I have a radio that I recently recapped and replaced a few out of tolorance resistors. The radio worked before the recap, as in it was able to pick up most stations but with some distortion. Since the recap, I am able to pick up only one station very weakly and even then it's not in the right spot on the dial. This may be a dumb question, but would the radio need to be aligned? Is it normal for a radio to be this far out of alignment after a recap job considering it worked before?

If you replaced any of the mica condensers with slightly off values, this could throw some things off. You should test mica condensers before you replace them. You could have also replaced another condenser with the wrong value. Perhaps you miswired something.

Thomas

Did you replace the mica caps inside the IF xfmrs? Otherwise, like Thomas, I tend to suspect a wiring error. You'll need to get out the schematic and laboriously trace all wiring with colored pencils.

I prefer that people not type in all caps, but here I go anyway:

AFTER FIRST REPLACING THE ELECTROLYTIC FILTER CAPS, THE FIRST ORDER OF BUSINESS IS TO GET THE RADIO WORKING, AFTER A FASHION, BY TROUBLESHOOTING. (YOUR RADIO ALREADY WAS WORKING, AFTER A FASHION.) NOT ONE TIME IN A HUNDRED WILL RECAPPING A NON-WORKING RADIO MAKE IT START WORKING.

AFTER YOU GET IT WORKING, AFTER A FASHION, YOU CAN THEN BEGIN WHOLESALE RECAPPING. AFTER EACH CAP IS REPLACED, PLAY THE RADIO TO MAKE SURE YOU HAVEN'T INADVERTENLY INTRODUCED A WIRING ERROR.

Please don't ask me how I learned this lesson.

At first I replaced only the filter electrolytics and that was when it started to sort of work. I then replaced all of the paper caps at once, so your probably right that I did mis-wire something. I'll dig the schematic out and see what I find

Forgot to mention, I've have not changed any of the mica caps, just the paper ones
:At first I replaced only the filter electrolytics and that was when it started to sort of work. I then replaced all of the paper caps at once, so your probably right that I did mis-wire something. I'll dig the schematic out and see what I find

You should definitely replace components one at a time. If you removed all of the old condensers together, this is bad practice. If you removed one and then replaced it with a new one, and then moved on to the next one, this is good practice. This helps you keep track of what you're doing. Surely the prior method is more assembly line like, but it leads to confusion.

Thomas

I did it that way, remove one, replace it, and move on to the next, but it was the first radio that I did a full recap on (about a year and a half ago)so I probably miswired something. I was still learning then. It's been sitting on my workbench for over a year and I'm thinking of getting back to it.

I know what you mean by the "assembly line" method. I had to do that with a GE model 221 6 tube AC/DC I worked on recently. When I pulled the chassis, I found 2 multisection electrolytics as well as a single all wired into the original filter cap. The old cap was still wired into the circuit. The way the rest of the paper caps were wired just didn't look right,it was a real hack job. I pulled them all and used the schematic to rebuild the way the caps and some of the resistors were wired. It was very nerve wracking, but the radio seems to work ok now.

Keep in mind, too, that some condensers have a code on them. Those little yellow metalized film condensers (which fit so nicely inside the old cardboard condenser tubes) often are coded, but not always. 473K, though, means 47 pF with three zeros added to it, making it 47000 pF, which, I guess, makes .047 MFD. If you were to order or accidently receive a 474K condenser, this would be .47 MFD. In audio circuits, this would pass too much bass as a bypass condenser. As a tone condenser it would kill the audio. In RF circuits it would make the AVC sluggish. If used as a filter on a screen grid, it would have little affect. As a cathode bypass condenser it may or may not affect the RF or AF.

If you were to have this discrepancy with a very small condenser used on, say, the oscillator coil, this would drastically change the frequency coverage. Also, be sure that you didn't disconnect or mis-wire the oscillator coil, if you did do anything with its wiring. You can check to see if the oscillator is working by checking the 1st grid's voltage. The 1st grid must be associated with the oscillator in order for it to have the required voltage. If your radio has a 6A7, 6A8, 12SA7, 1LA6, 1A6, etc., pentagrid converter tube, the 1st grid is usually associated with the oscillator. Its voltage should be between -5 and -7 volts if the oscillator is working. Just so that you know, I learned that trick from NORM. If you don't have negative voltage here, then your oscillator isn't working. This will cause your radio to only tune in a few stations, and possibly none.

