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Tube AM, dead, only 910Khz and noise... Can we fix it?

elnaldo

elnaldo

Lunatic Member
Hello. I'm restoring an old console, (schematic attached) and after 1st power-on, I discover the AM is dead, just noises than change when I move the tuner cap, and a barely audible 910Khz station, that get stronger if I touch the antenna wire with my fingers.

The console looks absolutely original, not touched, so I didn't turn ant pot, coil or screw. The resistors I've checked were all within specs, but I've just checked some random ones, not all of them.

The only "maintenance" I did was: Replaced the filter caps C30 and C34. And the output coupling caps C32 C33, And C35 and C36 at the output tubes.

I've used 22uF instead of the 16uF at C30. C34 is 32+32uF in my unit, instead of the 50+50uF shown in the schematic. I've used 2 x 47uF caps.

The amp works perfectly, I trued it with an mp3 player and sounds awesome!!!!

I don't have a scope, just a PC based one, but I've read about feeding signals from a working tuner, to align another tuner.

Can you point me to the first steps to get this working? It seems there are just a few components to check....

(It has a short wave tuner too, but it's absolutely silent, nothing, but I guess nobody will care about that...)

Here is a schematic,
http://dl.dropboxusercontent.com/u/1640933/combinado/Ranser CE 1020 A -.pdf

and some Hi-res picts if you are courious:
(BTW, what's that white "pipe" at top-left in pict 1110300? It's directly connected to the antenna wire)

http://dl.dropboxusercontent.com/u/1640933/combinado/P1110300_HI-RES.JPG

http://dl.dropboxusercontent.com/u/1640933/combinado/P1110268.JPG

http://dl.dropboxusercontent.com/u/1640933/combinado/P1110291.JPG
 
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I think I'd start by cleaning tube pins and sockets. Have you connected an external antenna to it? If not, that's another item to address. A lot of more modern receivers came with a cheap but useable AM loop antenna. If you have one around hook it up and see if reception improves.
I don't know how much is available on shortwave anymore but a good antenna is a requirement for that as well.
 
good long antenna wire first and a ground if it has a fitting for ground .
then rock the tuner tubes to see if it gets any better .
 
There are 2 wires for "antenna", a red one, connected to those coils, and a black one connected to the chassis. Both like 1 feet long.

I've added like 3 feet of wire to the red one, but left the black one alone, I don't know where to connect that ground...

How should I connect that "loop "? I have a portable stereo with that loop antenna...
 
i used to connect ground to a copper water pipe in the house . mains power ground should be the same thing as long as its connected properly .
the loop ought to work as long as its for am
 
if you get no joy with the antenna for fun try connecting a long wire to the tuning cap .there should be 1 or 2 soldered on wires .try touching the long wire to one of those .not the ground though .
it looks like it would do with a good dusting off in the pictures . that could help if it was dusted off a bit .
 
there are 4 preset capacitors by the looks of things . you could if daring mark them up and turn one at a time to see if reception improves if not move it back and try next one ..start at closest to antenna connection .
cant make out schematic but at a guess there is 2 for regular am and 2 for short wave .
its been a long time since i played with old radios .
 
I have worked with some radios that were lost in the forest as far as alignment was concerned, but start by tuning to the one station you can recieve, then adjust your trimmers on the tuning gang for strongest signal first. If there are no trimmers on the tuning gang, then determine which set underneath is for Am/MW. The one set of blades that is a smaller diameter is the oscillator section, use that bring the pointer to the correct location on the tuning dial as the last step. You can use a 5 foot section of wire to the antenna terminal. The two trimmers on the bottom of the chassis, image 0300 shows them- they are used for peaking the antenna and oscillator adjustment on ShortWave (usually) and the other should be AM/MW- although once in a while the oscillator trimmers for both bands are on one and the antenna trimmers are on the other. Once the IF's have been peaked, and the AM/MW section peaked, then adjust the shortwave trimmers. If you peak to Shortwave first, that should not pose a problem, but some radios will have interaction between bands. Stations announce their broadcast frequency at the top of the hour, and there are time standard stations in Canada, US, France, and I think Brazil. The US stations are on 5Mhz, 10Mhz and 15 Mhz reliably.

Next step is to see if you have any stations at the top end of the dial, if you find one, then adjust the IF's for strongest signal and narrowest tuning- rock the tuning dial back and forth to make sure the tuning is sharp. Then go back and double check the AM/MW trimmers and check for linearaity across the tuning dial, so 600 Khz lines up and 1500 Khz lines up. If they are located too close- detune both IF's slightly to broaden the tuning across the dial antil they are right. You can peak the IF's on Shortwave if you choose. Then it is a matter of the antenna trimmer and the oscillator trimmer to peak AM/MW reception.

Oh, and that white tube is most probably a silver mica capacitor. I have a jar of smaller ones.

