DC voltages 1/2 normal

[boblpohl]

I am workjing on a Westinghouse WR182 an All American Five radio. All my AC voltages seem to be OK (about 6V higher than called for on the schematic). However all the DC voltages in the radio seem to be about 1/2 of what they should be or a little less.

I get a slight hum when touching the grid of the 12SQ7.

Overall there is no reception and I get a very low hum in the speaker and no volume, and no reception.

What should I be looking for to correct this?

Thanks

Bob Pohl

[Johnnysan]

Bad filter capacitors or bad 35Z5.

[Curt Reed]

Make sure you are hooking your negative meter lead to the correct point in the circuit. Not all AC/DC sets use the chassis as B-.
Curt
_________________
Curt, N7AH
(Connoisseur of the cold 807) CW forever!

[Dale Saukerson]

Two models, WR-182 and WR-182A--which is yours ?

One uses field coil as choke, the other uses tapped output transformer as choke. The radio has a defective power supply or a short that is loading it down so hard that voltages are half of normal.

Knowing which model you have we can better help you to find the problem.

Have you replaced any caps yet ?
_________________
Dale Saukerson.
Diverted by scratch building

[boblpohl]

It is very frustrating to try to understand what's going on. The transformer that is under the chasis has two leads in and two leads out, which I guess makes it a WR182.

However I have absolutely no idea where the field coil is that shows on the schematic between the two electrolitic caps.

I got frustrated and replaced both electrolitics....no change. I have a hum and no volume. I do not receive anything. All capacitors have been replaced.

I don't know why the DC volatge is so low.

As I understand it the rectifier tube changes AC to pulsating DC and the electrolitic caps smooth the DC. What I don't understand is why the electrolitics are not attached to the 35Z5.

I have one electrolitic cap attached to pin 4 of the 50L6 and the other attached to pin 5 of the 12SK7 and the negative to the first of the three on the volume control. This is the way it was when I opened it up.

I have to be honest and say that reading a schematic is like reading Greek. Lines just end in a "triangle of three lines" which apparently means it takes up somewhere else, but there any number of these symbols on a schematic, so I guess it finally goes into space.

I've read six books on repairing old radios and I think I know less now than before I started.

Frustrating!

Bob Pohl
K8RLP

I know theory but have no practical experience and theory alone doesn't get it. Practice makes good.

[Oldbear]

Sorry for this long-winded response, but maybe it will clear things up a little.

On this diagram, the "triangles of three lines" are the "common" or B- buss. All those points are connected together but the interconnecting wires are not shown for the sake of simplicity. If they showed them on the drawing, it would make a confusing tangle of lines. So they reasoned, anyway.

The point to remember is that they are all connected together. The order in which they are connected in the radio will bear little resemblence to the order they appear on the drawing. This often makes it hard to trace wiring in the radio, but makes it easier to understand the theoretical operation from the drawing.

DC measurements need to be taken relative to this B- buss. You put your negative meter lead at any one of the points denoted by the symbol. Then your positive meter lead goes to the place to be measured.

In many radios the chassis is also the B- buss and the negative meter lead would go there. But not in this radio. The chassis is isolated from the B- buss.
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The field coil (if there is one) is part of the speaker. It's the big coil sticking out the back of the speaker. It's actually an electro-magnet and is replaced by a permanent magnet in more modern speakers. There will be two wires from it going down into the circuitry. Each wire should be traceable to the positive of each of the two filter capacitors. There will also be two wires from the speaker (voice coil) going to the output transformer.

If there is no coil sticking out the back of the speaker with wires coming from it, then it must be a permanent magnet speaker and would seem to indicate you have the model WR-182A. But that would call for three wires from the output transformer. (in addition to the two wires to the speaker).

But if you definitely have no field coil, and definitely have only two wires from the output transformer, then someone may have modified things, perhaps to replace the speaker. They may have substituted a 450 ohm resistor for the field coil. Or they may have mucked it up and put in nothing to replace the field coil, which would explain the set being inoperative.

[boblpohl]

Terry:

Thank You. Just to give you an idea of how much you helped me....I thought the field coil was the transformer that usually sits on top of the speaker and the electromagnetic coil was just that. The books are not very clear to an idiot. A lot of my books are classroom books from the 1940's and early 50's. Obviously I don't have a teacher to point out anything to me, so I get confused. Even the newer books on old radio repair assume too much for a novice.

You are the first guy to take time to actually explain some of the basics to be and get me to understand. Again thank you.

The WR182 has an electromagnetic field coil and by putting the positives of the electrolitics on the leads to the filed coil and putting the negative on the 12SK7 the volume came up and works.

I don't receive any stations, but it's a start.

Bob Pohl

[boblpohl]

Now the DC voltage on pin 4 of the 50L6 reads 106 and the schematic calls for 90 V. Is that too high?

Understanding how the electrolitics are wired sure changed the voltages.

Bob Pohl

[jkaetzjr]

It is a bit high but not a cause of the problem, perhaps a symptom. Measure to voltage on pins 3 and pin 8 of the 50L6 to see if it is about what the schematic calls for. Then check voltage on pin 6 of the 6SQ7. If all read in the ball park, turn the volume control full on and touch the tip of a screwdriver blade to the center terminal of it, letting your finger touch the blade. This introduces an AC voltage into the grid of the first audio tube and should result in a healthy hum. Let us know what you get.

