Philips B6X12A on the fritz…

[Don_Zalmrol]

I'm in the final process of repairing my radio (still waiting on one backorder… )
The resistors I'm replacing really are off and not slightly off…

R6 that is connected to the EM80 valve should be 470K, and is only showing 2,145M Ohms!
(I've checked the color band and it was definitely a 470K resistor!)

So now I'm checking & measuring every other resistor again, that might seem showing distress with the same discoloration and wear like R6…

I've also changed the mains connection with a 3-wire cable and grounded (earthed) and fused the radio for safety.

[Don_Zalmrol]

So my restoration escapades are almost at an end!

Every resistor and cap that was bad, is now replaced with a new one.
Many of the carbon composite resistor where horrible off and not with a small margin…
(See post 21, that was the biggest run off I've found…)

Some small things I notice:
R1 becomes very hot, you can see smoke coming from it (very faint smoke)

R1 is 120R/4W, so I'm thinking of changing it to a 120R/5W (cement) I still have laying around. Or I can put that one parallel with the 4W, that way the current is cut in half…

Unless this is normal?

There is still some hum, bet very faint and barely noticeable!
I still need to test the rest of the radio, but on FM it works like a charm!

I also changed the voltage selection from 220V to 245V, because my house receives 230V from the mains…

Does somebody have some tips for testing it?

Thank you all for your help so far!

EDIT:

I've added the Philips resistor reference table, It's quite difficult to find a clear one…
Left: the resistor representation as seen on the circuit schematics
Middle: the power dissipation (in Watts)
Right: the tolerance range

[Don_Zalmrol]

Damned, LW, MW, SW aren't working…

All the heaters are on, but nothing not even a crackle from the LW, MW, SW when I press their buttons…
Tomorrow I will test the gram input!

[Herald1360]

R1 looks like it's in series between the rectifier cathode and the reservoir capacitor, so it carries the full HT current plus any ripple current through the capacitor. On the face of it, two EL84s plus a handful of other valves will take somewhat less than 150mA so the dissipation in R1 should be less than about 3W- in other words the resistor should be OK. It may just be burning off fingerprints or dust as it will run extremely hot (200deg plus) at it's full rating if it's a wirewound type.

Maybe measure the voltage drop across it when the set's running? If the dc component is >150mA there's something taking too much current......

[Don_Zalmrol]

Hi Chris, Thx for the reply!

The current through R1 is (stable) around 125mA.
The original resistor has a power dissipation of 5,5W, the new one I've placed only dissipates 4W

The drop voltage above R1 is around 15V
The drop voltage above R66 is around 93V

The power running through that resistor is 1,875W (125mA*15V), so the replacement resistor (4W) is enough.

I did one very stupid thing and later realized what I did…
I've soldered the new components to the valve sockets with the valves still in them…

Could the LW/MW/SW valves be busted?

Since FM (ECC85) still works and is connected to the detector (EAA91) these two valves are OK.

It's strange, their heaters are working but you can't hear any sound coming from them through the speakers… Not even a crackle but a hum…

FM and PU work very well, almost crystal clear (the antenna wire I've used is quite simple, and you need to turn the PU volume up a bit…)

Cheers,

Laurens

[Nickthedentist]

Originally Posted by Don_Zalmrol

I did one very stupid thing and later realized what I did…
I've soldered the new components to the valve sockets with the valves still in them…

Rarely a problem, Laurens, I do it all the time and have never had anything bad happen.

The problem is almost certainly that you've connected one of the new components in the wrong place, or used something of the wrong value (e.g. a 10K resistor instead of a 10R one). Professional repair men will tell you that it's a good idea to check that the set still works after every single new component is fitted, otherwise finding the fault you've introduced can be hard and time-consuming.

Good luck.

Nick.

[Don_Zalmrol]

That's a relief Nick!

I've rechecked every connection and I think I've found my problem!

I've accidentally changed R2 from 56K to 10K…
R66 is directly connected to the LW/MW/SW valve (B2 -> ECH81).

Instead of receiving something between 54V(AM) - 65V(FM) it received 94V…

Now I'm afraid I've killed my ECH81 valve by this error…

The rest of the connections seem to be in done correctly (checked it with old photos I've made before the changes!), but I will recheck it again…

[Herald1360]

ECH81 is a valve- it's unlikely to have suffered any ill effects! In any case, the FM signal has to go through it, so the heptode part at least must still be working.

Lack of AM signals.... is the oscillator (triode section of ECH81) working? That's one function that is common to all AM bands, but not FM. Pretty much every other stage is used for both FM and AM, though some operating conditions may vary between the two.

