04-21-2013, 05:22 PM
Well, the reason was as I expected it a stupid one: when I reconnected the tuning cap, I soldered back the pentagrid's cap but forgot the antenna coil.
I noticed that when I connected the generator - it was coming through but extremely weak....
Well, it sings where it's supposed to...mostly, and the alignment seems to be where it should be, with a single problem: at the Short Wave band when I use the generator the beep disappears right about between 8MHz and 7.5MHz. I knew the tuning cap is OK as at the BC band it works in the same position.
So I theorized the oscillator is not oscillating starting about 7.5MHz and connected the scope to the IF coil output...I was correct, the oscillation sharply decreases at about 8.5 and fully disappears after 8MHz.
6A7 is my pentagrid. Since it oscillates otherwise I think the coils are OK (I think I checked the continuity but will check again just for s..ts and goggles).
The pentagrid was the single weaker tube: the pentode section is supposed to test at about 1000uMho and it gives me about 700. Although I don't see how that can kill the oscillation.
Have to see if there are old micas there...not sure they can do that though.
Anyone has experience with something like that - part of the band is bad? The other part is OK and is very well aligned.
Oh...hadn't checked the voltages yet. Have to do that to see if the regimes are OK.
I noticed that when I connected the generator - it was coming through but extremely weak....
Well, it sings where it's supposed to...mostly, and the alignment seems to be where it should be, with a single problem: at the Short Wave band when I use the generator the beep disappears right about between 8MHz and 7.5MHz. I knew the tuning cap is OK as at the BC band it works in the same position.
So I theorized the oscillator is not oscillating starting about 7.5MHz and connected the scope to the IF coil output...I was correct, the oscillation sharply decreases at about 8.5 and fully disappears after 8MHz.
6A7 is my pentagrid. Since it oscillates otherwise I think the coils are OK (I think I checked the continuity but will check again just for s..ts and goggles).
The pentagrid was the single weaker tube: the pentode section is supposed to test at about 1000uMho and it gives me about 700. Although I don't see how that can kill the oscillation.
Have to see if there are old micas there...not sure they can do that though.
Anyone has experience with something like that - part of the band is bad? The other part is OK and is very well aligned.
Oh...hadn't checked the voltages yet. Have to do that to see if the regimes are OK.
