Invicta (Model 40)

[chompy1]

Morning All,

It has very low/poor audio output on MW and LW. I have tried replacement
valves, but no joy.

What are your thoughts? Thanks in advance.

Paul

[cathoderay57]

Could be a multitude of reasons. Is audio OK on FM? Which valves did you swap, and are you sure that the replacements are any good? Does an external aerial wire help? Jerry

[chompy1]

audio on FM is spot on. I have tried a new EABC80, a new EF80, a new EF89 and a new ECH81. I will try an external aerial wire. When I touch the LW and MW aerial, I can hear stations quite clearly.

Are the red capacitors the mica type? Paul

[cathoderay57]

The red caps are ceramic and will be fine; no need to touch them unless physically crushed or leads broken. Since the set works OK on FM the valves are almost certainly OK. Check for broken or loose connections on the coils on the ferrite rod. I don't have access to the service sheet at present, but if there are any instructions about sliding the coils along the rod to improve alignment then follow them. Don't fiddle with any of the trimmers at this point because you could make matters worse. Jerry

[chompy1]

I have tried an external aerial wire and it made no difference. I have checked the connections of the coils on the ferrite rod and they are OK. There are 2 capacitors which have clear plastic body, which might be polystyrene capacitors. Could the culprit be one of those?

[Silicon]

In post 3 you state that you can hear stations on MW and LW clearly when you touch the aerial.

Is the aerial a wire in the aerial socket, a ferrite rod, or something else?

[chompy1]

the coils on the ferrite rod

[cathoderay57]

The polystyrene caps are extremely unlikely to be the culprit. As a first easy fix try sliding the coils along the ferrite rod as described in Trader Sheet #1432. L12 for LW and L11 for MW. If that doesn't improve things the next best step is to measure the anode, screen and cathode voltages of V2, 3 and 4 and compare with those quoted in the Trader Sheet. Jerry

[Silicon]

There is usually a low voltage on the tuning capacitor Stator vanes that tune the aerial circuit of valve superhet radios.
The vanes often connect directly to the mixer grid.

I sometimes connect a short wire to that stator solder connection.
If reception improves it could indicate that there is a problem with the coils, capacitors and switches on the aerial side of the mixer valve.

I don't have the Invicta 40 schematic in front of me so you need to check the circuit.

[chompy1]

thanks Guys. Unfortunately, I don't have the circuit diagram either. I will try what you guys have suggested. Paul

[cathoderay57]

The Trader Sheet can be purchased here https://www.service-data.com/product...39/3917/t12939 Jerry