20-12-2018, 04:57 PM
Hi, Derek, welcome to the forum where I'm sure you will be very happy.
I'm a little confused by this, though:
Surely, if the AF stages are in perfect working order at this stage, you've already got an audio monitor so, no further facility is needed?
When checking the alignment, it is vital not to let the AGC mask the true peak. It is possible to override the AGC but is not usually necessary on a radio if you follow the correct procedure: keep the volume control setting high (you might want to turn it down briefly when operating the wave-change switch) and the RF level as low as possible. If the volume increases whilst adjusting the alignment (assuming it is necessary), reduce the RF level, not the audio level!
This also applies to checking the alignment without a signal generator: find the weakest stations you can and, if the volume increases appreciably, find an even weaker one! (Sets fitted with frame or ferrite rod aerials can use the directional properties of these aerials as an RF level control by rotating the set to get the desired, low, level signal)
I'm a little confused by this, though:
(20-12-2018, 01:24 PM)coopzone Wrote: 4, Time to start the RF side if this has not pointed you in a direction yet. Feed in your IF frequency, preferable with modulation. Check for signal at the volume control using ether a scope, bench amplifier (i use a pcb lm386+9v+speaker cost about £2.00 from ebay), or an old crystal earphone - be careful it can be very loud.
Surely, if the AF stages are in perfect working order at this stage, you've already got an audio monitor so, no further facility is needed?
When checking the alignment, it is vital not to let the AGC mask the true peak. It is possible to override the AGC but is not usually necessary on a radio if you follow the correct procedure: keep the volume control setting high (you might want to turn it down briefly when operating the wave-change switch) and the RF level as low as possible. If the volume increases whilst adjusting the alignment (assuming it is necessary), reduce the RF level, not the audio level!
This also applies to checking the alignment without a signal generator: find the weakest stations you can and, if the volume increases appreciably, find an even weaker one! (Sets fitted with frame or ferrite rod aerials can use the directional properties of these aerials as an RF level control by rotating the set to get the desired, low, level signal)
