Radiogram, no sound

[73's de Edd]

.

Sir . . . . . . . Raz-a-ma-tazz *****

HOUSTON WE HAVE LIFT OFF . . . . . . .and we are now getting good telemetry buzz . . . . .errrrr . . . good instrument readings from *****

You say . . . . .
The multi meter i am now using is a digital meter and its called ISO-TECH.

The prior one that you were using must have been an "ISOLATED" TECH . . .with all of its erroneous readings.

This new meter only balked on you, at the plate of he EL84, and using its 3200 max display format , that blinking might have merely indicated an overange.

If you look at my first entry on the scene and consult that schematic, you will see the most dominant marking on the schematic is a yellow square.
Which I intended to remind you of as the LAST thing after having analyzed the sets problem.
Looks like its importance has NOW transitioned to number one.

Failure Analysis:

Your readings now seem tell us that the onset of failure for your set was the development of leakage in the .01 ufd cap that couples audio from the plate of the EABC80 to the firstus gridamus of the EL84 auio output tube.
The design of the EL84 audio output stage is such that they are lifting the cathode of the EL84 above ground by the resistance (180 ohms) of its cathode resistor.
If you were then to place the DVM + probe on its cathode and use the - probe to measure the voltage at the 1st grid it would be ~negative 7-8V DC 1st grid bias..
That biasing level would then produce a clean sounding class A operation of the stage.
Now if there is even the very slightest DC voltage that might leak through that .01 capacitor from the plate voltage of the EABC80 into that EL84 1st grid circuit it would then start offsetting that tubes proper bias level.
When it offsets and decreases from the negative voltage state and then transitions into creating a positive voltage , that EL84 starts an upward spiral in conduction and starts pulling a fierce current thru the EL84.
(You have confirmed that . . . a . . .la . . .HOT Fingers ! )
Simultaneously, that progressively higher current/power drain is taxing the capabilities of your EZ80, the audio output transformer and the main power transformer.
Since you are pulling down the voltage on the plate of the EL84 . . . . .remember, that you noted the gradual decrease of its B+ volage.
The sets electrolytic filter capacitors of C48-C49 and C50 are no longer able to produce a pure DC B+ level at this degree of power drain, so sawtooth ripples of AC are starting to develop , superimposed with the DC and that is the HUMMMMMM that you were hearing, being produced by that quasi AC waveform. .
Had you watched the plate of the EL84, in that dark room test, its plate should have eventually taken on a slight cherry red color.

Next Step . . . . . . .initiating . . . . . . .The Fix :

You need to clip the lead of the C43--.01 ufd cap free at its / the lead that connects to the R29 / 47K and the R24 / 680K resistor junction.
( Do duly note that on some olde ray-dee-oo skee-matics, you just have to grin and bear it on their clarity of labeling parts with your main assist of being able to read the label or color coding of a part itself.
That then only leaves the clarity of the R or C of a part designator and its number, but fortunately, they usually assign them sequentially, as they travel across the schematic page.)
Sometimes, even being able to GET a copy of an old schematic, ends up in your having to make the best read of it, as is possible.
(Archaeologists poking around and finding Dead Sea Scrolls, best make the best of them, and not keep poking around in hoping to find a tablets REVISED editions.)

Fire up the set again and after warm up, DC voltage meter the plate (P9) of the EABC80 to see what it is . . .expecting approx 75 VDC.
Then move + probe over to the now free end of the .01 cap and see how much voltage was leaking thru to upset the EL84's specified negative 7-8 VDC.
To positively confirm, take a clip lead that has one end grounded and bring its free lead up to short out your metered junction and see the voltage drop to ZERO.
Then after removing that clip lead, see what DC voltage level rises up.
A good modern replacement cap with the now typical polyethylene , polystyrene or mylar dielectrics usually only show less than a volt of static DC voltage bleed thru.
You should now know just how BAD the situation was, with that old paper capacitor.
Get a new replacement capacitor and if you want a service / reliability benchmark on into the next millennium, get a 400 or 600 VDC rated one.
Replace that capacitor.

With the bias shifted on the EL84 and having the resultant weight of an "elephant on its back", before,the EL84 was not even aware of some pip squeak little audio signal trying to come in from the EABC80.

NOW, your phono input or even the radio proper might operate, if you have that suspected one bad IF stage tube (with its open filament) having been replaced now.

Standing by . . . .

ADDENDA:
I now see that our honorable and esteemed colleague . . . GPG . . . .had come on the scene while I was poking this info up earlier .
I was thinking of the eventual need of clipping out that capacitor, for its replacement.
His tube sockets pin measurement method lets you initiate a leakage voltage check with AND without the loading effect of having the EL84 being in circuit.