A model number is a plus, as this will allow me to consult the schematic.

Thomas

It's a Western Air Patrol 6-M3T that I posted about awhile back.

Check the oscillator's first grid voltage first. Then we'll see what's going on. You probably have a dead oscillator for one reason or another.

Thomas

The radio has a 6A8 converter. On the schem, would the oscillator coil be the one between the 6A8 and 6K7 or the one between the 6H6 and the 6K7? What pin on the 6a8 would the first grid be? The voltage would be measured between first grid and ground or chassis, right? Here's the schematic:

http://www.nostalgiaair.org/Resources/584/M0023584.htm

:Check the oscillator's first grid voltage first. Then we'll see what's going on. You probably have a dead oscillator for one reason or another.
:
:Thomas

:The radio has a 6A8 converter. On the schem, would the oscillator coil be the one between the 6A8 and 6K7 or the one between the 6H6 and the 6K7? What pin on the 6a8 would the first grid be? The voltage would be measured between first grid and ground or chassis, right? Here's the schematic:
:
:http://www.nostalgiaair.org/Resources/584/M0023584.htm
:
:Hi Brian,

::Check the oscillator's first grid voltage first. Then we'll see what's going on. You probably have a dead oscillator for one reason or another.
::
::Thomas

Brian,

Looking at the 6A8 socket from the bottom locate the socket index and count around clockwise from the index to pin #5. That is the oscillator grid.

Radiodoc

Thank you. I thought that's what it would be. To measure the voltage, it would be between pin 5 and B- or ground, right?

:Thank you. I thought that's what it would be. To measure the voltage, it would be between pin 5 and B- or ground, right?

Brian,

That should be sufficient. The power supply transformer centertap is above ground thru a resistor to supply bias for the output tube. I have seen radios that referenced voltage measurements to the centertap and others with a similar power supply reference to the chassis. You can even measure the grid voltage between the cathode (pin 8) and grid. We just need to know if the oscillator is running with a minus voltage on it of around minus 7 to minus 10 volts. The minus lead of the volt-ohm meter will go to the grid and the plus lead to ground or B minus.

Radiodoc

I will check that when I get home from work in about 2 hours and see what I get.

::Thank you. I thought that's what it would be. To measure the voltage, it would be between pin 5 and B- or ground, right?
:
:Brian,
:
:That should be sufficient. The power supply transformer centertap is above ground thru a resistor to supply bias for the output tube. I have seen radios that referenced voltage measurements to the centertap and others with a similar power supply reference to the chassis. You can even measure the grid voltage between the cathode (pin 8) and grid. We just need to know if the oscillator is running with a minus voltage on it of around minus 7 to minus 10 volts. The minus lead of the volt-ohm meter will go to the grid and the plus lead to ground or B minus.
:
:Radiodoc
:

If the cathode of the 6A8 is connected to the chassis, and the oscillator coil is connected to the chassis in some way, then you should reference the voltage to the chassis. Remember to hook up your meter backwards because you'll be reading a negative voltage on the grid. This negative voltage is due to an abundance of electrons collecting on the grid. Your meter will read a positive voltage, but since your negative lead is connected to the grid, the grid is actually the negative item.

Thomas

The cathode is grounded through a .05mfd cap and a 200ohm wirewound resistor and the coil is thru a 1 mfd on one side and unmarked on the schem on the other side.

:If the cathode of the 6A8 is connected to the chassis, and the oscillator coil is connected to the chassis in some way, then you should reference the voltage to the chassis. Remember to hook up your meter backwards because you'll be reading a negative voltage on the grid. This negative voltage is due to an abundance of electrons collecting on the grid. Your meter will read a positive voltage, but since your negative lead is connected to the grid, the grid is actually the negative item.
:
:Thomas

Chassis.

