to dry thoroughly. Soak the now-dry mat with the safing material as above. While the cabinet is drying, collect all the other detritus (brush, towels, razor, whatever) into the garbage/leaf & lawn bag. Pour the remaining soap solution over it so that it becomes a soapy mess. Seal the bag and bag it a second time. If there are ANY leaks in the first bag, bag it a third time. Dispose of the bags with your township's hazardous materials regulations, or in a regular landfill, NOT an incinerator or where the trash may be incinerated. Remove, double-bag and dispose of the mask filter also. You will use a new one for each session.

A bit long-winded as always, but the proverbial ounce of prevention covers many pounds of care in this case.

Above section on asbestos written by:
Peter Wieck