73's de Edd





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[Arouse1973]

Oh, so sorry Duke37.
I did mean you (Trevor), it was a genuine mistake..

Thanks
Adam

.? Lol

 

[Martaine2005]

Sorry Adam!! It was supposed to be funny.
I had my usual confused head on..
But I think you get the picture!

Ada........I mean Martin.

 

[rematzz]

Sorry it has been a week since I last posted but it has been a very busy week for me.
I measured p2, p3 and p7 of EL84 with the neg on the chassis.
P2 was 0.40VDC and kept rising.
P3 was 6.35VDC and kept rising.
And p7 was 6.80VDC and kept rising.
Without EL84 p2 was 0.47VDC.
P3 was -00.1VDC.
And p7 was 0VDC and that pin seemed a little be loose.

I checked p9 of EABC80 and it was 70VDC and it was dropping.

The capacitor to p3 of EL84 and the capacitor to p2 of EABC80 has already been replaced, also all of the measurements has been with those two replaced.
The resistor on p3 of EL84 looks a bit black, I'am not sure if that is due to dirt.

 

[duke37]

EL84
The grid p2 should be close to zero Change C60.
The cathode P3 should be about 7V above the grid so the results you have are reasonable.
The anode P7 should be about 260V see the table so the value you get is wrong. I do not see how you get significant voltage on the cathode without a considerable voltage on the anode, perhaps the screen (G3, P9 not measured) is taking too much current.

You will need to find why the anode has no supply, Does the output transformer have a connection through it? A faulty C60 could have made the EL84 pass sufficient current to burn out the transformer.

What do you mean by kept rising? Please describe this better.

 

[rematzz]

i meant that it started with the voltage that i noted and carried on going up and up.

it might sound like a silly question, but how do i test if there is a conection through the output transformer?

 

[duke37]

i meant that it started with the voltage that i noted and carried on going up and up.

it might sound like a silly question, but how do i test if there is a conection through the output transformer?

But how fast did it rise, did it creep up over minutes or zoom up in a few seconds?

Measure the resistance from the anode of the EL84 to one of the other primary connections, look on the circuit diagram to see where they are. I use an analog meter for this since some digital meters have a hissy fit with inductances. If your meter passes significant current, then the speaker will crackle as current is increased or decreased.

Make sure the set is turned off and the HT capacitors are discharged befor doing this.

 

[73's de Edd]

.



Your readings that were taken with the IDM69. . . . below

The multimeter i am now using is a digital meter and its called ISO-TECH model number is IDM69.
I unpluged EL84, put the negative probe on chassis and positive on p7, i measured it in DC and the multimeter screen just flashed.
I put EL84 back in and measured voltage in DC, negative probe on chassis and positive to p7,it measured 6.5V and kept rising.
Measured p9 in DC on EL84 with negative probe on chassis and positive to p9, it measured 213.5V and kept dropping.
I measured both sides of r27 in DC and negative probe on chassis and positive to r27, one side measured 356V and the other was 308.5V.
I measured AC voltage of EZ80 on p1 with negative probe on chassis and positive to p1, it was 291V, i did the same with p7 and it was also 291V.
I measured AC of EZ80 with one probe on p4 and one on p5, it measured 6.85V.
I measured DC of EZ80 with negative probe on chassis and positive to p3, it measured 360V.

I unpluged the set and measured the resistance on EZ80, with one probe on chassis and the other on p1 it was 169.7 ohms.
I did same on p7 it was 161.6 ohms.
Checked resistance on p4 between p5 and it was 00.4 flicking to 5 and flicking back again.
Checked resistance on p1 between p7 and it was 0.332k ohms.
Checked resistance on chassis and p1 of EZ80 and it was 173.6 ohms.

All valves light up orange and EL84 was so hot after i turned it off that i burnt my hand and that was about 5 mins after turning it off.


Those readings at the top are EXACTLY what would be expected, when you took them with that IDM69 meter, any chance that you are now trying to use that other meter ?

The only fault modes that come to mind are :

That you have the meter in AC instead of DC mode ?
Or that your meters negative ground is not at the same point that you were using before, when you got those good readings at the top?
(Pin 5 of the audio and I.F. tubes seem to be a valid ground. )
Or that you might be counting tube pins CCW from the bottom of the tube/socket instead of CW.

Did I understand that you have replaced the .01 capacitor between the pin 9 of the EABC80 and the 47K and 680K junction that ties into the EL84.


Here is your UNITIZED new / old first production run schematic for that set :
(18 carat gold with platinum laced interlay frame) . . .