I looked at the other 2 images, and the only trimmers are those underneath. The IF's are just one slug. If you only have a magnetic screwdriver, you need to pull it away as you get close to the ideal peak as the screwdriver will alter the resonance just by being close. It takes a little practice, but once you get the knack of it, you can get them right very fast.
 
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Thank, I'll try to follow this... perhaps with more questions... I didn't want to miss-align th etuner, it's factory sealed, all the IF coils...

The antenna tries, didn't success. I get more and louder noise, but no better reception. Actually, being ME the antenna (holding the wire), I can get a 2nd station, near the only one.

The trimmers, I figured the antenna trimmers are together, and the other 2 are the oscillator trimmers. I managed to follow the schematic and the wiring, and located the AM ones.

I think I'll turn them first, before messing with the IF coils... What is the goal on this? What should I get doing this? match something? modify oscillator freq?

Now, turning the dial all the way down, I get louder noise. It fades and almost dissapear when I go all the way UP with the dial.
 
The oscillator trimmers are to line the pointer up with the proper frequency on the dial. Make sure its mechanically correct first though. Normally there is a dot or some other indication with the pointer all the way at one end of the dial that the pointer should match up with. Once you have it mechanically right, the trimmers are used to get the thing on frequency. The antenna trimmers you peak for strongest reception.

If the IF transformers are still marked with factory paint, its a reasonable guess that they are still somewhere close to correct. I'd definitely mess with those last if you know for certain nobody else has.
 
well, tweaking the antenna trimmer, I can get 790, 910 and 950 KHz, but too noisy.

If I set it to strongest 910KHz, I loose the 790... I had to set in between the strong 790 and strong 910, to get both stations.

turning the "tone" pot to the lowest position is listenable, but nothing too clear... I don't think this is usable compared with today's standards, and just 3 stations...
 
hm, thats not normal at all. It doesn't have an RF amp stage, but with a length of wire for an antenna it should recieve reasonably well. 10 feet or so ought to be enough to pull in any reasonably strong local stations.

Possible the IF strip is oscillating. If you get that same noise with no antenna, maybe try carefully moving parts around with an insulated tool in the area you replaced parts. Sometimes old sets are very picky about their parts locations, and moving something just a little can cause trouble. If the strip was oscillating, it would generate noise, and would force the AGC to minimum sensitivity.
 
I've read this morning about that, that at those freqs, the position of a component, even the size of the solder drop can make a difference....

And I moved some components, no too much, but rotated some caps to look the values, moved here and there some ceramic capacitors, and so...

Could the tubes be bad, or the fact that I get some stations discard that?

I think it's something with the oscillator. It must be a way to set it again. The 3 stations are audible, normal volume, noisy. Closing the tune capacitor (higher freq stations) teh noise increases, until it's all noise. Opening, the noises dissapear. And the station I can tune are in the middle +-.

There are just 4 things to move: An antenna coil L1, with it's trimmer cap C5, and an oscillator coil L3, with it's trimmer capacitor C3 in parallel...

Can I measure something there, to see what's going on?

I'll measure some voltages tonight...
 
If this has been mentioned, sorry, but 910 khz is most likely a harmonic of your 455 khz IF, not an actual station.
 
elnaldo said:
I've read this morning about that, that at those freqs, the position of a component, even the size of the solder drop can make a difference....

And I moved some components, no too much, but rotated some caps to look the values, moved here and there some ceramic capacitors, and so...

Could the tubes be bad, or the fact that I get some stations discard that?

I think it's something with the oscillator. It must be a way to set it again. The 3 stations are audible, normal volume, noisy. Closing the tune capacitor (higher freq stations) teh noise increases, until it's all noise. Opening, the noises dissapear. And the station I can tune are in the middle +-.

There are just 4 things to move: An antenna coil L1, with it's trimmer cap C5, and an oscillator coil L3, with it's trimmer capacitor C3 in parallel...

Can I measure something there, to see what's going on?

I'll measure some voltages tonight...
Click to expand...

If the voltages on the B supply from the EZ81 are very low compared to what the schematic shows- those filter caps may be close to failure and should be replaced.

A weak tube is still a possibility. It was assumed you had already checked those. But not a big issue. The 6BA6 would be the main suspect to be low on emission as would the ECH81. If the 6AV6 is weak, you miss quite a few stations as well, but I have seen some radios where that tube was marginal and the set worked fine.

If the tubes show a little weak, sometimes you can "clean them up" while they are under test by increasing the heater voltage for a moment and letting them sit for about 1/4 to 1/2 a minute at the higher heater voltage. Let them cool as they will show more emission while hotter, but sometimes this brings fresh heater material to the surface and the tube will test as acceptable in many cases once cooled.

There is a small electrolytic- upper right corner of the image 300, it is potentially a problem. It is not one with a good track record.

