18-08-2019, 11:59 AM
Hey!
That 200K resistor I replaced shouldn't have failed!
Thinking about it, even with a dead short coupling capacitor, and the pentode section passing grid current, (it glowed blue briefly until I switched off!), I tested the old 200K from the bin again, it wasn't completely open but near 700K, the first new one WAS dead though. Red black black orange space red? 200K 2% right? (From an RS development kit) tested a new one, 200K, OK, tack that in. Second replacement measured 17.5K....
Hmm, one failed, one wrong value. Checked the price of that kit on RS...not what you would pay unless you are expecting a quality product! Possible that it was near its maximum working voltage with the dead capacitor maybe?
Never trust new parts either?
Hey presto! Good volume and clear sound. No need to get a new valve just yet.
First question. I've to test why the FM band won't work now, the EBF80 is working on the MW. IF, so....is it reasonably safe to assume it's working on the FM. IF?
Second question, do I need to test the FM. IF with the SIG generator set at 10.7MHz with modulation?
Third question. If Q2 answer is yes, what deviation should I set to modulate the 10.7MHz test signal, (is it the same as the transmitted deviation, or is it a proportion of it, never thought about that before?)
Enough electronics and creative writing for now!
Thanks,
Amie.
That 200K resistor I replaced shouldn't have failed!
Thinking about it, even with a dead short coupling capacitor, and the pentode section passing grid current, (it glowed blue briefly until I switched off!), I tested the old 200K from the bin again, it wasn't completely open but near 700K, the first new one WAS dead though. Red black black orange space red? 200K 2% right? (From an RS development kit) tested a new one, 200K, OK, tack that in. Second replacement measured 17.5K....
Hmm, one failed, one wrong value. Checked the price of that kit on RS...not what you would pay unless you are expecting a quality product! Possible that it was near its maximum working voltage with the dead capacitor maybe?
Never trust new parts either?
Hey presto! Good volume and clear sound. No need to get a new valve just yet.
First question. I've to test why the FM band won't work now, the EBF80 is working on the MW. IF, so....is it reasonably safe to assume it's working on the FM. IF?
Second question, do I need to test the FM. IF with the SIG generator set at 10.7MHz with modulation?
Third question. If Q2 answer is yes, what deviation should I set to modulate the 10.7MHz test signal, (is it the same as the transmitted deviation, or is it a proportion of it, never thought about that before?)
Enough electronics and creative writing for now!
Thanks,
Amie.
