I think that it is not oscillating because you only get sound when the gang is almost fully meshed. All slugs have been played with.

The cct is completely different. It has the 1P5 as a RF stage before the 1A7G, then the 2nd 1P5.

Drawing it up makes no sense. for example. The L.O. dosnt seem to be connected in a way that will make it oscillate. Maby I just cant follow what is happening in it.

I thought it was similar to a cct shown in RT&H Sept 1946 (page 39) but from what I can tell it is a little different because my set has an areal coil that connects the Loop antenna to the first 1P5.

Any Ideas??

It's a Superhetrodyne if the oscillator is not working you will not get anything. This rather suggests it is.

The audio output from these sets is not much more than a quarter of a watt, so it will not blast you out of the room.

I would suggest that the majority of the problem is manifest in "tweedle dee or tweedle dumb" stuffing up the IF transformers and everything else by screwing the slugs.

In order to sort this out you are going to have to work backwards through the set. It would appear that the audio is trying to work, inject a signal (not big) into the centre of the volume control. Do be aware that those resistors with caps do fail and I would still recommend rough checking them.

If its high in circuit, unsolder one end & check it properly; it probably still will be high. I normally check these as I do the caps (saves work later).

Once you are confident the amp is working then start aligning the IF's. That is always done last one first. I would suggest things will improve from there.

Check the outside plates of the tuning gang rotor, they are the normal ones to get bent. A bent oscillator one that is shorting will kill it. Lack of emmission and voltage or a weak valve will also see the oscillator die at high frequency.

Marc

Well So Far...

I have checked the tuning gang. Its fine with no bent or rubbing plates.

I set the frequency gen that I borrowed to about 550kHz with AM tone modulation and was able to get a tone eventually out of the speaker by adjusting all the IF coils one at a time.

Now for the strange part..
I varied the frequency out of the gen a bit and the tone went away like it should. This is where it gets strange.... The position that I left the dial of the gen output was set at 450kHz By pure fluke! I started to get radio signals to tune over the band as I varied the radio tuning.

I switched off the tone part of the gen and now I am able to tune stations.... BUT ONLY WITH THE GEN SET TO 455 ish. If I turn the gen off the signal dies. if I vary the frequency of the gen I can make the signals completely die or at a certain point they come in strong almost to distortion. but when at this particular frequency I can't get any other station. I have to set it back at 455 again to find another station. Then you can vary the frequency gen at a completely different frequency to make the station die and then stronger. Returning the frequency gen to 455 allows tuning across the entire band pulling in stations weak but able to be heard.

Does this mean that my local oscillator in the radio isn't working and I have a dead 1A7G or something around the LO coil is wrong. The coil looks good and meters out ok with dc meter.

The way I hooked up the gen was to the antenna with a 0.05μF 400v cap (Just what I had sitting on the bench at the time).

Any ideas???

The IF is likely 455kHz. There is a procedure in the Astor section of AORSM's & a couple of others.

In order to get the IF's back on track you need to put the signal into the last IF first and get it right before moving backwards to to the first one. Astor normally put the signal into the grid (cap still on) via a 0.01mfd cap (15- 50mW) They only use 200pF on the antenna.

Sort the IF coils out first. I normally use a CRO as that enables me to see the resonant coupling. The CRO would also show the oscillator to be dead or alive. You can also use a transistor radio of the same IF close to the oscillator and see if it can pick up the signal. the two will hetrodyne as the Gang is swung. If the oscillator is running.

It is likely that the oscillator coil has been "adjusted" and will be way off frequency. That is usually set with the dial at 600kHz.

If the set only tunes with the sig gen and a signal cannot be found with the transistor radio. Then start looking at everything around the Converter. Voltages resistors dry joints etc.

See how you go.....

Marc

Thanks for that.

I will look tomorrow and get back to you. I dont have a spare valve. Do you know of an alternate that might do the job (i dont mind changing the heater voltage just for this valve to test and see if the set will work) All valve heaters are in parallel at the moment and I will sort something out if needed.

The battery valves are not that easy to come by. A 1B7 has the some pin outs & filament voltage. needs slightly more screen current.

Heaters will have to stay in parallel. The fact that the sig gen causes signal to go through would cause me to suspect components first and valve last.

Check the oscillator coil as well, often when components are changed the fine wire gets broken at the lug. It could also have corrosion damage. I have seen as many as three coils lost in one radio, due to that.

Marc

Hi Marc (and others that have helped)

Its been a while but I thought I would let you know. I have changed out ALL resistors in the set after one of them fell apart when trying to take it out to test. This still didn’t fix the radio. I tried looking at the LO with my CRO but couldn’t find anything happening. I then went to the multi-meter again to see a voltage but nothing…

I finally got a hold of a 1A7G. Put it in and now the set is working very well.

I set up the IFs using the sig gen that I borrowed to 455kHz using the method you suggested above and now the set is great (well as good as a 1940 battery set can be)


With a working set I got out my meter and as soon as I put it near the LO pins of the 1A7G the set stops. It is a decent digital meter so I thought that it wouldn’t load down too much just goes to show that you cant believe your test equipment all the time!