73's de Edd


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[rematzz]

haven't had much time to do many tests, but i did manage to test the output transformer and i couldn't get a connection from it, it was as if nothing was there, i tested this while the set was turned off and the digital multimeter in ohms mode. could the output transformer be dead, if so what rating output transformer would i replace it with as there is nothing wrote on the one thats in.

 

[duke37]

The transformer has a tap so that the current goes one way to the set and the other way to the EL84. The part going to the set is working since you have voltage on the screen.
You could replace the output part with a transformer from another radio or TV set. Output transformers are similar since most of them have valves of similar power output but few have the tap.

A better alternative if you are interested in keeping things as near as possible to the original is to get the transformer rewound. Modern wire would have better insulation. The transformer probably failed due to excess current caused by the leaking capacitor feeding the grid of the EL84.

The forum 'vintage-radio' has information on a few people who will rewind the transformer. This would be better than the bodge I suggested. In the next millenium I intend to get my coil winder working.

 

[73's de Edd]

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Sir rematzz . . . . .


Edd to rematzz . . .Edd to rematzz . . . . .come in please . . .testing 1-2-3 testing 3-2-1 Do you read me ?.


Am I forever getting ignored?

Or am I, just not observing the PROPER olde tyme English Gentlemens protocol ?

Or am I just not receiving due course of attention . . . . . .due to my lowerly class of being an upstart 87 year old bastard from "the American colonies".


Back on day one, you mentioned a hum coming from the units speaker,( after you let the sets tubes warm up about 30 seconds.) that is probably not still true ? . . . .


Also I had made query as to your now having changed out the .01 ufd coupling capacitor between the plate of the EABC80 and the first grid of the EL84.

Is that now being the case ?


Back when you were coming up with no voltages, where it was logical for there to BE voltages, and with the capability of hearing of a hum.

Looks like the subtlety of the SOMEWHAT low voltage on the pin 7 of the EL84 , sort of escaped us with the initial BREAKTHROUGH ! of your new metering with the new IDM69, having finally found the presence of main B+ voltages on the Easy 80.

PLUS your passing on the ohmmic values that you read across the power transformers high voltage secondary winding's.

That is being much in the order of the way you should now be finding resistive continuity, on your audio output transformers primary windings.


If that set has been running for years, with an ever exponentially increasing leaky .01, feeding to the 1st grid of the EL84, the increased current pull thru the plate side of the audio output transformer just may have EVENTUALLY led to that winding's demise, with the popping open of that winding..

USUALLY in a dynamic test and evaluation of this design of set, that transformer is coming in at 99 of some 100 potential other problem suspects.

With you not having to expend even a cent of your HARD EARNED munney, let me fill you in on a low technology method of answering if the AF out transformer is at fault, and a testing work around to temporarily produce sound from the system.

BTW with a power down condition of the set and making an ohms test from the center lead (YELLOW) of the AF out transformer to the RED and by using that GOOD IDM 69 for metering, you should expect a reading in the high hundreds of ohms. So we already KNOW that winding is intact, by its passing B+ thru it to R27 .

Move ohm testing from RED, over to to BLUE , keeping the common YELLOW and the ohms should be very-very high, only enough to let that 9v leak thru to the EL84 plate #7.

Now here is the procedure, and its using no or MINIMAL instrumentation utilization . . . . . .

We will be using Alley Opp protocol and within that, be utilizing Cave Man 101 . . . . .ver 1.0


Technical Aspects Explained :

Re . . . . . . .Why that odd audio output transformer ?


Normal signal flow is for B+ to flow down the YELLOW-BLUE output transformer path and there may be some undesirable AC component called ripple present.

It shows up in the speaker as a different degree of hum, in accordance to its strength. It is permissible to hear a bit of hum if your ear is being placed right up against the speaker.

AND the AF audio output stage is MORE tolerant of SOME ripple than the OTHER earlier audio stage, since IT would amplify that ripple up before presenting it to the output stage to amplify further and then create an even greater degree of hum.

Here is where I might loose you, but if there is ripple passing thru the YELLOW-BLUE transformer winding path, it will induce a like ripple into the yellow red winding, but it will be inverted 180 degrees in phase from that of the initial YELLOW-BLUE ripple signal.

Now when normal B+ ripple at the Yellow lead passes thru that YELLOW-RED winding, the two phases now present will interact with each other to end up with an overall production of LESS ripple voltage content coming out of the end RED lead than was initially present.

