1951 radio " Graetz Super 158W " serious sound problem

[Station X]

So was I.

The chassis layout doesn't give valve designations, only types. It would be reasonable to assume that the Ist AF Amp is next to the EL41. Let's see what the OP comes up with.

[Radio Wrangler]

I wonder if the manufacturer had stability problems with the EL41 stage. There are stopper resistors in the connections to both g2 and g1.

Oscillation could be upsetting voltage readings all over the place. It's something to look out for when readings don't seem to make sense

David

[Lef de art]

The second EAF42 makes sound in the speaker when i touch the pin2 and pin6

Second EAF42 Voltages
Pin1=0
Pin2=190
Pin3=0
Pin4=0. Connected to ground
Pin5=0
Pin6=0
Pin7=0 connected to ground
Pin8=0

[Station X]

Definitely a problem there.

I'd start by investigating why there's no voltage on pin 5 the screen grid.

[Lef de art]

The pin5 is connected to a 800k resistor. The resistor in my multimeter says 0 !!!

[Station X]

Some meters display 0L to denote an out of range reading or open circuit.

Check the DC voltage from each end of that resistor to chassis.

The resistor may be open circuit or the 0.25uF capacitor connected to it could be short circuit.

[Lef de art]

I just replaced the 800K resistor and the radio WORKS !!!

Oh my god !
I don't have words to thank you guys !!!!

[Station X]

That wasn't too hard was it? It's voltage readings every time for me.

[Lef de art]

Originally Posted by Station X

That wasn't too hard was it? It's voltage readings every time for me.

Indeed ... But i want to be honest ... Without your guys help, this it was something impossible for me..

Radio and me we thank you very very much

[Nuvistor]

Glad you got there, I am sure it’s sounds excellent.
If you want to repair more radios I can recommend this part of this web site, well worth a read and some understanding of how the radio works will help in your repairs.
https://www.vintage-radio.com/repair...ion/index.html

[ms660]

Originally Posted by Station X

That wasn't too hard was it? It's voltage readings every time for me.

Me too, when I did field servicing all I had was an Avo, the Avo and an uninsulated screwdriver shaft for finger contact cracked most faults.

Lawrence.

[Lef de art]

Originally Posted by Nuvistor

Glad you got there, I am sure it’s sounds excellent.
If you want to repair more radios I can recommend this part of this web site, well worth a read and some understanding of how the radio works will help in your repairs.
https://www.vintage-radio.com/repair...ion/index.html

I will read it carefully Frank.
Thanks

[Lef de art]

Good morning guys. One more question please.

Now the radio plays as it was before the sound problem appear.
But from the first moment I bought it in the FM almost in all stations even in the low volume the sound is distorted. It is like the station is Very laoud injected to the amplifier.
This doesn't happens in the AM or LW where the stations are weaker.
Even when i connect my phone in audio input the sound is perfect .
The distortion appears in FM strong stations.
The Voices and the bass are heavily distorted.

I understand that somewhere some more resistors are out of value. Any idea where approximately to look ?
At the end i will check all af them but still any suggestion will be helpful.
Thanks again

[Radio Wrangler]

In fault-finding, the first thing to do is to inspect everything visually, and maybe give things a gentle pull to check for loose connections.

It's amazing how many faults can be found this way. Some sets turn up where one joint never got soldered at the factory, and they have worked for many years until.... also you find burned components, bulging or cracked capacitors. These are the easiest fixes

The second thing you do is to go through it checking DC voltages against the service sheet. Many faults don't just affect the signal flow, they affect DC conditions, and this makes them easy to find.

Together, these two approaches will sort out the majority of faults. The ones left are going to be the more challenging ones where you either inject signals at different points down the receiver to see where the break is, or you follow a signal down the chain to see where it stops.


I expect your radio has a separate RF section for VHf FM. It is likely to share IF amplifiers, but have separate IF transformers, and then it will have a separate frequency discriminator in place of the AM detector.

The sort of valves used in FM front ends were short-lived and gave a lot of problems. Bad alignment of the IF and discriminator can give lots of distortion.

David

[Nuvistor]

I am using the circuit from radio museum. There is an electrolytic capacitor 5uf circuit designated 111 on the ratio detector EB41 valve.
Has this been replaced and if so did you connect it correctly + to chsssis?
Check the resistors in the same circuit.
You may be lucky and find the fault in that area, if not it’s back to fault find techniques noted in post #54 by David.

[Richardgr]

What is the condition of that 100u cathode bypass capacitor, connected to the cathode of the EL41? It is not impossible that the rigours of time and heat have gotten to it. Does it look intact, with no signs of distress - especially where it is sealed?

Edit: still had a page to read and now I see problem resolved! I tend to be too trusting of resistors when I am digging around an old radio, so a good lesson to me.

[Lef de art]

Originally Posted by Nuvistor

I am using the circuit from radio museum. There is an electrolytic capacitor 5uf circuit designated 111 on the ratio detector EB41 valve.
Has this been replaced and if so did you connect it correctly + to chsssis?
Check the resistors in the same circuit.
You may be lucky and find the fault in that area, if not it’s back to fault find techniques noted in post #54 by David.

Hello Frank.
I replaced the 5uf capacitor from the first Day so is not from there.
After my work i wil search the area for faults in resistors.

Hello #David . Thanks for the message. i try to make things as you write but I can't find the service manual with the Voltages for this Radio.
I have the schematic but not the Voltages and i have search everywhere in the Web.
Unfortunately i Don't have the experience to understand what voltages are correct without the service manual.

[Nuvistor]

Circuit with voltages at radio museum. There are three circuits on that page, one has voltages and currents noted next to each pin on the valves.
https://www.radiomuseum.org/r/graetz_158w.html

There are restrictions on downloads for non members but I think it’s 3 per day and 10 within 30 days so you can download the complete manual in a few days. I think the first diagram has the voltages.

[ms660]

Voltages and currents also on this schematic:

https://nvhrbiblio.nl/schema/Graetz_158W.pdf

Lawrence.

[Lef de art]

Originally Posted by ms660

Voltages and currents also on this schematic:

https://nvhrbiblio.nl/schema/Graetz_158W.pdf

Lawrence.

Sorry i ask but I can't figure out where the tube ECH42 voltage are marked .
If you please explain me it will be helpful for me in the future.