Working on getting a Western Electric 142A amplifier up and running. When I obtained it, the power transformer was toast. I sent it off to Gary Brown at TRS and he rebuilt the power transformer. He did an amazing job, you would never tell it from when it came from the factory.
Just going through the amp making sure everything is up to par before bringing it up on a variac. The amp has 7 factory .05MF cornell-dubilier coupling capacitors in it. They all test in range value wise but on my Sprague Tel-Ohmike 6A, they are all showing around .6-1.3A of leakage at 600v.
Really torn on what to do about these. Trying to leave the amp as original as possible but at the same time, would like to get it functional.
Would love your input or thoughts. Sort of an engineering question but also one of historic nature...
Mark
Just going through the amp making sure everything is up to par before bringing it up on a variac. The amp has 7 factory .05MF cornell-dubilier coupling capacitors in it. They all test in range value wise but on my Sprague Tel-Ohmike 6A, they are all showing around .6-1.3A of leakage at 600v.
Really torn on what to do about these. Trying to leave the amp as original as possible but at the same time, would like to get it functional.
Would love your input or thoughts. Sort of an engineering question but also one of historic nature...
Mark
You should know what type of coupling caps those are.
Are they film/foil types combined with paper? Than its safe if they have good values and low leakage.
Are they only PIOs? Than they might be only safe if the leakage is very low.
I measured big oil caps and they only have typical 30uA@500V. But those are much bigger than your small coupling caps.
So beware of the old bakelite PIOs of some Manufacturers. Often not trustworthy to work correct after so long decades of usage.
Are they film/foil types combined with paper? Than its safe if they have good values and low leakage.
Are they only PIOs? Than they might be only safe if the leakage is very low.
I measured big oil caps and they only have typical 30uA@500V. But those are much bigger than your small coupling caps.
So beware of the old bakelite PIOs of some Manufacturers. Often not trustworthy to work correct after so long decades of usage.
Trying to research the physical composition now, got a few emails off to some WE experts. The good news is with them in circuit and the amp running, the most I'm getting is .09v of leakage across to the grids of the following stage. Have had it on for about a day now and continuing to monitor.
mark
I've seen a number of amps slowly bias themselves off from increasing leakage, like within a half hour. Usually if you power them down and right back up again, they play fine, repeating the same half hour cycle. If you aren't experiencing anything like that after a day, they are probably going to keep running fine.
PS: also here in W-S
PS: also here in W-S
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