[Don_Zalmrol]

I'm at my work right now, so checking the schematics will be a bit tricky…
But yes, the FM part runs trough it.

The radio has it's own build in AM antenna for receiving the LW/MW/SW (ferrite core with 2x copper windings).

On the outside of the housing I have 4 connectors and one small pin to change the AM settings.

I only use one of the FM pins with a small cable as temporary testing antenna.
Normally my cable from the cable company is connected to it with 1 pin (+ side) on one of the FM pins and the GND (- side) to the ground of the radio.

But since my radio has a build in antenna, shouldn't I get any signal or even static noise?

[Don_Zalmrol]

Here is the connection schematic from the backplate of the radio

[Don_Zalmrol]

A quick question about the antenna input.

If I want to use FM coming from the cable-company (wall socket with FM splitter) for this radio I need set my radio to the third picture and plug the + side from the cable into the FM input and the - side from the cable into the GND of the radio antenna socket.

What do I need to do with the AM side?
Just change the middle connection to the bottom middle connection for NO AM reception,
or does this enables the internal AM antenna?
And for AM reception to the right.

Tonight I will fix my mistake with R66, I will chain the 10K and a 47K resistor in series to get 57K. And measure the voltages from that point.

I will also change R1 4 to a 5W cement resistor, I have a spare laying around.
It's still smoking and becoming quite hot… and yet the current is 125mA…

Cheers,

Laurens

[Don_Zalmrol]

I've measured the voltages coming from R66.
R66 (10K + 47K = 57K)

FM: 63V
SW: 68V
MW: 52V
LW: 53V
PU: 66V

The voltage for SW seems strange, as it should be around 54V (AM) and it is showing 68V which is for FM (65V)…

FM and PU are working perfectly and crystal clear, except I need to turn the volume more up when using the PU. (3 original carbon composite resistors are still connected to the volume pot, however these are in good working condition and right values!)

To be honest I only use FM and PU (mostly FM). But I want the problem for LW, MW, SW fixed, because I'm a bit afraid that this isn't good for the other valves and is rubbing me in the wrong way as a failure

So I'm still looking for that faulty component/ cable in my radio…

[Nickthedentist]

Originally Posted by Don_Zalmrol

FM and PU are working perfectly and crystal clear, except I need to turn the volume more up when using the PU.

What are you feeding the PU sockets from?

[Don_Zalmrol]

My Sony record player with a small (Velleman) HQ pre-amp, this is then connected to the 5 pin input of the radio.

[Nickthedentist]

I don't think the radio is at fault in this respect then, your preamp just doesn't have quite enough gain.

It should be easy enough to adjust the preamp to make the sound levels the same on FM as PU.

Nick.

[Don_Zalmrol]

Idd that could be the case.

I think that there might be something wrong with my ECH81 (B2) valve.
Since that is the first stage the AM signals (LW/MW/SW) go trough.

The thing is that I don't have any replacement valves laying around, so I will first test it further out before looking for a "test" valve…

[Don_Zalmrol]

On pin 8 from the ECH81 valve I measure 110VAC instead of 136VAC as described in the schematics. This could be the result of the new resistors or one of the old trim caps that is a bit off, unless I'm mistaken, which could be…

[Don_Zalmrol]

Found the culprit!

It was R11 (220K/1W), I've accidentally soldered it on the wrong trim cap… (missed 1 pin and soldered it on it's neighboring trim cap…).

Now for a good test run on all wavelengths. (FM, PU, MW and LW are working, SW is giving static, but that's normal. Since it only goes from 16 meters till 50 meters. And in Belgium AM isn't in use by our stations…).

For the rest it's sound unbelievable crystal clear on FM and clear with some static on MW and LW!

This is probably coming from the age of the valves for AM detection and filtering…

I just need to make one small change with R66 I've changed it to 57K by chaining 47K and 10K together. This is giving me a voltage drop of 20V, on the schematics is written that the voltage should be 136V (now only receiving 116V) for pin 8 of the ECH81 valve.

And I changed R1 120R/4W metal-oxide resistor to 120R/5W cement resistor.
The smoking and stanch is gone and seems to be running a bit cooler and more stable…

Some points that I want to point out that I find strange:
- Balance control*
- High tone pot*
- Low tone pot*

* Not working or I can't hear any difference…

For the rest everything is working beautifully!

Thank you all for your help!

Cheers,

Laurens

PS: Nick, 2 down 1 to go… :p

[SeanStevens]

You should find that th etone controls ONLY work when no tone selector is in operation.

SEAN

[Don_Zalmrol]

You are right, same goes for the balance.
Balance control only works on PU mode.

Will test these settings tonight!

Cheers,

Laurens