10-04-2013, 08:58 AM
Disappointment: I depotted the detector interstage transformer. One of the wires had broken off inside, so I had to pull the transformer all the way out of the can. There was plenty left to work with, unfortunately, BOTH sides of the transformer are open. 
Not a total disaster, I can use one of my Hammond transformers and mount it in the original can, which I have soaking in brush cleaner to remove the remainder of the tar. I had hoped, though, that I wouldn't have to use a $40 transformer. C'est la vie.
Did some experimentation tonight. I was trying to 'dim it down' a bit, because the balance of the audio is way toward the bright side (as in no bass at all). At first, I experimented with different capacitor values between plate and cathode of the 1st audio stage. This did make a difference in tonal balance, but just didn't quite give me what I was looking for. Then I struck upon the idea of negative feedback. I grounded one side of the 8 ohm output from the output transformer and connected the other speaker lead through a .001 cap to the grid of the 1st audio tube. This made a significant improvement in audio quality, including almost completely removing any second and third order harmonics in the output. It takes a bit more of the high end than I would like, but I don't have any smaller sized caps in stock. I guess I'll put another .001 in series and see what happens. I don't want to lose the bass I've gained (as well as better volume) though.
I think tomorrow I'll depot that last transformer. These things are a real pain to work with, but I want to try to keep the original look to the chassis, so I need that can. Who knows, maybe I can find the missing wires for that one and repair it. Wish me luck.
Not a total disaster, I can use one of my Hammond transformers and mount it in the original can, which I have soaking in brush cleaner to remove the remainder of the tar. I had hoped, though, that I wouldn't have to use a $40 transformer. C'est la vie. Did some experimentation tonight. I was trying to 'dim it down' a bit, because the balance of the audio is way toward the bright side (as in no bass at all). At first, I experimented with different capacitor values between plate and cathode of the 1st audio stage. This did make a difference in tonal balance, but just didn't quite give me what I was looking for. Then I struck upon the idea of negative feedback. I grounded one side of the 8 ohm output from the output transformer and connected the other speaker lead through a .001 cap to the grid of the 1st audio tube. This made a significant improvement in audio quality, including almost completely removing any second and third order harmonics in the output. It takes a bit more of the high end than I would like, but I don't have any smaller sized caps in stock. I guess I'll put another .001 in series and see what happens. I don't want to lose the bass I've gained (as well as better volume) though.
I think tomorrow I'll depot that last transformer. These things are a real pain to work with, but I want to try to keep the original look to the chassis, so I need that can. Who knows, maybe I can find the missing wires for that one and repair it. Wish me luck.