This sets output transformer selection and windings are utilizing an olde design principle called hum bucking. In olden tymes capacitance in the 4-8 and 16 ufd values were being the norm, with higher capacitance being hard and expensive to accomplish.
With the utilization of hum bucking, they are letting two 180 degree phase differences in hum signals work against each other to greatly minimize the final hum output from a power supply.
Now a days, electrolytic capacitors up in the 100's of ufd at higher working voltages are readily available and cheap.

If that info was technically . . .. . . . .WHOOOOOSH . . . . right over the head, my shifting to a mathematical analogy might be somewhat helpful in clarifying the prior situation.

Say the ripple content of the main B+ at transformer YELLOW lead is assigned a mean value of +10 and the induced ripple signal into YELLOW-RED is being -9 (since its being 180 degrees phase shifted from the main B+ ripple.

After they have mixed, passing from YELLOW lead to RED lead thru the transformer , the SUM of an initial strong +10 ripple and an induced -9 ripple level is yielding a +1 ripple level, with that +1 being a LOT less ripple than we initially had with the starting +10 ripple value.

Diabolically clever . . . .those damn olde tyme radio design engineers . . . . but probably, the loudest . . . .HOOORRRRRRAAAAYYYYY . . . just might have come from the financial departments bean counters, with the saving of many dollars per set, by need of a less pricey set of electrolytic filter capacitors.


Now , in resuming the B+ flow path, with the next sub B+ filtering cap being just past the R27 dropping resistor, at the C49 filter and it will now produce a lot more effective filtering action with that ALREADY reduced ripple coming into it.

Then after a further sub-sub B+ drop using R21, then only 6-8 ufd of filtering is needed at C48 to finally supply sub-sub B+ it to your ripple sensitive 1st audio stages plate at pin 9 of the EABC80.


Hum Bucking . . . . . see the graphic depiction at the bottom of the post. ***


Now . . . . . How To Do It To It:

(Fully utilizing Cave Man 101)


All this requires is a few wire swaps, we will want to lift the RED and BLUE audio output transformer wires, we know that YELLOW to BLUE winding is a dud, but the YELLOW to RED is a good winding. So you solder the RED wire onto the plate (#7) of the EL84 and you now have to restore B+ to the REST of the set, since you stole it, when you lifted the RED wire. (The BLUE wire is left floating.)

That B+ restoration is done by installing a clip leaded test wire (+++) to the YELLOW wire connection( which has its connection origin over at pins 3 or 4 of the Easy 80 power rectifier tube.) That receives one clip lead and the remaining clip goes to the side of the R27 resistor that had normally received the transformers RED wire.

(+++) If you don't have such, test lead with attached end clips, use stranded hook up wire and strip the very tips, tin the wire ends and tack solder them onto the mentioned connection points .

You now have yourself a good output transformer winding connected to the EL84, but now at a slight lower impedance match than the original YELLOW- BLUE path, but it will cause far less overload / misery on the EL84 than it WAS being subjected to, during the last days of the YELLOW- BLUE winding.

Plus, we are only going to ask for about 5 minutes of its time for a test.

Check to see that the unit was not left in PHONO position, select the AM band as its more likely to work, ( IF you NOW have a new IF tube installed in place of the one that you said had an open filament.)

Fire up ye ole unit . . . .if the wind is out of the South Southwest . . . . .the temperature is hovering between 75-79 degrees . . . . .you just heard the engine strains of an olde Citroen passing down the lolly . . . and the planets are properly aligned . . . . then . . . .after a bit of knob kerblitzing . . . .your set just might have radio sounds emanating forthwith !

If not, lets now see, if all of the power supply, audio output, audio output transformer, first audio amplifier and volume control are working.

Power down the set.

This test will be done by connecting yet another clip test lead wire between the pin 4 of the EL84 and its other connection can be made to a choice of three. The top side of the volume control OR to the .005 C43 cap that is coming up to that volume control connection OR to the 100k R20 resistor lead that ALSO comes into those common connections. . . .your choice, on any of the last ones , by easiest access.

Then you turn the volume control down to minimum.

Power up the set and then, after tube warm up, see if bringing up the volume control will produce a progressively louder HUMMMMM until it shakes the stored dust layers and cob webs from the speaker.

If so, those mentioned portions passed all tests with flying colors .You done GOOOOD !


If all operations pass, I will post you on replacement technique and the proper and cheeep repair parts next time.



Hum Bucking . . . .Graphically Explained . . . . .***

73's de Edd




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[rematzz]

am sorry edd i wasn't ignoring you on purpose. i've been busy with work and i've only been replying to the last post, sorry.

i tried the test with the output transformer and got nothing. i tried the test with el84 and c43, no hum at all. the hum i could here when i first posted was very quiet but i can't here it now

 

[73's de Edd]

.