I get -4.35volts between pin 5 and the chassis. I don't know if it matters, but I get +63millivolts between pin5 and pin8. Also I notice a little blip of static when the neg lead is on pin 5 and I touch pos lead to either ground or pin 8

:The cathode is grounded through a .05mfd cap and a 200ohm wirewound resistor and the coil is thru a 1 mfd on one side and unmarked on the schem on the other side.
:
:
::If the cathode of the 6A8 is connected to the chassis, and the oscillator coil is connected to the chassis in some way, then you should reference the voltage to the chassis. Remember to hook up your meter backwards because you'll be reading a negative voltage on the grid. This negative voltage is due to an abundance of electrons collecting on the grid. Your meter will read a positive voltage, but since your negative lead is connected to the grid, the grid is actually the negative item.
::
::Thomas

-4.35 volts is okay. It is kind of weak. Tune over the dial and see if it changes.

Thomas

I tried what you suggested. The voltage remains steady at -4.35 until about 1000kz, then it starts to drop steadily until just below 1400kz. The voltage I read then is -.4 volts. Then it starts to rise to -3.3 volts by the time I get to the top end of the dial. I should also add as the voltage is dropping or rising, the readings fluctuate when I stop tuning and let it sit. But the overall trend is as I mentioned above.

The IF on this radio is 456kz which seems to have a connection to the frequencies at voltage drop, bottom out, and then voltage rise at the end of the band. I don't know if it means anything or if it's just coincidence.

Interesting. With most of my radios, the voltage tapers to -5 volts at the low end of the dial, and goes to -7 volts or more negative towards the high end of the dial.

Thomas

Maybe check the condenser and the resistor at the 6A8 cathode. Check the resistor for proper value and the condenser for leakage. Here's something else you can try, though, too. You replaced some parts, right? Your RF section is where the problem is. Put back in the old parts in this section...especially in the oscillator section, which seems to be performing poorly. See if this brings things back to life. If one part suddenly brings things back to life, then this is where the trouble lies. Tell us what the value of the old part and new part is.

We've probably hit this point before, but check to see that nothing else got unsoldered when you soldered in new parts. Check these key areas first...where you did work. Make sure that no solder is blobbing onto something else.

Thomas

I think I usnderstand where the osc. section is, but not sure on the RF. Would part of this be the 6K7 the remote cutoff RF pentode? I did not replace the wirewound R4 or R15 (they are the type that look like a short cloth covered wire but with resist. color markings and metal tips) but may have bent them too much when putting in the new caps.

RF stands for Radio Frequency. This would be any section which deals with Radio Frequencies. Anything after the second detector is Audio Frequency. That said, focus on the RF section. This would include the oscillator, since the oscillator oscillates at radio frequency levels. It would also include Intermediate Frequency amplification sections. I believe that your radio employs one of these sections, and has two transformers--one before and one after the IF amplifier tube. This would probably be the 6K7.

Thomas

I checked the condenser and resistor to the 6A8 cathode. The cap was one that I had replaced with a .068mf 400v. The 200 ohms wirewound resistor tested at 199.6 ohms on the meter, so that seems ok. I had not yet replaced the cap and resistor on the 6K7 cathode, but when I checked the cap, it was showing some leakage, the resistor was ok. So I'll have to replace the cap on that one.

The only components I replaced, was the paper caps and a few of the resistors. On the caps, I of course used equal value or higher if I didn't have an exact match. On some of the resistors, I didn't have exact values, so I used as close as I had. For example on R5 I used a 470k instead of a 500k. On R10 and R11 I used 68k instead of 70k, R2 used 39k instead of 40k. Would lower value resistors make the radio dead when it worked before the recap and the new resistors?

I traced the schematic out to make sure I didn't have any mis-wiring and everything matches up with the schematic. I have not traced the rectifier section yet.

Your resistor values seem fine. What condensers did you replace, and what are the exact figures given on your replacement condensers? Give me the EXACT numbers and letters found on your condensers.....this well tell me whether they're coded or not. Regarding that cathode condenser, you should replace it if it's leaky, but if the leakage isn't down around the parallel resistance, it won't likely affect set performance. For now, though, replace it. If the set worked before with that leaky condenser, though, it isn't likely the problem.