[gary rabbitt]

Hi Bob,


Don't forget, that some AC voltages are a lot higher today compared to when the set was designed. Thus you may see slight increase to your voltages shown on the diagram.

You mention about a transformer that sits on the speaker. That wold be the output transformer. If your speaker doesn't have one, then it might be the one under the chassis.

The Field coil is right in the center rear of the speaker where the magnet on a modern speaker is. That way when the current flows, it creates the magnet. It also acts as a choke for the filter system so it serves a double duty.

"The books are not very clear to an idiot."
You are not an idiot
I am sure some books out there assume you know a lot about electronics so they talk well beyond what a new hobbiest would know.

Let us know how you come along.
Gary.

[boblpohl]

Thanks Guys!!!

50L6 pin 3 reads 98V and the schematic says 100

50L6 pin 8 reads 7.4v and the schematic says 5.2

12SQ7 pin 6 reads 70V and the schematic says 6.1 with an asterick which says voltage could be higher.

In applying a screw driver to the 12SQ7 pion 6 I get a hiss/hum, but not very loud.

Bob

[deltysdal]

I read the long explanation also and it was great. Thanks.
_________________
Yes, I can.

[boblpohl]

I agree that too often the answers assume that the guy asking the question knows more than he knows. I'm sure that there are a lot of us who need basic help and long explanations. I need that and I got it.

Still have a problem, but I'm ahead of where I was.

Bob

[jkaetzjr]

If you were touching the blade of screwdriver hum should be quite apparent. The voltages are in the ball park but the slightly higher voltage on pin 8 of the 50L6 indicates it is drawing excess current. There is a capacitor from pin 6 of the 12SQ7 to pin 5 of the 50L6. It should be replaced, and occasionally the 50L6 will draw too much current because it is defective. The 70 volts on pin 6 of the 12SQ7 is a bit high and could indicate a weak 12SQ7 but the reason it is much higher than in the chart is because the original reading was taken with a less sensitive meter so the reading isn't actually what voltage is there. Modern high resistance meters take less current from the circuit it is measuring so reads closer to the actual voltage present.

[Norm Leal]

Hi Bob

Touching pin #2 on the 12SQ7 should cause a lot louder hiss/hum that pin #6. If it does the audio circuits are operating, 12SQ7 and 50L6 tubes.

Voltage will be higher on pin #6 if you use a modern meter. The original meter may have been rated 1000 ohms/volt? This will load down the voltage reading.

Slightly higher voltsage reading may be due to the AC line? Higher pin #8 voltage on 50L6 can be cathode resistor being higher in value? These are not problems although the cap between pin #6 on 12SQ7 and pin #5 on 50L6 should be replaced.

Since you don't have a signal the 12SA7 stage may not be oscillating? Measure voltages on 12SA7 and 12SK7 tubes.

http://www.nostalgiaair.org/Pa ... 024258.pdf
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Norm

[boblpohl]

Thgank You.

I had originally replaced that capacitor. I just took it apart and checked the capacitance and it checks out fine.

I have a feeling that the voltages are about as close as they are going to get.

I am not picking up any thing on AM or SW and it doesn't appear to be an antenna problem. I've tired several things such as putting my hand over the loop antenna and nothing. I added my long wave wire to the set and nothing.

What could that be? What should I look for?

Bob

[boblpohl]

12SQ7
Pin 2 -.9 VDC with a loud buzz
* Pin 4 -380 VDC with a loud buzz (taken several times)
Pin 6 69 VDC

12SK7
Pin 2 36 VAC
* Pin 4 -253 VDC (taken several times)
Pin 5 .06 schematic calls for 1.3 V DC
Pin 6 106 VDC schematic calls for 90 VDC
Pin 7 23 VAC
Pin 8 106 VDC

12SA7
Pin 2 12 VAC
Pin 3 106 VDC schematic calls for 90 VDC
Pin 4 106 VDC schematic calls for 90
Pin 5 1.5 VDC schematic calls for 1.3 VDC
Pin 7 .06 VAC

It appears that Pin 4 of the 12SK7 and Pin 4 of the 12SQ7 are way out of specs.

Why and what to do?

Bob

[Norm Leal]

Hi Bob

Pin #2 of 12SQ7 with a loud buzz is good. Audio circuits are operating.

Pin #4 can only read that kind of voltage is something is oscillating that shouldn't. Is the secondary of the IF Transformer open? You can check it with an ohm meter with power off. Resistance should be around 10 ohms. (Believe this will be ok)

Is the 12SK7 metal with pin #1 grounded? If glass it may need a shield. Pin #4 is tied to AVC. Is the .05 mf, under the 12SA7, in the circuit. This should stop the high voltage reading. (oscillation) (Most likely this cap is missing or on the wrong pin?)
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Norm

[boblpohl]

Secondary IF Transformer reads 52 ohms, if I got the correct pins. I checked the 12SK7 pins 6 & 8.

12SK7 Pin 1 is grounded
Pin 4 - Have to look up what & where AVC is. (Automatic
Volume Control - read that somewhere)

There are three .05mf caps in the radio, none connected to the 12SK7.

Bob

[Oldbear]

Those two high voltages are probably ertzatz readings. It sometimes happens to digital voltmeters when measuring DC in the presence of a strong high freqency AC signal. As Norm says, that signal could be the result of an unwanted oscillation. The capacitors indicated below should help prevent such a thing from happening. Make sure they are all present, good, and connected correctly. Are the three tubes the metal types like they should be?

_________________
Terry Davidson