Sir rematzz. . . . .

I don't kow what radio / electronics parts you might have on hand , or can borrow, but do you have anywhere from a 470 ohm on up to a 10,000 ohm 2 watts or more resistor ?
Also in using your GOOD meter, did you find DC B+ on the plate of the EL 84 after that output transformer wiring swap ?

73's de Edd

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[rematzz]

Hi edd i haven't got any resistors on hand and am not sure where abouts on el84 i would find DC B+

 

[duke37]

.

Sir rematzz. . . . .

I don't kow what radio / electronics parts you might have on hand , or can borrow, but do you have anywhere from a 470 ohm on up to a 10,000 ohm 2 watts or more resistor ?
Also in using your GOOD meter, did you find DC B+ on the plate of the EL 84 after that output transformer wiring swap ?

73's de Edd

.

To translate, B+ is the high tension voltage.
The plate is the anode.
EL84
1 -
2.Grid 1
3.K Cathode
4.Heater
5.Heater
6.-
7.Anode
8.-
9.Grid 3 (screen)

If the anode does not have a high voltage on it then a lot of current could go to the screen and damage it by overheating.
The grid (P2) should never be positive.

Trevor

 

[rematzz]

i just tested el84 with test leads still in place. p2 measured 1.300VDC and it was rising fast. p7 measured 7.40VDC and rising slowly. p9 measured 213VDC and slowly dropping.

 

[duke37]

There could be four problems.
1. A bad valve
2. A leaky capacitor feeding the grid P2
3. A poor high voltage supply to the anode.
4 A leaky valve holder.

You did not measure the total current through the valve by measuring the cathode voltage.
You MUST MUST MUST keep the grid voltage down, you can do this by temporarily connecting it to ground (use a wire with a crock clip at each end)
You can measure the anode current by passing it through a 1k resistor supplied from the reservoir capacitor. The voltage at the anode should be not far from the screen voltage.

If grounding the grid makes the voltages reasonable, then change the capacitor feeding the grid.
It looks as if you may have blown the primary of the output transformer. Check its resistance and measure the voltage across it to get the anode current.

Remember to discharge the capacitors before connecting a resistance meter.

 

[73's de Edd]

.

Sir rematzz . . . . . . . .


Make one change to Trevor's given tube pins, 3 and 9 on their functions of the EL84 audio output tube:
With his:

To translate, B+ is the high tension voltage.
The plate is the anode.

EL84
1 -
2.Grid 1
3.K Cathode + Grid 3 (supressor)
4.Heater
5.Heater
6.-
7.Anode
8.-
9.Grid 2 (screen)

It seems that you still have the minor wire swaps still in place . . . . . by my text interpretation of your # 56 Post.


Trevor sez:

It looks as if you may have blown the primary of the output transformer. Check its resistance and measure the voltage across it to get the anode current.

With the way you have swapped the wiring around , we are NOW using the GOOD half of the audio output transformer, just for our temporary testing.

As per the possibility of the pin 7 of the socket of the EL84 being "carbonized" and passing plate/anode voltage directly off to ground, we can ascertain that by the next test.

Your voltage tests have always shown very little voltage on pin 7 of the EL 84, while it should be a high voltage in the order of that which you are reading on the pin 9 screen grid.

What we want to do now is to test the voltage on the pin 7 of the EL84 again BUT THIS time the probes are to be on that pin before the tubes warm up after being turned on by the power switch.
I believe that the EZ80 will warm up before the EL84 does, and for that short time frame, that the high voltage will have risen higher than it had before.
Then that measured 1.3 on pin 2 is your problem, so use a jumper clip / wire to temporarily short pin 2 to ground and your pin 2 voltage should shoot up to the expected higher voltage level.
If so, then the C43 .01 ufd cap that you supposedly have ALREADY replaced, must also have some DC voltage leaking thru it from plate resistor R42 of the EABC80 tube.
That shorting of the pin 2 to ground , would have confirmed that possibility by letting the pin 7 voltage SHOOT up in value, to be in the vicinity of the screen voltage on pin 9 .

Lets see what that order of testing now reveals . . . . . .



73's de Edd'


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[rematzz]

thanks trevor and edd for the help so far.

i no longer have the test leads in place as i had a friend have a look at it while he's in england. he only had time to check the voltages that i had checked and confirmed that i had checked them right. he has also said to bypass the amp and check everything is working on that said.

so i was just wondering if disconnected the red and yellow wires leading to the output transformer, would that be bypassing the amp ?

 

[rematzz]

also i will do your tests when i get some spare time edd.