You didn't disconnect any other wires in your condenser/resistor replacement, did you? There's no chance that you mixed up IF transformer wires or something? Well, once I see your new condenser values, I should have an idea as to whether the new ones are correct or not.

Thomas

Seems this is kind of late in the game, but have you tested the 6A8 tube? Have you tried replacing it?

Thomas

That was one of the first things I did. The tube I have in right now tests at 85 on a Heathkit TC-2 tester.

:Seems this is kind of late in the game, but have you tested the 6A8 tube? Have you tried replacing it?
:
:Thomas

I replaced C6, C9, and C11 with 1mfd 400v coding 105k 400v. C10 with a .1 400v coding 104k 400v, C14 and C17 with .033mfd 630v these were actually marked this way, no coding, C8 and C12 with .068mfd 400v coded 683k 400v, C18 .33mfd 400v coded 334k 400v, C23 with a 33mfd 50v electrolytic did have a 25mfd 50v electrolytic (could this be the problem), C20 with a .006mfd 1600v orange drop coded 16PSD60-602K1600V, C15 with .01mfd 400v coded 103 400v, C19 with .033 630v marked this way. C21 and C22 replaced with a multi-section electrolytic 10/10mfd 450v.

I used the yellow tubular caps unless otherwise noted.

I did not replace or test any of the mica caps since these rarely have problems according to what I've read here on the forums. I did have to disconnect a few wires to get at the paper caps, but I drew a diagram before I did and made sure I reconnected the wires according to the diagram I drew.

Well, all of the condensers you mention are fine. Replacing the electrolytic with a slightly higher value will do no harm (33 MFD). Seems you kept fairly close with the other condensers. I recommend that you test those micas. If you cannot find any wiring errors, then something else is wrong. You may go through and re-test your new condensers, just to see if any of them have shorted. Micas don't usually short, but the do on occasion, and sometimes the material inside isn't even mica. There's a color code on most which tells whether mica or paper was used, but unless you know the color code, or unless it's given, you won't know whether paper or mica was used. My DeWald BT-100 television used micamold condensers all over the place, and most of them were the paper type. Most of them were shorted or leaky, too.

Thomas

To test a mica cap, I would test it on a multi-meter just like a paper cap, for leakage or short, right? Also if I find I do need to replace one,would the silver mica caps at AES be good replacements? Also is voltage critical? My schematic doesn't list voltages on the micas and I did see a couple of them that did not have markings

You test it like any other cap. Don't touch the meter leads or the leakage in your fingers will make you think that the condenser is leaky. Remove the condenser from the circuit so that other components don't give you the illusion of leakage. Silver mica condensers from AES will work fine. If you can crack open the old unit and hollow it out a bit, you can fit a small ceramic cap inside. Glue it shut and it'll look pretty original.

Regarding voltage, as I recall, your set is an AC/DC model, so voltages don't go over 150. You will be fine with 200 volt units, but standard sizes are 400 and 600, so go with either 400 or 600. This leaves plenty of slack for static charges and such, which on rare occasion form carbon trails. The occasion is rare enough that some may be laughing at me for suggesting such a thing. At any rate, 400 and 600 are standard, and afford a lot of electrical room to work with, so go with them.

Thomas

The set is actually AC only with a transformer. Ceramic caps are ok? I thought they tended to drift as they heat up.

:You test it like any other cap. Don't touch the meter leads or the leakage in your fingers will make you think that the condenser is leaky. Remove the condenser from the circuit so that other components don't give you the illusion of leakage. Silver mica condensers from AES will work fine. If you can crack open the old unit and hollow it out a bit, you can fit a small ceramic cap inside. Glue it shut and it'll look pretty original.
:
:Regarding voltage, as I recall, your set is an AC/DC model, so voltages don't go over 150. You will be fine with 200 volt units, but standard sizes are 400 and 600, so go with either 400 or 600. This leaves plenty of slack for static charges and such, which on rare occasion form carbon trails. The occasion is rare enough that some may be laughing at me for suggesting such a thing. At any rate, 400 and 600 are standard, and afford a lot of electrical room to work with, so go with them.
:
:Thomas
:
:

I've used ceramic caps with no problems....depends on the circuit. For now stick to mica and experiment later if you wish, once the set is working properly.

