Predicta Rectifier Question - Videokarma.org TV - Video

PredictaNoob · #1 04-30-2010, 02:19 AM

I could use some advise from the group, please. While go over the chassis of my Debutante (10L43 chassis), I found a solid state rectifier installed (ECG508).
Now I am stuck. I can't decide whether to leave it and work with this modification, or to remove it and go back to a 1G3GT tube rectifier.
What would you do?

leadlike · #2 04-30-2010, 03:00 AM

Wow-that is a real oddball. Really unusual considering the tube that thing is replacing is a component that rarely fails. If it were mine, I would drop in a 1B3, since the diode that is in now is pretty old. 1B3s are plentiful and cheap.

PredictaNoob · #3 04-30-2010, 04:59 AM

That's what I was thinking as well. But looking at the scorching on the socket and cage made me wonder if that had something to do with the mod being added in the first place. I've noticed a couple of other strange rigs on the main board as well, that may or may not be related to this gizmo.

All I knew for sure was that I immediately and instinctively did not like this solid state device intruding inside my television.

kx250rider · #4 04-30-2010, 11:06 AM

An ECG-508 is a 3A3 replacement, but should work fine in there. Only thing is, it might cause more high voltage since a silicon diode is more efficient than the tube. When you convert a B+ supply from a 5U4 to a solid state bridge rectifier, you have to change the value of the main B+ resistor(s), and preferably install a delayed startup relay to allow the other tubes to warm up before giving B+. If not, there's an unloaded surge that can blast the capacitors. That should not be a problem here with the stick diode in the Predicta because the flyback will still run up slowly with the horizontal oscillator. But you probably will have a couple KV extra HV.

Charles

PredictaNoob · #5 05-01-2010, 05:50 AM

So you don't think extra KV will cause a problem?

holmesuser01 · #6 05-01-2010, 09:47 AM

I worked in a shop in the early 1980's that had alot of these stick rectifiers in sets we repaired. We used them because the new tubes we were finding (Lindal, etc) were not working out for us. We never had one fail. That said, that was 30 years ago. ECG (Sylvania,) and RCA SK-series were the main semiconductor suppliers that we used. I dont know about now.

Findm-Keepm · #7 05-01-2010, 06:35 PM

Make sure you have a filament supply for the 1G3 - it looks like it's been removed - it should enter the HV cup from the same side as the 2nd Anode lead exits.

Cheers,

PredictaNoob · #8 05-02-2010, 07:00 AM

Quote:

Originally Posted by Findm-Keepm

Make sure you have a filament supply for the 1G3 - it looks like it's been removed - it should enter the HV cup from the same side as the 2nd Anode lead exits.

Cheers,

I assume you mean IF I go back to using the 1G3, right?

Although, I've decided to see what kind of KV I'll get out of the stick diode. If the voltages are acceptable, I think I'm going to just leave it.
I still have about half of the resistors to test, and I'm still waiting on the caps to arrive, and I'm going to restuff the cans, so I've got plenty to keep me busy for the foreseeable future.

Oh yeah, and I haven't even mentioned the cosmetics. Going with a "non-standard" color scheme and grille cloth, (once again, WAF raising gesture). I also used an electrostatic rust removal technique on the rusty parts of the chassis. It worked reasonably well, and now I am just sanding for uniformity and polishing. I'm still considering painting the chassis just for the rust prevention aspect. I'll post some pictures as things progress. For now, here is the color/grille cloth scheme.