The IF's are actually the 2 square cans on top of the chassis that have the adjustable slug- they have one slug each..

Those beneath the chassis are fixed value and L1, L2,L3 and L4.

If the tubes test okay, check the resistors around the ECH81 to see if they have changed from their original values.

With a meter, you should see voltage at pin 5 of the ECH81 and 6BA6. This plate voltage develops through the IF's, so if there is no voltage, an IF may be open. You should have about 80 volts on pin 8 of the ECH81 as well.

If you have a capacitor tester- the simple type where the eye tube just tells if the cap has merit and also if the cap is shorted- this is the fastest way to check the merit of the capacitors in this type of set- check the other caps (Mallory). Those appear to be better quality Mallory, but those can still fail. They would fail "open" more than anything.
 
If this has been mentioned, sorry, but 910 khz is most likely a harmonic of your 455 khz IF, not an actual station.
Click to expand...

I was thinking exactly this, that's the reason I´ve posted the # station I can get... And it's tuned inside a noise, so it's not a clear station.

I think I need to: Be sure the IF coils and circuit are tuned to 455 or close to that.. I'm thinking to inject signal from another working tuner before the 6BA6 tube (coupled with a capacitor), and be sure the 2nd IF coil is tuned. Then, inject a signal before the ECH81, and tune the 1st IF coil.

Then, try to align the antenna and oscillator, following some tutorial to do it without a signal generator.

If the voltages on the B supply from the EZ81 are very low compared to what the schematic shows- those filter caps may be close to failure and should be replaced.

A weak tube is still a possibility. It was assumed you had already checked those. But not a big issue. The 6BA6 would be the main suspect to be low on emission as would the ECH81. If the 6AV6 is weak, you miss quite a few stations as well, but I have seen some radios where that tube was marginal and the set worked fine.

If the tubes show a little weak, sometimes you can "clean them up" while they are under test by increasing the heater voltage for a moment and letting them sit for about 1/4 to 1/2 a minute at the higher heater voltage. Let them cool as they will show more emission while hotter, but sometimes this brings fresh heater material to the surface and the tube will test as acceptable in many cases once cooled.

There is a small electrolytic- upper right corner of the image 300, it is potentially a problem. It is not one with a good track record.

The IF's are actually the 2 square cans on top of the chassis that have the adjustable slug- they have one slug each..

Those beneath the chassis are fixed value and L1, L2,L3 and L4.

If the tubes test okay, check the resistors around the ECH81 to see if they have changed from their original values.

With a meter, you should see voltage at pin 5 of the ECH81 and 6BA6. This plate voltage develops through the IF's, so if there is no voltage, an IF may be open. You should have about 80 volts on pin 8 of the ECH81 as well.

If you have a capacitor tester- the simple type where the eye tube just tells if the cap has merit and also if the cap is shorted- this is the fastest way to check the merit of the capacitors in this type of set- check the other caps (Mallory). Those appear to be better quality Mallory, but those can still fail. They would fail "open" more than anything.
Click to expand...

Regarding the caps, I've replaced the electrolytic, filters and that 100uF you see at top right corner. My unit doesn't have that EZ81 rectifier, it has diodes.

I leaved the mallory alone, since the output coupling caps were the same, and measured both OK.

I'll measure the voltages you suggest and see if I can get something... But I think the tubes are OK. The noise is amplified quite loud, I guess if they were bad they wouldn't produce that sound. But I'm not an expert...

The small coils under the chassis have screws, sealed with wax, but adjustable I think.
 
OK, I have a plan...

Extracted from the web, instructions to "align" an AM tuner without instruments. I don't know how accurate/dangerous could it be.

But this is what I'd do, seeing the tuner is dead: (and marking and regstering everything, to go back if needed)

- Assume the IF coils are OK, since they are factory adjusted.
- Check voltages at the tubes, to see they are working
- Check continuity from antenna connection, antenna and oscillator coils to check they are not broken.

Align AM doing this:

1- close all the tuning capacitor, and try to tune 590KHz local station, rotating the oscillator coil core (L3). (I have another tuner to listen to that station)

2- tune some station near 640KHz, and adjust antenna coil L1 for max volume.

3- open all the tuning capacitor, try to locate an station near 1600KHz. Adjust the antenna trimmer capacitor (C5) for max volume.

4- adjust the oscillator trimmer (C3) if needed. It's factory adjusted now.

5- if needed, tweak the IF coils a bit.

Any advice, specially any "don't do that because ...." will be welcome !!!!

Schematic link, again: http://dl.dropboxusercontent.com/u/1640933/combinado/Ranser CE 1020 A -.pdf
 
OK, I'm cleaning everything right now... Contact cleaner 0 residue, + isopropylic alcohol...

I've already cleaned the switches before the 1st power-on.
 
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