Thanks for the reply. Last I checked having the variac around 90% gave me the recommened 117V, but that was a different location. Will re-check and decide what to do. It's not so much the operating B+ I'm concerned about as the initial jump up which goes to 400ish volts when the caps are rated for 450. Probably still okay but I like large safety margins
I am familiar with the transformer trick to drop line voltage, IIRC you anti-phase the primary with the secondary and drop the total voltage by the amount the secondary is rated for.
I'll also see about some circuitry to kill that dot; perhaps it is normal but I'm pretty sure it's way too intense to be good for the phosphor... and that's with brightness and contrast at minimum when I shut off the set.
Edit: What kind of keywords should I be using to locate a circuit to fix this? I tried a few things that immediately came to mind but I'd imagine there's a specific term I don't know that would help immensely... and I did try "afterglow" without much luck) Could it be cured with an appropriate resistor to bleed off the HV quickly at poweroff?
Edit2: seems like the magic words are "spot killer". Mostly patents and unhelpful passing references, but this gem did turn up:
Quote:
Originally Posted by wa2ise
I think all you really needed to do to build a spot killer was to bypass to B+ the brightness line feeding the CRT grid 1. This in sets that fed the video into the CRT cathode. SO when the set was turned off, the B+ would collapse, and the bypassed grid would be pushed very negative, cutting off the cathode. and the cathode cools off by the time the time constant of the cap and resistances around it bleeds off charge.
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Looking at my schematic I think I do have a cathode-driven set... so what type and size of capacitor would I be looking at?
Edit 3: More looking at the schematic... looks like G2 is AC coupled to B+ already... which would presumably achieve the same effect vs G1. The spot doesn't immediately appear when power is killed... the raster collapses and fades but then the spot comes back. Perhaps upping the value of this capacitor (C70, .03µF) would do the job?
Will venture into vertical height land shortly. I don't _think_ there's a miswire as it all made sense when I was verifying the schematic against the chassis and hunting caps to replace... but you never know. I very much suspect it's related to the replaced VBO and height control bodge job though; the control is definitely the wrong value called for in the schematic and some other resistors in that chain were replaced too because I noticed they didn't have a full 360° wrap around the lugs like the factory ones do.
On that note... is it a good idea to run these sets tilted on their sides for access to the underside while working? I recall reading that it's generally not good since it means any sag in your filaments will result in a heater->cathode short.
Last thing for now... I pulled 3 bumblebee caps from this set... are audiophiles still going nuts over those? If so... where's the best non-fleabay place to sell them?
