Discussion in '"Boat Anchor" & Classic Equipment' started by AF6LJ, Jul 11, 2014.
Several of us in northern CA chatted with Sue this morning. The Swan sounds very good!
I spent the morning troubleshooting the receiver problem. To recap no S-meter, low sensitivity, and poor automatic gain control.
The problem appeared to be ether in the AGC amplifier / detector circuit or or in the second IF.
The AGC circuit voltages seemed okay, anything within twenty percent is good after all........
Now my attention was directed toward the second IF, the voltages didn't seem right and the control grid voltage was on the positive side of zero, where you don't want to see it. I was suspicious that I had a bad tube but I need to check the screen voltage on the IF amp first. Yup it was low, the cathode voltage was all out of whack and the plate voltage was fine. Looks like a screen to control grid short. A trip to the closet for the tube caddy yielded the 12BA6 I needed. With the new tube the radio was powered up and an additional twenty plus DB of receiver gain, and a functioning S-meter were the reward for finding the bad tube.
Things seem to be working but I still have a little distortion in the receiver audio, so that needs to be investigated. Once everything is working a good alignment will be in order.
Pictures to follow.
Oh and as a side note...
It isn't that often you find bad tubes in a receiver. That is usually the last thing I consider.
We need to do a Swan to Swan QSO.
been sitting here listening to it while I play FireFall........
I need to get to the bottom of the distortion in the RX audio.
When I get back from the Post Office tomorrow, I am going to investigate that issue....
I just can't imagine U walking all the way to the POST OFFICE!!! That would be like me walking all the way to North park! Thanks, I'll drive instead!
It's what I do. Remember when I showed you the path I use to walk to and from work every day.
The Post Office is two thirds of the way.
Oh and I have a lead on the audio distortion, I'll explore that tomorrow....
Power supply restoration looks good. Glad it works. The bad 12BA6 may be why it was put on the shelf. The distorted audio is probably a leaky coupling cap.
Some might point out that the diodes and resistors in the power supply weren't actually "bad" and didn't absolutely have to be replaced. However, I think it is a good idea to replace them all, as was done, because the cost is minimal and the difficulty of replacing afterwards is much greater.
I'll let you know tomorrow.
Between the band conditions and more likely, my lousy New York City antenna, I couldn't hear you guys... I'm intrigued by a transceiver that has more than the usual 100W of power! You gave me the bug, 6FL!
Did you get a brick with it, to keep it from drifting off the table?