Help with Invicta valve set

[cathoderay57]

OK. How do you propose to check the alignment? The instructions in the Trader Sheet are usually helpful, but I'm wondering if you have a signal generator? Cheers, Jerry

[Gabe001]

He has a signal generator Jerry, see post 21.

[Sideband]

Originally Posted by LXSTEIN45

I am starting to think this could be a case of severe miss-alignment folks? I will brave the isolation transformer next couple of days and hook my scope up to see what the IF and LO is doing in relation to dial position I think.

You should keep things simple. In all my 50 years of repairing radio's I have NEVER used a scope to align an AM radio and I don't really know what it is going to show you (and I only used a scope once with an FM radio when I used a wobbulator for the first time).

Just use your signal generator to go through the set starting with the last IF transformer and the generator adjusted to the IF frequency (usually 470Khz but might be 465Khz). Follow the alignment instructions keeping the output of the generator as low as possible (with the volume of the radio set near max). As the IF's peak up, reduce the output of the generator (this avoids AGC action).

When it comes to RF alignment, there are usually data marks on the back of the tuning scale that you align the tuning pointer to and then adjust the signal generator to the required frequency in the alignment instructions and then adjust the oscillator coil until you hear the tone from the generator. You might need to increase the output of the generator to start with but again as the tuned circuits come into line, you reduce the output of the generator to as low as possible. It really is quite easy but you need to be familiar with the generator.

Going back to the use of a scope, the only time a scope would be used is possibly in the alignment of a top-range receiver where a wobbulator would be used with it to assist in getting the IF bandwidth perfect. A scope on it's own is of no real use other than perhaps for checking that the oscillator is actually working. You only need a signal generator for a standard domestic AM receiver. Some people also like to connect an analogue meter switched to a low voltage AC range across the loudspeaker to measure the audio tone 'peak' during alignment.

[ms660]

A 'scope is the better peak indicator when aligning, a meter would be second, human hearing's ok to get you in the ball park but isn't very good for the fine final.

Lawrence.