05-06-2014, 08:16 AM
Glad to hear that you've traced and rectified the fault Robin - always a good feeling!
As to test gear, Paul Stenning's signal generator is a nice design, and other simple sig gennys such as the Tech TE20D often appear on e-bay. But that said, unless a radio has been got at and twiddled with, you won't often need to use a signal generator, because such things as IF alignment is rarely far off what it should be. Sometime people do have an irresistible urge to twiddle with the trimmers and cores of coils in the front end, upsetting the tracking, but most old sets I've worked on haven't been fiddled with and if out of curiosity I check the alignment, I don't often find it's far out.
In terms of priorities, I'd put a signal injector/tracer next on your list because it can help you pinpoint whether the fault is in the AF stage, the IF stage or front end by signal injection and tracing. For example, on a dead transistor set - a Bush TR82 say, if it's got AFxxx transistors in it, people will often jump to conclusions that the transistors are duff. That may be so - it may not. Poke a signal from an injector into the volume control slider and if you get a loud tone from the speaker that means the AF stage is working. Then apply the tracer probe to the volume control and if you hear no signals, apply the probe to pin 6 of IFT3. If you get signals there, it's the detector diode that's failed, which is hiding inside the IFT can. No need to go to the trouble of removing the IFT, which is a fiddly job - just tag a new germanium diode (the right way round!) across pins 5 & 6 of the IFT pins, and you're sorted. Altogether, about 15 minutes work from start to finish.
You can make a signal tracer (just a small amplifier with a suitable detector probe for RF signals), from an old speaker/amp as used for computers, which often pop up at car boot sales and in charity shops for a couple of pounds, then make a little injector. Simpler still, you could use the excellent Velleman K7000 injector/tracer kit which still sell for a tenner from ESR Electronics and others. I posted a thread on that and on fault tracing on the forum some time ago. You'll find it here:
http://golbornevintageradio.co.uk/forum/...p?tid=1504
You'll find the kit here:
http://www.esr.co.uk/products/frame_test-equipment.htm
Every success with your next project Robin!
As to test gear, Paul Stenning's signal generator is a nice design, and other simple sig gennys such as the Tech TE20D often appear on e-bay. But that said, unless a radio has been got at and twiddled with, you won't often need to use a signal generator, because such things as IF alignment is rarely far off what it should be. Sometime people do have an irresistible urge to twiddle with the trimmers and cores of coils in the front end, upsetting the tracking, but most old sets I've worked on haven't been fiddled with and if out of curiosity I check the alignment, I don't often find it's far out.
In terms of priorities, I'd put a signal injector/tracer next on your list because it can help you pinpoint whether the fault is in the AF stage, the IF stage or front end by signal injection and tracing. For example, on a dead transistor set - a Bush TR82 say, if it's got AFxxx transistors in it, people will often jump to conclusions that the transistors are duff. That may be so - it may not. Poke a signal from an injector into the volume control slider and if you get a loud tone from the speaker that means the AF stage is working. Then apply the tracer probe to the volume control and if you hear no signals, apply the probe to pin 6 of IFT3. If you get signals there, it's the detector diode that's failed, which is hiding inside the IFT can. No need to go to the trouble of removing the IFT, which is a fiddly job - just tag a new germanium diode (the right way round!) across pins 5 & 6 of the IFT pins, and you're sorted. Altogether, about 15 minutes work from start to finish.
You can make a signal tracer (just a small amplifier with a suitable detector probe for RF signals), from an old speaker/amp as used for computers, which often pop up at car boot sales and in charity shops for a couple of pounds, then make a little injector. Simpler still, you could use the excellent Velleman K7000 injector/tracer kit which still sell for a tenner from ESR Electronics and others. I posted a thread on that and on fault tracing on the forum some time ago. You'll find it here:
http://golbornevintageradio.co.uk/forum/...p?tid=1504
You'll find the kit here:
http://www.esr.co.uk/products/frame_test-equipment.htm
Every success with your next project Robin!
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
