It's been a while since I posted an update on this project. I expected to finish this last weekend, but alas, no. I have gotten my work on the preamp section. It's a very interesting circuit, and I will post a full description, and hopefully a schematic, when i get the thing working. But let me just fill you in on a few challenges.
First, the amp was wired by "Chico". Chico did a pretty nice job, overall, but really had a thing about that brown sticky stuff that Ampeg loved to put all over the insides of their amps. I first became annoyed when I discovered that Chico had used it to glue the Astrons to the board, meaning that when you pull the cap from the board the paper wrapping remains and is virtually impossible to remove. That, coupled with the fact that there were a few that I am guessing at the value of were glued *value side down*, was really annoying. He also got the brown stuff all over the solder joints, which did not please me at all. I removed what I could, but it still made for a lot of stinky smoke.
Anyway, then I got sidetracked. When the amp did not give me tube hiss when I connected everything, I decided I needed to trace through the circuit. This required dusting off my tone generator and oscilloscope, both of which have not seen the light of day for at least 10 years. Neither worked. So, I've got the oscilloscope working well enough, but the tone generator is still pretty shaky. I may have to just use a phone app for this purpose, but that's just not my style.
I'd much rather use the enormous and ancient Heathkit IG-82, so I'm starting to debug that. One way or another, I should be able to complete the 835 this coming weekend. Right now I'm waiting for some resistors that I've found have failed in the power amp chassis.
First, the amp was wired by "Chico". Chico did a pretty nice job, overall, but really had a thing about that brown sticky stuff that Ampeg loved to put all over the insides of their amps. I first became annoyed when I discovered that Chico had used it to glue the Astrons to the board, meaning that when you pull the cap from the board the paper wrapping remains and is virtually impossible to remove. That, coupled with the fact that there were a few that I am guessing at the value of were glued *value side down*, was really annoying. He also got the brown stuff all over the solder joints, which did not please me at all. I removed what I could, but it still made for a lot of stinky smoke.
Anyway, then I got sidetracked. When the amp did not give me tube hiss when I connected everything, I decided I needed to trace through the circuit. This required dusting off my tone generator and oscilloscope, both of which have not seen the light of day for at least 10 years. Neither worked. So, I've got the oscilloscope working well enough, but the tone generator is still pretty shaky. I may have to just use a phone app for this purpose, but that's just not my style.
I'd much rather use the enormous and ancient Heathkit IG-82, so I'm starting to debug that. One way or another, I should be able to complete the 835 this coming weekend. Right now I'm waiting for some resistors that I've found have failed in the power amp chassis.