Thomas

If a shorted condenser is causing the trouble, though, you aren't going to get the radio working until you start replacing condensers. It is best to test each condenser for shorts and leakage. This way you get an idea as to what is causing some of the trouble. Most of my radios have been rejuvenated by replacing condensers. Usually people don't play around with the adjustments in back. It is probably a good idea to test continuity of all components. Resistors should be on value. Coils should have some continuity, and should match resistances given in schematic, if they are given, and condensers should have no continuity except for a brief charge-up. They should have ABSOLUTELY NO leakage.

THomas

Brian:
Tube testing is a nice pass-time for rainy afternoons or when trying to balance output amps for matched sets etc.. but what you need is some very simple big chunk troubleshooting when a radio is not working.
What I do is this...perhaps if you don't already know these simple step this may help you.
1) make sure the filaments light up
2.) check b+...
3.) replace electrolytics on power filter.. then repeat step two.
4.) If the radio is not playing go to step 6
5,) Start to replace each paper cap testing the radio after each so you'll get to see how each one changed things.
6. If radio is not playing.. check audio output by placing finger on the cap off the center tap of the volume control. if it makes noise.. good.. the audio section works. go on to step 9
7. If no audio check speaker field coil.. but that usualy shows up if bad in the power supply if the field coil is used as a choke.
8.) Try substituting a spare speaker and connect directly to the new speaker's audio transformer from the final audio tube.
9.) If the audio works but no stations come in..and if you have a scope.. place the scope probe on or near the RF section local oscillator coil. You should see something at least... typically a signal that is 455kc above the station you are tuned to.
10. If that is there and you still don't get a station test the IF transformers.
11. Tune your signal generator to 455kc and insert it in the RF section or even the antenna.. then see if you can tune the IFs....

If you can... you don't have a problem with the radio but maybe your hearing aid battery needs replacement.... lol

The basic goal here is just to keep it as simple as possible y'know? K.I.S.S. =(keep it simple stupid)?

It's easy to get lost if you don't think about each section as a simple functional block.If you do ... you'll find it's fun.. and less of a mystery.
Peter

Before you ever power up a radio you should go through and check all condensers for shorts and leakage. If you power up that radio, even if slowly, and a condenser is shorted in the right circuit, it'll burn something else out (like an expensive transformer, or a transformer which is impossible to find).

First thing you should do whenever you get a new radio is test condensers and tubes. Replace obviously bad tubes and any leaky condensers. Then observe wiring. If wiring looks fine, power up slowly. If radio performs well, great. If not, check resistors. You should probably check resistors anyway. If any are way off value, they may cause fluke problems down the line. Then, if resistors don't fix the problem, you check transformers and coils.

Using the radio to test itself is poor practice.

Thomas

Of course one should always do the safety checks on a new-arrival 'dead' radio...
What my point was is simply that if you have a radio that you are ALREADY troubleshooting...you need to follow a simple block-diagram testing process to narrow down or to localize the problem

Thomas... do think I was suggesting using the radio to test itself?.. (hardly.. lol)
:
:Using the radio to test itself is poor practice.
:
:Thomas

PLEASE START A NEW "THREAD", OTHERWISE WE WILL AGAIN EXPAND THE FORUM LIST TILL IT RUNS OFF THE PAGE HORIZONATLLY, AS WE DID IN JANUARY.

Thanks... Rich
#############################

:Of course one should always do the safety checks on a new-arrival 'dead' radio...
:What my point was is simply that if you have a radio that you are ALREADY troubleshooting...you need to follow a simple block-diagram testing process to narrow down or to localize the problem
:
:Thomas... do think I was suggesting using the radio to test itself?.. (hardly.. lol)
::
::Using the radio to test itself is poor practice.
::
::Thomas

Ah.

Thomas