[Penthode]

I spent the day replacing only the paper capacitors I feel would be under stress in circuit positions where subjected to high voltage. The electrolytics reformed nicely with each leaking under 1 mA at rated full voltage.

The paper capacitors, as expected all exhibited various degrees of leakage. my rational in retaining some is if the capacitors have under 1 Megohm in parallel with it. I performed futher tests on the paper capacitors which displayed a worrying thermal runaway failure mode. I placed 350 volts DC across a 0.05 uF 400v capacitor from the set. It showed just over 3mA leakage. However the leakage must have generated internal heat which increased the leakage current. within a minute or so, I witnessed the leakage current begin to accelerate and at 15mA, I removed the voltage. I let the capacitor cool and an hour later i repeated the test with leakage starting at 3mA and rising over time as before. I then reduced the voltage to 20volts and the leakage current was insignificant and remained steady.

I then tested the 0.1 uF 1000v capacitor which is used in the B+ Boost circuit as a filter. At 500VDC, it showed only 0.5mA. However I took a heat gun and raised the temperature of the capacitor only to the point of wax beginning to melt. The leakage increased with the heat. So I ended up replacing all the paper capacitors in the circuits with applied high voltage only except for one: at some point the 6BG6 Horiz Output screen bypass capacitor was replaced with a white bumblebee type. I applied 400v and heated it but the leakage remained at 0.1mA. Do not know what it is composed of or even if it was a paper diectric capacitor. I left it in.

I had a couple of old Black Beauties (0.25uF 400V and 0.1uF 1000V) which I substituted for the wax ones in the set. The Black Beauties under full (or near full in the case of the 1000v unit) showed little or no leakage even when heated.

I replaced the two 0.01uF capacitors from power line to chassis with two Orange Drops rated at 1600v.

I have included a picture of the underside so you may examine for yourself the capacitor replacement work I did today.

POWER UP.

Next came the moment of truth. I inserted the 10BP4, plugged in a cheater and switched it on. I had the chassis on its side to detect any wisps of smoke.

After switching on and waiting about 30 seconds, I heard the vertical sweep start. I advanced the brightness to rotate the ion trap and was rewarded with noise on the screen. I adjusted focus and haven't even touched the Vertical linearity or Vertical Height. I set my Sencore VA62 to and the 721TS to Channel 5 and was rewarded with a picture.

I immediately saw the horizontal hold began to drift and there was a 0.002uF on the Horizontal Frequency Control grid which I was earlier hesitant to replace. I replaced it and the horizontal frequency drift ceased.

Find below a picture of the chassis underside and a picture of the image which immediately popped up. No audio yet and next is the 'soak test to see what will fail. Remember this has been a minimalist rejuvenation and I suspect until a prolonged stress something will fail. Let us see over the coming weeks. More to follow.....