20-12-2018, 01:24 PM
Hi,
I would suggest you chop the problem up a bit. When you say low output it could be in the RF stage but it's just as likely in the audio or detector stage, so try and test each stage as you go. for example:
1, start with voltages compared against the trader sheet, Any low? fix this first.
2, audio. Is the speaker ok - you can connect another one or connect it to another radio maybe? I mention this because in the past i had a radio where the speaker had gone rusty! and the cone had very restricted movement - end result very quiet.
3, If it's a AC only set and has a GRAM/Record deck input connect an audio source to that - do you get plenty of volume? If it's an AC/DC set and ONLY if you signal source is battery operated (without earth, i use an old mp3 player) you can connect it via a 0.01 to the volume control. You should also take all the other precautions needed to stay safe if doing this.
If it's low audio at this stage you know you need to start on the AF side of things, in particular check cathode resistors etc.
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.
5, Last check RF amp/mixer stage. Mostly looking for voltages to be correct, you probably need a scope to see more. But it's worth checking connections, switches, coils (for o/c) etc - again i had a DAC90 where it worked but low signal and it turned out one connection to the frame areal was loose. Quick clean and replace all was good.
Hope it helps, remember always try to break a problem down into smaller chunks.
Derek
I would suggest you chop the problem up a bit. When you say low output it could be in the RF stage but it's just as likely in the audio or detector stage, so try and test each stage as you go. for example:
1, start with voltages compared against the trader sheet, Any low? fix this first.
2, audio. Is the speaker ok - you can connect another one or connect it to another radio maybe? I mention this because in the past i had a radio where the speaker had gone rusty! and the cone had very restricted movement - end result very quiet.
3, If it's a AC only set and has a GRAM/Record deck input connect an audio source to that - do you get plenty of volume? If it's an AC/DC set and ONLY if you signal source is battery operated (without earth, i use an old mp3 player) you can connect it via a 0.01 to the volume control. You should also take all the other precautions needed to stay safe if doing this.
If it's low audio at this stage you know you need to start on the AF side of things, in particular check cathode resistors etc.
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.
5, Last check RF amp/mixer stage. Mostly looking for voltages to be correct, you probably need a scope to see more. But it's worth checking connections, switches, coils (for o/c) etc - again i had a DAC90 where it worked but low signal and it turned out one connection to the frame areal was loose. Quick clean and replace all was good.
Hope it helps, remember always try to break a problem down into smaller chunks.
Derek
